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