title: Degradation of glial glutamate transporter mRNAs is selectively blocked by inhibition of cellular transcription.
abstract: Recent studies have demonstrated that the expression of the glial glutamate transporters GLT-1 (glutamate transporter 1) and GLAST (glutamate aspartate transporter) is regulated both in vivo and in vitro. For example, co-culturing with neurons, treatment with N:(6), 2'-O:-dibutyryladenosine 3':5'-cyclic monophosphate (dbcAMP), and treatment with epidermal growth factor all increase the steady-state levels of GLT-1 and GLAST protein in astrocyte cultures. These changes in protein expression are correlated with increased mRNA levels. In the present study, the degradation of GLT-1 and GLAST mRNAs was examined in control and dbcAMP-treated astrocyte cultures after inhibiting transcription with actinomycin D. Although one would predict that inhibition of transcription would cause a decrease in GLT-1 and GLAST mRNAs and that this decrease would depend on the rate of mRNA degradation, the levels of GLT-1 and GLAST mRNAs did not decrease even after 24 h of treatment with actinomycin D. Withdrawal of dbcAMP caused the levels of GLT-1 and GLAST mRNAs to fall to basal levels within 24 h, but this degradation was blocked if actinomycin D was added at the time of dbcAMP withdrawal. Importantly, actinomycin D did not block the degradation of c-fos mRNA also induced by dbcAMP in these cultures. Inhibition of translation with cycloheximide did not stabilize GLT-1 but partially attenuated the degradation of GLAST mRNA. Although the mechanism of this effect remains to be defined, these studies suggest that GLT-1 and GLAST mRNAs belong to a select class of inducible mRNAs stabilized by inhibitors of transcription. The possible relevance of these data to astrocyte differentiation is briefly discussed.
authors.affiliation: Departments of Pediatrics and Pharmacology, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia 19104-4318, USA.
authors.forename: O A
authors.initials: OA
authors.lastname: Zelenaia
authors.forename: M B
authors.initials: MB
authors.lastname: Robinson
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics*
chemical_list: D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D011500:Protein Synthesis Inhibitors; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D003609:Dactinomycin; D003994:Bucladesine; D003513:Cycloheximide