Yes-associated protein (YAP) is an essential driver of hepatocellular carcinoma (HCC) progression and the ubiquitin-proteasome system controls its abundance. However, the role of ubiquitin-specific protease 40 (USP40) in YAP stability remains unclear. Here, USP40 was first identified as a novel regulator of YAP abundance and its target genes in HCC cells. USP40 interacted with YAP to remove the lysine 48 (K48)-linked polyubiquitination of YAP at K252 and K315 sites, thereby maintaining YAP stability. USP40 facilitated the proliferation, colony formation, migration and spheroid formation of HCC cells and promoted HCC growth in a YAP-dependent manner. In turn, YAP transcriptionally activated USP40 expression in HCC cells. RNA sequencing analysis showed that about 37% of USP40-regulated genes overlapped with YAP-regulated genes. Interestingly, stiffness-induced USP40 upregulation was abolished by YAP knockdown, and USP40 knockdown attenuated stiffness-induced YAP accumulation in HCC cells. Clinical data demonstrated that USP40 was positively associated with YAP expression in HCC tissues and its high expression indicated a poor prognosis. In conclusion, the USP40/YAP positive feedback loop contributes to HCC progression, suggesting that USP40 may be a promising drug target for anti-HCC.

中文翻译：

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USP40 通过 YAP/USP40 正反馈环促进肝细胞癌进展

Yes相关蛋白（YAP）是肝细胞癌（HCC）进展的重要驱动因素，泛素-蛋白酶体系统控制其丰度。然而，泛素特异性蛋白酶 40 (USP40) 在 YAP 稳定性中的作用仍不清楚。在此，USP40 首次被鉴定为 HCC 细胞中 YAP 丰度及其靶基因的新型调节剂。 USP40 与 YAP 相互作用，去除 YAP K252 和 K315 位点上赖氨酸 48 (K48) 连接的多聚泛素化，从而保持 YAP 稳定性。 USP40促进HCC细胞的增殖、集落形成、迁移和球体形成，并以YAP依赖性方式促进HCC生长。反过来，YAP 转录激活 HCC 细胞中的 USP40 表达。 RNA测序分析显示，约37%的USP40调控基因与YAP调控基因重叠。有趣的是，YAP 敲低消除了硬度诱导的 USP40 上调，并且 USP40 敲低减弱了 HCC 细胞中硬度诱导的 YAP 积累。临床数据表明，HCC组织中USP40与YAP表达呈正相关，其高表达提示预后不良。总之，USP40/YAP 正反馈环有助于 HCC 进展，表明 USP40 可能是一个有前景的抗 HCC 药物靶点。