A dominant negative inhibitor of the Egr family of transcription regulatory factors suppresses cerebellar granule cell apoptosis by blocking c-Jun activation.
To investigate the role of the Egr family of transcription regulatory factors in neuronal apoptosis, we examined the effect of a dominant negative Egr inhibitor construct in a well characterized in vitro paradigm, cerebellar granule cell death induced by withdrawal of depolarizing concentrations of extracellular potassium. We found that this apoptotic stimulus increases the activity of a reporter gene driven by the Egr response element and that a dominant negative inhibitor of Egr-mediated transcription blocks granule cell apoptosis. In contrast, apoptosis of immature granule cells induced by cytosine arabinoside is not inhibited by the Egr inhibitor construct. Because activation of c-Jun is an essential step in granule cell death induced by potassium deprivation, but not cytosine arabinoside, we asked whether the Egr inhibitor acts by influencing c-Jun activation or its ability to induce apoptosis. We found that the Egr inhibitor does not block the ability of a constitutively active c-Jun construct to induce apoptosis in these cells but does suppress activation of c-Jun-mediated transcription induced by lowering extracellular potassium concentration. Furthermore, the Egr inhibitor blocks the ability of MEKK1 [mitogen-activated protein kinase (MAPK) kinase kinase 1], an upstream kinase capable of stimulating the JNK (c-Jun N-terminal protein kinase)-c-Jun pathway, to induce apoptosis and activate c-Jun. Together, these studies indicate that the Egr family of transcription factors plays a critical role in neuronal apoptosis and identify c-Jun activation as an important downstream target of the Egr family in this process.
Levkovitz
Y
Y
Departments of Neuroscience, Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Baraban
J M
JM
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D003561:Cytarabine / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051766:Early Growth Response Protein 1; D005799:Genes, Dominant; D017930:Genes, Reporter / Q000187:drug effects; D006801:Humans; D017874:Immediate-Early Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008970:Molecular Weight; D005810:Multigene Family; D010446:Peptide Fragments / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D016335:Zinc Fingers / Q000502:physiology
D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D017874:Immediate-Early Proteins; D010446:Peptide Fragments; D014157:Transcription Factors; D003561:Cytarabine; D017346:Protein Serine-Threonine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; D011188:Potassium