Ras-dependent ERK activation by the human G(s)-coupled serotonin receptors 5-HT4(b) and 5-HT7(a).
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.
Norum
Jens Henrik
JH
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.
Hart
Kent
K
Levy
Finn Olav
FO
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*
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