Tumor Necrosis Factor Receptor-2 Signals Clear-Cell Renal Carcinoma Proliferation via Phosphorylated 4E Binding Protein-1 and Mitochondrial Gene Translation

Abstract

Clear-cell renal cell carcinoma (ccRCC), a tubular epithelial malignancy, secretes tumor necrosis factor (TNF), which signals ccRCC cells in an autocrine manner via two cell surface receptors, TNFR1 and TNFR2, to activate shared and distinct signaling pathways. Selective ligation of TNFR2 was shown to drive cell cycle entry of malignant cells via a signaling pathway involving epithelial tyrosine kinase, vascular endothelial cell growth factor receptor type 2, phosphatidylinositol-3-kinase, Akt, ^pSer727-Stat3, and mammalian target of rapamycin. In this study, phosphorylated 4E binding protein-1 (4EBP1) serine 65 (^pSer65-4EBP1) is identified as a downstream target of this TNFR2 signaling pathway. ^pSer65-4EBP1 expression is significantly elevated relative to total 4EBP1 in ccRCC tissue compared with normal kidneys, with signal intensity increasing with malignant grade. Selective ligation of TNFR2 with the TNFR2-specific mutein increases ^pSer65-4EBP1 expression in organ cultures that co-localizes with internalized TNFR2 in mitochondria and increases expression of mitochondrially encoded COX (cytochrome c oxidase subunit) Cox1, as well as nuclear-encoded Cox4/5b subunits. Pharmacologic inhibition of mammalian target of rapamycin reduces both TNFR2-specific mutein-mediated phosphorylation of 4EBP1 and cell cycle activation in tumor cells while increasing cell death. These results signify the importance of ^pSer65-4EBP1 in mediating TNFR2-driven cell-cycle entry in tumor cells in ccRCC and implicate a novel relationship between the TNFR2/^pSer65-4EBP1/COX axis and mitochondrial function.