Kinome-Wide Screening Identifies FAK as a Novel Post-Translational Regulator of PD-L1 Stability and Immune Evasion in Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer charac-terized by limited treatment options and poor prognosis. Although immune checkpoint inhibitors targeting the PD-1/PD-L1 axis have shown clinical promise, many TNBC pa-tients exhibit resistance or limited response, underscoring the need to understand reg-ulatory mechanisms of PD-L1 expression. Here, we performed a kinome-wide inhibitor screen using a HEK293A cell line stably expressing a NanoLuc-tagged PD-L1 construct lacking its endogenous promoter to identify post-translational regulators of PD-L1 sta-bility. We identified focal adhesion kinase (FAK) as a novel modulator of PD-L1. FAK inhibition significantly decreased PD-L1 levels in HEK293A cells but paradoxically in-creased PD-L1 expression in TNBC cell lines (BT549, Hs578T). Mechanistically, FAK directly interacts with PD-L1 to modulate its stability independently of its kinase activity. Functionally, FAK inhibition enhanced membrane PD-L1 expression and reduced T-cell-mediated cancer cell killing, suggesting increased immune evasion. These findings reveal a novel role for FAK in immune modulation and suggest that combining FAK inhibitors with PD-L1 blockade may offer a promising strategy for TNBC treatment.