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

Scott, P. H., Belham, C. M., Al-Hafidh, J., Chilvers, E. R., Peacock, A. J., Gould, G. W. and Plevin, R. (1996) 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. Biochemical Journal, 318(3), pp. 965-971. (doi: 10.1042/bj3180965) (PMID:8836145) (PMCID:PMC1217712)

Abstract

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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Scott, Dr Pamela
• Authors: Scott, P. H., Belham, C. M., Al-Hafidh, J., Chilvers, E. R., Peacock, A. J., Gould, G. W., and Plevin, R.
• College/School: College of Medical Veterinary and Life Sciences > School of Life Sciences
• Journal Name: Biochemical Journal
• Publisher: Portland Press Ltd.
• ISSN: 0264-6021
• ISSN (Online): 1470-8728
• Published Online: 15 September 1996