Tumor necrosis factor receptor 2-signaling in CD133-expressing cells in renal clear cell carcinoma

Compared to normal kidney, renal clear cell carcinomas (ccRCC) contain increased numbers of interstitial, non-hematopoietic CD133(+)cells that express stem cell markers and exhibit low rates of proliferation. These cells fail to form tumors upon transplantation but support tumor formation by differentiated malignant cells. We hypothesized that killing of ccRCC CD133(+) (RCC(CD133+)) cells by cytotoxic agents might be enhanced by inducing them to divide. Since tumor necrosis factor-alpha (TNF), signalling through TNFR2, induces proliferation of malignant renal tubular epithelial cells, we investigated whether TNFR2 might similarly affect RCC(CD133+)cells. We compared treating organ cultures of ccRCC vs adjacent nontumour kidney (NK) and RCC(CD133+) vs NK CD133(+) (NK(CD133+)) cell cultures with wild-type TNF (wtTNF) or TNF muteins selective for TNFR1 (R1TNF) or TNFR2 (R2TNF). In organ cultures, R2TNF increased expression of TNFR2 and promoted cell cycle entry of both RCC(CD133+) and NK(CD133+) but effects were greater in RCC(CD133+). In contrast, R1TNF increased TNFR1 expression and promoted cell death. Importantly, cyclophosphamide triggered much more cell death in RCC(CD133+) and NK(CD133+)cells pre-treated with R2TNF as compared to untreated controls. We conclude that selective engagement of TNFR2 by TNF can drives RCC(CD133+) proliferation and thereby increase sensitivity to cell cycle-dependent cytotoxicity.