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

The IL-6/STAT3 and TNF alpha/NF kappa B 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 TNF alpha. The molecular mechanisms that regulate TNFR2 remain undefined. This study used colon cancer cell lines to test the hypothesis that IL-6 and TNF alpha induce TNFR2 via STAT3 and/or NF kappa B. Basal and IL-6 + TNF alpha-induced TNFR2 were decreased by pharmacologic STAT3 inhibition. NF kappa B inhibition had little effect on IL-6+ TNF alpha-induced TNFR2, but did inhibit induction of endogenous IL-6 and TNFR2 in cells treated with TNF alpha alone. Chromatin immunoprecipitation (ChIP) revealed cooperative effects of IL-6 + TNF alpha to induce STAT3 binding to a -1,578 STAT response element in the TNFR2 promoter but no effect on NF kappa B 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-6- and TNF alpha-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; 9(12); 1718-31. (C) 2011 AACR.