Tumor necrosis factor-α induces epithelial-mesenchymal transition of renal cell carcinoma cells via a nuclear factor kappa B-independent mechanism

Chronic low dose of tumor necrosis factor-alpha (TNF-alpha) stimulation promotes tumorigenesis by facilitating tumor proliferation and metastasis. The plasma levels of TNF-alpha are increased in patients with renal cell carcinoma (RCC). Furthermore, high-grade clear cell RCC cell lines secrete more TNF-alpha than low-grade ones, and allow low-grade cell lines' gain of invasive ability. However, the molecular mechanism of TNF-alpha in mediating progression of RCC cells remains unclear. In the present study, TNF-alpha induced epithelial-mesenchymal transition (EMT) of RCC cells by repressing E-cadherin, promoting invasiveness and activating matrix metalloproteinase (MMP) 9 activity. RCC cells underwent promoted growth in vivo following stimulation with TNF-alpha. In addition, TNF-alpha induced phosphorylation of extracellular signal-regulated kinase, nuclear factor kappa B (NF-kappa B) and Akt in a time-dependent manner, and increased nuclear translocation and promoter activity of NF-kappa B. To investigate the role of NF-kappa B activation in TNF-alpha-induced EMT of RCC, we employed chemical inhibitors (NF-kappa B activation inhibitor and Bay 11-7082) and transfected dominant-negative (pCMV-I kappa B alpha M) and overexpressive (pFLAG-p65) vectors of NF-kappa B. While overexpression of NF-kappa B p65 alone could induce E-cadherin loss in RCC, EMT phenotypes and MMP9 expressions induced by TNF-alpha were not reversed by the inhibitors of NF-kappa B activation. These results suggest that the TNF-alpha signaling pathway is involved in the tumorigenesis of RCC. However, NF-kappa B activation is not crucial for invasion and EMT enhanced by TNF-alpha in RCC cells.