APOBEC3A-Driven Suppression of Luminal Differentiation in Bladder Cancer and Functional Rescue Through PPARγ Activation

The APOBEC3 family of cytidine deaminases, especially APOBEC3A (A3A) and APOBEC3B (A3B), plays an important dual role in cancer by contributing to both DNA mutations and changes in gene expression that influence how tumors develop and differentiate. Bladder cancer is highly diverse, with luminal and basal/squamous subtypes that differ in prognosis and response to treatment. Although APOBEC3-related mutation patterns are common in urothelial carcinoma, growing evidence suggests these enzymes may also drive tumor progression by altering transcriptional programs. In this study, we examined how overexpression of A3A and A3B affects luminal differentiation and whether these effects can be prevented or reversed through activation of PPARγ using rosiglitazone. We used doxycycline-inducible systems in murine bladder cancer cell lines representing luminal (UPFL.1 mA3KO) and basal/squamous (BBN963) phenotypes. Protein and gene expression changes were analyzed using western blotting and RT-PCR. Overexpression of APOBEC3 led to reduced expression of key luminal transcription factors, including PPARγ, FOXA1, and GATA3, indicating a shift toward a basal/squamous phenotype. Short-term treatment with a PPARγ agonist increased luminal marker expression and strongly induced ANGPTL4, confirming activation of the pathway. In a longer 7-day model, sustained APOBEC3 expression suppressed PPARγ activity, though rosiglitazone was able to partially restore it. Importantly, pre-treatment with rosiglitazone was more effective than post-treatment in maintaining expression of FABP4 and ANGPTL4, suggesting that early activation of PPARγ signaling may help protect against APOBEC3-driven repression. Overall, these findings support a model in which APOBEC3 promotes a shift toward squamous differentiation by suppressing luminal transcription programs. They also suggest that timely activation of PPARγ signaling can partially counteract these effects. This work highlights the plasticity of bladder cancer and identifies PPARγ as a potential therapeutic target for reversing APOBEC3-driven changes.