BASAL AND ACIDIC FIBROBLAST GROWTH FACTOR-INDUCED ATRIAL-NATRIURETIC-PEPTIDE GENE-EXPRESSION AND SECRETION IS INHIBITED BY STAUROSPORINE

We examined the mechanisms involved in the activation of atrial natriu retic peptide (ANP) gene expression and secretion in response to acidi c fibroblast growth factor (aFGF) by studying the effects of staurospo rine, a protein kinase C inhibitor, and 12-O-tetradecanoyl phorbol 13- acetate (TPA), an activator of protein kinase C, on basal and aFGF-ind uced ANP messenger RNA (mRNA) and immunoreactive ANP (IR-ANP) levels i n cultured neonatal rat cardiac myocytes. Acidic FGF caused a dose- an d time-dependent increase in IR-ANP and immunoreactive N-terminal frag ment of proANP (IR-NT-proANP) release into the culture medium from ven tricular but not from atrial myocytes. In ventricular cells, 50 ng/ml aFGF for 24 or 48 h resulted in a 70% or 181% increase, respectively, in the accumulation of IR-ANP into the culture medium. Acidic FGF also stimulated ANP gene expression significantly; after 48 h of incubatio n, the ANP mRNA levels of aFGF-treated ventricular myocytes were 205% (P < 0.001) higher than those of control cells. Staurosporine alone at concentration of 10 nM significantly decreased the basal IR-ANP and I R-NT-proANP secretion, and inhibited the aFGF-induced increase in ANP mRNA and IR-ANP levels in ventricular myocytes. TPA (100 nM) alone sig nificantly stimulated ANP gene expression and secretion but these effe cts were not augmented by combining aFGF with TPA. High performance li quid chromatographical analysis showed that atrial and ventricular myo cytes maintained in serum-free medium were capable of secreting proces sed, ANP(99-126) sized material, and that aFGF did not alter the proce ssing of ANP in ventricular cultures. These results demonstrate that a FGF is a potent stimulator of ANP gene expression and secretion in cul tured neonatal rat ventricular but not in atrial cells. The observatio ns that (a) staurosporine completely abolished the effects of aFGF on ANP gene expression and release and (b) ANP secretory and gene express ion inducing effects of phorbol ester were not augmented by aFGF, sugg est an important role of protein kinase C in mediating aFGF-induced AN P gene expression and secretion.