Dual role for transcription factor AP-2 in the regulation of the major fetal promoter P3 of the gene for human insulin-like growth factor II.
The human insulin-like growth factor II (IGF-II) gene contains four promoters that are differentially active during cell growth and development. Promoter 3 (P3) is the most active promoter in fetal and non-hepatic adult tissues. In addition to its expression during development, P3 is also the major promoter in many tumour tissues and IGF-II-expressing cell lines. Here we show that AP-2 has a dual function in P3 regulation in vivo as well as in vitro. In cells expressing low levels of endogenous AP-2, AP-2 overexpression activates P3, whereas P3 promoter activity is inhibited in cells containing abundant AP-2. Four potential AP-2-binding sites were identified in footprinting studies with recombinant AP-2. One of these AP-2-binding sites is located within the previously identified element P3-4 that contains two adjacent binding sites for IGF-II promoter-binding proteins IPBP3 and IPBP4/5. By applying binding competition assays and mutational analysis it is shown that AP-2 interferes with IPBP3 binding and transactivation in vivo as well as in vitro. Furthermore, AP-2 can bind additional elements in the proximal P3 promoter that also contribute to AP-2-mediated transactivation as shown by transient transfection assays. From these results we conclude that AP-2 is an important regulator in vivo and in vitro of IGF-II P3 activity.
Laboratory for Physiological Chemistry, Graduate School of Developmental Biology, Utrecht University, Stratenum, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
L E
LE
Rietveld
A M
AM
Koonen-Reemst
J S
JS
Sussenbach
P E
PE
Holthuizen
D001483:Base Sequence; D001667:Binding, Competitive; D002460:Cell Line; D004247:DNA; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005333:Fetus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D007335:Insulin-Like Growth Factor II; D004247:DNA