The ability of C/EBP beta but not C/EBP alpha to synergize with an Sp1 protein is specified by the leucine zipper and activation domain.
The rat CYP2D5 P-450 gene is activated in the liver during postnatal development. We previously showed that liver-specific transcription of the CYP2D5 gene is dictated by a proximal promoter element, termed 2D5, that is composed of a binding site for Sp1 or a related factor, and an adjacent cryptic C/EBP (CCAAT/enhancer-binding protein) site. Despite the fact that both C/EBP alpha and C/EBP beta are expressed abundantly in liver, only C/EBP beta is capable of stimulating the 2D5 promoter in HepG2 hepatocarcinoma cells. In addition, activation of the 2D5 promoter by C/EBP beta is completely dependent on the presence of the Sp1 site. Domain switch experiments reveal that C/EBP beta proteins containing either the leucine zipper or the activation domain of C/EBP alpha are unable to stimulate the 2D5 promoter yet are fully capable of transactivating an artificial promoter bearing a high-affinity C/EBP site. Thus, the leucine zipper and the activation domain of C/EBP beta are absolutely required to support transactivation of the 2D5 promoter. Using Drosophila cells that lack endogenous Sp1 activity, we show that the serine/threonine- and glutamine-rich activation domains A and B of Sp1 are required for efficient cooperatively with C/EBP beta. Furthermore, analysis of c/ebp beta-deficient mice shows that mutant animals are defective in expression of a murine CYP2D5 homolog in hepatic cells, confirming the selective ability of C/EBP beta to activate this liver-specific P-450 gene in vivo. Our findings illustrate that two members of a transcription factor family can achieve distinct target gene specificities through differential interactions with a cooperating Sp1 protein.
Lee
Y H
YH
Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
Williams
S C
SC
Baer
M
M
Sterneck
E
E
Gonzalez
F J
FJ
Johnson
P F
PF
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004247:DNA / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004330:Drosophila; D015870:Gene Expression; D016350:Leucine Zippers; D008099:Liver / Q000378:metabolism; D051379:Mice; D015394:Molecular Structure; D009687:Nuclear Proteins / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D016329:Sp1 Transcription Factor / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation
D022762:CCAAT-Enhancer-Binding Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016329:Sp1 Transcription Factor; D004247:DNA; D003577:Cytochrome P-450 Enzyme System