Activation of second messenger-dependent protein kinases induces muscarinic acetylcholine receptor desensitization in rat thyroid epithelial cells.
Internalization and phosphorylation of G protein-coupled receptors (GPCR) are considered two important regulatory events of receptor signal transduction. In Fischer rat thyroid (FRT) epithelial cells, we have shown that muscarinic acetylcholine receptor (mAChR) stimulation induces intracellular Ca2+ mobilization via Ca2+ store release, capacitative Ca2+ entry and voltage-dependent Ca2+ channels activation. In the present study, the role of mAChR internalization and phosphorylation on receptor signalling pathway was examined by means of intracellular Ca2+ measurement in these cells. Exposure of FRT cells to carbachol (Cch), a mAChR agonist, resulted in a desensitization of receptor-mediated intracellular Ca2+ mobilization and induced the internalization of constitutively expressed mAChR in this cell type. Treatment of FRT cells with hypertonic sucrose, which markedly reduced agonist-receptor complex internalization, or phenylarsine oxide (PAO) diminished the Cch-induced intracellular Ca2+ response. Moreover, pretreatment of cells with phorbol-12-myristate-13-acetate (PMA), an activator of protein kinase C (PKC), completely abolished Cch-evoked Ca2+ mobilization, whereas it was significantly increased by the preincubation of cells with GF109203X, a selective inhibitor of PKC. We also found a marked decrease on Cch-stimulated Ca2+ mobilization in pretreated FRT cells with forskolin, an activator of protein kinase A (PKA), but the preincubation of cells with genistein, an inhibitor of protein tyrosine kinases, had no effect on Ca2+ mobilization induced by Cch. These findings seem to indicate that mAChR in FRT cells exhibit a desensitization, which may be mediated, at least in part, through activation of second messenger-dependent protein kinases and that receptor internalization could be necessary for signalling.
Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain.
Mercedes
M
Montiel
Juan
J
Quesada
Eugenio
E
Jiménez
D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004847:Epithelial Cells / Q000737:chemistry / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology*; D013395:Sucrose / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000031:analogs & derivatives* / Q000494:pharmacology; D013961:Thyroid Gland / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*
D001152:Arsenicals; D015220:Calcium Channels; D007211:Indoles; D008301:Maleimides; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; C029341:oxophenylarsine; D005576:Colforsin; C016658:phorbolol myristate acetate; D013395:Sucrose; D002217:Carbachol; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium