title: Cell-specific signaling of the 5-HT1A receptor. Modulation by protein kinases C and A.
abstract: Heterologous expression of the rat 5-HT1A receptor in stably transfected GH4C1 rat pituitary cells (clone GH4ZD10) and mouse Ltk- fibroblast cells (clone LZD-7) (Albert, P.R., Zhou, Q.-Y., VanTol, H.H.M., Bunzow, J.R., and Civelli, O. (1990) J. Biol. Chem. 265, 5825-5832) was used to characterize the cellular specificity of signal transduction by the 5-HT1A receptor. We demonstrate that the 5-HT1A receptor, acting via pertussis toxin-sensitive G proteins, can change its inhibitory signaling phenotype and become a stimulatory receptor, depending on the cell type, differentiation state, or intracellular milieu of the cell in which it is expressed. When expressed in pituitary GH4ZD10 cells, activation of 5-HT1A receptors decreased both basal and vasoactive intestinal peptide-enhanced cAMP accumulation and blocked (+/-)-Bay K8644-induced influx of calcium, inhibitory responses which are typical of neurons which endogenously express this receptor. Similarly, 5-hydroxytryptamine (5-HT) also inhibited adenylyl cyclase in fibroblast LZD-7 cells, reducing the forskolin-induced enhancement of cAMP levels by 50%, but did not alter basal cAMP levels. In contrast to GH4ZD10 cells, where 5-HT had no effect on basal or thyrotropin-releasing hormone-induced phosphatidylinositol turnover, 5-HT enhanced the accumulation of inositol phosphates and induced a biphasic increase in [Ca2+]i in LZD-7 cells. These dominant stimulatory actions of 5-HT, as well as the inhibitory effects, were absent in untransfected cells and displayed the potency and pharmacological specificity of the 5-HT1A receptor, indicating that the 5-HT1A subtype coupled to both inhibitory and stimulatory pathways in the fibroblast cell. The actions of 5-HT in GH and L cells were blocked by 24-h pretreatment with pertussis toxin, suggesting that inhibitory G proteins (Gi/G(o)) mediate both inhibitory and stimulatory signal transduction of the 5-HT1A receptor. However, the 5-HT-induced stimulatory pathway in fibroblasts was blocked selectively by acute (2-min) pretreatment with TPA, an activator of protein kinase C. This action of protein kinase C was potentiated by activation of protein kinase A, indicating that the expression of the stimulatory pathway of the 5-HT1A receptor in LZD-7 cells is modulated by second messengers.
authors.affiliation: Department of Pharmacology, McGill University, Montreal, Quebec, Canada.
authors.forename: Y F
authors.initials: YF
authors.lastname: Liu
authors.forename: P R
authors.initials: PR
authors.lastname: Albert
mesh_terms: D037361:Adenylate Cyclase Toxin; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D007700:Kinetics; D007739:L Cells; D051379:Mice; D008954:Models, Biological; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D010716:Phosphatidylinositols; D011985:Receptors, Serotonin; D010566:Virulence Factors, Bordetella; D012701:Serotonin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011494:Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium