Data from Induction of PD-L1 Expression by the EML4–ALK Oncoprotein and Downstream Signaling Pathways in Non–Small Cell Lung Cancer

Abstract

<div>Abstract<p><b>Purpose:</b> Therapies targeted to the immune checkpoint mediated by PD-1 and PD-L1 show antitumor activity in a subset of patients with non–small cell lung cancer (NSCLC). We have now examined PD-L1 expression and its regulation in NSCLC positive for the <i>EML4</i>–<i>ALK</i> fusion gene.</p><p><b>Experimental Design:</b> The expression of PD-L1 at the protein and mRNA levels in NSCLC cell lines was examined by flow cytometry and by reverse transcription and real-time PCR analysis, respectively. The expression of PD-L1 in 134 surgically resected NSCLC specimens was evaluated by immunohistochemical analysis.</p><p><b>Results:</b> The PD-L1 expression level was higher in NSCLC cell lines positive for <i>EML4</i>–<i>ALK</i> than in those negative for the fusion gene. Forced expression of EML4–ALK in Ba/F3 cells markedly increased PD-L1 expression, whereas endogenous PD-L1 expression in <i>EML4</i>–<i>ALK</i>–positive NSCLC cells was attenuated by treatment with the specific ALK inhibitor alectinib or by RNAi with ALK siRNAs. Furthermore, expression of PD-L1 was downregulated by inhibitors of the MEK–ERK and PI3K–AKT signaling pathways in NSCLC cells positive for either <i>EML4</i>–<i>ALK</i> or activating mutations of the EGFR. Finally, the expression level of PD-L1 was positively associated with the presence of <i>EML4</i>–<i>ALK</i> in NSCLC specimens.</p><p><b>Conclusions:</b> Our findings that both EML4–ALK and mutant EGFR upregulate PD-L1 by activating PI3K–AKT and MEK–ERK signaling pathways in NSCLC reveal a direct link between oncogenic drivers and PD-L1 expression. <i>Clin Cancer Res; 21(17); 4014–21. ©2015 AACR</i>.</p></div>