Signaling and Regulation Cytokine Induction of Tumor Necrosis Factor Receptor 2 Is Mediated by STAT3 in Colon Cancer Cells

The IL-6/STAT3 and TNFa/NFkB pathways are emerging as critical mediators of inflammation-associated colon cancer. TNF receptor (TNFR) 2 expression is increased in inflammatory bowel diseases, the azoxymethane/ dextran sodium sulfate (AOM/DSS) model of colitis-associated cancer, and by combined interleukin (IL) 6 and TNFa. Themolecular mechanisms that regulate TNFR2 remain undefined. This study used colon cancer cell lines to test the hypothesis that IL-6 and TNFa induce TNFR2 via STAT3 and/or NFkB. Basal and IL-6 þ TNFa– induced TNFR2 were decreased by pharmacologic STAT3 inhibition. NFkB inhibition had little effect on IL-6þ TNFa–induced TNFR2, but did inhibit induction of endogenous IL-6 and TNFR2 in cells treated with TNFa alone. Chromatin immunoprecipitation (ChIP) revealed cooperative effects of IL-6 þ TNFa to induce STAT3 binding to a 1,578 STAT response element in theTNFR2 promoter but no effect onNFkB binding to consensus sites. Constitutively active STAT3 was sufficient to induce TNFR2 expression. Overexpression of SOCS3, a cytokine-inducible STAT3 inhibitor, which reduces tumorigenesis in preclinical models of colitis-associated cancer, decreased cytokine-induced TNFR2 expression and STAT3 binding to the 1,578 STAT response element. SOCS3 overexpression also decreased proliferation of colon cancer cells and dramatically decreased anchorage-independent growth of colon cancer cells, even cells overexpressing TNFR2. Collectively, these studies show that IL-6and TNFa-induced TNFR2 expression in colon cancer cells is mediated primarily by STAT3 and provide evidence that TNFR2 may contribute to the tumor-promoting roles of STAT3. Mol Cancer Res; 1–14.