Role of Forkhead Box P3 in Interferon γ-mediated PD-L1 Expression and Bladder Cancer Epithelial-to-Mesenchymal Transition.

Antagonism of the PD-1/PD-L1 axis is a critical therapeutic strategy for advanced bladder cancer patients. Interferon gamma (IFNgamma) functions as a key regulator of programmed death-ligand 1 (PD-L1) in both immune as well as cancer cells. Forkhead Box P3 (FOXP3) is a transcription factor synonymous in T regulatory cell function, but with increasingly described functions in cancer cells. Here we investigated the relationship between FOXP3 and PD-L1 in bladder cancer. We showed that FOXP3 is critical in the ability for IFNgamma to activate PD-L1 in bladder cancer cells. FOXP3 can bind to the PD-L1 promoter and induces a gene program that leads to regulation of multiple immune-related genes and genes involved in epithelial-to-mesenchymal transition (EMT). Using in vitro and in vivo human and murine models, we showed that FOXP3 can influence bladder cancer EMT as well as promote cancer metastases. Furthermore, FOXP3 may be a convergent factor for multiple activators of PD-L1 including by the chemotherapeutic cisplatin.