Abstract 981: Activation of EGF receptor in macrophages inhibits M2 polarization and suppresses proliferation and epithelial-to-mesenchymal transition in gastric epithelial cells

Abstract

Abstract Background & Aims. Tumor-associated macrophages, predominantly polarized to M2 phenotype, produce mediators, such as EGF and HB-EGF, to promote tumor invasion, angiogenesis, and immunosuppression. It is clear that activation of EGF receptor (EGFR) in tumor cells accelerates tumorigenesis. However, therapy to inhibit EGFR activity is not universally efficacious, suggesting possible resistance of EGFR inhibition in tumor cells or different functions of EGFR in other cell types for tumor cell growth. We have demonstrated that activation of EGFR in macrophages down-regulates IL-10 and up-regulates TNF production in response to inflammatory stimuli. This study was designed to determine the roles of EGFR activation in M2 polarization of macrophages and proliferation and epithelial-to-mesenchymal transition (EMT) in gastric epithelial cells. Methods. Mouse RAW 264.7 macrophages and peritoneal macrophages isolated from wt and kinase-defective Egfrwa5 mice were treated with IL-4 (10 g/ml), to induce M2 polarization, for 15 min to 24 h in the presence or absence of an EGFR kinase inhibitor, AG1478. EGFR activation and expression of M2 markers, Arg1 and YM1 were detected by Western blot and real time PCR, respectively. Conditioned media from IL-4 treated macrophages was used to treat mouse conditionally immortalized stomach epithelial cells (ImSt) and ImSt with EGFR knock out (EGFR−/−ImSt). Cell proliferation was examined by MTT assay and EdU labeling and EMT by real time PCR analysis of Snail and vimentin expression. Results. IL-4 transactivated EGFR in RAW 264.7 and peritoneal macrophages from wt mice. Inhibition of EGFR kinase activity by AG1478 enhanced IL-4-stimulated Arg1 and YM1 expression in RAW 264.7 cells. IL-4-stimulated Arg1 and YM1 expression in peritoneal macrophages from Egfrwa5 mice was significantly higher than those from wt mice, which suggests that EGFR activation suppresses M2 polarization. Conditioned-media from IL-4-reated RAW 264.7 cells stimulated EGFR activation, cell proliferation, and Snail and vimentin expression in ImSt, but not in ImSt EGFR−/− cells, which suggests that EGFR in gastric epithelial cells is required for M2 macrophahe-producted factors to promote growth and EMT. IL-4 treatment of ImSt did not show any of these effects, Furthermore, proliferation in ImSt by conditioned media from IL-4-treated peritoneal macrophages from Egfrwa5 mice was significantly higher than that by macrophages from wt mice, indicating that activation of EGFR in macrophages suppresses production of factors for promoting gastric epithelial cell growth. Conclusion. EGFR activation in macrophages inhibits M2 polarization and production of growth factors for gastric epithelial cell growth and EMT. These results provide novel information to understand cell-type specific (epithelial vs macrophage) EGFR activation in regulation of tumorigenesis. Citation Format: Gang Zhao, Liping Liu, D. Brent Polk, Richard M. Peek, Xishan Hao, Hui Li, Fang Yan. Activation of EGF receptor in macrophages inhibits M2 polarization and suppresses proliferation and epithelial-to-mesenchymal transition in gastric epithelial cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 981. doi:10.1158/1538-7445.AM2015-981