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PU.1 is essential for the differentiation of haemopoietic precursors and is strongly implicated in leukaemogenesis, yet the protein interactions that regulate its activity in different myeloid lineages are still largely unknown. In the present study, by combining fluorescent EMSA (electrophoretic mobility-shift assay) with MS, we reveal the presence of hnRNP K (heterogeneous nuclear ribonucleoprotein K) in molecular complexes that PU.1 forms on the CD11b promoter during the agonist-induced maturation of AML (acute myeloid leukaemia)-derived cells along both the granulocytic and the monocytic lineages. Although hnRNP K and PU.1 act synergistically during granulocytic differentiation, hnRNP K seems to have a negative effect on PU.1 activity during monocytic maturation. Since hnRNP K acts as a docking platform, integrating signal transduction pathways to nucleic aciddirected processes, it may assist PU.1 in activating or repressing transcription by recruiting lineage-specific components of the transcription machinery. It is therefore possible that hnRNP K plays a key role in the mechanisms underlying the specific targeting of protein-protein interactions identified as mediators of transcriptional activation or repression and may be responsible for the block of haemopoietic differentiation. [ABSTRACT FROM AUTHOR]

hnRNP K is a highly conserved nucleocytoplasmic shuttling protein, which associates with RNAs through synergistic binding via its three KH domains. hnRNP K is required for proper nuclear export and translational control of its mRNA targets, and these processes are controlled by hnRNP K's movement between subcellular compartments. Whereas the nuclear export and localization of hnRNP K that is associated with mRNP complexes has been well studied, the trafficking of hnRNP K that is unbound to mRNA has yet to be elucidated. To that end, we expressed an EGFP-tagged RNA binding-defective form of hnRNP K in intact Xenopus embryos, and found it was rapidly degraded in vivo . Deleting hnRNP K's nuclear localization signal (NLS), which contains two prospective ubiquitination sites, rescued the protein from degradation. These data demonstrate a novel activity for the NLS of hnRNP K in regulating the protein's stability in vivo when it is unbound to nucleic acids. [ABSTRACT FROM AUTHOR]

Mortalin/mtHsp70/Grp75 (mot-2), a heat shock protein 70 family member, is an essential chaperone, enriched in cancers, and has been shown to possess pro-proliferative and anti-apoptosis functions. An allelic form of mouse mortalin (mot-1) that differs by two amino acids, M618V and G624R, in the C terminus substrate-binding domain has been reported. Furthermore, genome sequencing of mortalin from Parkinson disease patients identified two missense mutants, R126W and P509S. In the present study, we investigated the significance of these mutations in survival, proliferation, and oxidative stress tolerance in human cells. Using mot-1 and mot-2 recombinant proteins and specific antibodies, we performed screening tofind their binding proteins and then identified ribosomal protein L-7 (RPL-7) and elongation factor-1 α (EF-1α), which differentially bind to mot-1 and mot-2, respectively. We demonstrate that mot-1, R126W, or P509S mutant (i) lacks mot-2 functions involved in carcinogenesis, such as p53 inactivation and hTERT/hnRNP-K (heterogeneous nuclear ribonucleoprotein K) activation; (ii) causes increased level of endogenous oxidative stress; (iii) results in decreased tolerance of cells to exogenous oxidative stress; and (iv) shows differential binding and impact on the RPL-7 and EF-1α proteins. These factors may mediate the transformation of longevity/pro-proliferative function of mot-2 to the premature aging/anti-proliferative effect of mutants, and hence may have significance in cellular aging, Parkinson disease pathology, and prognosis. [ABSTRACT FROM AUTHOR]

Lung cancer is one of the most common malignancies worldwide, but its pathogenesis remains unknown. The current study examined the effects of heterogeneous nuclear ribonucleoprotein K (hnRNP K)-targeted small interfering RNA (siRNA) on the growth and apoptosis of lung cancer cells in vitro. The expression of hnRNP K was studied by the SP method of immunohistochemistry in lung tissue samples of 70 cases of lung cancer. hnRNP K siRNA were transfected into human lung cancer cell line, A549, using Lipofectamine 2000. Cells transfected with siRNAn and untreated served as controls. The inhibitory effect of siRNA on the expression of hnRNP K mRNA and protein was detected by reverse transcription polymerase chain reaction and western blot analysis. The change in cell cycling and cell apoptosis of siRNA-treated cells was detected by flow cytometry. The rates of positive hnRNP K expression in lung tumors of diameters ≤3, 3-5 and ≥5 cm, were 38.5, 95.2 and 91.7%, respectively. A significant difference was identified between lung tumors with diameters of ≤3 and ≥3 cm (P<0.01). The expression of hnRNP K mRNA was significantly inhibited in siRNA-transfected cells compared with that in control cells (P<0.05). Notably, hnRNP K protein decreased in hnRNP K siRNA-transfected cells, but exhibited no effect on the control groups. siRNA targeting human hnRNP K effectively inhibited the growth of lung cancer cell line, A549, and the distribution of the cell cycle. The apoptosis rate was 4.79% and the number of cells increased in the G0/G1 phase from 37.21 to 85.60% and decreased in the S and G2/M phases from 47.71 to 13.50% and 14.00 to 0.32%, respectively, following 24 h of transfection. hnRNP K siRNA promotes A549 apoptosis and the apoptosis rate was 4.79% (P<0.01). Therefore, hnRNP K siRNA may inhibit the proliferation of A549 cells. In addition, hnRNP K promotes the growth of lung cancer cells and, therefore, hnRNP K siRNA may inhibit the growth and increase the apoptosis of lung cancer cells. [ABSTRACT FROM AUTHOR]

Background: Aberrant alternative splicing plays critical role in aging and age-related diseases. Heterogeneous nuclear ribonucleoproteins (hnRNPs) reportedly regulate RNA splicing process. Whether and how hnRNPs contribute to age-related neurodegenerative diseases, especially Alzheimer's disease (AD), remain elusive. Methods: Immunoblotting and immunostaining were performed to determine expression patterns and cellular/subcellular localization of the long isoform of hnRNP D-like (L-DL), which is a hnRNP family member, in mouse hippocampus. Downregulation of L-DL in WT mice was achieved by AAV-mediated shRNA delivery, followed by memory-related behavioural tests. L-DL interactome was analysed by affinity-precipitation and mass spectrometry. Alternative RNA splicing was measured by RNA-seq and analyzed by bioinformatics-based approaches. Downregulation and upregulation of L-DL in APP/PS1 mice were performed using AAV-mediated transduction. Results: We show that L-DL is specifically localized to nuclear speckles. L-DL levels are decreased in the hippocampus of aged mouse brains and downregulation of L-DL impairs cognition in mice. L-DL serves as a structural component to recruit other speckle proteins, and regulates cytoskeleton- and synapse-related gene expression by altering RNA splicing. Mechanistically, these splicing changes are modulated via L-DL-mediated interaction of SF3B3, a core component of U2 snRNP, and U2AF65, a U2 spliceosome protein that guides U2 snRNP's binding to RNA. In addition, L-DL levels are decreased in APP/PS1 mouse brains. While downregulation of L-DL deteriorates memory deficits and overexpression of L-DL improves cognitive function in AD mice, by regulating the alternative splicing and expression of synaptic gene CAMKV. Conclusions: Our findings define a molecular mechanism by which hnRNP L-DL regulates alternative RNA splicing, and establish a direct role for L-DL in AD-related synaptic dysfunction and memory decline. [ABSTRACT FROM AUTHOR]

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a member of the hnRNP family, which exists in the nucleus and the cytoplasm simultaneously. It is a multifunctional protein that can participate in a variety of regulatory progressions of gene expression and signal transduction, such as chromatin remodeling, transcription, RNA alternative splicing and translation. hnRNP K not only directly binds to the kinases, but also recruits the associated factors regarding transcription, splicing and translation to control gene expression, and therefore, it serves as a docking platform for integrating transduction pathways to nucleic acid-directed processes. Numerous studies also show that abnormal expression of hnRNP K is closely associated with the tumor formation. This protein is overexpressed in numerous types of cancer and its aberrant cytoplasmic localization is also associated with a worse prognosis for patients. These results consistently indicate that hnRNP K has a key role in cancer progression. To understand the hnRNP K pathophysiological process in tumor disease, the previous research results regarding the association between hnRNP K and tumors were reviewed. [ABSTRACT FROM AUTHOR]

Heterogeneous nuclear ribonucleoprotein K (hnRNP K), an evolutionarily conserved protein, is involved in several important cellular processes that are relevant to cell proliferation, differentiation, apoptosis, and cancer development. However, details of hnRNP K expression during mammalian oogenesis and preimplantation embryo development are lacking. The present study investigates the expression and cellular localization of K protein in the mouse ovaries and preimplantation embryos using immunostaining. We demonstrate, for the first time, that hnRNP K is abundantly expressed in the nuclei of mouse oocytes in primordial, primary and secondary follicles. In germ vesicle (GV)-stage oocytes, hnRNP K accumulates in the germinal vesicle in a spot distribution manner. After germinal vesicle breakdown, speckled hnRNP K is diffusely distributed in the cytoplasm. However, after fertilization, the K protein relocates into the female and male pronucleus and persists in the blastomere nuclei. Localization of K protein in the human ovary and ovarian granulosa cell tumor (GCT) was also investigated. Overall, this study provides important morphological evidence to better understand the possible roles of hnRNP K in mammalian oogenesis and early embryo development. [ABSTRACT FROM AUTHOR]

Background: Protein immunoprecipitation (IP) coupled with MS provides means to interrogate protein complexes and their posttranslational modifications (PTMs). In a typical protein IP assay antibodies are conjugated to protein A/G beads requiring large amounts of antibodies, tube transfers and centrifugations. Results: As an alternative, we present Matrix-IP, beads-free microplate-based platform with surface-immobilized antibodies. Assay utilizes standard 96-well polypropylene PCR plates that are laboratory-fabricated with UV-C light and then protein A/G coated prior to IP reaction. We demonstrate application of Matrix-IP platform in MS analysis of heterogeneous nuclear ribonucleoprotein K (hnRNP K) interactome and PTMs. Conclusion: Matrix-IP is time-saving, easy to use high throughput method adaptable for low sample amounts and automation. [ABSTRACT FROM AUTHOR]

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is importantly involved in the regulation of development, DNA damage response, and several human diseases. The molecular mechanisms that control the expression of hnRNP K are largely unknown. In the present study, we investigated the detailed mechanism of the transcriptional regulation of human hnRNP K gene. Two activating and one repressive elements located in the proximal segment of the transcriptional initiation site were identified in hnRNP K gene. A 19 bp-region was responsible for the inhibitory activities of the repressor element. Twenty proteins were identified by DNA-affinity purification and mass spectrometry analyses as binding partners of the primary activating element in the hnRNP K promoter. Chromatin immunoprecipitation and EMSA analysis confirmed the binding of Sp1 with hnRNP K promoter. Sp1 enhanced the promoter activity, increased the expression of hnRNP K, and reduced the mRNA level of angiotensinogen, a gene known to be negatively regulated by hnRNP K. In summary, the current study characterized the promoter elements that regulate the transcription of human hnRNP K gene, identified 20 proteins that bind to the primary activating element of hnRNP K promoter, and demonstrated a functional effect of Sp1 on hnRNP K transcription. [ABSTRACT FROM AUTHOR]

Background Overexpression of heterogeneous nuclear ribonucleoprotein K (hnRNP K), a DNA/RNA binding protein, is associated with metastasis in nasopharyngeal carcinoma (NPC). However, the mechanisms underlying hnRNP K-mediated metastasis is unclear. The aim of the present study was to determine the role of matrix metalloproteinase (MMP) in hnRNP K-mediated metastasis in NPC. Methods We studied hnRNP K-regulated MMPs by analyzing the expression profiles of MMP family genes in NPC tissues and hnRNP K-knockdown NPC cells using Affymetrix microarray analysis and quantitative RT-PCR. The association of hnRNP K and MMP12 expression in 82 clinically proven NPC cases was determined by immunohistochemical analysis. The hnRNP K-mediated MMP12 regulation was determined by zymography and Western blot, as well as by promoter, DNA pull-down and chromatin immunoprecipitation (ChIP) assays. The functional role of MMP12 in cell migration and invasion was demonstrated by MMP12-knockdown and the treatment of MMP12-specific inhibitor, PF-356231. Results MMP12 was overexpressed in NPC tissues, and this high level of expression was significantly correlated with high-level expression of hnRNP K (P = 0.026). The levels of mRNA, protein and enzyme activity of MMP12 were reduced in hnRNP K-knockdown NPC cells. HnRNP K interacting with the region spanning -42 to -33 bp of the transcription start site triggered transcriptional activation of the MMP12 promoter. Furthermore, inhibiting MMP12 by MMP12 knockdown and MMP12-specific inhibitor, PF-356231, significantly reduced the migration and invasion of NPC cells. Conclusions Overexpression of MMP12 was significantly correlated with hnRNP K in NPC tissues. HnRNP K can induce MMP12 expression and enzyme activity through activating MMP12 promoter, which promotes cell migration and invasion in NPC cells. In vitro experiments suggest that NPC metastasis with high MMP12 expression may be treated with PF-356231. HnRNP K and MMP12 may be potential therapeutic markers for NPC, but additional validation studies are warranted. [ABSTRACT FROM AUTHOR]

Hepatocellular carcinoma (HCC) is the third highest cause of cancer-related deaths globally. One of the cellular hallmarks of this disease is dysregulation of apoptosis, and a better understanding of this process is important if progress is to be made toward effectively treating HCC. Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a RNA-binding protein that is implicated in apoptosis and is upregulated in various cancers, including HCC. In this study, we report new evidence for a crucial role of hnRNP K in suppressing apoptosis in HCC cells. We used the chemotherapeutic agent 5-fluorouracil to induce apoptosis in HCC cell lines and found that hnRNP K was downregulated, independent of both p53 and caspases. Prolonged downregulation of hnRNP K using small interfering RNA (siRNA) significantly decreased cell viability and increased apoptosis in HCC cell lines in a p53-independent manner. Moreover, enhanced tumor necrosis factor-related apoptosis-inducing ligand potency, independent of BH3-interacting domain death agonist (BID) cleavage, was also observed in hnRNP K siRNA-treated cells. Examination of the underlying mechanism revealed that hnRNP K suppresses the activity of various caspases through controlling transcription of the caspase inhibitor XIAP. Taken together, this study establishes that hnRNP K plays an antiapoptotic role in HCC cell lines, independent of p53 status, via the maintenance of high levels of endogenous caspase inhibitors, and also identifies hnRNP K as a possible therapeutic marker for cancer treatment. [ABSTRACT FROM AUTHOR]

Human cytomegalovirus (HCMV) is the most frequent viral cause of congenital defects and HCMV infection in immunocompromised patients may trigger devastating disease. Cytotoxic lymphocytes control HCMV by releasing granzymes towards virus-infected cells. In mice, granzyme M (GrM) has a physiological role in controlling murine CMV infection. However, the underlying mechanism remains poorly understood. In this study, we showed that human GrM was expressed by HCMV-specific CD8+ T cells both in latently infected healthy individuals and in transplant patients during primary HCMV infection. We identified host cell heterogeneous nuclear ribonucleoprotein K (hnRNP K) as a physiological GrM substrate. GrM most efficiently cleaved hnRNP K in the presence of RNA at multiple sites, thereby likely destroying hnRNP K function. Host cell hnRNP K was essential for HCMV replication not only by promoting viability of HCMV-infected cells but predominantly by regulating viral immediate-early 2 (IE2) protein levels. Furthermore, hnRNP K interacted with IE2 mRNA. Finally, GrM decreased IE2 protein expression in HCMV-infected cells. Our data suggest that targeting of hnRNP K by GrM contributes to the mechanism by which cytotoxic lymphocytes inhibit HCMV replication. This is the first evidence that cytotoxic lymphocytes target host cell proteins to control HCMV infections. [ABSTRACT FROM AUTHOR]

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) mediates antiapoptotic activity in part by inducing downstream antiapoptotic genes. To systematically identify hnRNP K targets in nasopharyngeal carcinoma (NPC), affymetrix chips were used to identify genes that were both overexpressed in primary NPC and downregulated by hnRNP K knockdown in NPC-TW02 cells. The resulting gene set included the antiapoptotic gene, FLIP, which was selected for further study. In cells treated with hnRNP K siRNA, TRAIL-induced apoptosis was enhanced and the FLIP protein level was reduced. Promoter, DNA pull-down and chromatin-immunoprecipitation assays revealed that hnRNP K directly interacts with the poly(C) element on the FLIP promoter, resulting in transcriptional activation. Through iTRAQ-mass spectrometric identification of proteins differentially associated with the poly(C) element or its mutant, nucleolin was determined to be a cofactor of hnRNP K for FLIP activation. Furthermore, FLIP was highly expressed in tumor cells, and this high-level expression was significantly correlated with high-level hnRNP K expression (P=0.002) and poor overall survival (P=0.015) as examined in 67 NPC tissues. A multivariate analysis confirmed that FLIP was an independent prognostic factor for NPC. Taken together, these findings indicate that FLIP expression is transcriptionally regulated by hnRNP K and nucleolin, and may be a potential prognostic and therapeutic marker for NPC. [ABSTRACT FROM AUTHOR]

Backgrounds: Heterogeneous ribonucleoproteins (hnRNPs) are involved in the metastasis-related network. Our previous study demonstrated that hnRNP K is associated with epithelial-to-mesenchymal transition (EMT) in A549 cells. However, the precise molecular mechanism of hnRNP K involved in TGF-β1-induced EMT remains unclear. This study aimed to investigate the function and mechanism of hnRNP K interacted with microtubule-associated protein 1B light chain (MAP 1B-LC1) in TGF-β1-induced EMT.Methods: Immunohistochemistry was used to detect the expression of hnRNP K in non-small-cell lung cancer (NSCLC). GST-pull down and immunofluorescence were performed to demonstrate the association between MAP 1B-LC1 and hnRNP K. Immunofluorescence, transwell assay and western blot was used to study the function and mechanism of the interaction of MAP 1B-LC1 with hnRNP K during TGF-β1-induced EMT in A549 cells.Results: hnRNP K were highly expressed in NSCLC, and NSCLC with higher expression of hnRNP K were more frequently rated as high-grade tumors with poor outcome. MAP 1B-LC1 was identified and validated as one of the proteins interacting with hnRNP K. Knockdown of MAP 1B-LC1 repressed E-cadherin downregulation, vimentin upregulation and actin filament remodeling, decreased cell migration and invasion during TGF-β1-induced EMT in A549 cells. hnRNP K increased microtubule stability via interacting with MAP 1B-LC1 and was associated with acetylated ɑ-tubulin during EMT.Conclusion: hnRNP K can promote the EMT process of lung cancer cells induced by TGF-β1 through interacting with MAP 1B-LC1. The interaction of MAP 1B/LC1 with hnRNP K may improve our understanding on the mechanism of TGF-β1-induced EMT in lung cancer. [ABSTRACT FROM AUTHOR]