RAS–Mitogen-Activated Protein Kinase Signal Is Required for Enhanced PD-L1 Expression in Human Lung Cancers

Abstract

Ectopic programmed cell death ligand 1 (PD-L1) expression in non-small cell lung cancers (NSCLCs) is related to immune evasion by cancer, and it is a molecular target of immune checkpoint therapies. Although some altered signals in NSCLCs are responsible for ectopic PD-L1 expression, the precise mechanisms remain obscure. Because we found a higher frequency of EGFR/KRAS mutations in NSCLC cell lines with high PD-L1 expression (p < 0.001), we evaluated the relationships between downstream signals and PD-L1 expression, particularly in three KRAS-mutant adenocarcinoma cell lines. The MEK inhibitor U0126 (20 μM) significantly decreased the surface PD-L1 levels by 50–60% compared with dimethyl sulfoxide (p < 0.0001). Phorbol 12-myristate 13-acetate stimulation (100 nM, 15 min) increased (p < 0.05) and two ERK2 siRNAs as well as KRAS siRNAs decreased (p < 0.05) PD-L1 expression. The transcriptional activity of the potential AP-1 site (+4785 to +5056 from the transcription start site) in the PD-L1 gene was demonstrated by luciferase assays, which was inhibited by U0126. The chromatin immunoprecipitation assay demonstrated the binding of cJUN to the AP-1 site. Two STAT3 siRNAs decreased PD-L1 expression by 10–32% in two of the three KRAS-mutant lung adenocarcinoma cell lines (p < 0.05), while the PI3K inhibitor LY294002 (40 μM) did not change the expression level. Supervised cluster analysis and gene set enrichment analysis between the PD-L1-high and -low NSCLCs revealed a correlation between PD-L1 expression and genes/pathways related to cell motility/adhesion. These results indicate that MAPK signaling is the dominant downstream signal responsible for ectopic PD-L1 expression, in which STAT3 is also involved to some extent. Furthermore, MAPK signaling may control the expression of PD-L1 and several genes related to enhanced cell motility. Our findings suggest that MAPK, along with STAT3, is important for determining PD-L1 expression, which could be useful for targeted therapies against lung cancers.

The importance of programmed death ligand 1 gene expression, epidermal growth factor receptor gene mutations and serum epidermal growth factor receptor levels in Turkish non-small cell lung cancer patients

“…[19] We found that lymph node involvement was associated with PD-L1 expression which is an important prognostic factor in resected NSCLC patients. The data obtained in the study of Sumitomo et al [21] on mitogen-activated protein kinase (MAPK) pathway displayed that PD-L1 was important in the MAPK pathway and like in our study, the EGFR mutations were significantly more common in cases with high PD-L1 expression.…”

Inhibition of RON kinase potentiates anti-CTLA-4 immunotherapy to shrink breast tumors and prevent metastatic outgrowth

“…61 In addition to its cell-intrinsic protumorigenic effects, MAPK signaling has also been implicated in the upregulation of checkpoint ligands such as PD-L1. 62,63 Therefore, combination of immunotherapy with MEK1/2 inhibitors has great potential to block both tumor-intrinsic and immune-mediated protumorigenic effects of the MAPK signaling pathway. Although MAPK signaling is important for early steps of T cell activation, 64,65 several studies have shown that MEK inhibitors reprogram the tumor microenvironment and potentiate responses to checkpoint immunotherapy.…”

Programmed cell death ligand 1 expression in cytologic and surgical non–small cell lung carcinoma specimens from a single institution: Association with clinicopathologic features and molecular alterations

“…Our study did demonstrate a significant correlation of PD‐L1 expression (PD‐L1 positivity, high PD‐L1 expression, and expression levels) with KRAS mutations but not with any other mutations. One study investigated the underlining mechanism regulating PD‐L1 expression in NSCLCs with KRAS mutations and found that mitogen‐activated protein kinase signaling along with signal transducer and activator of transcription 3 was crucial for PD‐L1 expression . In our study cohort, the surgical specimens with molecular testing (n = 99) showed more cases with KRAS mutations than the cytologic specimens with molecular testing (n = 91).…”