Curcumin inhibits IFN-γ induced PD-L1 expression via reduction of STAT1 Phosphorylation in A549 non-small cell lung cancer cells.

Background: Immune evasion in non-small cell lung cancer (NSCLC) is largely mediated by programmed death-ligand 1 (PD-L1), which is upregulated by interferon-gamma (IFN-γ)-induced STAT1 activation. Targeting this pathway may improve immunotherapy outcomes. Curcumin, a natural polyphenol, has been reported to modulate various oncogenic signaling pathways, but its role in inhibiting IFN-γ-driven PD-L1 expression in NSCLC remains unclear.

Methodology: The NSCLC cell line A549 were treated with curcumin (50 µM) for 2 h before stimulation with IFN-γ (500 U/ml). Western blot, qRT-PCR, and immunofluorescence microscopy were used to evaluate STAT1 phosphorylation, PD-L1 expression, and the localization of phosphorylated STAT1 (p-STAT1). The expression of interferon-stimulated genes (ISGs), including SOCS1 and ISG15, was also examined. Additionally, the Resazurin assay was performed to assess cell viability.

Results: IFN-γ significantly induced STAT1 phosphorylation, leading to a time-dependent upregulation of PD-L1 expression. Immunofluorescence confirmed that p-STAT1 is translocated to nucleus. Curcumin treatment inhibited STAT1 phosphorylation by 68% (p < 0.001), leading to a marked reduction in PD-L1 expression. Moreover, curcumin suppressed IFN-γ-induced SOCS1 (63%) and ISG15 (54%) expressions, indicating a broader effect on STAT1-mediated immune evasion. Finally, curcumin enhanced IFN-γ-mediated growth inhibition, reducing cell viability by 47% at 48 h (p < 0.01).

Conclusion: Curcumin effectively inhibits IFN-γ-induced STAT1 phosphorylation and PD-L1 expression, downregulates ISGs, and enhances IFN-γ-mediated tumor suppression. These findings suggest that curcumin may serve as a therapeutic adjuvant in NSCLC, potentially improving immune checkpoint inhibitor (ICI) efficacy.