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-dependent manner (EC ≈ 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 (cPLA) phosphorylation, and cAMP synthesis which indicated a key role for MAP kinase in the activation of cPLA. Further, PDGF stimulated the rapid release of arachidonic acid and synthesis of prostaglandin E (PGE) which could be inhibited by a cPLA inhibitor (AACOCF). Calcium mobilization was required for PDGF-induced arachidonic acid release and PGE synthesis but not for MAPK activation, whereas PKC was required for PGE-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, arachidonic acid release, and PGE synthesis in human arterial smooth muscle cells.