期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1998
卷号：95
期号：7
页码：3467-3471
DOI：10.1073/pnas.95.7.3467
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：During adipogenesis, CCAAT/enhancer binding protein (C/EBP) serves as a pleiotropic transcriptional activator of adipocyte genes. Previously, we identified dual repressive elements in the C/EBP gene and a putative transacting factor (C/EBP undifferentiated protein, 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 {approx}50 kDa) revealed that the repressor is (or contains) an isoform of the transcription factor, AP-2. Electrophoretic mobility shift and Western blot analysis on purified CUP and preadipocyte nuclear extracts confirmed the identity of CUP as AP-2. Both AP-2 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-2/CUP, an AP-21 expression vector, cotransfected with a C/EBP promoter-reporter construct into 3T3-L1 adipocytes, inhibited reporter gene transcription. Taken together with previous results, these findings suggest that in preadipocytes the C/EBP gene is repressed by AP-2/CUP, which, upon induction of differentiation, is down-regulated, allowing expression of the gene.
