Cholesteryl ester transfer protein (CETP) is expressed in human adipocytes, where it acts to promote selective uptake of HDL-CE (Benoist, F., M. McDonnell, P. Lau, R. Milne, and R. McPherson. 1997. J. Biol. Chem. 272: 23572;-23577). In contrast to other major sterol-responsive genes such as 3-hydroxy-3-methylglutaryl coenzyme A reductase CETP expression is up-regulated rather than down-regulated in response to cholesterol. To define elements involved in cholesterol-mediated up-regulation of CETP gene expression, deletion derivatives of the CETP promoter were cloned into a luciferase reporter construct and transfected into the human liposarcoma cell line SW872, cultured in the presence or absence of lipoproteins. A fragment associated with a positive cholesterol response was identified between nucleotides -361 and -138 (relative to the initiation site of transcription) of the promoter. This region contains a tandem repeat of a sequence known to mediate sterol dependent regulation of the hamster HMG-CoA reductase gene. We have putatively denoted this region, the cholesterol response element (CRE). Using gel mobility shift assays we demonstrate that both YY1 and SREBP-1 interact with the CRE of CETP. Furthermore, in transient co-transfection experiments, both YY1 and SREBP-1a were found to trans-activate, in a dose-dependent manner, the luciferase activity of constructs harboring the CRE. We also demonstrate that SREBP-2, is able to trans-activate a luciferase construct harboring the CRE although much less effectively as compared to SREBP-1. Finally, functional analysis of the CRE confirms its regulatory role in modulating CETP gene expression through its interaction with YY1 and SREBP-1a.
Animals CCAAT-Enhancer-Binding Proteins