Activation of a mitogen-activated protein kinase (ERK2) by the 5-hydroxytryptamine1A receptor is sensitive not only to inhibitors of phosphatidylinositol 3-kinase, but to an inhibitor of phosphatidylcholine hydrolysis.
A variety of receptors coupled to GTP-binding regulatory proteins (G proteins) initiate signals that culminate in activation of the mitogen-activated protein kinases ERK1 and ERK2. We demonstrate here that the human 5-HT1A receptor expressed in Chinese hamster ovary cells similarly promotes activation of ERK1 and ERK2, but that the pathway used does not conform entirely to those proposed previously for G protein-coupled receptors. Activation of ERK2 by the 5-HT1A receptor-selective agonist 8-hydroxy-N,N-dipropyl-2-aminotetralin hydrobromide (8-OH-DPAT) was inhibited completely by pertussis toxin and substantially by prolonged treatment of cells with phorbol 12-myristate 13-acetate. The implied requirement for protein kinase C, however, was negated in studies with bisindolylmaleimide and Ro-31-8220, which, although completely inhibiting activation of ERK2 by phorbol ester, had no impact on activation by 8-OH-DPAT. The anticipated inhibition by the tyrosine kinase inhibitors genistein and herbimycin A, moreover, was marginal at best. As expected for a Gi-coupled receptor, the inhibitors of phosphatidylinositol 3-kinase wortmannin and LY294002 inhibited activation of ERK2, albeit only partly (70%). Of significance, an inhibitor of a phosphatidylcholine-specific phospholipase C, tricyclodecan-9-yl-xanthogenate (D609), caused a similar degree of inhibition. When the two types of inhibitors were combined, an almost complete inhibition was achieved. Our data suggest that phosphatidylinositol 3-kinase and phosphatidylcholine-specific phospholipase C represent components of different, but partly overlapping pathways that can account almost entirely for the activation of ERK2 by the 5-HT1A receptor.
Cowen
D S
DS
Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6084, USA.
Sowers
R S
RS
Manning
D R
DR
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D006868:Hydrolysis; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines / Q000494:pharmacology; D009636:Norbornanes; D037342:Pertussis Toxin; D010713:Phosphatidylcholines / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011985:Receptors, Serotonin / Q000378:metabolism*; D044263:Receptors, Serotonin, 5-HT1; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D000077191:Wortmannin
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000730:Androstadienes; D001952:Bridged-Ring Compounds; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002867:Chromones; D005576:Colforsin; D000242:Cyclic AMP; D004791:Enzyme Inhibitors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D009636:Norbornanes; D037342:Pertussis Toxin; D010713:Phosphatidylcholines; D019869:Phosphatidylinositol 3-Kinases; D010726:Phosphodiesterase Inhibitors; D017853:Phosphotransferases (Alcohol Group Acceptor); D011493:Protein Kinase C; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D017366:Serotonin Receptor Agonists; D013859:Thiocarbamates; D013871:Thiones; D010738:Type C Phospholipases; D010566:Virulence Factors, Bordetella; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C046498:tricyclodecane-9-yl-xanthogenate