title: Muscarinic-receptor-mediated inhibition of insulin-like growth factor-1 receptor-stimulated phosphoinositide 3-kinase signalling in 1321N1 astrocytoma cells.
abstract: In 1321N1 astrocytoma cells, stimulation of the IGF-1 (insulin-like growth factor-1) receptor increased the association of PI3K [phosphoinositide (PI) 3-kinase] activity with IRS-1 (insulin re-ceptor substrate 1), and increased the cellular concentration of PtdIns(3,4,5)P3. Carbachol, acting on M3 muscarinic receptors, inhibited insulin-, but not PDGF (platelet-derived growth factor)-, stimulated responses by approximately 50%. The inhibition of IRS-1-associated PI3K activity by carbachol (i) was rapid (<1 min), persistent (> or =60 min) and potent (half-maximal concentration approximately 1 microM); (ii) was reproduced by stimuli for several phospholipase-C-coupled receptors; (iii) was prevented by the inhibition of protein kinase C, but not by chelation of intracellular Ca2+; and (iv) was not blocked or reproduced by inhibitors or stimuli respectively of mitogen-activated protein kinase, PI3K, protein kinase B or the mammalian target of rapamycin. However, the effects of carbachol were prevented by sodium vanadate, a protein tyrosine phosphatase inhibitor, and were accompanied by reduced insulin-stimulated IRS-1 tyrosine phosphorylation and recruitment of the 85 kDa regulatory subunit of PI3K to IRS-1, but not by reduced IGF-1 receptor kinase activity. The inhibitory effect of carbachol was reproduced by okadaic acid, a protein serine/threonine phosphatase inhibitor, but not by PDGF, yet all three agents stimulated the serine phosphorylation of IRS-1 at residues Ser312, Ser616 and Ser636/639, albeit to different extents. Thus muscarinic receptors may inhibit insulin signalling by promoting IRS-1 tyrosine dephosphorylation and/or by uncoupling IRS-1 from the stimulated IGF-1 receptor by stimulating IRS-1 serine phosphorylation. However, the proportion of IRS-1 molecules phosphorylated at a particular site or the phosphorylation of additional IRS-1 serine residues other than those noted above must be important.
authors.affiliation: The Division of Cell Signalling, School of Life Sciences, MSI/WTB Complex, University of Dundee, Dow St, Dundee DD1 5EH, Scotland, UK. i.h.batty@dundee.ac.uk
authors.forename: Ian H
authors.initials: IH
authors.lastname: Batty
authors.forename: Ian N
authors.initials: IN
authors.lastname: Fleming
authors.forename: C Peter
authors.initials: CP
authors.lastname: Downes
mesh_terms: D001254:Astrocytoma / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D015759:Ionomycin / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D002118:Calcium; D002217:Carbachol; D015544:Inositol 1,4,5-Trisphosphate; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D015759:Ionomycin; D020928:Mitogen-Activated Protein Kinases; D019319:Okadaic Acid; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D010768:Phosphoserine; D019000:Phosphotyrosine; D010982:Platelet-Derived Growth Factor; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1; D011976:Receptors, Muscarinic; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D013755:Tetradecanoylphorbol Acetate; D010738:Type C Phospholipases; C526292:IRS1 protein, human