Ubiquitin-Specific Protease 49 Interacts with Bax to Modulate Apoptosis

Bax, a key member of the B-cell lymphoma 2 (Bcl-2) protein family, is essential for inducing mitochondrial apoptosis. In this study, we employed yeast two-hybrid screening to identify ubiquitin-specific protease 49 (USP49) as a binding partner of Bax. Subsequent immunoprecipitation and glutathione S-transferase (GST) pull-down assays confirmed their direct interaction. Functional assays showed that USP49 reduces Bax polyubiquitination at multiple lysine residues within ubiquitin, with the strongest effects observed on K11, K29, K33, and K63 linkages. In contrast, its effect on K48-linked ubiquitination was weak and insufficient to influence Bax protein stability, indicating that USP49 does not regulate Bax abundance through proteasomal degradation. Instead, RT-qPCR analysis revealed that USP49 overexpression significantly increased Bax mRNA levels, and this effect was maintained under apoptosis stimuli (UV, H2O2, and STS), indicating transcriptional regulation largely independent of stress-induced damage, whereas its effect was modest and not statistically significant under starurosporine treatment. Collectively, these findings demonstrate that USP49 regulates Bax primarily through K29/K33/K63-linked ubiquitination and transcriptional upregulation, highlighting its role as a stress-responsive modulator of apoptosis and a potential therapeutic target in cancer. Moreover, under DNA damage condition (UV), USP49 overexpression marked enhanced apoptosis.