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 has been proposed to regulate acetylcholinesterase (AChE) expression in chick muscle; however, its role in mammalian enzyme is not known. We provide several 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 transfected into cultured chick myotubes. Application of cAMP and forskolin induced the expression of chick AChE but reduced human AChE promoter-driven luciferase 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 Activating 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 approximately 1.8- to approximately 2.5-fold, but the luciferase activity 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 enzymes, 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 cultured myotubes was still retained. These findings suggest that a cAMP-dependent pathway is contrasting activation and repression of AChE expression in chick and human muscles.
Choi
R C
RC
Department of Biology, Department of Biochemistry, Molecular Neuroscience Center, The Hong Kong University of Science and Technology, Clear Water Bay Road, Hong Kong, China.
Siow
N L
NL
Zhu
S Q
SQ
Wan
D C
DC
Wong
Y H
YH
Tsim
K W
KW
D000110:Acetylcholinesterase / Q000235:genetics*; D051697:Activating Transcription Factor 1; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004268:DNA-Binding Proteins; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D008322:Mammals; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000201:enzymology*; D016297:Mutagenesis, Site-Directed / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000502:physiology; D011485:Protein Binding / Q000235:genetics; D013045:Species Specificity; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
D051697:Activating Transcription Factor 1; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D000242:Cyclic AMP; D000110:Acetylcholinesterase