The Effects And Mechanisms Of Epidermal Growth Factor Receptor Activation In Macrophages Polarization And Function

Macrophages are lymphocytes coming of the myeloid lineage.Macrophages possess phenotypic plasticity that can be classified into two types,M1 and M2macrophages.M1,also called classically activated macrophages,play roles in innate immunity（such as phagocytosis and production of nitric oxide and reactive oxygen intermediates）and adaptive immunity（such as macrophages serve as antigen presenting cells and produce pro-inflammatory cytokines）.M2,also called alternatively activated macrophage.They have effects on reducing immune activity and produce growth factors to the immune microenvironment.Tumor associated macrophages are the kind of special macrophages with M2 phenotypes,which promote proliferation,invasion,metastasis and angiogenesis.Lots of studies have reported that epidermal growth factor receptor（EGFR）signaling pathways activated in epithelium and tumor cells can promote the proliferation and malignant transformation.But the role and mechanism of EGFR activation in macrophages in their M2 polarization and the effect of epithelial-to-mesenchymal transition in epithelial cells are remain unclear.So that the purpose of our research is to determine the roles of EGFR activation in macrophages in M2 polarization and its effects on proliferation and EMT in gastrointestinal epithelial cells.We studied the role of EGFR in the IL-4 signaling pathway.IL-4 stimulates EGFR transactivation and down-regulation both in Raw 264.7 macrophages and wt peritoneal macrophages,which can been inhibited by both metalloproteinase inhibitors inhibitors（GM6001 and TAPI-1）and EGFR kinase inhibitor（AG1478）.We also find that inhibition of EGFR in macrophages up regulates IL-4 induced STAT6 activation,HB-EGF production and M2 polarization.Next,we studied how EGFR in macrophages regulates gastrointestinal epithelial cells development.IL-4-conditioned medium from wt macrophages stimulates EGFR activation in gastric epithelial cells（ImSt cells）,which is enhanced by the medium from Egfr^wa5 macrophages.IL-4-conditioned medium from Egfr^wa5 macrophages induced high level of ImSt cells and colonic tumor cells growth,as compared to that by the conditioned-medium from wt macrophages.IL-4 conditioned medium from macrophages promotes EMT in gastric epithelial cells and colonic tumor cells,which can be enhanced by inhibition of EGFR activation in macrophages.At last,in the colonic xenograft model,IL-4-conditioned medium from macrophages isolated from EGFR knockout mouse(Egfr^fl/flLysM-Cre mice),compared with the conditioned medium from those isolated from wt mouse（Egfr^fl/fll/fl mice）,promoted the colony formation and tumor growth.Thus,our results suggest that activation of EGFR in macrophages inhibits M2polarization and production of growth factors for gastrointestinal epithelial cell growth and EMT.These results provide information to understand cell-type specific（epithelial vs macrophage）EGFR activation in regulation of tumorigenesis.