Ubiquitin-Specific Peptidase 36 Suppresses Apoptosis in Hepatocellular Carcinoma by Stabilizing Caspase-8
HAN Junjun, YU Weiming, ZHAO Wenyan, JIN Zhaoqing, YANG Ziqiang, CHEN Weiqing, CHEN Feihua, GONG Mouchun*
USP36 (ubiquitin-specific peptidase 36), a key deubiquitinating enzyme encoded by the USP36 gene, modulates protein stability and function by removing ubiquitin modifications. It plays crucial roles in intracellular signal transduction, protein degradation, and cell cycle regulation. However, its functions and mechanisms in HCC (hepatocellular carcinoma) remain largely elusive. This study first investigated the expression levels of USP36 in HCC and their correlation with clinical prognosis using bioinformatic analysis. Subsequently, this article established USP36-overexpressing and knockdown HepG2 and Huh7 HCC cell lines. A series of in vitro assays, including MTT, Transwell, wound healing, flow cytometry, and TUNEL, were performed to evaluate cell proliferation, migration, invasion, and apoptosis under stimulation with EGF and TNF-α. The protein expression levels of total Caspase-8 and its activated form, Cleaved-Caspase-8, were analyzed by Western blot. These results revealed that USP36 was significantly upregulated in HCC tissues. Furthermore, high USP36 expression was negatively correlated with OS (overall survival), PFS (progression-free survival), DFS (disease-free survival), and RFS (recurrencefree survival) in patients with HCC. In vitro, upon stimulation with EGF and TNF-α, overexpression of USP36 led to a significant increase in total Caspase-8 protein levels but a decrease in its active form, Cleaved-Caspase-8. Concurrently, USP36 overexpression enhanced cell proliferation, migration, and invasion, while substantially inhibiting apoptosis. Conversely, knockdown of USP36 resulted in decreased total Caspase-8, increased Cleaved-Caspase-8 expression, attenuated cell proliferation, migration, and invasion, and promoted apoptosis. In conclusion, these findings suggest that USP36 exerts a pro-tumorigenic role in the development and progression of HCC. Mechanistically, USP36 stabilizes Caspase-8, thereby inhibiting extrinsic apoptosis and promoting the proliferation, migration, and invasion of tumor cells. These findings highlight USP36 as a promising potential therapeutic target for HCC treatment.
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