The cyclic AMP-mediated expression of acetylcholinesterase in myotubes shows contrasting activation and repression between avian and mammalian enzymes

Cyclic adenosine 3',5'-monophosphate (cAMP)-dependent signalling pathway ha s been proposed to regulate acetylcholinesterese (AChE) expression in chick muscle; however, its role in mammalian enzyme is not known. We provide sev eral lines of evidence to suggest that the cAMP-mediated AChE expression in myotube is oppositely regulated between avian and mammalian enzymes. Human AChE promoter was tagged with luciferase, namely Hp-Luc, which was transfe cted into cultured chick myotubes. Application of cAMP and forskolin induce d the expression of chick AChE but reduced human AChE promoter-driven lucif erase activity. Transfection of cDNAs encoding active mutants of G proteins altered the intracellular cAMP level in myotubes as well as the expression of chick and human AChE. When the constitutively active forms of Activatin g Transcription Factor-1 (EWS/ATF-1 oncogene) were over expressed in Hp-Luc transfected myotubes, the expression of chick AChE transcript and protein increased from similar to1.8- to similar to2.5-fold, but the luciferase act ivity was decreased by over 60%. Overexpression of cAMP-responsive element binding protein (CREB) in Hp-Luc transfected myotubes markedly enhanced the cAMP-mediated AChE expression in up- and downregulated chick and human enz ymes, respectively. in addition, CREB bound the CRE sequence of human AChE promoter. Mutation on the CRE site markedly enhanced the expression of the promoter-driven luciferase; however, its response to cAMP inhibition in cul tured myotubes was still retained. These findings suggest that a cAMP-depen dent pathway is contrasting activation and repression of AChE expression in chick and human muscles.