Glutamate activates c-fos in glial cells via a novel mechanism involving the glutamate receptor subtype mGlu5 and the transcriptional repressor DREAM.
Activation of c-fos in brain is related to coupling of neuronal activity to gene expression, but also to pathological conditions such as seizures or excitotoxicity-induced cell death. Glutamate activates c-fos in neurons through the calcium-dependent phosphorylation of CREB by ERK and/or CaMKIV kinase pathways downstream NMDA-receptors. In glial cells, however, the activation of c-fos by glutamate is poorly understood. Because glial cells actively modulate neuronal excitability and the brain's response to injury, we studied the mechanisms by which glutamate activates c-fos in rat cortical glial cells. Glutamate potently induced c-fos mRNA in a calcium-dependent manner, as demonstrated by using the calcium chelator BAPTA-AM. Glutamate-induced c-fos mRNA expression was not sensitive to inhibitors of ERK, p38(MAPK), or CaMK pathways, indicating that glial c-fos is activated by a distinct mechanism. Thapsigargin abolished the glutamate effect on c-fos mRNA, indicating ER calcium mobilization. Additionally, glutamate induction of c-fos mRNA was sensitive to the mGluR5 antagonist MPEP but not the NMDA-R antagonist MK-801. In luciferase reporter assays, DRE, which actively represses c-fos by binding the calcium-binding transcriptional repressor DREAM, was activated by glutamate, whereas SRE and CRE were not. Finally, glutamate caused the nuclear export of DREAM in astrocytes, and transfection of astrocytes with a mutant variant of DREAM that constitutively binds DNA inhibited glutamate-induced c-Fos expression. These findings are in sharp contrast to the mechanism described in neurons and suggest a novel pathway activated by glutamate in glial cells that employs mGluR5, ER calcium, and the derepression of c-fos at the DRE.
Edling
Ylva
Y
Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden. ylva.edling@ki.se
Ingelman-Sundberg
Magnus
M
Simi
Anastasia
A
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D051605:Kv Channel-Interacting Proteins / Q000235:genetics / Q000378:metabolism*; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects / Q000378:metabolism*; D050436:Regulatory Elements, Transcriptional / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; C578937:Grm5 protein, rat; C496760:Kcnip3 protein, rat; D051605:Kv Channel-Interacting Proteins; D009498:Neurotoxins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D012097:Repressor Proteins; D018698:Glutamic Acid