Heat shock protein 70 suppresses astroglial-inducible nitric-oxide synthase expression by decreasing NFkappaB activation.
In brain glial cells, expression of calcium independent nitric-oxide synthase (NOS-2) is induced following stimulation with bacterial endotoxin (lipopolysaccharide (LPS)) and/or pro-inflammatory cytokines. We have investigated the effects of heat shock (HS), which can reduce inflammatory responses in several cell types, on the induction of glial NOS-2 expression. Preincubation of cells for 20-60 min at 43 degrees C decreased subsequent levels of NOS-2 induction, with a maximal 80% reduction after 60 min of HS. Following HS, cells were refractory to NOS inducers for up to 4 h, after which time little or no suppression was observed. HS reduced cytosolic NOS-2 enzymatic activity (3-fold), steady state mRNA levels (2-3-fold), and gene promoter activity (by 50%). HS also reduced LPS-induced nuclear accumulation of transcription factor NFkappaB p65 subunit, suggesting perturbation of NFkappaB activation. A role for HS protein (HSP) 70 in NOS-2 suppression by HS is supported by the demonstration that 1) transfection with human HSP70 cDNA partially replicated HS effects; 2) antisense, but not sense, oligonucleotides directed against rat HSP70 partially blocked HS effects; and 3) rat fibroblasts stably expressing human HSP70 did not express NOS-2 in response to LPS plus cytokines. As with heat-shocked cells, HSP70-expressing cells also exhibited decreased NFkappaB p65 subunit nuclear accumulation. These results demonstrate that in glial cells, as well as other cell types, NOS-2 induction can be modulated by the HS response, mediated at least in part by HSP70 expression.