title: Ras-dependent ERK activation by the human G(s)-coupled serotonin receptors 5-HT4(b) and 5-HT7(a).
abstract: Receptor tyrosine kinases activate mitogen-activated protein (MAP) kinases through Ras, Raf-1, and MEK. Receptor tyrosine kinases can be transactivated by G protein-coupled receptors coupling to G(i) and G(q). The human G protein-coupled serotonin receptors 5-HT(4(b)) and 5-HT(7(a)) couple to G(s) and elevate intracellular cAMP. Certain G(s)-coupled receptors have been shown to activate MAP kinases through a protein kinase A- and Rap1-dependent pathway. We report the activation of the extracellular signal-regulated kinases (ERKs) 1 and 2 (p44 and p42 MAP kinase) through the human serotonin receptors 5-HT(4(b)) and 5-HT(7(a)) in COS-7 and human embryonic kidney HEK293 cells. In transfected HEK293 cells, 5-HT-induced activation of ERK1/2 is sensitive to H89, which indicates a role for protein kinase A. The observed activation of ERK1/2 does not require transactivation of epidermal growth factor receptors. Furthermore, 5-HT induced activation of both Ras and Rap1. Whereas the presence of Rap1GAP1 did not influence the 5-HT-mediated activation of ERK1/2, the activation of ERK1/2 was abolished in the presence of dominant negative Ras (RasN17). ERK1/2 activation was reduced in the presence of "dominant negative" Raf1 (RafS621A) and slightly reduced by dominant negative B-Raf, indicating the involvement of one or more Raf isoforms. These findings suggest that activation of ERK1/2 through the human G(s)-coupled serotonin receptors 5-HT(4(b)) and 5-HT(7(a)) in HEK293 cells is dependent on Ras, but independent of Rap1.
authors.affiliation: Merck Sharp and Dohme Cardiovascular Research Center, Institute for Surgical Research and Department of Pharmacology, Rikshospitalet University Hospital, University of Oslo, N-0316 Oslo, Norway.
authors.forename: Jens Henrik
authors.initials: JH
authors.lastname: Norum
authors.forename: Kent
authors.initials: K
authors.lastname: Hart
authors.forename: Finn Olav
authors.initials: FO
authors.lastname: Levy
mesh_terms: D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D011985:Receptors, Serotonin / Q000378:metabolism*; D044422:Receptors, Serotonin, 5-HT4; D011994:Recombinant Proteins / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D011985:Receptors, Serotonin; D011994:Recombinant Proteins; C104425:serotonin 7 receptor; D044422:Receptors, Serotonin, 5-HT4; D012701:Serotonin; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019205:GTP-Binding Protein alpha Subunits, Gs; D018631:ras Proteins