Signaling from G protein-coupled receptors to the c-jun promoter involves the MEF2 transcription factor. Evidence for a novel c-jun amino-terminal kinase-independent pathway.
The c-Jun amino-terminal kinases (JNKs) are a subfamily of mitogen-activated protein kinases that phosphorylate c-Jun and ATF2, and it has been postulated that phosphorylated c-Jun enhances its own expression through AP-1 sites on the c-jun promoter. In this study, we asked whether signals activating JNK regulate the c-jun promoter. Using NIH 3T3 cells expressing G protein-coupled m1 acetylcholine receptors as an experimental model, we have recently shown that the cholinergic agonist carbachol, but not platelet-derived growth factor, potently elevates JNK activity. Consistent with these findings, carbachol, but not platelet-derived growth factor, increased the activity of a c-jun promoter-driven reporter gene (for chloramphenicol acetyltransferase). However, coexpression of JNK kinase kinase (MEKK) effectively increased JNK activity, but resulted in surprisingly limited induction of the c-jun promoter. This raised the possibility that pathway(s) distinct from JNK control the c-jun promoter, and prompted us to explore which of its regulatory elements participate in transcriptional control. We observed that deletion of the 3' AP-1 site diminished chloramphenicol acetyltransferase activity in response to carbachol, but only to a limited extent. In contrast, deletion of a MEF2 site dramatically reduced expression, and deletion of both the MEF2 and 3' AP-1 sites abolished induction. Furthermore, cotransfection with MEF2C and MEF2D cDNAs potently enhanced the activity of the c-jun promoter in response to carbachol, and stimulation of m1 receptors, but not direct JNK activation, induced expression of a MEF2-responsive plasmid. Taken together, these data strongly suggest that MEF2 mediates c-jun promoter expression by G protein-coupled receptors through a yet to be identified pathway, distinct from that of JNK.
Coso
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Oral and Pharyngeal Cancer Branch, NIDR, National Institutes of Health, Bethesda, Maryland 20892-4330, USA.
Montaner
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Fromm
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Lacal
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Prywes
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Teramoto
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Gutkind
J S
JS
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016758:Genes, jun; D048031:JNK Mitogen-Activated Protein Kinases; D064326:MEF2 Transcription Factors; D051379:Mice; D020928:Mitogen-Activated Protein Kinases; D018006:Myogenic Regulatory Factors; D011401:Promoter Regions, Genetic; D011950:Receptors, Cholinergic / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*
D004268:DNA-Binding Proteins; D064326:MEF2 Transcription Factors; C578041:Mef2c protein, mouse; C578044:Mef2d protein, mouse; D018006:Myogenic Regulatory Factors; D011950:Receptors, Cholinergic; D014157:Transcription Factors; D002217:Carbachol; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins