title: Elevated Rac1 activity changes the M3 muscarinic acetylcholine receptor-mediated inhibition of proliferation to induction of cell death.
abstract: Although muscarinic acetylcholine receptors (mAChRs) regulate proliferation in many cell types, the signaling pathways involved are unclear. The participation of the small GTPases Rac1 and RhoA in M(3) mAChR-mediated inhibition of proliferation was investigated by activating M(3) mAChRs stably transfected in Chinese hamster ovary cells stably coexpressing hemagglutinin (HA)-tagged wild-type or mutant Rac1 or RhoA proteins. Activation of M(3) mAChRs activates both Rac1 and RhoA and inhibits cell proliferation in all cell lines tested. mAChR-mediated inhibition of proliferation is diminished in cells expressing dominant-negative HA-Rac1(Asn17) (m3DNRac) but is enhanced in cells expressing HA-Rac1 (m3WTRac) or constitutively active HA-Rac(Val12) (m3CARac). The activation of mAChRs in m3WTRac and m3CARac cells also induces apoptosis. Expression of wild-type or mutant RhoA proteins does not alter mAChR-mediated inhibition of proliferation. mAChR-induced inhibition of proliferation is abrogated in all cell lines when Galpha(q/11) signaling is terminated by transient expression of the COOH-terminal fragment of phospholipase C (PLC-beta1ct), the NH(2)-terminal fragment of G protein-coupled receptor kinase, or the regulator of G protein signaling 2. Pretreatment of all cells expressing wild-type or mutant Rac1 proteins with edelfosine, a phosphatidylinositol-specific PLC inhibitor, or Go 6976, which inhibits conventional protein kinase C (PKC) isoforms, diminishes the M(3) mAChR's ability to inhibit proliferation. Our results identify Galpha(q/11), PLC, and PKC as participants in the M(3) mAChR-mediated inhibition of cell proliferation. These findings indicate that in the context of high Rac1 activity, but not RhoA activity, M(3) mAChR-mediated activation of these participants triggers cell death.
authors.affiliation: Molecular Pharmacology Laboratory, One Guthrie Square, Sayre, PA 18840, USA.
authors.forename: Shulamith H
authors.initials: SH
authors.lastname: Shafer
authors.forename: Carol L
authors.initials: CL
authors.lastname: Williams
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D016466:CHO Cells; D016923:Cell Death / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D006224:Cricetinae; D005260:Female; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D015870:Gene Expression; D007365:Intercellular Junctions / Q000502:physiology; D007527:Isoenzymes / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D043643:Receptor, Muscarinic M1 / Q000502:physiology; D043587:Receptor, Muscarinic M3 / Q000502:physiology*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000378:metabolism* / Q000502:physiology; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011493:Protein Kinase C; D010738:Type C Phospholipases; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein