CCAAT/enhancer binding proteins alpha and beta are transcriptional activators of the brown fat uncoupling protein gene promoter.

Primary brown adipocytes differentiated in culture were transiently transfected with plasmids containing different extensions of the 5'-flanking region of the rat uncoupling protein gene placed upstream of the bacterial chloramphenicol acetyltransferase reporter gene. Co-transfection of expression vectors for CCAAT/enhancer binding protein (C/EBP) alpha and C/EBP beta trans-activated the rat uncoupling protein gene promoter due to sequences in the 5' proximal region. DNAse I footprint analysis showed the presence of two C/EBP binding sites at positions -457/-440 and -335/-318, which interact with purified C/EBP beta as well as with C/EBP proteins present in brown fat or liver nuclear extracts. Two copies of each site placed upstream of the enhancerless SV40 promoter confer C/EBP alpha and C/EBP beta responsiveness to this heterologous promoter when co-transfected into HepG2 cells. It is concluded that the UCP gene is a target for C/EBP-dependent transcriptional regulation. This suggests that the C/EBP family of transcription factors is involved in the establishment of the characteristic phenotype of the brown adipocyte.