A regulatory role for cAMP in phosphatidylinositol 3-kinase/p70 ribosomal S6 kinase-mediated DNA synthesis in platelet-derived-growth-factor-stimulated bovine airway smooth-muscle cells.
In bovine airway smooth-muscle cells platelet-derived growth factor (PDGF) and endothelin (Et-1) stimulate sustained and comparable activation of mitogen-activated protein kinase (MAP kinase) but display very different mitogenic efficacies, with PDGF inducing 50 times more DNA synthesis than Et-1. To examine additional signalling pathways which may be involved in this response, we investigated the role of phosphatidylinositol 3-kinase (PtdIns 3-kinase)/p70 ribosomal protein S6 kinase (p70s6k) in mediating PDGF- and Et-1-induced mitogenesis, and whether inhibition of this pathway may underly the ability of cAMP to inhibit cell proliferation. PDGF stimulated an increase in PtdIns 3-kinase activity and a sustained 15-fold increase in p70s6k activity that was abolished by both wortmannin and rapamycin. Et-1, however, stimulated only a 2-fold increase in p70s6k activity that was rapamycin-sensitive but wortmannin-insensitive. DNA synthesis stimulated by PDGF (50-fold) and Et-1 (2-fold) followed a similar pattern of inhibition. Pretreatment with phorbol ester did not affect p70s6k activation in response to PDGF. Raising intracellular cAMP levels using forskolin, however, resulted in a marked time-dependent inhibition of p70s6k activity, a decrease in the tyrosine phosphorylation of the PtdIns 3-kinase p85 subunit and reduced PtdIns 3-kinase activity. Forskolin also inhibited PDGF-stimulated DNA synthesis. These results suggest that PtdIns 3-kinase-dependent activation of p70s6k may determine mitogenic efficacy of agonists that generate comparable MAP kinase signals. Negative regulation of PtdIns 3-kinase by cAMP may play an important role in the inhibition of airway smooth-muscle cell proliferation.
Scott
P H
PH
Department of Physiology & Pharmacology, University of Strathclyde, Royal College, Glasgow, Scotland, UK.
Belham
C M
CM
al-Hafidh
J
J
Chilvers
E R
ER
Peacock
A J
AJ
Gould
G W
GW
Plevin
R
R
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis*; D019332:Endothelin-1 / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011090:Polyenes / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D014132:Trachea / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000077191:Wortmannin
D000730:Androstadienes; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D005576:Colforsin; D000242:Cyclic AMP; D004247:DNA; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D010982:Platelet-Derived Growth Factor; D011090:Polyenes; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D000077191:Wortmannin