MUSCARINIC ACETYLCHOLINE-RECEPTORS ACTIVATE EXPRESSION OF THE EGR GENE FAMILY OF TRANSCRIPTION FACTORS

In order to search for genes that are activated by muscarinic acetylch oline receptors (mAChRs), we used an mRNA differential display approac h in HEK293 cells expressing m1AChR. The zinc-finger transcription fac tor genes Egr-1, Egr-2, and Egr-3 were identified. Northern blot analy ses confirmed that mRNA levels of Egr-1, Egr-2, and Egr-3 increased re adily after m1AChR stimulation and that a maximum was attained within 50 min. At that time, Egr-4 mRNA was also detectable. Western blots an d electromobility shift assays demonstrated synthesis of EGR-1 and EGR -3, as well as binding to DNA recognition sites in response to m1AChR activation. Activation of m1AChR increased transcription from EGR-depe ndent promoters, including the acetylcholinesterase gene promoter. Act ivity-dependent regulation of Egr-1 mRNA expression and EGR-1 protein synthesis was also observed in cells expressing m2, m3, or m4AChR subt ypes, Increased EGR-1 synthesis was mimicked by phorbol myristate acet ate, but not by forskolin, and receptor-stimulated EGR-1 synthesis was partially inhibited by phorbol myristate acetate down-regulation. Tog ether, our results demonstrate that muscarinic receptor signaling acti vates the EGR transcription factor family and that PKC may be involved in intracellular signaling. The data suggest that transcription of EG R-dependent target genes, including the AChE gene, can be under the co ntrol of extracellular and intracellular signals coupled to muscarinic receptors.