MECHANISM OF HEAT-SHOCK PROTEIN-72 INDUCTION IN PRIMARY CULTURED ASTROCYTES AFTER OXYGEN-GLUCOSE DEPRIVATION

Induction of stress proteins is thought to be important in the protect ion of cells from a variety of environmental insults including heat, h ypoxia and ischemia. The aim of this study was to compare the mechanis m of induction of heat shock protein 72 (HSP72) in primary cultures of murine cortical astrocytes by heat and combined oxygen-glucose depriv ation (OGD), a model of in vitro ischemia. S-35-methionine labeling an d immunoblotting showed increased HSP72 synthesis and accumulation las ting for up to 24 h following heat or OGD. Heat induced a markedly gre ater amount of HSP72 mRNA and protein than did OGD. We then sought evi dence of heat shock transcription factor-1 (HSF-1) activation. An incr ease in apparent molecular weight of nuclear HSF-1 after heat or OGD w as observed consistent with increased phosphorylation. To seek an expl anation of the difference between heat and OGD as inducers of HSP72 we examined the binding activity of HSP72+13 to other proteins. More cel lular protein was found to co-immunoprecipitate with HSP72+73, and mor e HSP72+73 was found in the pellet fraction after heat shock compared to OGD. These results suggest that HSP72 induction is regulated in ast rocytes at least in part at the level of HSF activation, by both heat and OGD. Reduced availability of free HSP72+73 in heated cells could b e responsible for the greater magnitude of HSP72 induction after heat compared to OGD.