HEAT STRESSING STIMULATES NUCLEAR-PROTEIN KINASE-C RAISING DIACYLGLYCEROL LEVELS - NUCLEAR-PROTEIN KINASE-C ACTIVATION PRECEDES HSP70 MESSENGER-RNA EXPRESSION

Protein kinase C (pKC) activity has been studied in rat liver after su bjecting animals to heat shocking. Nuclear pKC activity was stimulated owing to heat shocking without any change in the cytosolic enzyme act ivity. The nuclear diacylglycerol levels were raised owing to heat str ess along with the stimulation of polarhead phospholipid hydrolysis. K inetically, the V-max Of nuclear pKC was enhanced as a result of heat shocking, with no change in apparent K-m and with concomitant phosphor ylation of nuclear lamin B-2. Western blot analysis as well as phorbol dibutyrate binding indicate that pKC protein levels did not change be cause of heat shocking. The stimulation of nuclear pKC under heat stre ss conditions represents an in vivo phenomenon and the enzyme stimulat ion precedes Hsp70 mRNA expression.