Control of adipocyte differentiation by CCAAT/enhancer binding protein alpha (C/EBP alpha).
Upon differentiation of 3T3-L1 preadipocytes into adipocytes transcription of many adipose-specific genes is coordinately activated. A differentiation-induced factor, later identified as C/EBP alpha, binds to and transactivates the promoters of these genes. Vector-directed expression of antisense C/EBP alpha RNA in preadipocytes blocked expression of C/EBP alpha, as well as adipose-specific mRNAs, and also prevented cytoplasmic triglyceride accumulation. Rescue of the 'adipocyte phenotype' was accomplished by transfection of the antisense cells with a complementary sense C/EBP alpha RNA expression vector. Using an IPTG-inducible double-vector LacSwitch C/EBP alpha expression system, it was found that differentiation can be induced without exogenous hormone inducers. These findings indicate that C/EBP alpha is not only required, but is sufficient, to trigger differentiation of 3T3-L1 preadipocytes. The C/EBP alpha gene promoter possesses a C/EBP binding site through which C/EBP alpha autoactivates its own expression. A nuclear protein referred to as CUP (C/EBP undifferentiated protein) that binds to a bipartite element in the C/EBP alpha promoter just 5' to the C/EBP binding site has been purified and characterized. During differentiation of preadipocytes, expression of CUP activity decreases as expression of C/EBP alpha increases. Evidence suggests that a CUP-containing protein complex bridges between the CUP (repression) and C/EBP (autoactivation) elements in the promoter and may maintains the C/EBP alpha gene in the repressed state prior to differentiation.
Lane
M D
MD
Department of Biological Chemistry, John Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Lin
F T
FT
MacDougald
O A
OA
Vasseur-Cognet
M
M
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology*; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D004247:DNA