title: Evidence for involvement of a GTP-binding protein in activation of Ca2+ influx by epidermal growth factor in A431 cells: effects of fluoride and bacterial toxins.
abstract: Aluminium fluoride (AlF4-), a G protein activator, was used to study a possible role of G protein in the control of the pathways for Ca2+ influx through plasma membrane of human carcinoma A431 cells. Fluorimetric measurements with the Ca2+ indicator Indo-1 have shown that addition of fluoride induces an increase in concentration of cytosolic free calcium ([Ca2+]in) due to both release of Ca2+ from intracellular stores and Ca2+ influx from the extracellular medium. The cells stimulated by fluoride became unresponsive to subsequent addition of epidermal growth factor (EGF), histamine and bradykinin. The Ca2+ signal induced by fluoride as well as one induced by EGF was inhibited by the pretreatment of cells with protein kinase C activator, phorbol myristate acetate (PMA). The pretreatment of the cells with pertussis toxin produced no effect on EGF-induced calcium response. In contrast, the pretreatment with cholera toxin (CTX) increased the basal level of [Ca2+]in and abolished the effect of EGF. The effects of CTX could not be reproduced by treating the cells with forskolin or IBMX, agents known to elevate cAMP content in the cell. Patch clamp experiments have shown that fluoride increases the activity of Ca(2+)-permeable channels identical to those activated by EGF from the extracellular side of the membrane [Mozhayeva et al. (1991) J. Membr. Biol. 124, 113-126]. The results obtained suggest the involvement of GTP-binding protein in signal transduction from the EGF receptor to Ca(2+)-permeable channel of plasma membrane in A431 cells.
authors.affiliation: Institute of Cytology, Russian Academy of Sciences, St Petersburg.
authors.forename: Y A
authors.initials: YA
authors.lastname: Kuryshev
authors.forename: A P
authors.initials: AP
authors.lastname: Naumov
authors.forename: P V
authors.initials: PV
authors.lastname: Avdonin
authors.forename: G N
authors.initials: GN
authors.lastname: Mozhayeva
mesh_terms: D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; D004815:Epidermal Growth Factor; D002772:Cholera Toxin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate; D005459:Fluorides; D002118:Calcium