The level and phosphorylation of Hsp70 in the rat liver cytosol after adrenalectomy and hyperthermia

Hepatic heat shock protein Hsp70 synthesis and in vitro phosphorylation were studied in the liver cytosol of intact, adrenalectomized and dexamethasone-administered adrenalectomized rats after 41°C whole body hyperthermic stress. Hsp70 was detected by immunoblotting with N27F3-4 monoclonal antibody recognizing both constitutive and inducible forms of the protein. A comparison between basal and heat stress-induced levels of the protein in the liver cytosol of the three groups of animals suggested that glucocorticoid hormones stimulate the basal synthesis of Hsp70 and inhibit its induction by stress. In both unstressed and hyperthermia-exposed animals, hepatic Hsp70 was detected as a phosphoprotein. The extent of its in vitro phosphorylation was found to be significantly reduced by heat stress or adrenalectomy, but dexamethasone failed to restore it to the original level.