CREB (cAMP response element binding protein) and C/EBPalpha (CCAAT/enhancer binding protein) are required for the superstimulation of phosphoenolpyruvate carboxykinase gene transcription by adenoviral E1a and cAMP.
In the present study, we observed superstimulated levels of cAMP-stimulated transcription from the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter in cells infected with wild-type adenovirus expressing 12 S and 13 S E1a proteins, or in cells expressing 13 S E1a alone. cAMP-stimulated transcription was inhibited in cells expressing only 12 S E1a, but slightly elevated in cells expressing E1a proteins with mutations in conserved regions 1 or 2, leading us to conclude that the superstimulation was mediated by conserved region 3 of 13 S E1a. E1a failed to enhance cAMP-stimulated transcription from promoters containing mutations that abolish binding by cAMP response element binding protein (CREB) or CCAAT/enhancer binding proteins (C/EBPs). This result was supported by experiments in which expression of dominant-negative CREB and/or C/EBP proteins repressed E1a- and cAMP-stimulated transcription from the PEPCK gene promoter. In reconstitution experiments using a Gal4-responsive promoter, E1a enhanced cAMP-stimulated transcription when chimaeric Gal4-CREB and Gal4-C/EBPalpha were co-expressed. Phosphorylation of CREB on serine-133 was stimulated in cells treated with dibutyryl cAMP, whereas phosphorylation of C/EBPalpha was increased by E1a expression. Our data support a model in which cAMP agonists increase CREB activity and stimulate PEPCK gene transcription, a process that is enhanced by E1a through the phosphorylation of C/EBPalpha.
Routes
J M
JM
Department of Medicine, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, CO 80206, USA.
Colton
L A
LA
Ryan
S
S
Klemm
D J
DJ
D017500:Adenovirus E1A Proteins / Q000502:physiology*; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000502:physiology*; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic / Q000502:physiology*
D017500:Adenovirus E1A Proteins; D022763:CCAAT-Enhancer-Binding Protein-alpha; D017362:Cyclic AMP Response Element-Binding Protein; D000242:Cyclic AMP