Transcription factor FBI-1 acts as a dual regulator in adipogenesis by coordinated regulation of cyclin-A and E2F-4.
Generation of new adipocytes plays a major role in the development of obesity. We previously have shown that transcriptional repressor factor that binds to IST (FBI)-1 exerts a dual effect in the process of adipogenesis by inhibiting proliferation and promoting differentiation of preadipocytes. The aim of the present study was to identify FBI-1 regulated molecular effectors that could account for these effects. Overexpressing FBI-1 in preadipocytes resulted in reduced expression of the cell cycle regulator cyclin A, which may explain FBI-1 induced inhibition of proliferation. Interestingly, FBI-1 repressed cyclin A promoter activity through an indirect mechanisms that did not involve direct binding of FBI-1 to the promoter sequence, but rather FBI-1 inhibition of transcriptional activator Sp1 binding to a regulatory element at -452 to -443. We also show that FBI-1 promotes terminal preadipocyte differentiation through a mechanism involving decreased levels of expression of the PPARgamma inhibitor E2F-4. FBI-1 significantly reduced E2F-4 promoter activity. Contrary to cyclin A, we found FBI-1-induced repression of E2F-4 is mediated by a direct mechanism via a FBI-1 regulatory element at -11 to -5. As function of transcriptional repressors normally depends on the presence of regulatory co-factors we also performed expression profiling of potential FBI-1 co-repressors throughout adipogenesis. In these experiments Sin3A and histon deacetylase (HDAC)-1 showed a similar expression pattern compared to FBI-1. Strikingly, co-immunoprecipitation studies revealed that FBI-1 binds Sin3A and HDAC-1 to form a repressor complex. Furthermore, by mutational analysis the amino terminal Poxvirus (POZ) domain of FBI-1 was found to be important for Sin3A and HDAC-1 binding. Taken together, FBI-1 is the first transcriptional repressor shown to act as a dual regulator in adipogenesis exerting repressor activities on target genes by both, direct and indirect mechanisms.
Laudes
Matthias
M
Department of Internal Medicine II and Centre of Molecular Medicine Cologne (CMMC), University of Cologne, Kerpener Strasse 62, 50937 Cologne, Germany. matthias.laudes@uk-koeln.de
Bilkovski
Roman
R
Oberhauser
Frank
F
Droste
Andrea
A
Gomolka
Matthias
M
Leeser
Uschi
U
Udelhoven
Michael
M
Krone
Wilhelm
W
D017667:Adipocytes / Q000166:cytology; D050156:Adipogenesis / Q000235:genetics; D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D002999:Clone Cells; D006224:Cricetinae; D003412:Cricetulus; D019925:Cyclin A / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D050704:E2F4 Transcription Factor / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D008938:Mitosis; D008957:Models, Genetic; D011401:Promoter Regions, Genetic / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism; D056264:Sin3 Histone Deacetylase and Corepressor Complex; D016329:Sp1 Transcription Factor / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*
D019925:Cyclin A; D004268:DNA-Binding Proteins; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D012097:Repressor Proteins; C099683:SIN3A transcription factor; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; C485514:ZBTB7A protein, human; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases; D056264:Sin3 Histone Deacetylase and Corepressor Complex