Abstract 2351: AXL and c-MET cross-talk in the regulation of PD-L1 expression on renal cancer cells
Authors: Balan Murugabaskar , Choueiri Toni , Pal Soumitro 
Published: August 2019

Abstract
Purpose: The purpose of this research is to study the cross-talk between receptor tyrosine kinases (RTKs) c-MET and AXL in renal cancer cells; and to explore if the blockade of AXL-c-MET pathways can restrict PD-L1-mediated growth and immune escape of renal cancer cells.
Background: c-MET and AXL are overexpressed in renal cell carcinoma (RCC). Upon binding with their respective ligands hepatocyte growth factor (HGF) and GAS6, c-MET and AXL activate a wide range of pathways, including tumor promoting events. Renal tumors show increased T cell infiltration, yet the T cells are rendered incapable of tumor rejection. The co-inhibitory molecules PD-1 and PD-L1 belong to cell surface glycoprotein B7 family that governs T cell function and proliferation. In RCC, tumor-infiltrating T cells express PD-1 and are associated with poor outcomes for patients. Similarly, PD-L1 expression on renal cancer cells hinders prognosis and indicates tumor aggressiveness. Therefore, PD-L1 in renal tumors may play a significant role in down-regulating host anti-tumor immune responses. Our recent report suggests that c-MET activation induces overexpression of PD-L1 in renal cancer cells; and the blockade of PD-L1 promotes immune-mediated killing of renal cancer cells. However, the cross talk between AXL and c-MET in the regulation of PD-L1 has not been studied in RCC.
Results: We have confirmed that both AXL and c-MET are overexpressed in human renal cancer cells (786-O and ACHN) when compared with normal renal tubular epithelial cells. We performed co-immunoprecipitation assays with c-MET antibody and found that c-MET forms a complex with AXL in renal cancer cells. We utilized siRNA-mediated gene silencing approach and found that the knock-down of AXL increased the sensitivity of 786-O and ACHN cells to apoptosis following treatment with XL-184 (a small molecule inhibitor of c-MET, AXL and VGFRs, obtained from Exelixis) as measured by flow cytometry in Annexin V/PI stained cells. We also found that GAS6 treatment enhanced HGF-induced expression of cytoprotective molecule Heme oxygenase-1 (HO-1) and anti-apoptotic molecules Bcl-2 and Bcl-xL in renal cancer cells. In both 786-O and ACHN cells, c-MET activation increased the cell surface expression of PD-L1 as measured by flow cytometry. Interestingly, GAS6 treatment further increased the expression of PD-L1, suggesting a synergistic action of RTKs AXL and c-MET in renal cancer cells. We also utilized a PD-L1 promoter-luciferase plasmid to measure PD-L1 promoter activity and found that GAS6 treatment enhanced HGF-induced effects on PD-L1 transcription. In mouse renal cancer cells (RENCA), which express very high levels of PD-L1, we observed a significant decrease in the expression of PD-L1 when AXL was knocked down in cells.
Conclusion: Together, our results demonstrate that AXL-mediated signaling enhances c MET-induced cytoprotection and PD-L1 expression on renal cancer cells.
Citation Format: Murugabaskar Balan, Toni Choueiri, Soumitro Pal. AXL and c-MET cross-talk in the regulation of PD-L1 expression on renal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2351.