title: Extracellular ATP stimulates an inhibitory pathway towards growth factor-induced cRaf-1 and MEKK activation in astrocyte cultures.
abstract: ATP, acting via P2Y, G protein-coupled receptors (GPCRs), is a mitogenic signal and also synergistically enhances fibroblast growth factor-2 (FGF-2)-induced proliferation in astrocytes. Here, we have examined the effects of ATP and FGF-2 cotreatment on the main components of the extracellular-signal regulated protein kinase (ERK) cascade, cRaf-1, MAPK/ERK kinase (MEK) and ERK, key regulators of cellular proliferation. Surprisingly, ATP inhibited activation of cRaf-1 by FGF-2 in primary cultures of rat cortical astrocytes. The inhibitory effect did not diminish MEK and ERK activation; indeed, cotreatment resulted in a greater initial activation of ERK. ATP inhibition of cRaf-1 activation was not mediated by an increase in cyclic AMP levels or by protein kinase C activation. ATP also inhibited the activation of cRaf-1 by other growth factors, epidermal growth factor and platelet-derived growth factor, as well as other MEK1 activators stimulated by FGF-2, MEK kinase 1 (MEKK1) and MEKK2. Serotonin, an agonist of another GPCR coupled to ERK, did not inhibit FGF-2-induced cRaf-1 activation, thereby indicating specificity in the ATP-induced inhibitory cross-talk. These findings suggest that ATP stimulates an inhibitory activity that lays upstream of MEK activators and inhibits growth factor-induced activation of cRaf-1 and MEKKS: Such a mechanism might serve to integrate the actions of receptor tyrosine kinases and P2Y-GPCRS:
authors.affiliation: Departments of Biofísica and Bioquímica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: G
authors.initials: G
authors.lastname: Lenz
authors.forename: D
authors.initials: D
authors.lastname: Gonçalves
authors.forename: Z
authors.initials: Z
authors.lastname: Luo
authors.forename: J
authors.initials: J
authors.lastname: Avruch
authors.forename: R
authors.initials: R
authors.lastname: Rodnight
authors.forename: J T
authors.initials: JT
authors.lastname: Neary
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008301:Maleimides / Q000494:pharmacology; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D009638:Norepinephrine / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D051381:Rats; D012701:Serotonin / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D016222:Fibroblast Growth Factor 2; D012701:Serotonin; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; C064758:Ro 31-8220; D009638:Norepinephrine