Phorbol 12-myristate 13-acetate triggers the protein kinase A-mediated phosphorylation and activation of the PDE4D5 cAMP phosphodiesterase in human aortic smooth muscle cells through a route involving extracellular signal regulated kinase (ERK)

AV6Phosphodiesterase 4D5 is the sole PDE4D CAMP phosphodiesterase isoform e xpressed in human aortic smooth muscle cells (HASMC). Phorbol 12-myristate 13-acetate (PMA) challenge of HASMC rapidly activated PDE4D5 through a proc ess ablated by the mitogen-activated protein kinase kinase inhibitor PD9805 9. PMA elicited an inhibitory effect on PDE4D5 activity in HASMC treated wi th the cyclooxygenase (COX) inhibitor indomethacin, the COX-2 selective inh ibitor NS-398, the phospholipase A(2) inhibitor quinacrine, and the cAMP-de pendent protein kinase A (PKA) inhibitor H89. PMA challenge of COS-1 cells elicited the rapid inhibition and phosphorylation of both recombinant and e ndogenous PDE4D5 in a manner ablated by PD98059 and not seen in S651A mutan t PDE4D5. PMA promoted the generation of PGE(2) in the medium of HASMC and caused activation of both extracellular signal-regulated kinase (ERK and PK A through a process ablated by indomethacin, NS-398, quinacrine, and PD9805 9. Exogenous prostaglandin (PG) E-2 increased CAMP levels and activated PKA in HASMC. COX-2 was expressed in HASMC but not in COS-1 cells. Forskolin c hallenge of COS-1 cells activated PDE4D5 by causing the PKA-mediated phosph orylation of Ser126 as detected using a novel phosphospecific antiserum. PM A challenge of HASMC elicited phosphorylation of the stimulatory PKA-specif ic phosphorylation site, Ser126 in PDE4D5 in a manner ablated by PD98059, i ndomethacin, and H89. We propose that, in HASMC, PMA activates PDE4D5 throu gh an ERK-controlled autocrine mechanism. This involves PGE(2) generation, which causes activation of adenylyl cyclase, allowing PKA to elicit net act ivation of PDE4D5 by phosphorylation at Ser126.