C/EBP-beta drives expression of the nutritionally regulated promoter IA of the acetyl-CoA carboxylase-alpha gene in cattle

Acetyl-CoA carboxylase-alpha (ACC-α) is the rate-limiting enzyme for de novo fatty acid synthesis. Among the four promoters expressing the bovine gene, promoter IA (PIA) is dominantly active and nutritionally regulated in lipogenic tissues. CCAAT/enhancer binding proteins are crucially involved in regulating the activity of this promoter. We examine here, which member of this family of transcription factors is most important for promoter activation. To differentiate the individual contribution of different members of the C/EBP family transcription factors controlling the ACC-α gene expression in cattle, we established vectors expressing full length (FL) or N-terminally truncated (δN) variants of the C/EBP factors (α, -β, -γ, and -ε) in mammalian cells. Using nuclear extracts of cells expressing the δN-C/EBP factors we determined in electrophoretic mobility shift assays that C/EBPα, -β and -ε, but not C/EBPγ may directly bind to the cognate C/EBP-binding site in the immediate ACC-α PIA. Co-transfection analyses of the various FL-C/EBP expression vectors together with a reporter gene driven by the ACC-α-PIA promoter demonstrated that C/EBPβ has the strongest activation potential. Hence, activity of this factor may be a key regulator of ACC-α-expression in lipogenic tissues.