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-like growth factor (IGF-I) to regulate cAMP metabolism and mitogen-activated protein kinase (MAP kinase) activity were compared in human arterial 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 kinase (PKA) activity occurred approximately 5 min after the addition of PDGF and rapidly declined thereafter. Incubating cells with PDGF and 3-isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor) enhanced the accumulation of cAMP and PKA activity by an additional 2.5-3-fold, whereas IBMX alone was essentially without effect, The PDGF-stimulated increase in cAMP was prevented by addition of the cyclooxygenase inhibitor indomethacin, consistent with release of prostaglandins stimulating cAMP. PDGF, but not IGF-I, stimulated MAPK activity, cytosolic phospholipase A(2) (cPLA(2)) phosphorylation, and cAMP synthesis which indicated a key role for MAP kinase in the activation of cPLA(2), Further, PDGF stimulated the rapid release of arachidonic acid and synthesis of prostaglandin E(2) (PGE(2)) which could be inhibited by a cPLA, inhibitor (AACOCF(3)), Calcium mobilization was required for PDGF induced arachidonic acid release and PGE(2) synthesis but not for MAPK activation, whereas PKC was required for PGE(2)-mediated activation of PKA. In summary, these results demonstrate that PDGF increases cAMP formation and PKA activity through a MAP kinase-mediated activation of cPLA(2), arachidonic acid release, and PGE(2) synthesis in human arterial smooth muscle cells.