The p53 pathway is a highly complex signaling network including several key regulators. HAUSP is a critical component of the p53 pathway acting as a deubiquitinase for both p53 and its key repressor Mdm2. Here, we identified a novel HAUSP-interacting protein, HLA-B-associated transcript 3 (Bat3) and found it to be capable of inducing p53 stabilization and activation via a HAUSP-dependent mechanism, resulting in cell growth inhibition. Surprisingly, the deubiquitylating enzymatic activity of HAUSP was not required for this phenomenon. Co-immunoprecipitation showed that p53 coexisted in a complex with Bat3 and HAUSP in vivo, and HAUSP may serve as a binding mediator to enhance the interaction between p53 and Bat3. Further studies revealed that formation of this three-protein complex interfered with the binding of p53 to its proteasome receptor S5a and promoted the accumulation of p53 in nucleus. Notably, Mdm2 protein abundance is also regulated by Bat3 in the presence of HAUSP. Overexpression of Bat3 and HAUSP increases Mdm2 protein levels without influencing the p53–Mdm2 interaction and Mdm2-mediated p53 ubiquitination, indicating that Bat3–HAUSP-mediated protein stabilization is not specific to p53 and different mechanisms may be involved in Bat3-mediated regulation of p53–Mdm2 pathway. Together, our study unravels a novel mechanism by which p53 is stabilized and activated by HAUSP-mediated interaction with Bat3 and implies that Bat3 might function as a tumor suppressor through the stabilization of p53.

Purpose: Cellular senescence serves as a double-edged sword in oncology, acting as a tumor suppressor and a promoter of a pro-tumorigenic environment post-chemotherapy, necessitating targeted removal strategies. To investigate whether inhibition of Bcl-xL (a key anti-apoptotic protein and senescent cell survival factor) leads to therapeutic failure by enabling senescent tumor cells to resist apoptosis, re-enter the cell cycle, and potentially drive tumor progression. Methods: We utilized pharmacological Bcl-xL inhibitors and shRNA-mediated Bcl-xL knockdown to disrupt Bcl-xL function in senescent tumor cells. The effects on cell fate, cell cycle regulators, and associated molecular pathways were analyzed. Results: Contrary to the expected induction of apoptosis, Bcl-xL inhibition facilitated the cell cycle re-entry of senescent tumor cells. This escape from senescence was driven by a marked reduction in the stability of the cell cycle inhibitor p27. The reduction occurred through increased cytoplasmic localization of p27 and reduced phosphorylation, leading to its proteasome-dependent degradation. Thus, Bcl-xL disruption initiates a pathway enabling senescence escape. Conclusion: Inhibiting Bcl-xL in senescent tumor cells promotes senescence escape rather than apoptosis, representing a significant paradigm shift in understanding senolytic drug mechanisms. These findings reveal the complex dual nature of senescence in cancer and underscore the critical need for careful design when combining senolytic agents with chemotherapeutics to prevent inadvertent tumor cell proliferation.