PKC inhibitors promote breast cancer immune evasion by maintaining PD-L1 stability.

Protein kinase C (PKC) regulates diverse biological functions of cancer cells and is a promising therapeutic target. However, clinical trials of PKC-targeted therapies have not yielded satisfactory results. Recent studies have also indicated a tumor-suppressive role of PKCs unclear molecular mechanisms. In this study, we found that PKC inhibition enhances CD8 T-cell-mediated tumor evasion and abolishes antitumor activity in immunocompetent mice. We further identified PKC as a critical regulator of programmed cell death-ligand 1 (PD-L1) and found that it enhances T-cell-dependent antitumor immunity in breast cancer by interacting with PD-L1 and suppressing PD-L1 expression. We demonstrated that PKC-mediated PD-L1 phosphorylation promotes PD-L1 degradation through transducin repeat-containing protein. Notably, the efficacy of PKC inhibitors was intensified by synergizing with anti-PD-L1 mAb therapy to boost antitumor T-cell immunity . Clinical analysis revealed that PKC expression is positively correlated with T-cell function and the interferon-gamma signature in patients with breast cancer. This study demonstrated the antitumor capability of PKC, identified potential therapeutic strategies to avoid tumor evasion PKC-targeted therapies, and provided a proof of concept for targeting PKC in combination with anti-PD-L1 mAb therapy as a potential therapeutic approach against breast cancer, especially TNBC.