FRA1 contributes to MEK-ERK pathway-dependent PD-L1 upregulation by KRAS mutation in premalignant human bronchial epithelial cells.
Mi-Heon Lee, Jane Yanagawa, Linh M. Tran, Tonya C. Walser, Bharti Bisht, Eileen Fung, Stacy J. Park, Gang Zeng, Kostyantyn Krysan, William D. Wallace, Manash K. Paul, Luc Girard, Boning Gao, John D. Minna, Steven M. Dubinett, Jay M. Lee
Abstract
, EGFR mutation, p53 knock-down, or both KRAS mutation and p53 knock-down were tested for levels of PD-L1, FRA1, and ERK activation (pERK). Our results showed that KRAS mutation alone, but not other genetic alterations, induced significantly higher expression of PD-L1 compared to its vector counterparts. The increased PD-L1 expression in the KRAS mutated cells was dramatically reduced by inhibition of ERK activation. Furthermore, the MEK-ERK pathway-dependent PD-L1 expression was markedly reduced by FRA1 silencing. Interestingly, FRA1 silencing led to inhibition of ERK activation, indicating that FRA1 plays a role in PD-L1 regulation via positive feedback of ERK activation. Correlation of PD-L1 and FRA1 mRNA expression was validated using human lung cancer specimens from The Cancer Genome Atlas (TCGA) and established NSCLC cell lines from Cancer Cell Line Encyclopedia (CCLE). FRA1 expression was significantly associated with PD-L1 expression, and high FRA1 expression was correlated with poor overall survival. Our findings suggest that oncogenic KRAS-driven PD-L1 expression is dependent on MEK-ERK and FRA1 in high risk, premalignant HBEC.