title: Epidermal growth factor receptor agonists increase expression of glutamate transporter GLT-1 in astrocytes through pathways dependent on phosphatidylinositol 3-kinase and transcription factor NF-kappaB.
abstract: The glial glutamate transporter GLT-1 may be the predominant Na(+)-dependent glutamate transporter in forebrain. Expression of GLT-1 correlates with astrocyte maturation in vivo and increases during synaptogenesis. In astrocyte cultures, GLT-1 expression parallels differentiation induced by cAMP analogs or by coculturing with neurons. Molecule(s) secreted by neuronal cultures contribute to this induction of GLT-1, but little is known about the signaling pathways mediating this regulation. In the present study, we determined whether growth factors previously implicated in astrocyte differentiation regulate GLT-1 expression. Of the six growth factors tested, two [epidermal growth factor (EGF) and transforming growth factor-alpha] induced expression of GLT-1 protein in cultured astrocytes. Induction of GLT-1 protein was accompanied by an increase in mRNA and in the V(max) for Na(+)-dependent glutamate transport activity. The effects of dibutyryl-cAMP and EGF were additive but were independently blocked by inhibitors of protein kinase A or protein tyrosine kinases, respectively. The induction of GLT-1 in both EGF- and dibutyryl-cAMP-treated astrocytes was blocked by inhibitors targeting phosphatidylinositol 3-kinase (PI3K) or the nuclear transcription factor-kappaB. Furthermore, transient transfection of astrocyte cultures with a constitutively active PI3K construct was sufficient to induce expression of GLT-1. These data suggest that independent but converging pathways mediate expression of GLT-1. Although an EGF receptor-specific antagonist did not block the effects of neuron-conditioned medium, the induction of GLT-1 by neuron-conditioned medium was completely abolished by inhibition of PI3K or nuclear factor-kappaB. EGF also increased expression of GLT-1 in spinal cord organotypic cultures. Together, these data suggest that activation of specific signaling pathways with EGF-like molecules may provide a novel approach for limiting excitotoxic brain injury.
authors.affiliation: Department of Pediatrics and Pharmacology, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: O
authors.initials: O
authors.lastname: Zelenaia
authors.forename: B D
authors.initials: BD
authors.lastname: Schlag
authors.forename: G E
authors.initials: GE
authors.lastname: Gochenauer
authors.forename: R
authors.initials: R
authors.lastname: Ganel
authors.forename: W
authors.initials: W
authors.lastname: Song
authors.forename: J S
authors.initials: JS
authors.lastname: Beesley
authors.forename: J B
authors.initials: JB
authors.lastname: Grinspan
authors.forename: J D
authors.initials: JD
authors.lastname: Rothstein
authors.forename: M B
authors.initials: MB
authors.lastname: Robinson
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D003994:Bucladesine / Q000378:metabolism; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000819:agonists* / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism; D013116:Spinal Cord / Q000378:metabolism; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000378:metabolism; D014316:Tritium
chemical_list: D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D017077:Culture Media, Conditioned; D016328:NF-kappa B; D012333:RNA, Messenger; D016211:Transforming Growth Factor alpha; D014316:Tritium; D004815:Epidermal Growth Factor; D003994:Bucladesine; D012964:Sodium; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors