TNF receptor I is required for induction of macrophage heat shock protein 70

Expression of heat shock proteins (HSP) is an adaptive response to cellular stress. Stress induces tumor necrosis factor (TNF)-alpha production. In tu rn, TNF-alpha induces HSP70 expression. However, osmotic stress or ultravio let radiation activates TNF-alpha receptor I (TNFR-I) in the absence of TNF -alpha. We postulated that TNF-alpha receptors are involved in the inductio n of HSP70 by cellular stress. Peritoneal Mf were isolated from wild-type ( WT), TNF-alpha knockout (KO), and TNFR (I or II) KO mice. Cells were cultur ed overnight and then heat stressed at 43 +/- 0.5 degreesC for 30 min follo wed by a 4-h recovery at 37 degreesC. Cellular HSP70 expression was induced by heat stress or exposure to endotoxin [lipopolysaccharide (LPS)] as dete rmined by immunoblotting. HSP70 expression induced by either heat or LPS wa s markedly decreased in TNFR-I KO M phi, whereas TNFR-II KO M phi exhibited HSP70 expression comparable to that in WT mice. Expression of HSP70 after heat stress in TNF-alpha KO M phi was also similar to that in WT mice, sugg esting that induction of HSP70 by TNFR-I occurs independently of TNF-alpha. In addition, levels of steady-state HSP70 mRNA were similar by RT-PCR in W T and TNFR-I KO M phi despite differences in protein expression. Furthermor e, the effect of TNFR-I appears to be cell specific, since HSP70 expression in splenocytes isolated from TNFR-I KO was similar to that in WT splenocyt es. These studies demonstrate that TNFR-I is required for the synthesis of HSP70 in stressed M phi by a TNF-independent mechanism and support an intra cellular role for TNFR-I.