Modification of the transforming growth factor β (TGF-β) signaling components by (de)ubiquitination is emerging as a key regulatory mechanism that controls cell signaling responses in health and disease. Here, we show that the deubiquitinating enzyme UBH-1 in Caenorhabditis elegans and its human homolog, ubiquitin C-terminal hydrolase-L1 (UCH-L1), stimulate DAF-7/TGF-β signaling, suggesting that this mode of regulation of TGF-β signaling is conserved across animal species. The dauer larva–constitutive C. elegans phenotype caused by defective DAF-7/TGF-β signaling was enhanced and suppressed, respectively, by ubh-1 deletion and overexpression in the loss-of-function genetic backgrounds of daf7, daf-1/TGF-βRI, and daf4/R-SMAD, but not of daf-8/R-SMAD. This suggested that UBH-1 may stimulate DAF-7/TGF-β signaling via DAF-8/R-SMAD. Therefore, we investigated the effect of UCH-L1 on TGF-β signaling via its intracellular effectors, i.e. SMAD2 and SMAD3, in mammalian cells. Overexpression of UCH-L1, but not of UCH-L3 (the other human homolog of UBH1) or of the catalytic mutant UCH-L1C90A, enhanced TGF-β/SMAD-induced transcriptional activity, indicating that the deubiquitination activity of UCH-L1 is indispensable for enhancing TGF-β/SMAD signaling. We also found that UCH-L1 interacts, deubiquitinates, and stabilizes SMAD2 and SMAD3. Under hypoxia, UCH-L1 expression increased and TGF-β/SMAD signaling was potentiated in the A549 human lung adenocarcinoma cell line. Notably, UCH-L1–deficient A549 cells were impaired in tumorigenesis, and, unlike WT UCH-L1, a UCH-L1 variant lacking deubiquitinating activity was unable to restore tumorigenesis in these cells. These results indicate that UCH-L1 activity supports DAF-7/TGF-β signaling and suggest that UCH-L1's deubiquitination activity is a potential therapeutic target for managing lung cancer.

中文翻译：

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进化上保守的去泛素酶 UBH1/UCH-L1 增强 DAF7/TGF-β 信号传导，抑制 dauer 幼虫形成，并增强肺部肿瘤发生。

通过（去）泛素化修饰转化生长因子 β (TGF-β) 信号成分正在成为控制健康和疾病中细胞信号反应的关键调节机制。在这里，我们发现秀丽隐杆线虫中的去泛素化酶 UBH-1 及其人类同源物泛素 C 末端水解酶-L1 (UCH-L1) 刺激 DAF-7/TGF-β 信号传导，表明 TGF-β 的这种调节模式-β 信号传导在动物物种中是保守的。在 daf7、daf-1/ 功能丧失的遗传背景中，ubh-1 缺失和过度表达分别增强和抑制由 DAF-7/TGF-β 信号传导缺陷引起的 dauer 幼虫-构成性秀丽隐杆线虫表型TGF-βRI 和 daf4/R-SMAD，但不是 daf-8/R-SMAD。这表明 UBH-1 可能通过 DAF-8/R-SMAD 刺激 DAF-7/TGF-β 信号传导。所以，我们研究了哺乳动物细胞中 UCH-L1 通过其胞内效应子（即 SMAD2 和 SMAD3）对 TGF-β 信号传导的影响。UCH-L1 的过表达，而非 UCH-L3（UBH1 的另一个人类同源物）或催化突变体 UCH-L1C90A 的过表达，增强了 TGF-β/SMAD 诱导的转录活性，表明 UCH-L1 的去泛素化活性是对于增强 TGF-β/SMAD 信号传导不可或缺。我们还发现 UCH-L1 相互作用、去泛素化并稳定 SMAD2 和 SMAD3。在缺氧条件下，A549 人肺腺癌细胞系中 UCH-L1 表达增加，TGF-β/SMAD 信号传导增强。值得注意的是，UCH-L1缺陷型A549细胞的肿瘤发生受到损害，并且与WT UCH-L1不同，缺乏去泛素化活性的UCH-L1变体无法恢复这些细胞的肿瘤发生。