NO regulates PDGF-induced activation of PKB but not ERK in A7r5 cells: implications for vascular growth arrest.
In addition to the well-documented role of nitric oxide (NO) as a vasodilator, NO has also been implicated in vascular smooth muscle cell (VSMC) growth arrest. Signaling mechanisms responsible for growth factor receptor-mediated VSMC proliferation include the extracellular signal-regulated kinase (ERK) and possibly the protein kinase B (PKB) cascade. Thus the present study was designed to test the hypothesis that, in A7r5 vascular smooth muscle-derived cells, platelet-derived growth factor (PDGF)-induced activation of either ERK or PKB is regulated by NO, which then modulates cellular proliferation and/or apoptosis. PKB-alpha was the predominant isoform of PKB expressed in A7r5 cells and was also expressed in rabbit carotid arteries and aortae. Phosphorylation of PKB-alpha and ERK induced by PDGF-BB was maximal within 5-15 min in A7r5 cells. Preincubation of A7r5 cells with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) resulted in a biphasic regulation of PDGF-stimulated PKB-alpha phosphorylation and bioactivity. Acute exposure to SNAP significantly augmented PDGF-induced activation of PKB-alpha, whereas prolonged incubation led to a marked diminution in PDGF-induced activation of PKB-alpha. In contrast, SNAP did not affect PDGF-induced activation of ERK at any time point. The cGMP-independent effects of SNAP on PDGF-induced activation of PKB-alpha were established with the use of an inhibitor of soluble guanylyl cyclase, ODQ, as well as a cell-permeable analog of cGMP, 8-bromo-cGMP. Prolonged treatment of A7r5 cells with SNAP led to a significant decrease in DNA synthesis without an appreciable increase in apoptosis. These data suggest that, after prolonged exposure to SNAP, NO selectively attenuates PDGF-induced increase in PKB-alpha activation, which in turn may contribute to diminished VSMC proliferation by mechanisms involving growth arrest but not apoptosis.
Sandirasegarane
L
L
Department of Pharmacology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA. lxs51@psu.edu
Charles
R
R
Bourbon
N
N
Kester
M
M
D000818:Animals; D001011:Aorta / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D000077214:Becaplermin; D001808:Blood Vessels / Q000254:growth & development; D002339:Carotid Arteries / Q000378:metabolism; D002460:Cell Line; D019332:Endothelin-1 / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000201:enzymology*; D009569:Nitric Oxide / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D020574:Proto-Oncogene Proteins c-sis; D011817:Rabbits; D051381:Rats; D026423:S-Nitroso-N-Acetylpenicillamine
D019332:Endothelin-1; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D020030:Nitric Oxide Donors; D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D020574:Proto-Oncogene Proteins c-sis; D000077214:Becaplermin; D009569:Nitric Oxide; D007334:Insulin-Like Growth Factor I; D026423:S-Nitroso-N-Acetylpenicillamine; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D010396:Penicillamine