title: Serotonin 5-HT1A receptor-mediated Erk activation requires calcium/calmodulin-dependent receptor endocytosis.
abstract: Many receptors that couple to heterotrimeric guanine nucleotide-binding (G) proteins mediate rapid activation of the mitogen-activated protein kinases, Erk1 and Erk2. The Gi-coupled serotonin (5-hydroxytryptamine (5-HT)) 5-HT1A receptor, heterologously expressed in Chinese hamster ovary or human embryonic kidney 293 cells, mediated rapid activation of Erk1/2 via a mechanism dependent upon both Ras activation and clathrin-mediated endocytosis. This activation was attenuated by chelation of intracellular Ca2+ and Ca2+/calmodulin (CAM) inhibitors or the CAM sequestrant protein calspermin. The CAM-dependent step in the Erk1/2 activation cascade is downstream of Ras activation, because inhibitors of CAM antagonize Erk1/2 activation induced by constitutively activated mutants of Ras and c-Src but not by constitutively activated mutants of Raf and MEK (mitogen and extracellular signal-regulated kinase). Inhibitors of the classical CAM effectors myosin light chain kinase, CAM-dependent protein kinases II and IV, PP2B, and CAM-sensitive phosphodiesterase had no effect upon 5-HT1A receptor-mediated Erk1/2 activation. Because clathrin-mediated endocytosis was required for 5-HT1A receptor-mediated Erk1/2 activation, we postulated a role for CAM in receptor endocytosis. Inhibition of receptor endocytosis by use of sequestration-defective mutants of beta-arrestin1 and dynamin attenuated 5-HT1A receptor-stimulated Erk1/2 activation. Inhibition of CAM prevented agonist-dependent endocytosis of epitope-tagged 5-HT1A receptors. We conclude that CAM-dependent activation of Erk1/2 through the 5-HT1A receptor reflects its role in endocytosis of the receptor, which is a required step in the activation of MEK and subsequently Erk1/2.
authors.affiliation: Howard Hughes Medical Institute and the Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Della Rocca
authors.forename: Y V
authors.initials: YV
authors.lastname: Mukhin
authors.forename: M N
authors.initials: MN
authors.lastname: Garnovskaya
authors.forename: Y
authors.initials: Y
authors.lastname: Daaka
authors.forename: G J
authors.initials: GJ
authors.lastname: Clark
authors.forename: L M
authors.initials: LM
authors.lastname: Luttrell
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
authors.forename: J R
authors.initials: JR
authors.lastname: Raymond
mesh_terms: D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D002966:Clathrin / Q000378:metabolism; D006224:Cricetinae; D004705:Endocytosis; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D011985:Receptors, Serotonin / Q000378:metabolism*; D044263:Receptors, Serotonin, 5-HT1; D011994:Recombinant Proteins / Q000378:metabolism