INDUCTION OF HEAT-SHOCK-PROTEIN-72 SYNTHESIS BY ENDOGENOUS TUMOR-NECROSIS-FACTOR VIA ENHANCEMENT OF THE HEAT-SHOCK ELEMENT-BINDING ACTIVITYOF HEAT-SHOCK-FACTOR-1

Endogenous tumor necrosis factor (enTNF) acts as a resistance factor a gainst cytotoxicity caused by heat by inducing manganous superoxide di smutase (MnSOD), thereby scavenging reactive oxygen free radicals. On the other hand, it is also well known that heat shock proteins (HSP) w hich are induced by heat stress behave as cytoprotective factor agains t this stress. However, the relationship of these two resistance facto rs is not elucidated yet. In the present study, we therefore proposed the possibility that enTNF enhances HSP72 expression. Heat-sensitive L -M (mouse tumorigenic fibroblast) cells, which normally do not express enTNF, were transfected with a nonsecretory-type human TNF-alpha expr ession vector to produce enTNF Stable transfectants showed resistance to heat treatment and an increase of HSP72 expression. Conversely, whe n HeLa (human uterine cervical cancer) cells, which normally produce a n appreciable amount of enTNF, were transfected with an antisense TNF- alpha mRNA expression vector to inhibit enTNF synthesis, their heat se nsitivity was enhanced and HSP72 expression was reduced by half. Altho ugh enTNF caused no difference in the level of heat shock factor (HSF) 1 in these cells, enTNF expression correlated well with the binding a ctivity of HSF-1 to a P-32-labeled synthetic oligonucleotide containin g the human heat shock element (HSE). These results indicate that enTN F participates not only in intrinsic resistance against heat via induc tion of MnSOD but also via enhancement of the HSE-binding activity of HSF 1 followed by augmentation of HSP72 expression.