DIFFERENTIAL EXPRESSION AND REGULATION OF HSP70 AND HSP90 BY PHORBOL ESTERS AND HEAT-SHOCK

Human peripheral blood monocytes (PBM) produce superoxide anions (O-2- radical-anion) by a process involving electron transfer from NADPH to O-2-radical-anion, catalyzed by the respiratory burst enzyme NADPH oxi dase. We have previously shown that phagocytosis, while activating NAD PH oxidase, induced in PBM the synthesis of heat shock (HS) proteins ( HSP). The present study was undertaken to establish whether this incre ase in HSP expression was related to O-2-radical-anion and/or to class ical second messengers such as protein kinase C (PKC). Thus, the effec ts of the PKC activator phorbol 12-myristate 13-acetate (PMA) were com pared with those of heat shock on the expression, in PBM, of the major HSP, hsp70 and hsp90, using biometabolic labeling, Western and Northe rn blotting, and gel mobility shift assays. PMA induced the accumulati on of mRNA and an increased expression of hsp90 and, to a lesser exten t, hsp/hsc70 (hsc is the cognate, constitutive form). This induction w as also observed in PBM from patients with chronic granulomatous disea se, a genetic defect in NADPH oxidase, and was abolished by the PKC in hibitors staurosporine and H-7. PMA did not cause activation of the HS factor, and the PMA-induced overexpression of HSP was not blocked by the transcriptional inhibitor actinomycin D. HSP-specific mRNA stabili ty was increased after PMA exposure as compared with heat shock. These results suggest that O-2-radical-anion is not involved in the PMA-med iated induction of hsp70 and hsp90 and that, in contrast to HS, PMA in creases the expression of HSP as a result of PKC-induced mRNA stabiliz ation rather than of transcriptional activation of HS genes.