Cholesteryl ester transfer protein gene expression is not specifically regulated by CCAAT/enhancer-binding protein in HepG2-cells

Cholesteryl ester transfer protein (CETP) mediates the exchange of neutral lipids among plasma lipoproteins and is expressed predominantly in liver an d intestine. In band shift assays employing nuclear extracts of HepG2 cells we identified C/EBP beta as the predominant C/EBP isoform involved in bind ing to the C/EBP consensus sequence within the 5' upstream region of the CE TP gene. This was demonstrated by supershift experiments using antibodies s pecific for C/EBP alpha, C/EBP beta and C/EBP delta and an oligonucleotide containing a single point mutation (CAAT --> CTAT) in this site. Expression of a CETP promoter-fragment/luciferase construct in transiently transfecte d HepG2 and CaCo-2 cells and enhancement of promoter activity by co-transfe ction with human C/EBP alpha in HepG2 cells could be influenced neither by the mutation in the consensus sequence nor by elimination of this site toge ther with a second potential binding site for C/EBP. Furthermore, transfect ion of HepG2 with human C/EBP alpha did not influence the synthesis of CETP by these cells. Our results indicate that the expression of C/EBP in HepG2 cells is not able (1) to influence specifically the expression of a transf ected CETP promoter dependent reporter through binding to C/EBP sites in th e promoter region and (2) to significantly enhance expression of the endoge nous CETP gene. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.