INHIBITION OF HORMONE-SENSITIVE LIPASE GENE-EXPRESSION BY CAMP AND PHORBOL ESTERS IN 3T3-F442A AND BFC-1 ADIPOCYTES

Hormone-sensitive lipase (HSL) catalyses the rate-limiting step in adi pocyte lipolysis. Short-term hormonal regulation of HSL activity is we ll characterized, whereas little is known about the control of HSL gen e expression. We have measured HSL mRNA content of 3T3-F442A and BFC-1 adipocytes in response to the cAMP analogue 8-(4-chlorophenylthio)-cA MP (8-CPT-cAMP) and to the phorbol ester phorbol 12-myristate 13-aceta te (PMA) by Northern blot, using a specific mouse cDNA fragment. Treat ment of the cells for 12 or 6 h with, respectively, 0.5 mM 8-CPT-cAMP or 1 mu M PMA produced a maximal decrease of about 60 % in HSL mRNA. T hese effects were unaffected by the protein-synthesis inhibitor anisom ycin, suggesting that cAMP and PMA actions were direct. The reduction in HSL mRNA was accompanied by a reduction in HSL total activity. The intra-cellular routes that cAMP and PMA follow for inducing such an ef fect seemed clearly independent. (i) After desensitization of the prot ein kinase C regulation pathway by a 24 h treatment of the cells with 1 mu M PMA, PMA action was abolished whereas cAMP was still fully acti ve. (ii) Treatment with saturating concentrations of both agents produ ced an additive effect. (iii) The synthetic glucocorticoid dexamethaso ne had no proper effect on HSL gene expression but potentiated cAMP ac tion without affecting PMA action. cAMP inhibitory action on HSL is un expected. Indeed, the second messenger of catecholamines is the main a ctivator of HSL by phosphorylation. We envision that a long-term cAMP treatment of adipocytes induces a counter-regulatory process that redu ces HSL content and, ultimately, limits fatty acid depletion from stor ed triacylglycerols.