Berberine induces PD-L1 degradation via the autophagy-lysosome pathway through the PI3K-Akt pathway and enhances immunogenic cell death in triple-negative breast cancer.

Objective: This study aimed to investigate the regulatory effect and molecular mechanism of Berberine (BBR) on programmed death-ligand 1 (PD-L1) expression in Triple-Negative Breast Cancer (TNBC) cells. Methods: Results: BBR reduced PD-L1 protein expression in TNBC cells in a time- and dose-dependent manner, decreased the membrane localization of PD-L1, and inhibited interferon-γ (IFN-γ)-induced PD-L1 upregulation. Mechanistically, BBR activated autophagy by inhibiting the PI3K-Akt pathway, leading to PD-L1 degradation primarily mediated by the autophagy-lysosome pathway, with minimal contribution from the proteasome under the conditions tested. Cycloheximide (CHX) pulse-chase assay confirmed the degradation kinetics of PD-L1. Experiments evaluating lysosomal function excluded the influence of abnormal lysosomal function, demonstrating that this degradation was independent of the ubiquitin-proteasome system and did not affect lysosomal function. Furthermore, BBR increased the expression and release of immunogenic cell death (ICD)-associated markers in TNBC cells, including calreticulin (CRT) exposure and high-mobility group box 1 (HMGB1) release. Conclusion: BBR can regulate PD-L1 degradation and induce ICD through the PI3K-Akt-autophagy pathway. Its mode of immune checkpoint degradation and immunogenic activation provides experimental evidence for the immunotherapy of TNBC.