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Circular RNAs (circRNAs) are reported to participate in the development of diverse human malignancies. This work investigated the mechanism of circSKA3 in modulating medulloblastoma progression. A total of 15 cases of medulloblastoma were collected in this work. Daoy cells were used to construct cell models. The expression level of circSKA3, microRNA-520 h (miR-520 h), and cyclin-dependent kinase 6 (CDK6) mRNA in tissues or cells was examined by quantitative real-time polymerase chain reaction (qRT-PCR). Western blot was employed to detect CDK6 protein expression. CCK-8 experiment, Transwell assay, and flow cytometry were applied to detect the regulatory effects of circSKA3 on cell proliferation, migration, invasion, and cell cycle. Dual-luciferase reporter gene experiment was executed to determine the relationship between circSKA3 and miR-520 h, and between miR-520 h and CDK6. circSKA3 was remarkably up-modulated in medulloblastoma tissues. CircSKA3 depletion markedly suppressed Daoy cell viability, migration, invasion, and cell cycle progression. CircSKA3 overexpression induced the opposite effects. circSKA3 could decoyed miR-520 h, which targeted the 3' UTR of CDK6. circSKA3 expression in medulloblastoma tissues was negatively correlated with miR-520 h expression and positively correlated with CDK6 expression. "Rescue" experiments revealed that miR-520 h down-modulation or CDK6 overexpression remarkably counteracted the inhibitory effect of circSKA3 knockdown on Daoy cells. circSKA3 facilitates medulloblastoma progression through miR-520 h/CDK6., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Lung adenocarcinoma (LUAD) is associated with poor prognosis. Identifying novel cancer targets and helpful therapeutic strategies remains a serious clinical challenge. This study detected differentially expressed genes in The Cancer Genome Atlas (TCGA) LUAD data collection. We also identified a predictive DNA biomarker, G protein-coupled receptor 37 (GPR37), which was verified as a prognostic biomarker with a critical role in tumor progression. In human LUAD specimens and microarray analyses, we determined that GPR37 was significantly upregulated and associated with a poor prognosis. GPR37 downregulation markedly inhibited the proliferation and migration of LUAD both in vitro and in vivo. Mechanistically, GPR37 could bind to CDK6, thereby facilitating tumor progression in LUAD by inducing cell cycle arrest at the G1 phase. GPR37 also facilitates tumorigenesis in xenograft tumors in vivo. High-throughput screening for GPR37-targeted drugs was performed using the Natural Products Library, which revealed the potential of Hypocrellin B to inhibit GPR37 and cell growth in LUAD. We demonstrated that Hypocrellin B suppressed LUAD cell proliferation and migration both in vitro and in vivo via GPR37 inhibition. Collectively, our findings reveal the role of GPR37 in LUAD progression and migration and the potential of GPR37 as a target for the treatment of LUAD. Thus, the specific inhibition of GPR37 by the natural product Hypocrellin B may possess the potential for the treatment of LUAD., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: Long non-coding RNA (lncRNA) HAND2-AS1 has been indicated to play biological roles in several cancers. However, whether HAND2-AS1 could exert its role in glioma remains unknown. We aimed to investigate the function of HAND2-AS1 in the proliferation, invasion and migration and to explore its underlying molecular mechanism in glioma cells., Methods: Reverse transcription-quantitative polymerase chain reaction analysis was conducted to determine the expression of HAND2-AS1 and cyclin-dependent kinases 6 (CDK6) in tissues or cells. Western blot analysis was used to detect the CDK6 protein expression. CCK-8 assay was adopted to determine the proliferation in glioma cell lines. Transwell assay was taken to evaluate the invasion and migration in glioma cell lines., Results: Our results revealed that HAND2-AS1 expression was significantly downregulated in the glioma tissues and cell lines. Moreover, overexpression of HAND2-AS1 attenuated the proliferation, invasion, and migration in glioma cell lines. However, overexpression of CDK6 could partially block the inhibitory role of HAND2-AS1 on cell proliferation as well as cell invasion and migration in glioma cell lines., Conclusion: LncRNA HAND2-AS1 may play a critical anti-tumorigenic role in glioma by negatively regulating CDK6 expression.

Background: Androgen deprivation therapy (ADT) is still the first-line treatment of prostate cancer (PCa). However, after a certain period of therapy, primary PCa inevitably progresses into castration-resistant PCa (CRPC). Enzalutamide (Enz) is an androgen receptor (AR) signal inhibitor which can delay the progression of CRPC and increase survival of patients with metastatic CRPC. However, the mechanisms involved in enzalutamide-resistant (EnzR) CRPC are still controversial. In the study, we used bioinformatic methods to find potential genes that correlated with the occurrence of EnzR CRPC., Methods: We collected RNA sequencing data of the EnzR CRPC cell line LNCaP (EnzR LNCaP) from GSE44905, GSE78201, and GSE150807. We found the hub genes from the three datasets. Then we tested the expression of the hub genes in different databases and the potential drugs that can affect the hub genes. Finally, we verified the hub gene expression and drug function., Results: From GSE44905, GSE78201 and GSE150807, we found 45 differentially expressed genes (DEGs) between LNCaP and EnzR LNCaP. Ten hub genes were found in the protein-protein interaction (PPI) network. The expression of hub gene and survival analysis were analyzed by different databases. We found that cyclin-dependent kinase 6 (CDK6) was highly expressed in both the EnzR LNCaP cell and PCa patients. Ten potential small molecules could suppress CDK6 expression as per "CLUE COMMAND" findings. Finally, we found the expression of CDK6 increased in both PCa patients' samples, CRPC and EnzR PCa cell lines. Three potential CDK6 inhibitors, namely apigenin, chrysin and fisetin, can decrease cell proliferation., Conclusions: The study proved that the abnormal overexpression of CDK6 may be a reason behind EnzR CRPC occurrence and suppression CDK6 expression may help treat EnzR CRPC., (© 2022. The Author(s).)

Identifying cell phenotypes is essential for understanding the function of biological macromolecules and molecular biology. We developed a noninvasive, label-free, single-cell Raman imaging analysis platform to distinguish between the cell phenotypes of the HeLa cell wild type (WT) and cyclin-dependent kinase 6 (CDK6) gene knockout (KO) type. Via large-scale Raman spectral and imaging analysis, two phenotypes of the HeLa cells were distinguished by their intrinsic biochemical profiles. A significant difference was found between the two cell lines: large lipid droplets formed in the knockout HeLa cells but were not observed in the WT cells, which was confirmed by Oil Red O staining. The band ratio of the Raman spectrum of saturated/unsaturated fatty acids was identified as the Raman spectral marker for HeLa cell WT or gene knockout type differentiation. The interaction between organelles involved in lipid metabolism was revealed by Raman imaging and Lorentz fitting, where the distribution intensity of the mitochondria and the endoplasmic reticulum membrane decreased. At the same time, lysosomes increased after the CDK6 gene knockout. The parameters obtained from Raman spectroscopy are based on hierarchical cluster analysis and one-way ANOVA, enabling highly accurate cell classification.

Cyclins and cyclin-dependent kinases (CDKs) regulate the cell cycle, which is important for cell proliferation and development. Cyclins bind to and activate CDKs, which then drive the cell cycle. The expression of cyclins periodically changes throughout the cell cycle, while that of CDKs remains constant. To elucidate the mechanisms underlying the constant expression of CDKs, we search for compounds that alter their expression and discover that the natural product fucoxanthinol downregulates CDK2, 4, and 6 expression. We then develop a method to immobilize a compound with a hydroxyl group onto FG beads ® and identify human ribosomal protein uS7 (also known as ribosomal protein S5) as the major fucoxanthinol-binding protein using the beads and mass spectrometry. The knockdown of uS7 induces G1 cell cycle arrest with the downregulation of CDK6 in colon cancer cells. CDK6, but not CDK2 or CDK4, is degraded by the depletion of uS7, and we furthermore find that uS7 directly binds to CDK6. Fucoxanthinol decreases uS7 at the protein level in colon cancer cells. By identifying the binding proteins of a natural product, the present study reveals that ribosomal protein uS7 may contribute to the constant expression of CDK6 via a direct interaction., (© 2022. The Author(s).)

Background: Glioblastoma is the most malignant primary brain tumor with dysregulated microRNAs affecting development and malignant transformation., Methods: Gene Expression Omnibus (GEO) dataset (GSE165937) was retrieved, and the differential expressed microRNAs were screened and testified by quantitative real-time PCR (qRT-PCR) in glioblastoma cells. miR-342-3p mimic was transfected into U87MG and U251MG cells. EdU staining, cell counting kit-8, and transwell assay were utilized to evaluate the proliferation, migration, and invasion of glioblastoma. The potential binding sequences between miR-342-3p and CDK6 were predicted and testified by TargetScan and luciferase reporter assay. Relative CDK6 and miR-342-3p expression were detected with qRT-PCR and Western blot., Results: Down-regulated miR-342-3p was observed in both glioblastoma tissues and cell lines. Over-expressed miR-342-3p prohibited glioblastoma cells proliferation, migration, and invasion, which could be rescued by further CDK6 transfection. Mechanically, miR-342-3p could directly bind with CDK6 as testified with luciferase analysis and down-regulated CDK6 expression., Conclusion: Down-regulated miR-342-3p may promote glioblastoma cells proliferation, migration, and invasion with up-regulated CDK6, which indicates that miR-342-3p/CDK6 might be a treatment target in glioblastoma development.

Objective: To study the expression and prognostic value of CDK6 in stomach cancer and the function of CDK4/6 inhibitor PD-0332991 on the proliferation of stomach cancer cells., Methods: Immunohistochemistry was used to detect the expression of CDK6 in stomach cancer tissues and adjacent normal tissues and to analyze the effect of CDK6 on clinicopathological parameters of stomach cancer patients. Kaplan-Meier plotter was employed to study the relationship between CDK6 and overall survival in stomach cancer. Western blot and RT-PCR were used to detect protein and gene expression of CDK6 in different cells. The effects of CDK4/6 inhibitor PD-0332991 on apoptosis and aging of stomach cancer cells were detected by flow cytometry and β -galactosidase aging staining assay. The effects of CDK4/6 inhibitor PD-0332991 on the invasion and migration of stomach cancer cells were explored by the wound healing experiment and the Transwell experiment. The supernatant of stomach cancer cells was collected, and the effect of CDK4/6 inhibitor PD-0332991 on tumor markers of stomach cancer cells was detected by biochemical immunoassay., Results: (1) CDK6 was highly expressed in stomach cancer tissues and cells. (2) Abnormally elevated CDK6 expression results in shorter survival in stomach cancer patients. (3) CDK4/6 inhibitor PD-0332991 could block the proliferation of stomach cancer cells, but not stomach epithelial proliferation. PD-0332991 could inhibit the secretion of pro-GRP by MGC 823. (4) PD-0332991 could advance the development of the apoptosis and senescence of stomach cancer cells and suppressed the invasion and migration of stomach cancer cells., Conclusion: CDK6 expression is elevated in gastric cancer, and the CDK4/6 inhibitor PD-0332991 can remarkably promote apoptosis and senescence of stomach cancer cells and effectively inhibit the migration and invasion of stomach cancer cells., Competing Interests: The authors declare that there are no conflicts of interest regarding the publication of this paper., (Copyright © 2022 Yu Liu et al.)

Background: Multidrug resistance (MDR) mediated by ATP binding cassette subfamily B member 1 (ABCB1/P-gp) is a major cause of cancer chemotherapy failure, but the regulation mechanisms are largely unknown., Methods: Based on single gene knockout, we studied the regulation of CDK6-PI3K axis on ABCB1-mediated MDR in human cancer cells. CRISPR/Cas9 technique was performed in KB-C2 cells to knockout cdk6 or cdk4 gene. Western blot, RT-PCR and transcriptome analysis were performed to investigate target gene deletion and expression of critical signaling factors. The effect of cdk4 or cdk6 deficiency on cell apoptosis and the cell cycle was analyzed using flow cytometry. In vivo studies were performed to study the sensitivity of KB-C2 tumors to doxorubicin, tumor growth and metastasis., Results: Deficiency of cdk6 led to remarkable downregulation of ABCB1 expression and reversal of ABCB1-mediated MDR. Transcriptomic analysis revealed that CDK6 knockout regulated a series of signaling factors, among them, PI3K 110α and 110β, KRAS and MAPK10 were downregulated, and FOS-promoting cell autophagy and CXCL1-regulating multiple factors were upregulated. Notably, PI3K 110α/110β deficiency in-return downregulated CDK6 and the CDK6-PI3K axis synergizes in regulating ABCB1 expression, which strengthened the regulation of ABCB1 over single regulation by either CDK6 or PI3K 110α/110β. High frequency of alternative splicing (AS) of premature ABCB1 mRNA induced by CDK6, CDK4 or PI3K 110α/110β level change was confirmed to alter the ABCB1 level, among them 10 common skipped exon (SE) events were found. In vivo experiments demonstrated that loss of cdk6 remarkably increased the sensitivity of KB-C2 tumors to doxorubicin by increasing drug accumulation of the tumors, resulting in remarkable inhibition of tumor growth and metastasis, as well as KB-C2 survival in the nude mice., Conclusions: CDK6-PI3K as a new target signaling axis to reverse ABCB1-mediated MDR is reported for the first time in cancers. Pathways leading to inhibition of cancer cell proliferation were revealed to be accompanied by CDK6 deficiency., (© 2022. The Author(s).)

Coronary artery disease (CAD) is a long-lasting inflammatory disease characterized by monocyte migration into the vessel wall leading to clinical events like myocardial infarction (MI). However, the role of monocyte subsets, especially their miRNA-driven differentiation in this scenario is still in its infancy. Here, we characterized monocyte subsets in controls and disease phenotypes of CAD and MI patients using flow cytometry and miRNA and mRNA expression profiling using RNA sequencing. We observed major differences in the miRNA profiles between the classical (CD14 ++ CD16 - ) and nonclassical (CD14 + CD16 ++ ) monocyte subsets irrespective of the disease phenotype suggesting the Cyclin-dependent Kinase 6 (CDK6) to be an important player in monocyte maturation. Between control and MI patients, we found a set of miRNAs to be differentially expressed in the nonclassical monocytes and targeting CCND2 (Cyclin D2) that is able to enhance myocardial repair. Interestingly, miRNAs as miR-125b playing a role in vascular calcification were differentially expressed in the classical subset in patients suffering from CAD and not MI in comparison to control samples. In conclusion, our study describes specific peculiarities of monocyte subset miRNA expression in control and diseased samples and provides basis to further functional analysis and to identify new cardiovascular disease treatment targets., (© 2022. The Author(s).)

Acute lymphoblastic leukemia (ALL) is a common malignancy in children. In this study, we aimed to explore putative mechanisms of microRNA-155-5p (miR-155-5p) involvement in childhood ALL (cALL) via interactions with casitas B-lineage lymphoma (CBL), interferon regulatory factor 4 (IRF4), and cyclin-dependent kinase 6 (CDK6). Bioinformatic analysis was performed initially to identify differentially expressed genes in cALL. The expression levels of miR-155-5p, CBL, IRF4, and CDK6 in peripheral blood lymphocytes from clinical ALL samples were determined using RT-qPCR and Western blot assays. A dual-luciferase reporter gene assay was used to ascertain a possible targeting relationship between miR-155-5p and CBL, CCK-8 assay and flow cytometry were used to measure cell activity and apoptosis of ALL cells. Co-IP was performed to investigate the interaction between CBL and IRF4 and the ubiquitination level of IRF4. Furthermore, in vivo validation was performed inducing xenograft tumor models with ALL cells in nude mice. As indicated by bioinformatic analysis, miR-155-5p and CDK6 were upregulated and CBL was downregulated in ALL. miR-155-5p was found to target CBL to inhibit CBL expression. miR-155-5p promoted the proliferation of ALL cells and inhibited their apoptosis by inhibiting the expression of CBL, which otherwise degraded IRF4 protein through ubiquitination, leading to inhibited CDK6 expression. Collectively, the results show that miR-155-5p can promote the development of cALL via the regulation on CBL-mediated IRF4/CDK6 axis., (© 2021. The Author(s), under exclusive licence to United States and Canadian Academy of Pathology.)

Background: Circular RNAs (circRNAs) are increasingly implicated in the development of oral squamous cell carcinoma (OSCC). Here, we explored the precise role of circRNA oxysterol binding protein like 10 (circ_OSBPL10, circ_0008549) in OSCC pathogenesis., Methods: Ribonuclease (RNase) R assay was performed to assess the stability of circ_OSBPL10. The levels of circ_OSBPL10, microRNA (miR)-299-3p and cyclin-dependent kinase 6 (CDK6) mRNA were gauged by qRT-PCR. CDK6 protein level was measured by western blot. Cell proliferation was detected by MTT and colony formation assays. Cell cycle distribution and apoptosis were measured by flow cytometry. Cell migration and invasion were evaluated using transwell assay. Dual-luciferase reporter assay was used to identify the relationship between miR-299-3p and circ_OSBPL10 or CDK6. Animal studies were performed to evaluate the role of circ_OSBPL10 in tumor growth in vivo., Results: Circ_OSBPL10 was up-regulated in OSCC tissues and cells. Silencing of circ_OSBPL10 hindered cell proliferation, cell cycle progression, colony formation, migration, invasion, and promoted apoptosis in vitro and diminished tumor growth in vivo. Mechanistically, circ_OSBPL10 directly targeted miR-299-3p, and circ_OSBPL10 silencing affected cell functional properties in vitro by up-regulating miR-299-3p. CDK6 was a direct and functional target of miR-299-3p. The circ_OSBPL10/miR-299-3p axis regulated cell functional properties in vitro via CDK6. Moreover, circ_OSBPL10 acted as a competing endogenous RNA (ceRNA) to regulate CDK6 expression through miR-299-3p., Conclusion: Our present findings first demonstrate that circ_OSBPL10 can regulate the functional behaviors of OSCC cells at least partially by miR-299-3p/CDK6 axis, highlighting circ_OSBPL10 as a promising therapeutic target for OSCC., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This study is aimed at exploring the biological functions and related mechanism of long noncoding RNA 704 (LINC00704) in the proliferation and cell cycle progression of nasopharyngeal carcinoma (NPC) cells. The expression of LINC00704 in NPC tissues and cells was quantified by quantitative real-time polymerase chain reaction (qRT-PCR). After LINC00704 was overexpressed or knocked down in NPC cell lines, cell counting kit-8 (CCK-8) assay, 5-bromo-2'-deoxyuridine assay, flow cytometry assay, and Transwell assay were adopted to detect the proliferation, cell cycle progression, migration, and invasion of NPC cells. The interaction between LINC00704 and ETS proto-oncogene 1 (ETS1) was verified by bioinformatics analysis, RNA pull-down assay, and RNA immunoprecipitation assay. Dual-luciferase reporter gene assay and chromatin immunoprecipitation followed by qPCR analysis were used to verify the binding status between ETS1 and the promoter region of cyclin-dependent kinase 6 (CDK6). The regulatory effects of LINC00704 and ETS1 on CDK6 expression were detected by Western blot. LINC00704 expression was elevated in NPC tissues and cells, which was significantly correlated with the advanced TNM stage and poor differentiation. LINC00704 overexpression promoted the multiplication, migration, and invasion of NPC cells and blocked the cell cycle progression while knocking down LINC00704 worked oppositely. LINC00704 could bind to ETS1, thus promoting CDK6 transcription. Knocking down LINC00704 inhibited the CDK6 expression in NPC cells. LINC00704 promotes CDK6 transcription by recruiting ETS1 to the promoter region of CDK6, thus promoting the malignant progression of NPC., (© 2022 The Authors. The Kaohsiung Journal of Medical Sciences published by John Wiley & Sons Australia, Ltd on behalf of Kaohsiung Medical University.)

Osteosarcoma is a high-grade bone-forming neoplasm, with a complex genome. Tumours frequently show chromothripsis, many deletions, translocations and copy number alterations. Alterations in the p53 or Rb pathway are the most common genetic alterations identified in osteosarcoma. Using spontaneously transformed murine mesenchymal stem cells (MSCs) which formed sarcoma after subcutaneous injection into mice, it was previously demonstrated that p53 is most often involved in the transformation towards sarcomas with complex genomics, including osteosarcoma. In the current study, not only loss of p53 but also loss of p16 Ink4a is shown to be a driver of osteosarcomagenesis: murine MSCs with deficient p15 Ink4b , p16 Ink4a , or p19 Arf transform earlier compared to wild-type murine MSCs. Furthermore, in a panel of nine spontaneously transformed murine MSCs, alterations in p15 Ink4b , p16 Ink4a , or p19 Arf were observed in eight out of nine cases. Alterations in the Rb/p16 pathway could indicate that osteosarcoma cells are vulnerable to CDK4/CDK6 inhibitor treatment. Indeed, using two-dimensional (n = 7) and three-dimensional (n = 3) cultures of human osteosarcoma cell lines, it was shown that osteosarcoma cells with defective p16 INK4A are sensitive to the CDK4/CDK6 inhibitor palbociclib after 72-hour treatment. A tissue microarray analysis of 109 primary tumour biopsies revealed a subset of patients (20-23%) with intact Rb, but defective p16 or overexpression of CDK4 and/or CDK6. These patients might benefit from CDK4/CDK6 inhibition, therefore our results are promising and might be translated to the clinic., (© 2021. The Author(s).)

CDK4/6 inhibitors arrest the cell cycle in G1-phase. They are approved to treat breast cancer and are also undergoing clinical trials against a range of other tumour types. To facilitate these efforts, it is important to understand why a cytostatic arrest in G1 causes long-lasting effects on tumour growth. Here, we demonstrate that a prolonged G1 arrest following CDK4/6 inhibition downregulates replisome components and impairs origin licencing. Upon release from that arrest, many cells fail to complete DNA replication and exit the cell cycle in a p53-dependent manner. If cells fail to withdraw from the cell cycle following DNA replication problems, they enter mitosis and missegregate chromosomes causing excessive DNA damage, which further limits their proliferative potential. These effects are observed in a range of tumour types, including breast cancer, implying that genotoxic stress is a common outcome of CDK4/6 inhibition. This unanticipated ability of CDK4/6 inhibitors to induce DNA damage now provides a rationale to better predict responsive tumour types and effective combination therapies, as demonstrated by the fact that CDK4/6 inhibition induces sensitivity to chemotherapeutics that also cause replication stress., (© 2022 The Authors. Published under the terms of the CC BY 4.0 license.)

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive T-cell malignancy with a poor prognosis with current therapy. Here we report genome-wide CRISPR-Cas9 screening of ATLL models, which identified CDK6, CCND2, BATF3, JUNB, STAT3, and IL10RB as genes that are essential for the proliferation and/or survival of ATLL cells. As a single agent, the CDK6 inhibitor palbociclib induced cell cycle arrest and apoptosis in ATLL models with wild-type TP53. ATLL models that had inactivated TP53 genetically were relatively resistant to palbociclib owing to compensatory CDK2 activity, and this resistance could be reversed by APR-246, a small molecule activator of mutant TP53. The CRISPR-Cas9 screen further highlighted the dependence of ATLL cells on mTORC1 signaling. Treatment of ATLL cells with palbociclib in combination with mTORC1 inhibitors was synergistically toxic irrespective of the TP53 status. This work defines CDK6 as a novel therapeutic target for ATLL and supports the clinical evaluation of palbociclib in combination with mTORC1 inhibitors in this recalcitrant malignancy.

Background: Colorectal cancer (CRC) is one of the lethal cancers with a high mortality rate worldwide and understanding the mechanisms behind its progression is critical for improving patients' prognosis and developing therapeutics. MiR-500a-3p has been demonstrated to be involved in the progression of several human cancers but its role in CRC remains unclear. The aim of this study is to uncover the expression pattern and mechanisms of action of miR-500a-3p during the CRC progression., Methods: The expression of miR-500a-3p and Cyclin-dependent kinases 6 (CDK6) in 134 CRC tissues were tested by quantitative PCR (qPCR) and immunohistochemistry staining (IHC), respectively. The effect of miR-500a-3p on cell proliferation was explored in vitro and in vivo. The glycolysis of CRC cells was determined by Mass Spectrometry and Seahorse XF 96 Extracellular Flux Analyzer. A dual-luciferase reporter assay was performed to validate the relationship between miR-500a-3p and CDK6., Results: miR-500a-3p was abnormally downregulated in CRC tissues and cell lines and was negatively associated with a worse prognosis. miR-500a-3p mimics impeded CRC cell proliferation in vitro and in vivo. miR-500a-3p inhibited glucose consumption, lactate and ATP production, and down-regulated the expression of hexokinase2 (HK2). In silico prediction combined with western blot and luciferase assay confirmed that CDK6 is a direct target of miR-500a-3p. Overexpression of CDK6 phenotypically rescued the inhibitory effect of miR-500a-3p on the proliferation and glycolysis of CRC cells., Conclusions: Our study revealed a potential tumor-suppressive role of miR-500a-3p in CRC, specifically targeting CDK6 and inhibiting cancer cell proliferation and aerobic glycolysis, which may provide new insights into novel prognostic biomarkers and therapeutic targets for CRC., (© 2022. The Author(s).)

The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have become the standard of care, in combination with antiestrogen therapy, for patients with hormone receptor-positive (HR+)/HER2- advanced breast cancer. Various preclinical and translational research efforts have begun to shed light on the genomic and molecular landscape of resistance to these agents. Drivers of resistance to CDK4/6i therapy can be broadly subdivided into alterations impacting cell-cycle mediators and activation of oncogenic signal transduction pathways. The resistance drivers with the best translational evidence supporting their putative role have been identified via next-generation sequencing of resistant tumor biopsies in the clinic and validated in laboratory models of HR+ breast cancer. Despite the diverse landscape of resistance, several common, therapeutically actionable resistance nodes have been identified, including the mitotic spindle regulator Aurora Kinase A, as well as the AKT and MAPK signaling pathways. Based upon these insights, precision-guided therapeutic strategies are under active clinical development. This review will highlight the emerging evidence, in the clinic and in the laboratory, implicating this diverse spectrum of molecular resistance drivers., (©2021 American Association for Cancer Research.)

Cervical cancer is a malignant tumor that severely threatens female health. Recently, more and more studies indicated that circRNA could function as a tumor activator or suppressor in cervical cell development. Therefore, we aimed to study the effect of circRNA CDK6 (circCDK6) on the development and biological behavior of cervical cancer. We used quantitative real-time PCR (qRT-PCR) to examine the circCDK6 expression level in cervical cancer cell lines. RNA-fluorescence in situ hybridization confirmed the location of circCDK6 and miR-449a in HeLa and CaSki cells, respectively. Then, the biological function of silencing circCDK6 in cellular proliferation, metastasis, and Epithelial-Mesenchymal Transition (EMT)-related process was determined. We also performed RNA Binding Protein Immunoprecipitation (RIP) and Dual-luciferase reporter assay to determine the relationship between the circCDK6 and miR-449a. Finally, the results showed that circCDK6 level remarkably increased in several cervical cancer cells, especially in Hela and CaSki cells. The miR-449a was further confirmed to be a potential target of circCDK6, and its expression increased by silencing circCDK6. The circCDK6 participated in tumorigenesis and cancer progression and might serve as a tumor suppressive factor in cervical cell progression via Epithelial-MesenchymalTransition (EMT) process by regulating miR-449a.

The immunomodulatory drugs (IMiDs) lenalidomide and pomalidomide are highly effective treatments for multiple myeloma. However, virtually all patients eventually relapse due to acquired drug resistance with resistance-causing genetic alterations being found only in a small subset of cases. To identify non-genetic mechanisms of drug resistance, we here perform integrated global quantitative tandem mass tag (TMT)-based proteomic and phosphoproteomic analyses and RNA sequencing in five paired pre-treatment and relapse samples from multiple myeloma patients. These analyses reveal a CDK6-governed protein resistance signature that includes myeloma high-risk factors such as TRIP13 and RRM1. Overexpression of CDK6 in multiple myeloma cell lines reduces sensitivity to IMiDs while CDK6 inhibition by palbociclib or CDK6 degradation by proteolysis targeting chimeras (PROTACs) is highly synergistic with IMiDs in vitro and in vivo. This work identifies CDK6 upregulation as a druggable target in IMiD-resistant multiple myeloma and highlights the use of proteomic studies to uncover non-genetic resistance mechanisms in cancer., (© 2022. The Author(s).)

Cyclin-dependent kinase 6 (CDK6) is an important protein kinase that regulates cell growth, development, cell metabolism, inflammation, and apoptosis. Its overexpression is associated with reprogramming glucose metabolism through alternative pathways and apoptosis, which ultimately plays a significant role in cancer development. In the present study, we have investigated the structural and conformational changes in CDK6 at varying pH employing a multi-spectroscopic approach. Circular dichroism (CD) spectroscopy revealed at extremely acidic conditions (pH 2.0-4.0), the secondary structure of CDK6 got significantly disrupted, leading to aggregates formation. These aggregates were further characterized by employing Thioflavin T (ThT) fluorescence. No significant secondary structural changes were observed over the alkaline pH range (pH 7.0-11.0). Further, fluorescence and UV spectroscopy revealed that the tertiary structure of CDK6 was disrupted under extremely acidic conditions, with slight alteration occurring in mild acidic conditions. The tertiary structure remains intact over the entire alkaline range. Additionally, enzyme assay provided an insight into the functional aspect of CDK at varying pH; CDK6 activity was optimal in the pH range of 7.0-8.0. This study will provide a platform that provides newer insights into the pH-dependent dynamics and functional behavior of CDK6 in different CDK6 directed diseased conditions, viz. different types of cancers where changes in pH contribute to cancer development., Competing Interests: The authors have declared that no competing interests exist.

Despite the development of predictive biomarkers to shape treatment paradigms and outcomes, de novo EGFR TKI resistance advanced non-small cell lung cancer (NSCLC) remains an issue of concern. We explored clinical factors in 332 advanced NSCLC who received EGFR TKI and molecular characteristics through 65 whole exome sequencing of various EGFR TKI responses including; de novo (progression within 3 months), intermediate response (IRs) and long-term response (LTRs) (durability > 2 years). Uncommon EGFR mutation subtypes were significantly variable enriched in de novo resistance. The remaining sensitizing EGFR mutation subtypes (exon 19 del and L858R) accounted for 75% of de novo resistance. Genomic landscape analysis was conducted, focusing in 10 frequent oncogenic signaling pathways with functional contributions; cell cycle, Hippo, Myc, Notch, Nrf2, PI-3-Kinase/Akt, RTK-RAS, TGF-β, p53 and β-catenin/Wnt signaling. Cell cycle pathway was the only significant alteration pathway among groups with the FDR p-value of 6 × 10 -4 . We found only significant q-values of < 0.05 in 7 gene alterations; CDK6, CCNE1, CDK4, CCND3, MET, FGFR4 and HRAS which enrich in de novo resistance [range 36-73%] compared to IRs/LTRs [range 4-22%]. Amplification of CDK4/6 was significant in de novo resistance, contrary to IRs and LTRs (91%, 27.9% and 0%, respectively). The presence of co-occurrence CDK4/6 amplification correlated with poor disease outcome with HR of progression-free survival of 3.63 [95% CI 1.80-7.31, p-value < 0.001]. The presence of CDK4/6 amplification in pretreatment specimen serves as a predictive biomarker for de novo resistance in sensitizing EGFR mutation., (© 2022. The Author(s).)

Standard radiation therapy (RT) does not reliably provide locoregional control for women with multinode-positive breast cancer and triple-negative breast cancer (TNBC). We hypothesized that CDK4/6 inhibition (CDK4/6i) would increase the radiosensitivity not only of estrogen receptor-positive (ER+) cells, but also of TNBC that expresses retinoblastoma (RB) protein. We found that CDK4/6i radiosensitized RB WT TNBC (n = 4, radiation enhancement ratio [rER]: 1.49-2.22) but failed to radiosensitize RB-null TNBC (n = 3, rER: 0.84-1.00). RB expression predicted response to CDK4/6i + RT (R2 = 0.84), and radiosensitization was lost in ER+/TNBC cells (rER: 0.88-1.13) after RB1 knockdown in isogenic and nonisogenic models. CDK4/6i suppressed homologous recombination (HR) in RB WT cells but not in RB-null cells or isogenic models of RB1 loss; HR competency was rescued with RB reexpression. Radiosensitization was independent of nonhomologous end joining and the known effects of CDK4/6i on cell cycle arrest. Mechanistically, RB and RAD51 interact in vitro to promote HR repair. CDK4/6i produced RB-dependent radiosensitization in TNBC xenografts but not in isogenic RB1-null xenografts. Our data provide the preclinical rationale for a clinical trial expanding the use of CDK4/6i + RT to difficult-to-control RB-intact breast cancers (including TNBC) and nominate RB status as a predictive biomarker of therapeutic efficacy.

Objective: This study aimed to investigate the relationship between miR-21 and lipopolysaccharide (LPS)-induced myocardial injury and its molecular and regulatory mechanisms., Methods: We constructed LPS-mediated myocardial injury model using C57BL/6J mice and H9c2 cells. In-vivo, in-vitro, RIP and dual-luciferase reporter assays were used to determine the effect of miR-21 on myocardial injury., Results: In-vivo and in-vitro results showed that the expression of miR-21 was increased in LPS-treated H9c2 cells and myocardial tissues of mice, and the pro-inflammatory cytokines (IL-1β, IL-6, IL-8 and TNF-α) and NF-κB pathway were activated in LPS-treated H9c2 cells. Besides, the B-cell lymphoma-2 (Bcl-2) and cyclin-dependent kinase 6 (CDK6) expression levels decreased, while Bax and cleaved caspase 9 levels increased in LPS-treated H9c2 cells. Inhibition of miR-21 could suppress LPS-induced apoptosis, inflammatory reactions and NF-κB activation to attenuate LPS-induced myocardial injury in H9c2 cells, and effectively improve survival of mice with sepsis. Most importantly, Bcl-2 and CDK6 were found to be the direct target of miR-21 using dual-luciferase reporter and RNA immunoprecipitation assays. Further gain-of-function assay demonstrated that Bcl-2 or CDK6 over-expression promoted the protective effects of miR-21 inhibitor on LPS-mediated myocardial cells., Conclusion: Our findings revealed that the down-regulation or antagonism of miR-21 protects myocardial cells against LPS-induced apoptosis and inflammation through up-regulating Bcl-2 and CDK6 expression, which provided a new insight for prevention and treatment of myocardial injury., (© 2021. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Background: Circular RNAs (circRNAs) have been reported to play critical roles in the malignant progression of diverse human cancers, including multiple myeloma (MM). This study aimed to explore the functional role and underlying mechanism of circ&#95;SEC61A1 in MM progression., Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) assay was performed to detect the expression levels of circ&#95;SEC61A1, microRNA (miR)-660-5p and cyclin-dependent kinase 6 (CDK6) mRNA. The localization of circ&#95;SEC61A1 in MM cells was tested by the subcellular fractionation location assay. Actinomycin D assay was conducted to determine the characteristics of circ&#95;SEC61A1. Cell proliferation was evaluated by colony formation assay, 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay and 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Western blot assay was exploited to examine the expression of proteins. Cell migration and invasion were tested via transwell assay, and cell apoptosis was measured by flow cytometry analysis. Dual-luciferase reporter assay was utilized to confirm the interaction between miR-660-5p and circ&#95;SEC61A1 or CDK6., Results: Circ&#95;SEC61A1 level was increased in MM tissues and cells. Circ&#95;SEC61A1 was a stable circRNA and mainly located in cytoplasm. Circ&#95;SEC61A1 silence restrained the proliferation, metastasis and expedited the apoptosis in MM cells. CDK6 was identified as the target of miR-660-5p, and circ&#95;SEC61A1 sponged miR-660-5p to positively regulate CDK6 expression. The inhibitory impacts of circ&#95;SEC61A1 knockdown on the progression of MM cells were mitigated by miR-660-5p inhibition. MiR-660-5p overexpression blocked the malignant phenotypes of MM cells by targeting CDK6., Conclusion: Our study manifested that circ&#95;SEC61A1 could accelerate MM progression at least partially through modulating miR-660-5p/CDK6 axis., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Everyone carries a set of genetic variants that contribute to regulation of the levels of blood cells, with unknown clinical impact. One of them, rs445 within the cell-cycle checkpoint gene CDK6, reduces the levels of myeloid cell types including granulocytes. We treated CD3+ T cells and whole blood with palbociclib in 41 individuals, who were stratified by genotype for analyses. In T cells we assessed cell cycle and apoptosis, whereas in whole blood, apoptosis in activated (CD11b+), unactivated (CD11b-) granulocytes, cytotoxic (CD8 + CD4-), and helper (CD8-CD4+) T cells. We find that rs445 modulates the immune response of CD8+ T cells. It also increases the level of apoptotic CD11b + activated granulocytes after palbociclib treatment, which, in synergy with neutropenia, may affect drug related adverse events. These results suggest that the effect of palbociclib treatment may depend on underlying genetically encoded individual immune response as well as the direct response to the drug., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Endothelial cells (ECs) are a critical component of the hematopoietic niche, and the cross-talk between ECs and leukemia was reported recently. This study aimed to determine the genes involved in the proliferation inhibition of endothelial cells in leukemia., Methods: Human umbilical vein endothelial cells (HUVEC) were cultured alone or co-cultured with K562 cell lines. GeneChip assays were performed to identify the differentially expressed genes. The Celigo, MTT assay, and flow cytometric analysis were used to determine the effect of RNAi DIDO on cell growth and apoptosis. The differently expressed genes were verified by qRT-PCR (quantitative real-time PCR) and western-blot., Results: In K562-HUVEC co-cultured cell lines, 323 down-regulated probes were identified and the extracellular signal-regulated kinase 5 (ERK5) signaling pathway was significantly inhibited. Among the down-regulated genes, the death inducer-obliterator gene ( DIDO ) is a part of the centrosome protein and may be involved in cell mitosis. As shown in the public data, leukemia patients with lower expression of DIDO showed a better overall survival (OS). The HUVEC cells were infected with shDIDO lentivirus, and reduced expression, inhibited proliferation, and increased apoptosis was observed in shDIDO cells. In addition, the expression of Cyclin-Dependent Kinase 6 ( CDK6 ) and Cyclin D1 ( CCND1 ) genes was inhibited in shDIDO cells. Finally, the public ChIP-seq data were used to analyze the regulators that bind with DIDO , and the H3K4me3 and PolII (RNA polymerase II) signals were found near the Exon1 and exon2 sites of DIDO ., Conclusion: The knock-down of DIDO will inhibit the proliferation of endothelial cells in the leukemia environment. The expression of DIDO may be regulated by H3K4me3 and the inhibition of DIDO may lead to the down-regulation of CDK6 and CCND1 . However, how DIDO interacts with CDK6 and CCND1 requires further study., Competing Interests: The authors declare that they have no competing interests., (© 2022 Cao et al.)

Background: Ovarian cancer (OC) is one of the most lethal gynecologic cancers. Growing evidence has proven that CDK4/6 plays a key role in tumor immunity and the prognosis of many cancers. However, the expression and function of CDK4/6 in OC remain unclear. Therefore, we aimed to explore the influence of CDK4/6 in OC, especially on immunity., Methods: We analyzed CDK4/6 expression and prognosis using The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO) and Genotype Tissue Expression (GTEx) data. Subsequently, we used the cytoHubba plug-in of Cytoscape software and starBase to identify the noncoding RNAs (ncRNAs) regulating CDK4/6. Finally, we verified the effect of CDK4/6 on immunity in OC cell lines and animal models., Results: CDK4/6 expression was higher in OC tissues than in normal ovarian tissues, and the high expression levels of CDK4/6 contributed to the immunosuppressive state of OC and were thus related to the poor prognosis of OC patients. This was also in general agreement with the results of OC cell line and animal experiments. Mechanistically, the CDK4/6 inhibitor palbociclib increased the secretion of interferon (IFN)-γ and the interferon-stimulated gene (ISG) response, thereby upregulating the expression of antigen-presenting molecules; this effect was partly dependent on the STING pathway and thus activated immunity in OC. Additionally, according to public data, the LRRC75A-AS1-hsa-miR-330-5p axis could inhibit the immune response of OC patients by upregulating CDK4/6, leading to a poor prognosis., Conclusion: CDK4/6 affects the immune microenvironment of OC and correlates with the prognosis of OC patients., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Liu, Huang, Cui, Zhou, Qin, Zhang, Li, Li, Guo, Yang, Li, Fan, Li, Fu, Liu, Hu, Xiao, Wang, Dou, Wang, Li, Yang, Liu, Peng, Qin, You, Lu and Sun.)

Long noncoding RN (IncRNA) placenta-specific 2 (PLAC2) plays a critical role in many cancer types. A previous study found that PLAC2 expression dysregulated in non-small cell lung cancer (NSCLC). However, its function in LSCC is not entirely known. The present study enrolled 68 lung squamous cell carcinoma (LSCC, a major subtype of NSCLC) patients (gender: 39 males and 29 females; age: 36 to 67 years old; mean age: 53.2 ± 5.5 years old). The expression levels of PLAC2 in two types of tissue (non-tumor and LSCC) were measured by quantitative PCR. LSCC cells H1581 and H1993 were transfected with PLAC2 and cyclin-dependent kinase 6 (CDK6) expression vectors and small interfering RNAs (siRNAs), as well as microRNA-29C (miR-29C) mimic and inhibitor to perform overexpression and knock-down experiment, respectively. PLAC2 was upregulated in LSCC and positively correlated with CDK6 but negatively correlated with miR-29C. During a 5-year follow-up, high expression levels of PLAC2 were found to be closely associated with poor survival. PLAC2 and CDK6 were significantly upregulated in LSCC cells, while miR-29C was remarkably downregulated. miR-29C was predicted to be a potential target of PLAC2, and RNA pull-down assay confirmed their direct interaction. Overexpression of PLAC2 led to upregulation of CDK6 and downregulation of miR-29C, while knock-down of PLAC2 showed opposite effects. Overexpression of miR-29C downregulated CDK6, while knock-down of miR-29C increased the expression levels of CDK6. However, the expression of PLAC2 was not affected by overexpression or knock-down of miR-29C. Overexpression of PLAC2 and CDK6 enhanced LSCC cell proliferation and cell cycle progression, while knock-down showed opposite effects. In addition, overexpression of miR-29C inhibited cell proliferation and cell cycle progression, while its knockdown display opposite effects. Moreover, overexpression of miR-29C suppressed the role of overexpression of PLAC2 in cell proliferation and cell cycle progression. In conclusion, PLAC2 upregulates CDK6 by downregulating miR-29C to promote LSCC cell proliferation.

Zinc figure CCCH-type containing 15 (ZC3H15), also called developmentally regulated GTP-binding protein 1 (DRG1) family regulatory protein 1 (DFRP1), is a zinc finger containing protein. Despite playing a role in cellular signaling, it is found overexpressed in acute myeloid leukemia and also an independent prognostic marker in hepatocellular carcinoma patients. However, the biological effect of ZC3H15 in malignant melanoma (MM) remains unexplored. The expression of ZC3H15 in patients was analyzed using the R2: Genomics Analysis and Visualization Platform database. Immunohistochemical analysis, western blot, and qRT-PCR were used to detect ZC3H15 expression in melanoma tissues and cell lines. MTT, BrdU, flow cytometry assay, transwell, and western blot were performed to explore the proliferation, cell cycle, invasion, and migration of melanoma cells. We undertaken colony formation assay in vitro and tumor xenograft in vivo to detect the tumorigenicity of melanoma cells. In the present study, ZC3H15 was demonstrated highly expressed in melanoma tissues and cells. Elevated ZC3H15 impairs the survival of melanoma patients. Meanwhile, attenuation of ZC3H15 in melanoma cells inhibited cell proliferation and induced cycle arrest at G0/G1 phase. Consistently, the expression of cell cycle-related proteins cyclin dependent kinase 4 (CDK4), CDK6, and cyclin D1 (CCND1) was decreased while p21 was upregulated. Furthermore, we found the migration and invasion abilities were inhibited in ZC3H15-knockdown melanoma cells. In addition, downregulation of ZC3H15 resulted in inhibition of colony formation abilities in vitro and tumorigenesis in vivo. ZC3H15 promotes proliferation, migration/invasion, and tumorigenicity of melanoma cells. As a promising biomarker and therapeutic target in MM, ZC3H15 is worthy of further exploration., Competing Interests: The authors declare that there is no conflict of interest regarding the publication of this paper., (Copyright © 2021 Qian Li et al.)

The prognosis of glioma is poor as its pathogenesis and mechanisms underlying cisplatin chemoresistance remain unclear. Nucleosome assembly protein 1 like 1 (NAP1L1) is regarded as a hallmark of malignant tumors. However, the role of NAP1L1 in glioma remains unknown. In this study, we aimed to investigate the molecular functions of NAP1L1 in glioma and its involvement in cisplatin chemoresistance, if any. NAP1L1 was found to be upregulated in samples from The Cancer Genome Atlas (TCGA) database. Immunohistochemistry indicated that NAP1L1 and hepatoma-derived growth factor (HDGF) were enhanced in glioma as compared to the para-tumor tissues. High expressions of NAP1L1 and HDGF were positively correlated with the WHO grade, KPS, Ki-67 index, and recurrence. Moreover, NAP1L1 expression was also positively correlated with the HDGF expression in glioma tissues. Functional studies suggested that knocking down NAP1L1 could significantly inhibit glioma cell proliferation both in vitro and in vivo , as well as enhance the sensitivity of glioma cells to cisplatin (cDDP) in vitro . Mechanistically, NAP1L1 could interact with HDGF at the protein level and they co-localize in the cytoplasm. HDGF knockdown in NAP1L1-overexpressing glioma cells significantly inhibited cell proliferation. Furthermore, HDGF could interact with c-Jun, an oncogenic transcription factor, which eventually induced the expressions of cell cycle promoters, CCND1/CDK4/CDK6. This finding suggested that NAP1L1 could interact with HDGF, and the latter recruited c-Jun, a key oncogenic transcription factor, that further induced CCND1/CDK4/CDK6 expression, thereby promoting proliferation and chemoresistance in glioma cells. High expression of NAP1L1 in glioma tissues indicated shorter overall survival in glioma patients.

To study the regulation of miR-148a-3p on CDK6 and its mechanism in the progress of acute myeloid leukemia (AML), differential miRNAs were analyzed by bioinformatics, and the miR-148a-3p levels in AML cell lines were detected. Results showed that miR-148a-3p played a crucial role in AML, and the level was lower in AML cells, especially in J111 and KG-1a cells. In J111 and KG-1a cells, the up-regulation of miR-148a-3p mimics blocked the cell growth by arresting cell cycle at G2/M and enhancing cell apoptosis. Transwell and EMT markers detection indicated that miR-148a-3p reduced the cell migration and invasion. Afterward, through bioinformatics analysis, it showed that the CDK6 is one of the direct target genes of miR-148a-3p. DLR assay confirmed the target regulation. CDK6 overexpression reversed the effects of miR-148a-3p on AML cells. Collectively, miR-148a-3p inhibited the process of AML cells through disturbing the CDK-6 expression, implying that the trageting miR-148a-3p might be regarded as effective therapy of AML.

Undifferentiated mesenchymal tumors arising from the inner lining (intima) of large arteries are classified as intimal sarcomas (ISA) with MDM2 amplification as their molecular hallmark. Interestingly, undifferentiated pleomorphic sarcomas (UPS) of the heart have recently been suggested to represent the cardiac analog of ISA due to morphological overlap and high prevalence of MDM2 amplifications in both neoplasms. However, little is known about ISAs and cardiac UPS without MDM2 amplifications and molecular data supporting their common classification is sparse. Here, we report a series of 35 cases comprising 25 ISAs of the pulmonary artery, one ISA of the renal artery and 9 UPS of the left atrium. Tumors were analyzed utilizing the Illumina Infinium MethylationEPIC BeadChip array, enabling copy number profile generation and unsupervised DNA methylation analysis. DNA methylation patterns were investigated using t-distributed stochastic neighbor embedding (t-SNE) analysis. Histologically, all ISAs and UPS of the left atrium resembled extra-cardiac UPS. All cases exhibited highly complex karyotypes with overlapping patterns between ISA and UPS. 29/35 cases showed mutually exclusive amplifications in the cell-cycle associated oncogenes MDM2 (25/35), MDM4 (2/35), and CDK6 (2/35). We further observed recurrent co-amplifications in PDGFRA (21/35), CDK4 (15/35), TERT (11/35), HDAC9 (9/35), and CCND1 (4/35). Sporadic co-amplifications occurred in MYC, MYCN, and MET (each 1/35). The tumor suppressor CDKN2A/B was frequently deleted (10/35). Interestingly, DNA methylation profiling (t-SNE) revealed an overlap of ISA and cardiac UPS. This "ISA" methylation signature was distinct from potential histologic and molecular mimics. In conclusion, our data reveal MDM4 and CDK6 amplifications in ISAs and UPS of the left atrium, lacking MDM2 amplification. We further report novel co-amplifications of various oncogenes, which may have therapeutic implications. Finally, the genetic and epigenetic concordance of ISAs and UPS of the left atrium further supports a shared pathogenesis and common classification., (© 2021. The Author(s).)

Purpose: AcSé-ESMART is a proof-of-concept, phase I or II, platform trial, designed to explore targeted agents in a molecularly enriched cancer population. Arms A and B aimed to define the recommended phase II dose and activity of the CDK4/6 inhibitor ribociclib with topotecan and temozolomide (TOTEM) or everolimus, respectively, in children with recurrent or refractory malignancies., Patients and Methods: Ribociclib was administered orally once daily for 16 days after TOTEM for 5 days (arm A) or for 21 days with everolimus orally once daily continuously in a 28-day cycle (arm B). Dose escalation followed the continuous reassessment method, and activity assessment the Ensign design. Arms were enriched on the basis of molecular alterations in the cell cycle or PI3K/AKT/mTOR pathways., Results: Thirty-two patients were included, 14 in arm A and 18 in arm B, and 31 were treated. Fourteen patients had sarcomas (43.8%), and 13 brain tumors (40.6%). Main toxicities were leukopenia, neutropenia, and lymphopenia. The recommended phase II dose was ribociclib 260 mg/m 2 once a day, temozolomide 100 mg/m 2 once a day, and topotecan 0.5 mg/m 2 once a day (arm A) and ribociclib 175 mg/m 2 once a day and everolimus 2.5 mg/m 2 once a day (arm B). Pharmacokinetic analyses confirmed the drug-drug interaction of ribociclib on everolimus exposure. Two patients (14.3%) had stable disease as best response in arm A, and seven (41.2%) in arm B, including one patient with T-acute lymphoblastic leukemia with significant blast count reduction. Alterations considered for enrichment were present in 25 patients (81%) and in eight of nine patients with stable disease; the leukemia exhibited CDKN2A/B and PTEN deficiency., Conclusion: Ribociclib in combination with TOTEM or everolimus was well-tolerated. The observed activity signals initiated a follow-up study of the ribociclib-everolimus combination in a population enriched with molecular alterations within both pathways., Competing Interests: Xavier PaolettiConsulting or Advisory Role: MSD Oncology, Daiichii Sankyo Jonathan RubinoResearch Funding: Roche/Genentech (Inst), Novartis (Inst), Bristol Myers Squibb/Celgene (Inst), Cyclacel (Inst), AstraZeneca (Inst), Taiho Oncology (Inst) Nicolas AndreResearch Funding: BMS (Inst)Travel, Accommodations, Expenses: BMS Isabelle AertsConsulting or Advisory Role: AstraZenecaTravel, Accommodations, Expenses: Jazz Pharmaceuticals Gilles VassalConsulting or Advisory Role: Bayer, Roche/Genentech, AstraZeneca, Bristol Myers Squibb, Lilly, Ipsen, NovartisTravel, Accommodations, Expenses: Bristol Myers Squibb, Roche Birgit GeoergerConsulting or Advisory Role: Roche/Genentech, Boehringer Ingelheim, Bayer, AZD, NovartisNo other potential conflicts of interest were reported.

Background: There is no effective therapy for patients with malignant pleural mesothelioma (MPM) who progressed to platinum-based chemotherapy and immunotherapy., Methods: We aimed to investigate the antitumor activity of CDK4/6 inhibitors using in vitro and in vivo preclinical models of MPM., Results: Based on publicly available transcriptomic data of MPM, patients with CDK4 or CDK6 overexpression had shorter overall survival. Treatment with abemaciclib or palbociclib at 100 nM significantly decreased cell proliferation in all cell models evaluated. Both CDK4/6 inhibitors significantly induced G1 cell cycle arrest, thereby increasing cell senescence and increased the expression of interferon signalling pathway and tumour antigen presentation process in culture models of MPM. In vivo preclinical studies showed that palbociclib significantly reduced tumour growth and prolonged overall survival using distinct xenograft models of MPM implanted in athymic mice., Conclusions: Treatment of MPM with CDK4/6 inhibitors decreased cell proliferation, mainly by promoting cell cycle arrest at G1 and by induction of cell senescence. Our preclinical studies provide evidence for evaluating CDK4/6 inhibitors in the clinic for the treatment of MPM., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Ovarian cancer is a kind of cancer from the female genital tract; the molecular mechanism still needs to be explored. lncRNA plays a vital role in tumorigenesis and development. Our aim was to identify oncogenic lncRNAs in ovarian cancer and explore the potential molecular mechanism. SNHG15 was initially identified by using GEO datasets (GSE135886 and GSE119054) and validated by tumor tissues and the cell line, identifying that SNHG15 was upregulated in ovarian cancer. Besides, high SNHG15 indicated poor prognosis in ovarian cancer. Furthermore, knockdown SNHG15 suppresses ovarian cancer proliferation and promotes apoptosis. Mechanistically, SNHG15 promotes proliferation through upregulated CDK6 via sponging miR-370-3p. Taken together, our findings emphasize the important role of SNHG15 in ovarian cancer, suggesting that SNHG15 may be a promising target for ovarian cancer., Competing Interests: The authors have no conflict of interests., (Copyright © 2021 Yi Wang et al.)

Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are considered a breakthrough in cancer therapy. Currently approved for breast cancer treatment, CDK4/6 inhibitors are extensively tested in other cancer subtypes. Frequently observed side effects include hematological abnormalities such as reduced numbers of neutrophils, erythroid cells and platelets that are associated with anemia, bleeding and a higher risk of infections. In order to understand whether the adverse effects within the hematopoietic system are related to CDK4 or CDK6 we generated transgenic mice that lack either CDK4 or CDK6 in adult hematopoiesis. Anemia and perturbed erythroid differentiation are associated with the absence of CDK6 but did not manifest in CDK4- deficient mice. Total CDK6 knockout mice accumulate the most dormant fraction of hematopoietic stem cells due to an impaired exit of the quiescent state. We recapitulated this finding by deleting CDK6 in adult hematopoiesis. In addition, unlike total CDK6 knockout, all stem cell fractions were affected and increased in numbers. The deletion of CDK6 was also accompanied by neutropenia which is frequently seen in patients receiving CDK4/6 inhibitors. This was not the case in the absence of CDK4; CDK4 deficiency resulted in elevated numbers of myeloid progenitors without translating into numeric changes of differentiated myeloid cells. By using Cdk4fl/fl and Cdk6fl/fl mice we assign side effects of CDK4/6 inhibitors predominantly to the absence of CDK6. These mice represent a novel and powerful tool that will enable to study the distinct functions of CDK4 and CDK6 in a tissue-dependent manner.

Objective: LINC00205, a bidirectional lncRNA, located at human chromosome 21q22.3, was recently characterized as an oncogenic molecule contributing to cell proliferation in several cancers, including hepatocellular carcinoma (HCC). In the present study, we aim to probe the new molecular mechanism for LINC00205 controlling the proliferation of HCC cells., Patients and Methods: The expression status of LINC00205, miR-26a-5p, as well as CDK6 in HCC tissues/cell lines was determined by quantitative real-time PCR (qPCR). The cell proliferative activity was measured by using the Cell Counting Kit (CCK)-8 assay. Flow cytometry was performed to analyze cell cycle progression and apoptosis induction. The interaction among LINC00205, miR-26a-5p and CDK6, as well as transcription efficiency of LINC00205 promoter were examined by Dual-Luciferase reporter assay. Western blot was conducted to evaluate the protein levels of CDK6 in SNU-449 cells. The direct interplay between YY1 and LINC00205 promoter was detected by ChIP-qPCR., Results: LINC00205 was strongly expressed in HCC tissues and cell lines. Elevated LINC00205 expression was positively associated with worse prognosis as well as pathological grade in HCC. Suppression of LINC00205 could impede the proliferation of HCC cells by triggering the G0/G1-phase cell cycle arrest and apoptosis in vitro. Mechanistically, we illustrated that LINC00205 could accelerate the proliferation of HCC cells by boosting CDK6 expression via sponging miR-26a-5p. Moreover, we unveiled that LINC00205 could be activated by transcription factor Yin Yang-1 (YY1) as its direct downstream target., Conclusions: LINC00205, a novel YY1-modulated lncRNA, can facilitate the proliferation of HCC cells through YY1/miR-26a-5p/CDK6 pathway, and may serve as a promising diagnostic biomarker and therapeutic target for HCC.

The mitotic phase is a vital step in cell division and may be involved in cancer progression, but it remains unclear whether genetic variants in mitotic phase-related pathways genes impact the survival of these patients. Here, we investigated associations between 31 032 single nucleotide polymorphisms (SNPs) in 368 mitotic phase-related pathway genes and overall survival (OS) of patients with nonsmall cell lung cancer (NSCLC). We assessed the associations in a discovery data set of 1185 NSCLC patients from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial and validated the findings in another data set of 984 patients from the Harvard Lung Cancer Susceptibility Study. As a result, we identified three independent SNPs (ie, CHEK1 rs76744140 T>C, PRIM2 rs6939623 G>T and CDK6 rs113181986 G>C) to be significantly associated with NSCLC OS with an adjusted hazard ratio of 1.29 (95% confidence interval = 1.11-1.49, P = 8.26 × 10 -4 ), 1.26 (1.12-1.42, 1.10 × 10 -4 ) and 0.73 (0.63-0.86, 1.63 × 10 -4 ), respectively. Moreover, the number of combined unfavorable genotypes of these three SNPs was significantly associated with NSCLC OS and disease-specific survival in the PLCO data set (P trend  < .0001 and .0003, respectively). Further expression quantitative trait loci analysis showed that the rs76744140C allele predicted CHEK1 mRNA expression levels in normal lung tissues and that rs113181986C allele predicted CDK6 mRNA expression levels in whole blood tissues. Additional analyses indicated CHEK1, PRIM2 and CDK6 may impact NSCLC survival. Taken together, these findings suggested that these genetic variants may be prognostic biomarkers of patients with NSCLC., (© 2021 UICC.)

Glioblastoma (GBM) is one of the most aggressive brain malignancies with high incidences of developing treatment resistance, resulting in poor prognoses. Glioma stem cell (GSC)-derived exosomes are important players that contribute to GBM tumorigenesis and aggressive properties. Herein, we investigated the inhibitory roles of GBM-N019, a novel small molecule on the transfer of aggressive and invasive properties through the delivery of oncogene-loaded exosomes from GSCs to naïve and non-GSCs. Our results indicated that GBM-N019 significantly downregulated the expressions of the mammalian target of rapamycin (mTOR), signal transducer and activator of transcription 3 (STAT3), and cyclin-dependent kinase 6 (CDK6) signaling networks with concomitant inhibitory activities against viability, clonogenicity, and migratory abilities of U251 and U87MG cells. Treatments with GBM-N019 halted the exosomal transfer of protein kinase B (Akt), mTOR, p-mTOR, and Ras-related protein RAB27A to the naïve U251 and U87MG cells, and rescued the cells from invasive and stemness properties that were associated with activation of these oncogenes. GBM-N019 also synergized with and enhanced the anti-GBM activities of palbociclib in vitro and in vivo. In conclusion, our results suggested that GBM-N019 possesses good translational relevance as a potential anti-glioblastoma drug candidate worthy of consideration for clinical trials against recurrent glioblastomas.

Ph+ ALL is a poor-prognosis leukemia subtype driven by the BCR-ABL1 oncogene, either the p190- or the p210-BCR/ABL isoform in a 70:30 ratio. Tyrosine Kinase inhibitors (TKIs) are the drugs of choice in the therapy of Ph+ ALL. In combination with standard chemotherapy, TKIs have markedly improved the outcome of Ph+ ALL, in particular if this treatment is followed by bone marrow transplantation. However, resistance to TKIs develops with high frequency, causing leukemia relapse that results in <5-year overall survival. Thus, new therapies are needed to address relapsed/TKI-resistant Ph+ ALL. We have shown that expression of cell cycle regulatory kinase CDK6, but not of the highly related CDK4 kinase, is required for the proliferation and survival of Ph+ ALL cells. Comparison of leukemia suppression induced by treatment with the clinically-approved dual CDK4/6 inhibitor palbociclib versus CDK6 silencing revealed that the latter treatment was markedly more effective, probably reflecting inhibition of CDK6 kinase-independent effects. Thus, we developed CDK4/6-targeted proteolysis-targeting chimeras (PROTACs) that preferentially degrade CDK6 over CDK4. One compound termed PROTAC YX-2-107, which degrades CDK6 by recruiting the Cereblon ubiquitin ligase, markedly suppressed leukemia burden in mice injected with de novo or TKI-resistant Ph+ ALL. The effect of PROTAC YX-2-107 was comparable or superior to that of palbociclib. The development of CDK6-selective PROTACs represents an effective strategy to exploit the "CDK6 dependence" of Ph+ ALL cells while sparing a high proportion of normal hematopoietic progenitors that depend on both CDK6 and CDK6 for their survival. In combination with other agents, CDK6-selective PROTACs may be valuable components of chemotherapy-free protocols for the therapy of Ph+ ALL and other CDK6-dependent hematological malignancies.

CDK4/6 inhibitors (CDK4/6i) combined with endocrine therapy have shown impressive efficacy in estrogen receptor-positive advanced breast cancer. However, most patients will eventually experience disease progression on this combination, underscoring the need for effective subsequent treatments or better initial therapies. Here, we show that triple inhibition with fulvestrant, CDK4/6i and AKT inhibitor (AKTi) durably impairs growth of breast cancer cells, prevents progression and reduces metastasis of tumor xenografts resistant to CDK4/6i-fulvestrant combination or fulvestrant alone. Importantly, switching from combined fulvestrant and CDK4/6i upon resistance to dual combination with AKTi and fulvestrant does not prevent tumor progression. Furthermore, triple combination with AKTi significantly inhibits growth of patient-derived xenografts resistant to combined CDK4/6i and fulvestrant. Finally, high phospho-AKT levels in metastasis of breast cancer patients treated with a combination of CDK4/6i and endocrine therapy correlates with shorter progression-free survival. Our findings support the clinical development of ER, CDK4/6 and AKT co-targeting strategies following progression on CDK4/6i and endocrine therapy combination, and in tumors exhibiting high phospho-AKT levels, which are associated with worse clinical outcome., (© 2021. The Author(s).)

Lung squamous cell carcinoma (LSCC) remains a leading cause of cancer death with few therapeutic options. We characterized the proteogenomic landscape of LSCC, providing a deeper exposition of LSCC biology with potential therapeutic implications. We identify NSD3 as an alternative driver in FGFR1-amplified tumors and low-p63 tumors overexpressing the therapeutic target survivin. SOX2 is considered undruggable, but our analyses provide rationale for exploring chromatin modifiers such as LSD1 and EZH2 to target SOX2-overexpressing tumors. Our data support complex regulation of metabolic pathways by crosstalk between post-translational modifications including ubiquitylation. Numerous immune-related proteogenomic observations suggest directions for further investigation. Proteogenomic dissection of CDKN2A mutations argue for more nuanced assessment of RB1 protein expression and phosphorylation before declaring CDK4/6 inhibition unsuccessful. Finally, triangulation between LSCC, LUAD, and HNSCC identified both unique and common therapeutic vulnerabilities. These observations and proteogenomics data resources may guide research into the biology and treatment of LSCC., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: Despite recent improvements in treatment technologies, such as surgical resection and chemoradiotherapy, the prognosis of patients with esophagogastric junction adenocarcinoma (EJA) remains poor due to early lymph node metastasis. Since few studies have investigated genes associated with lymph node metastasis in EJA, we aimed to screen lymph node metastasis-associated genes and clarify their expression status and prognostic significance in EJA., Methods: The differential frequency of mutations between carcinoma and para-carcinoma tissues from 199 cases with EJA was detected using targeted next-generation sequencing (tNGS). Following a stratified analysis to determine that gender has no effect on the frequency of gene mutations, lymph node metastasis-related genes, including CDK6, MET, NOTCH1, and LRP1B, were screened, and CDK6 and LRP1B were selected for further study as they displayed significant differences in mutation rates. Differences in their expression status were verified using immunohistochemical (IHC) staining in 18 CDK6- and 17 LRP1B-mutated samples and a randomly matched control group., Results: tNGS revealed that CDK6 and LRP1B mutation frequencies were significantly different between EJA cases with (N ≥ 1) or without (N = 0) lymph node metastasis. In particular, CDK6 mutation frequency was expected less, whereas that of LRP1B was remarkably higher in cases with stage N0 than in those with stage N ≥ 1. IHC staining confirmed significant differences in CDK6 and LRP1B expression status between the study and control cohorts. Chi-square tests revealed that a high CDK6 expression status correlated significantly with smoking history (p = 0.044), T stage (p = 0.035), N stage (p = 0.000), and advanced TNM stage (p = 0.001) in EJA, whereas a high LRP1B expression status only correlated with BMI (p = 0.013) and N stage (p = 0.000). Furthermore, as confirmed by survival status investigation, a high LRP1B expression status predicted good prognosis, and a high CDK6 expression status was an independent predictor of poor prognosis in patients with EJA., Conclusions: Taken together, the findings of this study demonstrate that a high CDK6 and LRP1B expression status promotes and inhibits lymph node metastasis in patients with EJA, respectively, suggesting that both CDK6 and LRP1B are significantly potential predictors of lymph node metastasis and prognosis in EJA., (© 2021 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)

Intrinsic resistance to CDK4/6 inhibitors hinders their clinical utility in cancer treatment. Furthermore, the predictive markers of CDK4/6 inhibitors in gastric cancer (GC) remain incompletely described. Here, we found that PAX6 expression was negatively correlated with the response to palbociclib in vitro and in vivo in GC. We observed that the PAX6 expression level was negatively correlated with the overall survival of GC patients and further showed that PAX6 can promote GC cell proliferation and the cell cycle. The cell cycle is regulated by the interaction of cyclins with their partner serine/threonine cyclin-dependent kinases (CDKs), and the G1/S-phase transition is the main target of CDK4/6 inhibitors. Therefore, we tested whether PAX6 expression was correlated with the GC response to palbociclib. We found that PAX6 hypermethylates the promoter of LATS2 and inactivates the Hippo pathway, which upregulates cyclin D1 (CCND1) expression. This results in a suppressed response to palbociclib in GC. Furthermore, we found that the induction of the Hippo signaling pathway or treatment with a DNA methylation inhibitor could overcome PAX6-induced palbociclib resistance in GC. These findings uncover a tumor promoter function of PAX6 in GC and establish overexpressed PAX6 as a mechanism of resistance to palbociclib., (© 2021 The Authors. Clinical and Translational Medicine published by John Wiley & Sons Australia, Ltd on behalf of Shanghai Institute of Clinical Bioinformatics.)

Background: This study aimed to explore the role of mesenchymal stromal cells (MSCs)-derived exosomes (MSCs-Exo) in the cerebral ischemia-reperfusion (I/R) injury., Methods: Exosomes were isolated from MSCs of adult C57BL/6J mice by the gradient centrifugation method. The expression of miR-26a-5p and CDK6 in MSCs-Exo and mice brain tissues were evaluated by qRT-PCR and western blot. miR-26a-5p mimics and miR-NC were transfected into MSCs, and exosomes were isolated from the MSCs stably expressing miR-26a-5p. Then MSCs-Exo-miR-26a-5p mimics or MSCs-Exo-miR-NC was injected into mice through the tail vein, or added into medium to stimulate BV-2 cells. Cell viability was evaluated by CCK-8 assay. Cell apoptosis was detected by flow cytometry. The apoptosis in brain tissues was evaluated by TUNEL staining assay. Bioinformatics analysis and luciferase reporter assay were performed to determine the binding relationship between miR-26a-5p and CDK6., Results: miR-26a-5p was downregulated and CDK6 was upregulated in MSCs-Exo of MCAO-mice and OGD-induced MSCs. MSCs-Exo-miR-26a-5p mimics significantly reduced cell apoptosis of OGD-injured BV-2 cells. MSCs-Exo-miR-26a-5p mimics significantly reduced the infarct volume of MCAO-induced mice. Luciferase reporter assay revealed that CDK-6 was a target of miR-26a-5p. In addition, MSCs-Exo-miR-26a-5p mimics significantly decreased the expression of CDK6 in both OGD-induced BV-2 cells and the brain tissues of MCAO-treated mice., Conclusion: Our results indicated that MSCs‑Exo attenuated I/R injury in mice by inhibiting microglia apoptosis might via exosomal miR-26a-5p mediated suppression of CDK6. Our study shed light on the application of MSC-Exo as a potential therapeutic tool for cerebral I/R injury.

Ovarian cancer is a predominant gynecologic malignancy and correlated with high mortality and severe morbidity. Exosomal microRNAs (miRNAs) play crucial roles in various processes during the progression of ovarian cancer, such as cell proliferation, apoptosis, and invasion. However, the function of exosomal miR-21-5p in ovarian cancer is still unknown. Here, we found that miR-21-5p was upregulated in ovarian cancer tissues, plasma exosomes of ovarian cancer patients, and exosomes from ovarian cancer cells. MiR-21-5p was incorporated in the exosomes from the ovarian cancer cells. In addition, 5-ethynyl-2'-deoxyuridine (Edu), a marker of cancer cell proliferation, was enhanced by miR-21-5p mimic while reduced by miR-21-5p inhibitor in ovarian cancer cells. MiR-21-5p mimic could increase, but miR-21-5p inhibitor could decrease the migration and invasion of cancer cells. Ovarian cancer cell apoptosis was induced by miR-21-5p inhibitor. Moreover, miR-21-5p inhibitor could up-regulate the expression of pro-apoptotic cleaved caspase3 and Bax while downregulate the expression of anti-apoptotic Bcl2 in the cells. Exosomal miR-21-5p inhibited the expression of cyclin-dependent kinase 6 (CDK6) by targeting its 3'-untranslated region (3'-UTR) at both the mRNA and protein levels. Tumorigenicity analysis in nude mice revealed that exosomal miR-21-5p could increase tumor volume, size, and weight of ovarian cancer in vivo. Besides, miR-21-5p targeted CDK6 in tumor tissues of nude mice. In conclusion, exosomal miR-21-5p contributes to the progression of ovarian cancer by regulating CDK6. Our findings will provide novel insights into the mechanism of exosomal miR-21-5p in the development of ovarian cancer. Exosomal miR-21-5p may serve as a potential target for the therapy of ovarian cancer.

The cyclin-dependent kinase 6 (CDK6) regulates the transition through the G1-phase of the cell cycle, but also acts as a transcriptional regulator. As such CDK6 regulates cell survival or cytokine secretion together with STATs, AP-1 or NF-κB. In the hematopoietic system, CDK6 regulates T cell development and promotes leukemia and lymphoma. CDK4/6 kinase inhibitors are FDA approved for treatment of breast cancer patients and have been reported to enhance T cell-mediated anti-tumor immunity. The involvement of CDK6 in T cell functions remains enigmatic. We here investigated the role of CDK6 in CD8+ T cells, using previously generated CDK6 knockout ( Cdk6 -/- ) and kinase-dead mutant CDK6 ( Cdk6 K43M ) knock-in mice. RNA-seq analysis indicated a role of CDK6 in T cell metabolism and interferon (IFN) signaling. To investigate whether these CDK6 functions are T cell-intrinsic, we generated a T cell-specific CDK6 knockout mouse model ( Cdk6 fl/fl CD4-Cre). T cell-intrinsic loss of CDK6 enhanced mitochondrial respiration in CD8+ T cells, but did not impact on cytotoxicity and production of the effector cytokines IFN-γ and TNF-α by CD8+ T cells in vitro . Loss of CDK6 in peripheral T cells did not affect tumor surveillance of MC38 tumors in vivo . Similarly, while we observed an impaired induction of early responses to type I IFN in CDK6-deficient CD8+ T cells, we failed to observe any differences in the response to LCMV infection upon T cell-intrinsic loss of CDK6 in vivo . This apparent contradiction might at least partially be explained by the reduced expression of Socs1 , a negative regulator of IFN signaling, in CDK6-deficient CD8+ T cells. Therefore, our data are in line with a dual role of CDK6 in IFN signaling; while CDK6 promotes early IFN responses, it is also involved in the induction of a negative feedback loop. These data assign CDK6 a role in the fine-tuning of cytokine responses., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Klein, Witalisz-Siepracka, Gotthardt, Agerer, Locker, Grausenburger, Knab, Bergthaler and Sexl.)

Since their discovery as drivers of proliferation, cyclin-dependent kinases (CDKs) have been considered therapeutic targets. Small molecule inhibitors of CDK4/6 are used and tested in clinical trials to treat multiple cancer types. Despite their clinical importance, little is known about how CDK4/6 inhibitors affect the stability of CDK4/6 complexes, which bind cyclins and inhibitory proteins such as p21. We develop an assay to monitor CDK complex stability inside the nucleus. Unexpectedly, treatment with CDK4/6 inhibitors-palbociclib, ribociclib, or abemaciclib-immediately dissociates p21 selectively from CDK4 but not CDK6 complexes. This effect mediates indirect inhibition of CDK2 activity by p21 but not p27 redistribution. Our work shows that CDK4/6 inhibitors have two roles: non-catalytic inhibition of CDK2 via p21 displacement from CDK4 complexes, and catalytic inhibition of CDK4/6 independent of p21. By broadening the non-catalytic displacement to p27 and CDK6 containing complexes, next-generation CDK4/6 inhibitors may have improved efficacy and overcome resistance mechanisms.