Transcription factor AP2 is required for expression of the rat transforming growth factor-alpha gene.
DNase I footprinting of the rat TGF alpha promoter in the presence of crude cell nuclear extract revealed three sites of protein-DNA interaction (Fp-A, Fp-B, Fp-C) in the region from -222 to +73. Mutation of specific sites within the Fp-A and Fp-B regions reduced expression of a TGF alpha promoter-reporter gene (TGF alphaLUC) from 50-90% in transiently transfected CHO cells, indicating the importance of protein/DNA interactions at these sites. Since Fp-A contained a perfect AP2 consensus sequence (5'-GCCNNNGGC-3') as its center, we investigated the possibility that AP2 binding is important for TGF alpha promoter activity. A double-stranded oligonucleotide spanning Fp-A displayed a distinct mobility shift in the presence of nuclear extract that was inhibited by an excess of known functional AP2-binding sequence. Moreover, a similar mobility shift occurred in the presence of purified AP2 protein, and the further addition of AP2 antibody produced a supershifted complex. More refined DNase I footprinting of a smaller, oligonucleotide probe in the presence of purified AP2 protein revealed a protected region that included the putative AP2 binding site. Additionally, co-transfection of an AP2 expression vector increased TGF alphaLUC expression 25-fold in Drosophila Schneider cells. These various findings corroborate a role for AP2 in TGF alpha promoter activity. The Fp-B region contains a T5 motif that has been previously suggested to function as an atypical TATA box. An Fp-B oligonucleotide displayed a specific gel mobility shift in the presence of a TATA binding protein (TBP)-TFIIA complex, and the further addition of TBP antibody produced a supershift. These results confirm that protein binding within Fp-B is functionally important, and they also indicate that the T5 motif functions as a TBP binding site.
Berkowitz
E A
EA
Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill 27599, USA.
Hecht
C P
CP
Azizkhan
J C
JC
Chen
X
X
Lee
D C
DC
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D016466:CHO Cells / Q000378:metabolism; D002460:Cell Line; D002461:Cell Line, Transformed; D006224:Cricetinae; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins; D004586:Electrophoresis / Q000379:methods; D004847:Epithelial Cells; D005786:Gene Expression Regulation; D008099:Liver / Q000166:cytology; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D035181:TATA-Box Binding Protein; D050656:Transcription Factor AP-2; D035561:Transcription Factor TFIIA; D014157:Transcription Factors / Q000378:metabolism*; D016211:Transforming Growth Factor alpha / Q000235:genetics* / Q000378:metabolism*
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D011994:Recombinant Proteins; D035181:TATA-Box Binding Protein; C493674:TfAP-2 protein, Drosophila; D050656:Transcription Factor AP-2; D035561:Transcription Factor TFIIA; D014157:Transcription Factors; D016211:Transforming Growth Factor alpha