泛素羧基端水解酶L1在人类疾病发生发展中的调控作用

泛素-蛋白酶系统(ubiquitin proteasome system,UPS)在细胞分裂、细胞信号转导以及细胞程序死亡的过程中起到非常重要的作用.此系统主要是靠泛素化酶和去泛素化酶来实施对于目的蛋白的快速精确调控.其中,泛素羧基端水解酶L1 (ubiquitin carboxy-terminal hydrolase L1,UCH-L1)是去泛素化酶家族中的一个重要的分子,是由223个氨基酸组成的一类半胱氨酸水解酶,通过识另和裂解目标蛋白上羧基末端第76位甘氨酸,可把泛素分子从目标蛋白的多聚泛素化链上切割下来,阻止目标蛋白被UPS系统降解,从而对目标蛋白的降解代谢负向调控.由此而产生游离的泛素单体,则进一步循环参与下一个目标蛋白的泛素化代谢.UCH-L1是一个多功能的分子,除了去泛素化酶功能,还有稳定泛素单体,泛素连接酶及参与细胞骨架蛋白调控,细胞微管形成等多功能作用.     

M phase phosphorylation of the epigenetic regulator UHRF1 regulates its physical association with the deubiquitylase USP7 and stability

UHRF1 (Ubiquitin-like, with PHD and RING finger domains 1) plays an important role in DNA CpG methylation, heterochromatin function and gene expression. Overexpression of UHRF1 has been suggested to contribute to tumorigenesis. However, regulation of UHRF1 is largely unknown. Here we show that the deubiquitylase USP7 interacts with UHRF1. Using interaction-defective and catalytic mutants of USP7 for complementation experiments, we demonstrate that both physical interaction and catalytic activity of USP7 are necessary for UHRF1 ubiquitylation and stability regulation. Mass spectrometry analysis identified phosphorylation of serine (S) 652 within the USP7-interacting domain of UHRF1, which was further confirmed by a UHRF1 S652 phosphor (S652ph)-specific antibody. Importantly, the S652ph antibody identifies phosphorylated UHRF1 in mitotic cells and consistently S652 can be phosphorylated by the M phase-specific kinase CDK1-cyclin B in vitro. UHRF1 S652 phosphorylation significantly reduces UHRF1 interaction with USP7 in vitro and in vivo, which is correlated with a decreased UHRF1 stability in the M phase of the cell cycle. In contrast, UHRF1 carrying the S652A mutation, which renders UHRF1 resistant to phosphorylation at S652, is more stable. Importantly, cells carrying the S652A mutant grow more slowly suggesting that maintaining an appropriate level of UHRF1 is important for cell proliferation regulation. Taken together, our findings uncovered a cell cycle-specific signaling event that relieves UHRF1 from its interaction with USP7, thus exposing UHRF1 to proteasome-mediated degradation. These findings identify a molecular mechanism by which cellular UHRF1 level is regulated, which may impact cell proliferation.     

Deubiquitinase OTUD6A promotes proliferation of cancer cells via regulating Drp1 stability and mitochondrial fission

Dynamin‐related protein 1 (Drp1) is a cytosolic protein responsible for mitochondrial fission and is essential in the initiation and development of several human diseases, including cancer. However, the regulation of Drp1, especially of its ubiquitination, remains unclear. In this study, we report that the ovarian tumor‐associated protease deubiquitinase 6A (OTUD6A) deubiquitylates and stabilizes Drp1, thereby facilitating regulation of mitochondrial morphology and tumorigenesis. OTUD6A is upregulated in human patients with colorectal cancer. The depletion of OTUD6A leads to lower Drp1 levels and suppressed mitochondrial fission, and the affected cells are consequently less prone to tumorigenesis. Conversely, the overexpression of OTUD6A increases Drp1 levels and its protein half‐life and enhances cancer cell growth. Therefore, our results reveal a novel upstream protein of Drp1, and its role in tumorigenesis that is played, in part, through the activation of mitochondrial fission mediated by Drp1.

Abbreviations

Drp1

dynamin‐related protein 1

DUBs

deubiquitinases

His‐ub

His‐ubiquitin

IB

immunoblot

IHC

immunohistochemistry

IP

immunoprecipitation

MARCH5

membrane‐associated ring‐CH‐type finger 5

Mfn1

mitofusin 1

Mfn2

mitofusin 2

NIK

NF‐κB‐inducing kinase

Opa1

optic atrophy 1

OTUs

ovarian tumor‐associated proteases

OTUD6A

ovarian tumor‐associated protease deubiquitinase 6A

     

USP22 deficiency in melanoma mediates resistance to T cells through IFNγ-JAK1-STAT1 signal axis

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泛素化/去泛素化过程调节雄激素受体影响前列腺癌进展的研究进展

泛素是由76个氨基酸组成的小分子蛋白质,广泛存在于真核细胞中。泛素结合到目的蛋白的过程称为泛素化,其逆过程为去泛素化,泛素化后激发下游信号复合体组装、蛋白质构象和活性的改变、蛋白水解、自噬、内呑、染色质重塑和DNA修复等过程。真核生物超过80%的蛋白降解由泛素化系统介导,泛素依赖性蛋白水解是一个极其复杂的过程,参与众多生物分子学过程。通过调节蛋白稳态,泛素化还能调节多种生物过程,包括细胞周期、细胞增殖、细胞凋亡等,这些都与肿瘤发生和进展密切相关。目前公认多种雄激素受体(AR)异常与前列腺癌进展关系密切,包括AR基因扩增、突变、剪切变异、AR活性增强等。多项研究证实泛素化/去泛素化过程调节AR表达水平和活性,影响AR信号途径,调节前列腺癌进展。本文主要综述泛素化/去泛素化与前列腺癌及AR的研究进展。     

Deubiquitinase PSMD14 promotes ovarian cancer progression by decreasing enzymatic activity of PKM2

Dysregulation of deubiquitination has been reported to contribute to carcinogenesis. However, the function and mechanism of deubiquitinating enzyme 26S proteasome non‐ATPase regulatory subunit 14 (PSMD14) in the progression of ovarian cancer (OV), the deadliest gynecological cancer, still remains to be characterized. The present study demonstrated that PSMD14 was overexpressed in OV tissues and its higher levels correlated with a higher International Federation of Gynecology and Obstetrics (FIGO) stage in OV patients. A high level of PSMD14 expression was related to poor survival in OV patients. Knockdown and overexpression experiments elucidated that PSMD14 stimulated OV cell proliferation, invasion, and migration in vitro. Repression of PSMD14 suppressed OV tumor growth in vivo. PSMD14 inhibitor O‐phenanthroline (OPA) effectively attenuated malignant behaviors of OV cells in vitro and OV tumor growth in vivo. Mechanistically, we uncovered that PSMD14 was involved in post‐translational regulation of pyruvate kinase M2 isoform (PKM2). PSMD14 decreased K63‐linked ubiquitination on PKM2, downregulated the ratio of PKM2 tetramers to dimers and monomers, and subsequently diminished pyruvate kinase activity and induced nuclear translocation of PKM2, contributing to aerobic glycolysis in OV cells. Collectively, our findings highlight the potential roles of PSMD14 as a biomarker and therapeutic candidate for OV.     

BAP1 suppresses prostate cancer progression by deubiquitinating and stabilizing PTEN

Deubiquitinase BAP1 is an important tumor suppressor in several malignancies, but its functions and critical substrates in prostate cancer (PCa) remain unclear. Here, we report that the mRNA and protein expression levels of BAP1 are downregulated in clinical PCa specimens. BAP1 can physically bind to and deubiquitinate PTEN, which inhibits the ubiquitination‐mediated degradation of PTEN and thus stabilizes PTEN protein. Ectopically expressed BAP1 in PCa cells increases PTEN protein level and subsequently inhibits the AKT signaling pathway, thus suppressing PCa progression. Conversely, knockdown of BAP1 in PCa cells leads to the decrease in PTEN protein level and the activation of the Akt signaling pathway, therefore promoting malignant transformation and cancer metastasis. However, these can be reversed by the re‐expression of PTEN. More importantly, we found that BAP1 protein level positively correlates with PTEN in a substantial fraction of human cancers. These findings demonstrate that BAP1 is an important deubiquitinase of PTEN for its stability and the BAP1‐PTEN signaling axis plays a crucial role in tumor suppression.

Abbreviations

BAP1

the BRCA1‐associated protein 1

DUBs

deubiquitinases

GEO

Gene Expression Omnibus

IP

immunoprecipitation

KEGG

the Kyoto Encyclopedia of Genes and Genomes

PCa

prostate cancer

PTEN

phosphatase and tensin homolog deleted on chromosome 10

qRT–PCR

quantitative real‐time polymerase chain reaction

TCGA

the Cancer Genome Atlas

USP

the ubiquitin–proteasome system

VM

vasculogenic mimicry