Resistance to tumor necrosis factor (TNF) cytotoxicity by autocrine TNF production is independent of intracellular signaling pathways

Abstract

We previously showed that autocrine tumor necrosis factor (TNF) production in the TNF-sensitive L929sA fibrosarcoma cell line induced TNF resistance, which is correlated with downmodulation of both TNF receptors on the cell surface. We now analyzed whether autocrine TNF production also interfered with intracellular TNF signaling pathways. The L929sA-CAT-R55i cell line, in which cell death can be induced by controlled cytoplasmic expression of a trimeric fusion protein between chloramphenicol acetyltransferase and the intracellular domain of TNF-R55 (CAT-R55i), was supertransfected with the murine TNF gene. Expression of the latter conferred resistance to cell death induced by exogenous TNF, while cytotoxicity induced by CAT-R55i was not impaired. This demonstrates that autocrine TNF did not induce intracellular mechanisms that block TNF signaling leading to cell death. Thus the induction of TNF resistance via autocrine TNF production in L929sA cells is solely due to downmodulation of TNF receptors on the cell surface.