Factor against Hyperthermic Cytotoxicity Endogenous Tumor Necrosis Factor Functions as a Resistant

One of the mechanisms of cytotoxicity by tumor necrosis factor (TNF) is the induction of reactive oxygen molecules. Cells producing endogenous tumor necrosis factor (enTNF) show resistance to the cy totoxicity of exogenous TNF by scavenging the reactive oxygen mole cules. The intracellular hydroxyl radical production is also known to be involved in the heat-induced cytotoxicity. In the present study, we there fore examined the possibility that enTNF may act as a protective protein against the heat-induced cytotoxicity in a manner similar to that of exogenous TNF. Heat-sensitive L-M (mouse tumorigenic fibroblast) cells, originally expressing no enTNF, were transfected with a human TNF expression vector to produce enTNF. The stable transfectants showed apparent resistance to heat treatment. Conversely, when HeLa (human uterine cervical cancer) cells, originally producing an appreciable amount of enTNF, were transfected with an antisense TNF mRNA expression vector to inhibit enTNF synthesis, their heat sensitivity was enhanced. Furthermore, L-M cells which were transfected with nonsecretory human TNF expression vector also acquired resistance to heat treat ment. In these cells, heat resistance correlated well with expression of enTNF and intracellular levels of manganous Superoxide disimilase. These results indicate that enTNF exerts its intracellular protective effect against the heat-induced cytotoxicity by scavenging reactive ox ygen with induced manganous Superoxide dismutase in a manner similar to that found in cells treated with exogenous TNF.