ATF-2 and C/EBPalpha can form a heterodimeric DNA binding complex in vitro. Functional implications for transcriptional regulation.
We screened an expression cDNA library with a radiolabeled C/EBPalpha fusion protein and isolated three independent cDNAs encoding ATF-2, a bZIP protein that binds cAMP response elements (CRE). This interaction requires the respective bZIP domains, which form a typical bZIP heterodimer with altered DNA binding selectivity. C/EBPalpha and ATF-2 homodimers bind CRE sites, but ATF-2:C/EBPalpha heterodimers do not. Heterodimers bind an asymmetric sequence composed of one consensus half-site for each monomer, and may thus have a unique regulatory function. As predicted, co-transfection of ATF-2 with C/EBPalpha results in decreased activation of transcription driven from consensus C/EBP-binding sites. In contrast, C/EBPalpha and ATF-2 function cooperatively to activate transcription driven by the asymmetric sequence. Both factors are expressed in liver, where immunoprecipitation experiments show that ATF-2 co-precipitates with C/EBPalpha. These results are consistent with the interpretation that C/EBPalpha and ATF-2 can associate in vivo. Moreover, the formation of ATF-2:C/EBPbeta heterodimers suggests that cross-family dimerization with ATF-2 may be a general property for C/EBP family proteins.
Shuman
J D
JD
Laboratory of Molecular Structure, NIAID, National Institutes of Health, Rockville, Maryland 20892-1727, USA. JShuman@atlas.niaid.nih.gov
Cheong
J
J
Coligan
J E
JE
D051698:Activating Transcription Factor 2; D000818:Animals; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D016350:Leucine Zippers; D046911:Macromolecular Substances; D009687:Nuclear Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011487:Protein Conformation; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
C497105:ATF2 protein, human; D051698:Activating Transcription Factor 2; C497107:Atf2 protein, rat; D022762:CCAAT-Enhancer-Binding Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D004247:DNA