TNF-a Induces Epithelial–Mesenchymal Transition of Renal Cell Carcinoma Cells via a GSK3b-Dependent Mechanism

TNF-a is a cytokine with antitumorigenic property. In contrast, low dose, chronic TNF-a production by tumor cells or stromal cells may promote tumor growth andmetastasis. Serum levels of TNF-a are significantly elevated in renal cell carcinoma (RCC) patients. Here, we showed that TNF-a induced epithelial–mesenchymal transition (EMT) and promoted tumorigenicity of RCC by repressing E-cadherin, upregulating vimentin, activatingMMP9, and invasion activities. In addition, TNF-a treatment inhibited glycogen synthase kinase 3b (GSK-3b) activity through serine-9 phosphorylation mediated by the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway in RCC cells. Inhibition of PI3K/AKT by LY294002 reactivated GSK-3b and suppressed the TNFa–induced EMTof RCC cells. Inactivation of GSK-3b by LiCl significantly increasedMMP9 activity and EMTof RCC cells. Activation of GSK-3b by transduction of constitutively activeGSK-3b into RCC cells suppressed TNFa–mediated anchorage-independent growth in soft agar and tumorigenicity in nude mice. Overexpression of a kinase-deficient GSK-3b, in contrast, potentiated EMT, anchorage-independent growth and drastically enhanced tumorigenicity in vivo. Most importantly, a 15-fold inactivation of GSK-3b activity, 3-fold decrease of E-cadherin, and 2-fold increase of vimentin were observed in human RCC tumor tissues. These results indicated that inactivation of GSK-3b plays a pivotal role in the TNF-a–mediated tumorigenesis of RCC.Mol Cancer Res; 1–11.