51. Derepression of the C/EBPα gene during adipogenesis: Identification of AP-2α as a repressor
- Author
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W. Shillinglaw, W. J. Henzel, M D Lane, J C McLenithan, Deborah E. Geiman, Q.-Q. Tang, and M.-S. Jiang
- Subjects
Gene isoform ,Repressor ,Biology ,Cell Line ,Mice ,Enhancer binding ,Adipocytes ,Animals ,Humans ,Promoter Regions, Genetic ,Derepression ,Regulation of gene expression ,Multidisciplinary ,Expression vector ,Ccaat-enhancer-binding proteins ,Nuclear Proteins ,Cell Differentiation ,Biological Sciences ,Molecular biology ,DNA-Binding Proteins ,Repressor Proteins ,Gene Expression Regulation ,Transcription Factor AP-2 ,Adipogenesis ,CCAAT-Enhancer-Binding Proteins ,Transcription Factors - Abstract
During adipogenesis, CCAAT/enhancer binding protein α (C/EBPα) serves as a pleiotropic transcriptional activator of adipocyte genes. Previously, we identified dual repressive elements in the C/EBPα gene and a putative transacting factor ( C /EBPα u ndifferentiated p rotein, or CUP) expressed by preadipocytes, but not adipocytes, that bind to these elements. In the present investigation, CUP was purified 17,000-fold from nuclear extracts of 3T3-L1 preadipocytes. Amino acid sequence and mass spectral analysis of tryptic peptides derived from purifed CUP (molecular mass ≈50 kDa) revealed that the repressor is (or contains) an isoform of the transcription factor, AP-2α. Electrophoretic mobility shift and Western blot analysis on purified CUP and preadipocyte nuclear extracts confirmed the identity of CUP as AP-2α. Both AP-2α protein and CUP binding activity are expressed by preadipocytes and then decrease concomitantly during differentiation of 3T3-L1 preadipocytes into adipocytes. Consistent with a repressive role of AP-2α/CUP, an AP-2α1 expression vector, cotransfected with a C/EBPα promoter-reporter construct into 3T3-L1 adipocytes, inhibited reporter gene transcription. Taken together with previous results, these findings suggest that in preadipocytes the C/EBPα gene is repressed by AP-2α/CUP, which, upon induction of differentiation, is down-regulated, allowing expression of the gene.
- Published
- 1998