title: M1 muscarinic receptors block caspase activation by phosphoinositide 3-kinase- and MAPK/ERK-independent pathways.
abstract: When PC12 cells are deprived of trophic support they undergo apoptosis. We have previously shown that survival of trophic factor-deprived PC12M1 cells can be promoted by activation of the G protein-coupled muscarinic receptors. The mechanism whereby muscarinic receptors inhibit apoptosis is poorly understood. In the present study we investigated this mechanism by examining the effect of muscarinic receptor activation on the serum deprivation-induced activity of key players in apoptosis, the caspases, in PC12M1 cells. The results showed that m1 muscarinic activation inhibits caspase activity induced by serum deprivation. This effect appeared to be caused by the prevention of activation of caspases such as caspase-2 and caspase-3, and not by the inhibition of existing activity. Muscarinic receptor activation also stimulated the mitogen-activated protein kinase/extracellular signaling-regulated kinase (MAPK/ERK) and phosphoinositide (PI) 3-kinase signaling pathways. The PI 3-kinase pathway inhibitors wortmannin and LY294002, as well as the MAPK/ERK pathway PD98059 inhibitor, did not however suppress the inhibitory effect of the muscarinic receptors on caspase activity. The results therefore suggested that the muscarinic survival effect is mediated by a pathway that leads to caspase inhibition by MAPK/ERK- and PI 3-kinase-independent signaling cascades.
authors.affiliation: Department of Neurobiochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel.
authors.forename: C
authors.initials: C
authors.lastname: Leloup
authors.forename: D M
authors.initials: DM
authors.lastname: Michaelson
authors.forename: A
authors.initials: A
authors.lastname: Fisher
authors.forename: T
authors.initials: T
authors.lastname: Hartmann
authors.forename: K
authors.initials: K
authors.lastname: Beyreuther
authors.forename: R
authors.initials: R
authors.lastname: Stein
mesh_terms: D000818:Animals; D017209:Apoptosis; D001285:Atropine / Q000494:pharmacology; D061945:Caspase Inhibitors; D020169:Caspases / Q000096:biosynthesis / Q000378:metabolism*; D002457:Cell Extracts; D016895:Culture Media, Serum-Free; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D010095:Oxotremorine / Q000494:pharmacology; D016716:PC12 Cells; D010447:Peptide Hydrolases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D001285:Atropine; D061945:Caspase Inhibitors; D020169:Caspases; D002457:Cell Extracts; D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; D020929:Mitogen-Activated Protein Kinase Kinases; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010095:Oxotremorine; D010447:Peptide Hydrolases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic; C108711:DEVDase