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

## TL;DR

This study finds that FAK, a protein involved in cell adhesion, unexpectedly increases PD-L1 levels in aggressive breast cancer cells, potentially helping cancer evade the immune system.

## Contribution

FAK is identified as a novel post-translational regulator of PD-L1 stability in triple-negative breast cancer.

## Key findings

- FAK inhibition paradoxically increases PD-L1 expression in TNBC cell lines.
- FAK directly interacts with PD-L1 to modulate its stability independently of kinase activity.
- FAK inhibition enhances PD-L1 on cell membranes and reduces T-cell-mediated cancer cell killing.

## Abstract

Triple-negative breast cancer (TNBC) is an aggressive subtype characterized by limited treatment options and poor prognosis. Although immune checkpoint inhibitors targeting the PD-1/PD-L1 axis have shown clinical promise, many TNBC patients exhibit resistance or limited response, underscoring the need to understand regulatory 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 stability. 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 increased PD-L1 expression in TNBC cell lines. 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.