Low-level expression of human <italic>ACAT2</italic> gene in monocytic cells is regulated by the C/EBP transcription factors

Abstract

Acyl-coenzyme A:cholesterol acyltransferases (ACATs) are the exclusive intracellular enzymes that catalyze the formation of cholesteryl/steryl esters (CE/SE). In our previous work, we found that the high-level expression of human ACAT2 gene with the CpG hypomethylation of its whole promoter was synergistically regulated by two transcription factors Cdx2 and HNF1α in the intestine and fetal liver. Here, we first observed that the specific CpG-hypomethylated promoter was correlated with the low expression of human ACAT2 gene in monocytic cell line THP-1. Then, two CCAAT/enhancer binding protein (C/EBP) elements within the activation domain in the specific CpG-hypomethylation promoter region were identified, and the expression of ACAT2 in THP-1 cells was evidently decreased when the C/EBP transcription factors were knock-downed using RNAi technology. Furthermore, ChIP assay confirmed that C/EBPs directly bind to their elements for low-level expression of human ACAT2 gene in THP-1 cells. Significantly, the increased expressions of ACAT2 and C/ EBPs were also found in macrophages differentiated from both ATRA-treated THP-1 cells and cultured human blood monocytes. These results demonstrate that the low-level expression of human ACAT2 gene with specific CpG-hypomethylated promoter is regulated by the C/EBP transcription factors in monocytic cells, and imply that the lowly expressed ACAT2 catalyzes the synthesis of certain CE/SE that are assembled into lipoproteins for the secretion.

The ACAT2 expression of human leukocytes is responsible for the excretion of lipoproteins containing cholesteryl/steryl esters

“…However, our previous studies have shown that in the human monocytic cells the low-level expression of ACAT2 gene with specific CpG-hypomethylated promoter is regulated by the C/EBP transcription factors [26]. Here, by investigating the human blood leukocytes and leukocytic cell lines, we first observed that in the human blood leukocytes, the same specific CpG sites (No.…”

“…With the ATRA-induced partial differentiation of THP-1 cells [29], we found that the expressions of ACAT2 and C/EBPs (α, β, and ε) were all evidently increased [26]. Therefore, we measured the FI of lipoproteins containing NBD22-steryl esters selectively inhibited by PPPA for the ACAT2-dependent lipoprotein excretion.…”

“…More recently, our studies showed that the low-level expression of human ACAT2 gene with specific CpG-hypomethylated promoter is regulated by the CCAAT/enhancer binding protein (C/EBP) transcription factors in monocytic cells [26]. However, the role of ACAT2 in the monocytic cells is still unknown, and the possibility that the increased expression of ACAT2 in the monocytic cells may be associated with some physiological/pathological role has not been examined.…”