cAMP activation of CAAT enhancer-binding protein-β gene expression and promoter I of acetyl-CoA carboxylase

Abstract

The acetyl-CoA carboxylase (ACC) gene contains two distinct promoters, denoted PI and PII. PI is responsible for the generation of class I ACC mRNAs which are induced in a tissue-specific manner under lipogenic conditions. PII generates class II ACC mRNAs which are expressed constitutively. During 30A5 preadipocyte differentiation, both promoters are activated; the preadipocytes must be pretreated with cAMP for this activation to occur. In this report, we present evidence that CAAT enhancer-binding protein-β (C/EBP-β) is induced and involved in the PI activation by cAMP. Expression of the reporter gene under the control of the PI promoter is activated within 3 h after treatment of 30A5 cells with a cyclic AMP analogue, 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, and 3-isobutyl-1-methylxanthine, in association with the accumulation of C/EBP-β mRNA and protein. These accumulations were inhibited in the presence of H8, a protein kinase inhibitor; H8 also inhibited activation of PI by cAMP. However, the induction of reporter gene expression and the increase of C/EBP-β mRNA by cAMP were not affected by treatment with tumor necrosis factor α, which completely inhibited the accumulation of C/EBP-α mRNA. Overexpression of C/EBP-β by transfection with the C/EBP-β gene led to increased binding of C/EBP-β to DNA and partial PI activation. cAMP did not affect the amount of C/EBP-β binding to the DNA but did promote phosphorylation of C/EBP-β and PI activation. As in the case of C/EBP-α, C/EBP-β bound to the CCAAT box of the PI promoter. These results indicate that cAMP not only induces, but also activates, bound C/EBP-β through phosphorylation for PI activation. Our studies also indicate that cAMP induces C/EBP-α. C/EBP-β induction, however, precedes that of C/EBP-α.