Cyclic AMP-mediated inhibition of transcription of the malic enzyme gene in chick embryo hepatocytes in culture. Characterization of a cis-acting element far upstream of the promoter.
Glucagon, acting via cAMP, inhibits transcription of the malic enzyme gene in chick embryo hepatocytes. In transiently transfected hepatocytes, fragments from the 5'-flanking DNA of the malic enzyme gene confer cAMP responsiveness to linked reporter genes. The major inhibitory cAMP response element at -3180/-3174 base pairs (bp) is similar to the consensus binding site for AP1. DNA fragments from -3134/-3115, -1713/-944, and -413/-147 bp also contain inhibitory cAMP response elements. The negative action of cAMP is mimicked by overexpression of the catalytic subunit of protein kinase A, inhibited by overexpression of a specific inhibitor of protein kinase A, and inhibited by overexpression of the T3 receptor; these results indicate involvement of the classical eukaryotic pathway for cAMP action and suggest interaction between the T3 and cAMP pathways. Sequence-specific complexes form between nuclear proteins and a DNA fragment containing -3192/-3158 bp of 5'-flanking DNA. In nuclear extracts prepared from cells treated with chlorophenylthio-cyclic AMP and T3, the complexes have different masses than those formed with extracts from cells treated with T3 alone. Antibodies to c-Fos or ATF-2 inhibit formation of the complex formed by proteins from cells treated with chlorophenylthio-cyclic AMP and T3 but not by those from cells treated with T3 alone. These results suggest an important role for c-Fos and ATF-2 in glucagon-mediated inhibition of transcription of the malic enzyme gene.
Mounier
C
C
Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA.
Chen
W
W
Klautky
S A
SA
Goodridge
A G
AG
D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D000242:Cyclic AMP / Q000502:physiology*; D008291:Malate Dehydrogenase / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology*; D014284:Triiodothyronine / Q000502:physiology
D009687:Nuclear Proteins; D018808:Transcription Factor AP-1; D014284:Triiodothyronine; D000242:Cyclic AMP; D008291:Malate Dehydrogenase