Hepatocellular carcinoma (HCC) has emerged as one of the most prevalent life-threatening cancers, and the high mortality rate is largely due to the metastasis. The sustained activation of Smad4 and transforming growth factor-β (TGF-β) is closely associated with advanced HCC metastasis. However, the regulatory mechanism underlying the aberrant activation of Smad4 and TGF-β pathway remains elusive. In this study, using a functional screen of USPs siRNA library, we identified ubiquitin-specific proteases USP10 as a deubiquitinating enzyme (DUB) that sustains the protein level of Smad4 and activates TGF-β signaling. Further analysis showed that USP10 directly interacts with Smad4 and stabilizes it through the cleavage of its proteolytic ubiquitination, thus promoting HCC metastasis. The suppression of USP10 by either shRNAs or catalytic inhibitor Spautin-1 significantly inhibited the migration of HCC cells, whereas the reconstitution of Smad4 was able to efficiently rescue this defect. Overall, our study not only uncovers the regulatory effect of USP10 on the protein abundance of Smad4, but also indicates that USP10 could be regarded as a potential intervention target for the metastatic HCC in Smad4-positive patients.

中文翻译：

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去泛素化酶USP10通过去泛素化和稳定Smad4蛋白促进肝细胞癌转移。

肝细胞癌（HCC）已经成为最普遍的威胁生命的癌症之一，其高死亡率很大程度上归因于转移。Smad4和转化生长因子-β（TGF-β）的持续激活与晚期HCC转移密切相关。但是，Smad4和TGF-β途径异常激活的调控机制仍然难以捉摸。在这项研究中，使用USPs siRNA文库的功能筛选，我们确定了泛素特异性蛋白酶USP10为维持Smad4蛋白质水平并激活TGF-β信号转导的去泛素化酶（DUB）。进一步的分析表明，USP10与Smad4直接相互作用，并通过其蛋白水解泛素的裂解而使其稳定，从而促进了HCC的转移。shRNA或催化抑制剂Spautin-1对USP10的抑制作用显着抑制了HCC细胞的迁移，而Smad4的重组能够有效地挽救该缺陷。总体而言，我们的研究不仅揭示了USP10对Smad4蛋白质丰度的调节作用，而且还表明USP10可被视为Smad4阳性患者转移性HCC的潜在干预目标。