title: Stimulation of M3 muscarinic receptors induces phosphorylation of the Cdc42 effector activated Cdc42Hs-associated kinase-1 via a Fyn tyrosine kinase signaling pathway.
abstract: The tyrosine kinase, activated Cdc42Hs-associated kinase-1 (ACK-1), is a specific effector of the Rho family GTPase Cdc42. GTP-bound Cdc42 has been shown to facilitate neurite outgrowth elicited by activation of muscarinic cholinergic receptors (mAChRs). Because tyrosine kinase activity is a requirement for neuritogenesis in several cell systems, we investigated whether endogenous mAChRs (principally of the M3 subtype) expressed in human SH-SY5Y neuroblastoma cells would signal to ACK-1. Incubation of cells with the cholinergic agonist oxotremorine-M (Oxo-M) induced an approximately 6-fold increase in the tyrosine phosphorylation of ACK-1 which was inhibited by atropine. ACK-1 phosphorylation was blocked by Clostridium difficile toxin B, an inhibitor of Rho family GTPases. In contrast, disruption of the actin cytoskeleton with cytochalasin D stimulated ACK-1 phosphorylation, and moreover, addition of Oxo-M to cells preincubated with this agent elicited a further increase in phosphorylation, indicating that an intact cytoskeleton is not required for mAChR signaling to ACK-1. Although stimulation of M3 mAChRs induces both an increase in intracellular Ca2+ and activation of protein kinase C (PKC), neither of these second messenger pathways was required for receptor-stimulated ACK-1 phosphorylation. Instead, inhibition of PKC resulted in a 2-fold increase in Oxo-M-stimulated ACK-1 phosphorylation, whereas acute activation of PKC with phorbol ester decreased ACK-1 phosphorylation. The agonist-induced tyrosine phosphorylation of ACK-1 was blocked by inhibitors of Src family kinases, and ACK-1 was coprecipitated with Fyn (but not Src) in an agonist-dependent manner. Finally, scrape loading cells with glutathione S-transferase fusion proteins of either the Fyn-SH2 or Fyn-SH3 domain significantly attenuated mAChR-stimulated ACK-1 tyrosine phosphorylation. The data are the first to show phosphorylation of ACK-1 after stimulation of a receptor coupled to neurite outgrowth and indicate that a Rho family GTPase (i.e. Cdc42) and Fyn are essential upstream elements of this signaling pathway.
authors.affiliation: Department of Pharmacology and Neuroscience Laboratory, Mental Health Research Institute, University of Michigan, Ann Arbor, Michigan 48104-1687, USA. Dan.Lines,am@UCHSC.edu
authors.forename: D A
authors.initials: DA
authors.lastname: Linseman
authors.forename: K A
authors.initials: KA
authors.lastname: Heidenreich
authors.forename: S K
authors.initials: SK
authors.lastname: Fisher
mesh_terms: D005246:Feedback; D020439:Growth Cones / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D011518:Proto-Oncogene Proteins; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; C081345:Cdc42Hs-associated kinase; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; D051076:Proto-Oncogene Proteins c-fyn; C403262:TNK2 protein, human; D011493:Protein Kinase C; D020764:cdc42 GTP-Binding Protein