PLATELET-DERIVED GROWTH-FACTOR STIMULATES PROTEIN-KINASE-A THROUGH A MITOGEN-ACTIVATED PROTEIN KINASE-DEPENDENT PATHWAY IN HUMAN ARTERIAL SMOOTH-MUSCLE CELLS

The abilities of platelet-derived growth factor (PDGF) and insulin-lik e growth factor (IGF-I) to regulate cAMP metabolism and mitogen-activa ted protein kinase (MAP kinase) activity were compared in human arteri al smooth muscle cells (hSMC), PDGF-BB stimulated cAMP accumulation up to 150-fold in a concentration depend ent manner (EC(50) approximate to 0.7 nM). The peak of cAMP formation and cAMP-dependent protein kina se (PKA) activity occurred approximately 5 min after the addition of P DGF and rapidly declined thereafter. Incubating cells with PDGF and 3- isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor) enhanc ed the accumulation of cAMP and PKA activity by an additional 2.5-3-fo ld, whereas IBMX alone was essentially without effect, The PDGF-stimul ated increase in cAMP was prevented by addition of the cyclooxygenase inhibitor indomethacin, consistent with release of prostaglandins stim ulating cAMP. PDGF, but not IGF-I, stimulated MAPK activity, cytosolic phospholipase A(2) (cPLA(2)) phosphorylation, and cAMP synthesis whic h indicated a key role for MAP kinase in the activation of cPLA(2), Fu rther, PDGF stimulated the rapid release of arachidonic acid and synth esis of prostaglandin E(2) (PGE(2)) which could be inhibited by a cPLA , inhibitor (AACOCF(3)), Calcium mobilization was required for PDGF in duced arachidonic acid release and PGE(2) synthesis but not for MAPK a ctivation, whereas PKC was required for PGE(2)-mediated activation of PKA. In summary, these results demonstrate that PDGF increases cAMP fo rmation and PKA activity through a MAP kinase-mediated activation of c PLA(2), arachidonic acid release, and PGE(2) synthesis in human arteri al smooth muscle cells.