The pathological significance of abnormal RON and PD-L1 expression in colorectal cancer

Abstract

Background: PD-L1 immunotherapy remains poorly efficacious in colorectal cancer. The RON receptor tyrosine kinase plays an important role in regulating tumor immunity. Here, we identify patterns of RON and PD-L1 expression and explore the clinical significance of these patterns in colorectal cancer. Methods: Gene expression data were obtained from the Gene Expression Omnibus database (GEO; n = 290) and patients at the First Affiliated Hospital, Zhejiang University School of Medicine (FAHZUSM; n = 381) and were analyzed to determine the prognostic value of RON and PD-L1 expression within the tumor cells and the tumor microenvironment of colorectal cancer. Human colorectal cancer cell lines were treated with BMS-777607 to explore the relationship between RON activity and PD-L1 protein expression. Signaling pathways and protein expression perturbed by RON inhibition were evaluated by cellular immunofluorescence and western blot. Results: In the GEO cohort, cut-off values for RON and PD-L1 expression of 7.70 and 4.30, respectively, were determined. Stratification of patients based on these cutoffs demonstrated that high expression of RON and PD-L1 associated with poor prognosis. In the FAHZUSM cohort, rates of high expression of RON in tumor cells, high PD-L1 expression in tumor cells and in tumor infiltrating monocytes, and both high RON and high PD-L1 expression in the tumor microenvironment were 121 (32%), 43 (11%), 91 (24%), and 51 (13.4%), respectively. High expression of RON and high expression of PD-L1 in the tumor cell compartment was significantly correlated (p < 0.001). High expression of RON and PD-L1 were independent prognostic factors for poorer overall survival. Concurrent high expression of both RON and PD-L1 in the tumor microenvironment was significantly associated with poor prognosis. In vitro , BMS-777607 inhibited the phosphorylation of RON, inhibited PD-L1 expression, and attenuated activation of the ERK1/2 and AKT signaling pathways in colorectal cancer cells. Conclusions: RON, PD-L1 and the crosstalk between these proteins plays an important role in predicting the prognostic value of colorectal cancer. Moreover, phosphorylation of RON upregulates the expression of PD-L1, which provides a novel approach to immunotherapy in colorectal cancer.