Tumor necrosis factor-alpha (TNFα) has emerged as a player in the progression of malignant tumors and is expressed in the tumor microenvironment of multiple tumor types including renal cell carcinoma (RCC). Key components of TNFα signaling include sphingolipids, particularly ceramide that serves as a source for ganglioside synthesis. Here we report that TNFα may promote tumor progression by stimulating renal tumors to produce gangliosides capable of inducing T lymphocyte apoptosis. In co-culture experiments RCC lines that had been pretreated with recombinant TNFα (50-250 ng/ml) demonstrate greater apoptogenic activity against T cells than either untreated RCC or TNFα alone. Both HPLC and immunostaining with an anti-GM2 antibody showed increased GM2 expression by tumor lines (SK-RC-45, SK-RC-54,SK-RC-26b) following 3-5 day incubation with TNFα. Similar results were observed when the transgene for TNFα was overexpressed in the SK-RC-45 line that typically expresses minimal levels of GM2 and TNFα. Compared to the parental line the transfected clone was more apoptogenic for T cells and produced significantly higher levels of TNFα along with GM2. Furthermore, anti-GM2 antibody significantly blocked T cell apoptosis mediated by either TNFα treated tumor cells or the RCC clone transfected with TNFα. These findings suggest that GM2 and TNFα are closely involved in RCC-induced apoptosis of T cells. This study also provides evidence that TNF signaling is involved in the acquisition of a distinct ganglioside assembly in tumor cells.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]