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BRCA1-associated protein 1 serves as a tumor suppressor in hepatocellular carcinoma by deubiquitinating and stabilizing PTEN.

ABSTRACT: BRCA1-associated protein 1 (BAP1) or its mutants have been known to play critical regulatory roles in tumor biology, yet their role in hepatocellular carcinoma (HCC) remains largely unclear. In this study, we detected the mutations of all the exons of BAP1 in 105 HCC patients using Sanger sequencing, and found eight somatic mutations in 6 (5.71%) patients. We also found that the mRNA and protein levels of BAP1 were markedly downregulated in HCC versus the adjacent non-tumor tissues. Wild-type BAP1 but not mutant BAP1 significantly inhibited HCC cell proliferation, invasion, epithelial-mesenchymal transition (EMT) in vitro, and tumor progression and metastasis in vivo. Mechanistically, BAP1 complexed with PTEN and stabilized PTEN via deubiquitination and, furthermore, negatively regulated HCC cell EMT by deactivating the AKT/GSK-3β/Snail pathway. However, those tumor-inhibitory effects of BAP1 were abolished by inactivating mutations. Clinically, low BAP1 expression was positively correlated to aggressive tumor phenotypes, which also independently associated with poorer recurrence-free survival and overall survival after curative hepatectomy. Conclusively, our results indicate that BAP1, significantly downregulated, somatically mutated and negatively regulating EMT in HCC, serves as a tumor suppressor of HCC by deubiquitinating and stabilizing PTEN.

SUBMITTER: Chen X

PROVIDER: S-EPMC8167693 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundP53 pathway inactivation plays an important role in the process of breast cancer tumorigenesis. Post-translational protein modification abnormalities have been confirmed to be an important mechanism underlying inactivation of p53. Numerous deubiquitinating enzymes are aberrantly expressed in breast cancer, and a few deubiquitination enzymes can deubiquitinate and stabilize p53. Here, we report that ovarian tumor (OTU) deubiquitinase 3 (OTUD3) is a deubiquitylase of p53 in breast carcinoma (BC).MethodsCorrelations between the mRNA expression levels of OTUD3, TP53 and PTEN and the prognosis of BC were assessed with the Kaplan-Meier Plotter tool. OTUD3 protein expression in 80 pairs of specimens in our cohort was examined by immunohistochemistry and western blotting. The relationship among OTUD3, p53, and p21 proteins was analyzed. Half-life analysis and ubiquitylation assay were performed to elucidate the molecular mechanism by which OTUD3 stabilizes p53. The interaction between OTUD3 and p53 in BC cells was verified by a co-immunoprecipitation assay and GST pulldown experiments. MTS assay for proliferation detection, detection of apoptosis induced by cisplatin and colony formation assay were employed to investigate the functional effects of OTUD3 on breast cancer cells.ResultsOTUD3 downregulation is correlated with a poor prognosis in BC patients. OTUD3 expression is decreased in breast cancer tissues and not associated with the histological grade. OTUD3 also inhibits cell proliferation and clone formation and increases the sensitivity of BC cells to apoptosis induced by chemotherapy drugs. Reduced OTUD3 expression accompanied by decreased p53 abundance is correlated with human breast cancer progression. Ectopic expression of wild-type OTUD3, but not its catalytically inactive mutant, stabilizes and activates p53. Mechanistically, OTUD3 interacts directly with p53 through the amino-terminal OTU region. Finally, OTUD3 protects p53 from murine double minute 2 (Mdm2)-mediated ubiquitination and degradation, enabling the deubiquitination of p53 in BC cells.ConclusionsIn summary, we found that OTUD3 may be a potential therapeutic target for restoring p53 function in breast cancer cells and suggest that the OTUD3-p53 signaling axis may play a critical role in tumor suppression.

Project description:BACKGROUND:Misregulation of the p53-mdm2 loop function is a major mechanism to promote hepatocellular carcinoma (HCC). RBM38, a member of the RNA recognition motif (RRM) family of RNA binding proteins (RBPs), plays a fundamental role in the posttranscriptional control of gene expression and regulatory functions in human tumors. A novel RBM38-p53-mdm2 autoregulatory feedback loop has been demonstrated. However, its mechanistic role in HCC remains unclear. METHODS:In the present study, we investigated the role and molecular mechanism of misregulation in the p53-mdm2 loop function by RBM38 in HCC. First we investigated the correlation of RBM38 activity and p53-mdm2 loop function in liver cancer cells and HCC tissues by western blot and quantitative RT-PCR. We then conducted functional assays to investigate the molecular roles of RBM38 in inhibiting liver cancer cells aggressiveness in vitro and suppressing tumorigenicity in vivo. RESULTS:We observed RBM38 protein expression was commonly silenced coupled with increased mdm2 and decreased wild type (wt) p53 in liver cancer cells and HCC tissues compared to the corresponding normal liver cells and adjacent liver tissues. RBM38 mRNA level was significantly lower in HCC than adjacent liver tissues, whereas mdm2 and wtp53 mRNA levels were similar between HCC and adjacent liver tissues. This implied that deactivation of RBM38 could disrupt the p53-mdm2 loop and promote HCC, even though p53 and mdm2 transcript amounts were stable. Then, we generated stable liver cancer cell lines with overexpressed RBM38 (RBM38-OE) and found that up-regulation of RBM38 could inhibit mdm2 and restore wtp53 expression. Luciferase assay shown that RBM38 destabilized the mdm2 transcript through binding to multiple AU-/U-rich elements in mdm2 3'-UTR. Furthermore, functional assays showed that ectopic expression of RBM38 could induce liver cancer cell apoptosis and senescence, inhibit proliferation and colony growth, and suppress migration and invasion in vitro. Lastly, RBM38 could suppress HCC tumorigenicity in vivo. CONCLUSION:Our findings suggested that RBM38 may be a core contributor in stabilizing the p53-mdm2 loop function to prevent HCC, and a potential novel target to provide a therapeutic strategy for HCC by inhibiting mdm2 and rescuing p53 from inactivation.

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BRCA1-associated protein 1 serves as a tumor suppressor in hepatocellular carcinoma by deubiquitinating and stabilizing PTEN.

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