16573655

pubmed:Citation

3

In the nervous system, astrocytes express different ratios of the two glial glutamate transporters, glutamate transporter subtype 1 (GLT-1) and glutamate/aspartate transporter (GLAST), but little is known about the signaling pathways that independently regulate their expression. Treatment with dibutyryl-cAMP, epidermal growth factor (EGF) or other growth factors both induces expression of GLT-1 and increases expression of GLAST in astrocyte cultures. The induction of GLT-1 is correlated with morphological and biochemical changes that are consistent with astrocyte maturation. Pharmacological studies suggest that phosphatidylinositol 3-kinase (PI-3K) and the nuclear transcription factor-kappaB (NF-kappaB) may be involved in the induction of GLT-1 expression. In several signaling systems Akt, also known as protein kinase B (PKB), functions downstream of PI-3K. In these present studies we used lentiviral vectors engineered to express dominant-negative (DN), constitutively active (CA), or null variants of Akt to study the possible involvement of Akt in the regulation of GLT-1. Expression of DN-Akt attenuated the EGF-dependent induction of GLT-1. Expression of CA-Akt caused a dose- and time-dependent increase in GLT-1 protein, increased GLT-1 mRNA levels, increased dihydrokainate-sensitive (presumably GLT-1 mediated) transport activity, and caused a change in astrocyte morphology to a more stellate shape, but had no effect on GLAST protein levels. Finally, the expression of CA-Akt increased the expression of a reporter construct containing a putative promoter fragment from the human homolog of GLT-1, called EAAT2. From these studies, we conclude that Akt induces the expression of GLT-1 through increased transcription and that Akt can regulate GLT-1 expression without increasing GLAST expression in astrocytes.

eng

IM

MEDLINE

0022-3042

Print

NLM

759-71

pubmed-meshheading:16573655-Animals, pubmed-meshheading:16573655-Animals, Newborn, pubmed-meshheading:16573655-Astrocytes, pubmed-meshheading:16573655-Blotting, Western, pubmed-meshheading:16573655-Bucladesine, pubmed-meshheading:16573655-Cells, Cultured, pubmed-meshheading:16573655-Cerebral Cortex, pubmed-meshheading:16573655-Drug Interactions, pubmed-meshheading:16573655-Epidermal Growth Factor, pubmed-meshheading:16573655-Excitatory Amino Acid Transporter 2, pubmed-meshheading:16573655-Gene Expression Regulation, pubmed-meshheading:16573655-Glial Fibrillary Acidic Protein, pubmed-meshheading:16573655-Glutamic Acid, pubmed-meshheading:16573655-Glycogen Synthase Kinase 3, pubmed-meshheading:16573655-Green Fluorescent Proteins, pubmed-meshheading:16573655-Immunohistochemistry, pubmed-meshheading:16573655-Lentivirus, pubmed-meshheading:16573655-Oncogene Protein v-akt, pubmed-meshheading:16573655-RNA, Messenger, pubmed-meshheading:16573655-Rats, pubmed-meshheading:16573655-Time Factors, pubmed-meshheading:16573655-Transfection, pubmed-meshheading:16573655-Tritium

Regulation of astrocytic glutamate transporter expression by Akt: evidence for a selective transcriptional effect on the GLT-1/EAAT2 subtype.

Journal Article, Comparative Study, Research Support, N.I.H., Extramural