cAMP-and rapamycin-sensitive regulation of the association of eukaryotic initiation factor 4E and the translational regulator PHAS-I in aortic smooth muscle cells.

LM Graves, KE Bornfeldt, GM Argast… - Proceedings of the …, 1995 - National Acad Sciences
LM Graves, KE Bornfeldt, GM Argast, EG Krebs, X Kong, TA Lin, JC Lawrence Jr
Proceedings of the National Academy of Sciences, 1995National Acad Sciences
Incubating rat aortic smooth muscle cells with either platelet-derived growth factor BB
(PDGF) or insulin-like growth factor I (IGF-I) increased the phosphorylation of PHAS-I, an
inhibitor of the mRNA cap binding protein, eukaryotic initiation factor (eIF) 4E.
Phosphorylation of PHAS-I promoted dissociation of the PHAS-I-eIF-4E complex, an effect
that could partly explain the stimulation of protein synthesis by the two growth factors.
Increasing cAMP with forskolin decreased PHAS-I phosphorylation and markedly increased …
Incubating rat aortic smooth muscle cells with either platelet-derived growth factor BB (PDGF) or insulin-like growth factor I (IGF-I) increased the phosphorylation of PHAS-I, an inhibitor of the mRNA cap binding protein, eukaryotic initiation factor (eIF) 4E. Phosphorylation of PHAS-I promoted dissociation of the PHAS-I-eIF-4E complex, an effect that could partly explain the stimulation of protein synthesis by the two growth factors. Increasing cAMP with forskolin decreased PHAS-I phosphorylation and markedly increased the amount of eIF-4E bound to PHAS-I, effects consistent with an action of cAMP to inhibit protein synthesis. Both PDGF and IGF-I activated p70S6K, but only PDGF increased mitogen-activated protein kinase activity. Forskolin decreased by 50% the effect of PDGF on increasing p70S6K, and forskolin abolished the effect of IGF-I on the kinase. The effects of PDGF and IGF-I on increasing PHAS-I phosphorylation, on dissociating the PHAS-I-eIF-4E complex, and on increasing p70S6K were abolished by rapamycin. The results indicate that IGF-I and PDGF increase PHAS-I phosphorylation in smooth muscle cells by the same rapamycin-sensitive pathway that leads to activation of p70S6K.
National Acad Sciences