Heat shock inhibits the cytotoxic action of TNF-alpha in tumor cells but does not alter its noncytotoxic actions in endothelial and adrenal cells.

We have previously demonstrated that a short heat treatment protects target cells from lysis by tumor necrosis factors (TNFs). Here we show that a similar heat treatment of human umbilical vein endothelial cells and human fetal adrenal cells does not alter noncytotoxic actions of TNF, suggesting that heat shock may specifically inhibit the cytotoxic action of TNF. To find clues to the mechanisms by which heat shock protects cells from TNF killing, its effects on TNF-alpha-TNF-receptor interactions, on the metabolism of the ligand, and on the expression of mRNAs for possible protective proteins were studied. The affinity of binding and the internalization of the ligand were slightly reduced after heat shock. These effects were, however, very vague and seen both in heat-responsive tumor cells and in endothelial and adrenal cells. Thus, it is unlikely that they could explain the heat-induced TNF resistance. Heat shock increased the expression of mRNAs for heat shock proteins (hsps) 27 and 70 in all the cells studied, but did not alter the expression of manganous superoxide dismutase (MnSOD) mRNA, which has previously been shown to play a crucial role in TNF resistance. Based on these results, we suggest that cells have multiple mechanisms to escape TNF-mediated lysis and that heat-induced protection from TNF killing may be mediated by hsps or other heat-inducible protective proteins, which act after receptor binding and protect cells from TNF-induced cellular damage without inhibiting the signal transduction mediating noncytotoxic effects of TNF.