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Notch signaling is aberrantly activated in approximately 30% of hepatocellular carcinoma (HCC), significantly contributing to tumorigenesis and disease progression. Expression of the major Notch receptor, NOTCH1, is upregulated in HCC cells and correlates with advanced disease stages, although the molecular mechanisms underlying its overexpression remain unclear. Here, we report that expression of the intracellular domain of NOTCH1 (NICD1) is upregulated in HCC cells due to antagonism between the E3‐ubiquitin ligase F‐box/WD repeat‐containing protein 7 (FBXW7) and the large scaffold protein abnormal spindle‐like microcephaly‐associated protein (ASPM) isoform 1 (ASPM‐i1). Mechanistically, FBXW7‐mediated polyubiquitination and the subsequent proteasomal degradation of NICD1 are hampered by the interaction of NICD1 with ASPM‐i1, thereby stabilizing NICD1 and rendering HCC cells responsive to stimulation by Notch ligands. Consistently, downregulating ASPM‐i1 expression reduced the protein abundance of NICD1 but not its FBXW7‐binding‐deficient mutant. Reinforcing the oncogenic function of this regulatory module, the forced expression of NICD1 significantly restored the tumorigenic potential of ASPM‐i1‐deficient HCC cells. Echoing these findings, NICD1 was found to be strongly co‐expressed with ASPM‐i1 in cancer cells in human HCC tissues (P < 0.001). In conclusion, our study identifies a novel Notch signaling regulatory mechanism mediated by protein–protein interaction between NICD1, FBXW7, and ASPM‐i1 in HCC cells, representing a targetable vulnerability in human HCC. [ABSTRACT FROM AUTHOR]

The F‐box and WD repeat domain containing 7 (FBXW7) tumour suppressor gene encodes a substrate‐recognition subunit of Skp, cullin, F‐box (SCF)‐containing complexes. The tumour‐suppressive role of FBXW7 is ascribed to its ability to drive ubiquitination and degradation of oncoproteins. Despite this molecular understanding, therapeutic approaches that target defective FBXW7 have not been identified. Using genome‐wide clustered regularly interspaced short palindromic repeats (CRISPR)‐Cas9 screens, focussed RNA‐interference screens and whole and phospho‐proteome mass spectrometry profiling in multiple FBXW7 wild‐type and defective isogenic cell lines, we identified a number of FBXW7 synthetic lethal targets, including proteins involved in the response to replication fork stress and proteins involved in replication origin firing, such as cell division cycle 7‐related protein kinase (CDC7) and its substrate, DNA replication complex GINS protein SLD5 (GINS4). The CDC7 synthetic lethal effect was confirmed using small‐molecule inhibitors. Mechanistically, FBXW7/CDC7 synthetic lethality is dependent upon the replication factor telomere‐associated protein RIF1 (RIF1), with RIF1 silencing reversing the FBXW7‐selective effects of CDC7 inhibition. The delineation of FBXW7 synthetic lethal effects we describe here could serve as the starting point for subsequent drug discovery and/or development in this area. [ABSTRACT FROM AUTHOR]

Abstract: The Aurora kinases (AURKA and AURKB) have attracted attention as therapeutic targets in head and neck squamous cell carcinomas. Aurora kinases were first defined as regulators of mitosis that localization to the centrosome (AURKA) and centromere (AURKB), governing formation of the mitotic spindle, chromatin condensation, activation of the core mitotic kinase CDK1, alignment of chromosomes at metaphase, and other processes. Subsequently, additional roles for Aurora kinases have been defined in other phases of cell cycle, including regulation of ciliary disassembly and DNA replication. In cancer, elevated expression and activity of Aurora kinases result in enhanced or neomorphic locations and functions that promote aggressive disease, including promotion of MYC expression, oncogenic signaling, stem cell identity, epithelial-mesenchymal transition, and drug resistance. Numerous Aurora-targeted inhibitors have been developed and are being assessed in preclinical and clinical trials, with the goal of improving head and neck squamous cell carcinoma treatment. [ABSTRACT FROM AUTHOR]

Collagen peptides (CP) have been shown to protect against osteoporosis. Yet, its mechanism on anti-osteoporosis remains unclear. Cell viability, levels of alkaline phosphatase (ALP), reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) of hydrogen peroxide (H 2 O 2)-induced oxidative stress in Saos-2 cells pretreated with CP were examined. The effect and regulatory of CP on FBXW7-p100-NF-κB axis and the relationship between the molecules were explored by overexpressing FBXW7, silencing p100 or NF-κB in Saos-2 cells. Western blot and RT-PCR were performed to determine the expressions of FBXW7, p100 and NF-κB. Hematoxylin & Eosin (H&E) staining was performed to determine morphological indexes of bone tissues in ovariectomized-induced osteoporosis rats treated with CP. CP increased cell viability, ALP and antioxidant activities in H 2 O 2 -induced oxidative stress in Saos-2 cells. Results on cell viability, ALP, antioxidant levels, protein and gene expression levels in FBXW7-overexpressed, p100-silenced and NF-κB-silenced Saos-2 cells indicate that FBXW7, p100 and NF-κB are the key regulators and CP treatment modulates FBXW7-p100-NF-κB axis in Saos-2 cells. In addition, pretreatment and treatment with CP in ovariectomized rats improved osteoporosis. CP could effectively prevent and alleviate osteoporosis. The protective effect of CP on osteoporosis was achieved in part by inhibiting oxidative damage of osteoblasts and promoting bone formation. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Our purpose was to detect the molecular mechanism of F-box and WD repeat domain containing 7 (FBXW7) in regulating cell growth and metastasis of oral squamous cell carcinoma (OSCC). PATIENTS AND METHODS: Real Time-quantitative Polymerase Chain Reaction (RT-qPCR) and Western blot were applied to calculate the messenger ribonucleic acid (mRNA) and protein levels of genes and miR-27a. The proliferation and invasive abilities were measured by methyl thiazolyl tetrazolium (MTT) and transwell assays. The. Kaplan-Meier method was conducted to evaluate the 5-year overall survival of oral squamous cell carcinoma patients. RESULTS: FBXW7 was downregulated while miR-27a was upregulated in OSCC tissues and cells compared with the corresponding adjacent tissues. Downregulation of FBXW7 or upregulation of miR-27a in OSCC tissues predicted poor outcome of OSCC patients. FBXW7 suppressed the growth through the phosphatidylinositol 3-hydroxy kinase/protein kinase B (PI3K/AKT) signaling pathway in OSCC cell line HSC3. FBXW7 inhibited the invasion-mediated epithelial-mesenchymal transition (EMT) in HSC3 cells. The expression of FBXW7 was mediated by miR-27a by directly binding to the 3'-untranslated region (3'-UTR) of FBXW7 in HSC3 cells. MiR-27a reversed partial roles of FBXW7 on the proliferation and invasion in OSCC cells. CONCLUSIONS: FBXW7 was mediated by miR-27a and could inhibit the proliferation through the PI3K/AKT pathway and invasion-mediated EMT in OSCC cell line. The newly identified miR-27a/FBXW7/PI3K/AKT axis provides novel insights into the pathogenesis of OSCC. [ABSTRACT FROM AUTHOR]

The absence of biomarkers to accurately predict anticancer therapy response remains a major obstacle in clinical oncology. We applied a genome‐wide loss‐of‐function screening approach in human haploid cells to characterize genetic vulnerabilities to classical microtubule‐targeting agents. Using docetaxel and vinorelbine, two well‐established chemotherapeutic agents, we sought to identify genetic alterations sensitizing human HAP1 cells to these drugs. Despite the fact that both drugs act on microtubules, a set of distinct genes were identified whose disruption affects drug sensitivity. For docetaxel, this included a number of genes with a function in mitosis, while for vinorelbine we identified inactivation of FBXW7, RB1, and NF2, three frequently mutated tumor suppressor genes, as sensitizing factors. We validated these genes using independent knockout clones and confirmed FBXW7 as an important regulator of the mitotic spindle assembly. Upon FBXW7 depletion, vinorelbine treatment led to decreased survival of cells due to defective mitotic progression and subsequent mitotic catastrophe. We show that haploid insertional mutagenesis screens are a useful tool to study genetic vulnerabilities to classical chemotherapeutic drugs by identifying thus far unknown sensitivity factors. These results provide a rationale for investigating patient response to vinca alkaloid‐based anticancer treatment in relation to the mutational status of these three tumor suppressor genes, and could in the future lead to the establishment of novel predictive biomarkers or suggest new drug combinations based on molecular mechanisms of drug sensitivity. [ABSTRACT FROM AUTHOR]

Gefitinib, an epidermal growth factor receptor–tyrosine kinase inhibitor (EGFR‐TKI), is an effective treatment for non‐small‐cell lung cancer (NSCLC) with EGFR activating mutations, but inevitably, the clinical efficacy is impeded by the emergence of acquired resistance. The tumor suppressor gene FBXW7 modulates chemosensitivity in various human cancers. However, its role in EGFR‐TKI therapy in NSCLC has not been well studied. Here, we demonstrate that the mice with deficient Fbxw7 have greater susceptibility to urethane‐induced lung tumor development. Through analysis of The Cancer Genome Atlas data, we show that deletion of FBXW7 occurs in 30.9% of lung adenocarcinomas and 63.5% of lung squamous cell carcinomas, which significantly leads to decrease in FBXW7 mRNA expression. The reduction in FBXW7 mRNA level is associated with poor overall survival in lung cancer patients. FBXW7 knockdown dramatically promotes epithelial–mesenchymal transition, migration, and invasion in NSCLC cells. Moreover, with silenced FBXW7, EGFR‐TKI‐sensitive cells become resistant to gefitinib, which is reversed by the mammalian target of rapamycin inhibitor, rapamycin. Furthermore, xenograft mouse model studies show that FBXW7 knockdown enhances tumorigenesis and resistance to gefitinib. Combination of gefitinib with rapamycin treatment suppresses tumor formation of gefitinib‐resistant (GR) FBXW7‐knockdown cells. In conclusion, our findings suggest that loss of FBXW7 promotes NSCLC progression as well as gefitinib resistance and combination of gefitinib and rapamycin may provide an effective therapy for GR NSCLC. [ABSTRACT FROM AUTHOR]

FBXW7 has been reported to be a candidate tumor suppressor gene on 4q31. Three isoforms (α-form, β-form, and γ-form) of FBXW7 are produced from mRNAs with distinct 5′ exons. Our previous study identified the specific suppression of the mRNA expression of the FBXW7 β-form in human gliomas. Because this form is the major FBXW7 isoform in the human brain, we elucidated the silencing mechanisms for the FBXW7 β-form in gliomas. No genetic alterations were found in the whole FBXW7 gene including putative promoter region of the β-form. Treatments with 5-azacytidine and trichostatin A did not induce re-expression. A sodium bisulfite-modification assay indicated that CpG sequences in the promoter of FBXW7 β-form were not methylated in glioma cells. Meanwhile we searched for the expression of FBXW7 and the sodium bisulfite sequences in normal human peripheral blood cells, and we surprisingly found that the mRNA expression of the FBXW7 β-form was highly suppressed and the CpG sequences in the promoter region of the FBXW7 β-form were heavily methylated. Our data suggest that the inactivation of the FBXW7 β-form plays an important role in the pathogenesis of gliomas and that an unknown mechanism(s) other than mutation and methylation is the major cause of the suppression of the FBXW7 β-form in gliomas. [ABSTRACT FROM AUTHOR]

Tissue stem cells undergo premature senescence under stress, promoting age-related diseases; however, the associated mechanisms remain unclear. Here, we report that in response to radiation, oxidative stress, or bleomycin, the E3 ubiquitin ligase FBW7 mediates cell senescence and tissue fibrosis through telomere uncapping. FBW7 binding to telomere protection protein 1 (TPP1) facilitates TPP1 multisite polyubiquitination and accelerates degradation, triggering telomere uncapping and DNA damage response. Overexpressing TPP1 or inhibiting FBW7 by genetic ablation, epigenetic interference, or peptidomimetic telomere dysfunction inhibitor (TELODIN) reduces telomere uncapping and shortening, expanding the pulmonary alveolar AEC2 stem cell population in mice. TELODIN, synthesized from the seventh β strand blade of FBW7 WD40 propeller domain, increases TPP1 stability, lung respiratory function, and resistance to senescence and fibrosis in animals chronically exposed to environmental stress. Our findings elucidate a pivotal mechanism underlying stress-induced pulmonary epithelial stem cell senescence and fibrosis, providing a framework for aging-related disorder interventions. • Stress-induced pulmonary senescence (SIPS) and fibrosis are mediated by FBW7 • FBW7 triggers telomere uncapping and DNA damage response through TPP1 degradation • FBW7 KO or TPP1 OE increases telomere capping, preventing SIPS and fibrogenesis • TELODIN disrupts FBW7 binding to TPP1 for pulmonary resistance to SIPS and fibrosis Environmental stressors such as bacterial toxins and radiation can cause premature aging and fibrosis. Wang et al. reveal that in mice exposed to radiation or the bacterial toxin bleomycin, the tumor suppressor protein FBW7 marks the telomere protein TPP1 for degradation, triggering telomere uncapping and shortening, cancer or stem cell aging, and pulmonary fibrosis. Targeting FBW7 by an 8-mer synthetic peptide mimetic protects telomeres, enhances pulmonary respiratory function, and prevents stress-induced lung premature aging and fibrosis. [ABSTRACT FROM AUTHOR]

Chemotherapy continues to be a major treatment strategy for various human malignancies. However, the frequent emergence of chemoresistance compromises chemotherapy efficacy leading to poor prognosis. Thus, overcoming drug resistance is pivotal to achieve enhanced therapy efficacy in various cancers. Although increased evidence has revealed that reduced drug uptake, increased drug efflux, drug target protein alterations, drug sequestration in organelles, enhanced drug metabolism, impaired DNA repair systems, and anti-apoptotic mechanisms, are critically involved in drug resistance, the detailed resistance mechanisms have not been fully elucidated in distinct cancers. Recently, F-box protein (FBPs), key subunits in Skp1-Cullin1-F-box protein (SCF) E3 ligase complexes, have been found to play critical roles in carcinogenesis, tumor progression, and drug resistance through degradation of their downstream substrates. Therefore, in this review, we describe the functions of FBPs that are involved in drug resistance and discuss how FBPs contribute to the development of cancer drug resistance. Furthermore, we propose that targeting FBPs might be a promising strategy to overcome drug resistance and achieve better treatment outcome in cancer patients. Lastly, we state the limitations and challenges of using FBPs to overcome chemotherapeutic drug resistance in various cancers. [ABSTRACT FROM AUTHOR]

• Only FBXW7α was found in human testis. • FBXW7 was mainly expressed in differentiated germ cells instead of stem cells. • Different expression patterns suggest different functions between mouse and human FBXW7. F-box and WD domain protein 7 (FBXW7) is reported to bind with c-Myc in mouse spermatogonial stem cells, regulating self-renewal; however, the pattern and stage of expression of FBXW7 in human testes are unclear. In the present study, we examined the expression of human FBXW7 in adult testis, and analyzed fixed sections from adult testes and fetal testes to determine the cell type-specific expression pattern of FBXW7. The results showed that FBXW7α and FBXW7β genes are expressed in the testis; however, only FBXW7α protein could be detected. FBXW7 was not detected in human spermatogonial stem cells. Interestingly, FBXW7 was mainly expressed in the cell nuclei of later stage germ cells and differentiated somatic cells. We also observed high FBXW7 expression in human fetal germ cells, particularly in prespermatogonia. Our results raised the possibility that FBXW7 has different functions in humans and mice. The cell type-specific expression pattern of FBXW7 suggests that it performs regulatory functions during the late stage of human spermatogenesis instead of being involved in the self-renewal of spermatogonial stem cells. [ABSTRACT FROM AUTHOR]

Introduction Rare, but clinically aggressive endometrial cancers exhibit high frequencies of somatic mutations in the FBXW7 (F-box and WD repeat domain-containing 7) tumor suppressor gene. In fact, somatic FBXW7 mutations have been reported in 17-30% of serous endometrial cancers, 11-28% of uterine carcinosarcomas, and 7-25% of clear cell endometrial cancers. Despite these high frequencies of mutation, the molecular effects of mutated FBXW7 in the context of endometrial cancers have not been determined. Materials and Methods We introduced six recurrent somatic FBXW7 mutations into serous endometrial cancer cells using transient transfection and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) editing and analyzed expression of potentially druggable proteins using Western blotting. The sensitivity of CRISPR-edited FBXW7-mutant serous endometrial cancer cells to targeted inhibitors was tested using cell viability assays; molecular and cellular effects of the inhibitors were studied using Western blotting, apoptosis assays and flow cytometry. Results FBXW7 mutations in transiently transfected and CRISPR-edited serous endometrial cancer cells resulted in increased Cyclin E1, steroid receptor coactivator 3 (SRC-3), c- MYC, Rictor, glycogen synthase kinase 3 (GSK3), P70S6 kinase, and protein kinase B (AKT) phosphorylated protein levels. CRISPR-edited FBXW7-mutant serous endometrial cancer cells also exhibited decreased viability in response to SI-2 (a SRC inhibitor) and dinaciclib (a cyclin dependent kinase (CDK) inhibitor) compared to parental cells. Decreased viability was associated with changes in cell cycle distribution and/or increased apoptosis. Conclusion Our findings provide the first direct biochemical evidence that FBXW7 mutations result in increased levels of potentially druggable proteins in serous endometrial cancer cells and demonstrate that some of these effects confer increased sensitivity to targeted agents in vitro. [ABSTRACT FROM AUTHOR]