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Guo D, Lu M, Hu X, Xu J, Hu G, Zhu M, Zhang X, Li Q, Chang CCY, Chang T, Song B, Xiong Y, Li B. Low-level expression of human ACAT2 gene in monocytic cells is regulated by the C/EBP transcription factors. Acta Biochim Biophys Sin (Shanghai) 2016; 48:980-989. [PMID: 27688151 PMCID: PMC5091289 DOI: 10.1093/abbs/gmw091] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Revised: 08/18/2016] [Accepted: 07/15/2016] [Indexed: 01/15/2023] Open
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.
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Affiliation(s)
- Dongqing Guo
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Ming Lu
- Department of General Surgery, Huashan Hospital, Fudan University, Shanghai 200040, China
| | - Xihan Hu
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Jiajia Xu
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Guangjing Hu
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Ming Zhu
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiaowei Zhang
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Qin Li
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Catherine C Y Chang
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Tayuan Chang
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Baoliang Song
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
- College of Life Sciences, The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Ying Xiong
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Boliang Li
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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Navarro-Imaz H, Rueda Y, Fresnedo O. SND1 overexpression deregulates cholesterol homeostasis in hepatocellular carcinoma. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:988-996. [DOI: 10.1016/j.bbalip.2016.05.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Revised: 05/18/2016] [Accepted: 05/24/2016] [Indexed: 01/06/2023]
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Lu M, Hu XH, Li Q, Xiong Y, Hu GJ, Xu JJ, Zhao XN, Wei XX, Chang CCY, Liu YK, Nan FJ, Li J, Chang TY, Song BL, Li BL. A specific cholesterol metabolic pathway is established in a subset of HCCs for tumor growth. J Mol Cell Biol 2013; 5:404-15. [PMID: 24163426 DOI: 10.1093/jmcb/mjt039] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The liver plays a central role in cholesterol homeostasis. It exclusively receives and metabolizes oxysterols, which are important metabolites of cholesterol and are more cytotoxic than free cholesterol, from all extrahepatic tissues. Hepatocellular carcinomas (HCCs) impair certain liver functions and cause pathological alterations in many processes including cholesterol metabolism. However, the link between an altered cholesterol metabolism and HCC development is unclear. Human ACAT2 is abundantly expressed in intestine and fetal liver. Our previous studies have shown that ACAT2 is induced in certain HCC tissues. Here, by investigating tissue samples from HCC patients and HCC cell lines, we report that a specific cholesterol metabolic pathway, involving induction of ACAT2 and esterification of excess oxysterols for secretion to avoid cytotoxicity, is established in a subset of HCCs for tumor growth. Inhibiting ACAT2 leads to the intracellular accumulation of unesterified oxysterols and suppresses the growth of both HCC cell lines and their xenograft tumors. Further mechanistic studies reveal that HCC-linked promoter hypomethylation is essential for the induction of ACAT2 gene expression. We postulate that specifically blocking this HCC-established cholesterol metabolic pathway may have potential therapeutic applications for HCC patients.
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Affiliation(s)
- Ming Lu
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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Ramajayam G, Vignesh RC, Karthikeyan S, Senthil Kumar K, Karthikeyan GD, Veni S, Sridhar M, Arunakaran J, Michael Aruldhas M, Srinivasan N. Regulation of insulin-like growth factors and their binding proteins by thyroid stimulating hormone in human osteoblast-like (SaOS2) cells. Mol Cell Biochem 2012; 368:77-88. [DOI: 10.1007/s11010-012-1345-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 05/16/2012] [Indexed: 11/25/2022]
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Zhang Z, Liu J, Xi Y, Yang R, Chen H, Li Z, Liu D, Liang C. Two novel cis-elements involved in hepatocyte nuclear factor 4α regulation of acyl-coenzyme A:cholesterol acyltransferase 2 expression. Acta Biochim Biophys Sin (Shanghai) 2012; 44:162-71. [PMID: 22155889 DOI: 10.1093/abbs/gmr102] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) is important for cholesterol ester synthesis and secretion. A previous study revealed that ACAT2 gene promoter activity was upregulated by hepatocyte nuclear factor 4α (HNF4α) through two sites around -247 and -311 of ACAT2 gene promoter. Here, we identified two novel cis-elements, site I (-1006 to -898) and site II (-38 to -29), which are important for HNF4α effect. In HepG2 cells, mutation of site I decreased ACAT2 gene promoter activity to one-fifth of that of the wild type, while mutation of site II reduced promoter activity to less than one-tenth of that of the wild type. In 293T cells, mutation of these two cis-elements profoundly impaired the HNF4α induction effect. When either of these two elements was inserted into pGL3-promoter, HNF4α induced promoter activity through the inserted element, while mutation of the element impaired HNF4α induction effect. In electrophoretic mobility shift assay and chromatin immunoprecipitation experiment, HNF4α bound to these two elements. Thus, the two cis-elements are important for HNF4α effect on ACAT2 gene transcription. We also showed that HNF4α positively regulates ACAT2 gene expression at mRNA level. Overexpression of HNF4α increased ACAT2 expression, whereas knockdown of HNF4α decreased ACAT2 expression. Peroxisome proliferator-activated receptor gamma coactivator 1α (PCG1α), a coactivator of HNF4α, increased ACAT2 expression, while small heterodimer partner (SHP), a corepressor of HNF4α, decreased ACAT2 expression. These results provide more insights into transcriptional regulation of ACAT2 expression.
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Affiliation(s)
- Zhuqin Zhang
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Science, Chinese Academy of Medical Sciences, Beijing, China
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Zhao YY, Guo L, Zhao XJ, Liu H, Lei T, Ma DJ, Gao XY. Transcriptional activation of insulin-like growth factor binding protein 6 by 17beta-estradiol in SaOS-2 cells. Exp Mol Med 2009; 41:478-86. [PMID: 19322032 DOI: 10.3858/emm.2009.41.7.053] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Osteoblasts can synthesize the insulin-like growth factors (IGFs) and the IGF-binding proteins (IGFBPs), which may either enhance or attenuate IGF-stimulated bone cell proliferation. Since estrogen induced osteoblastic differentiation and proliferation through an estrogen-responsive gene in target cells, we investigated the effects of estrogen on IGFBP-6 expression in the human osteoblastic-like cell line SaOS-2. Expressions of IGFBP-6 protein and mRNA increased 2.8 and 2-fold, respectively, in the presence of 17-beta-estradiol (E2) (0.01 to 1 micronM) and estrogen receptor (ER) in SaOS-2 cells. On the other hand, E2 induced a 2-fold increase in SaOS-2 cell proliferation. To identify genomic sequences associated with estrogen responsiveness, the 5'-promoter region (-44 to +118) of the IGFBP-6 gene was cloned into a chloramphenicol acetyltransferase (CAT) reporter vector. E2 induced a 3-fold increase in CAT activity in SaOS-2 cells transiently transfected with this construct. Identification of the estrogen-responsive element (ERE) [5-CCTTCA CCTG-3] (-9 to +1) in this IGFBP-6 gene promoter region was confirmed using electromobility shift assays and deletion analysis. This functional ERE was important for E2-induced trans-activation of the IGFBP-6 gene. These results demonstrate that E2 exhibits a positive effect on IGFBP-6 gene transcription through estrogen-liganded ER binding to the functional ERE in the IGFBP-6 gene promoter in SaOS-2 cells.
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Affiliation(s)
- Yu-yan Zhao
- Department of Endocrinology, First Affiliated Hospital, China Medical University, Shenyang 110001, China.
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Abstract
The storage of fatty acids and fatty alcohols in the form of neutral lipids such as triacylglycerol (TAG), cholesteryl ester (CE), and wax ester (WE) serves to provide reservoirs for membrane formation and maintenance, lipoprotein trafficking, lipid detoxification, evaporation barriers, and fuel in times of stress or nutrient deprivation. This ancient process likely originated in actinomycetes and has persisted in eukaryotes, albeit by different molecular mechanisms. A surfeit of neutral lipids is strongly, perhaps causally, related to several human diseases such as diabetes mellitus, obesity, atherosclerosis and nonalcoholic fatty liver disease. Therefore, understanding the metabolic pathways of neutral lipid synthesis and the roles of the enzymes involved may facilitate the development of new therapeutic interventions for these syndromes.
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Affiliation(s)
- Aaron R Turkish
- Department of Pediatrics, Columbia University Medical Center, 630 W. 168th St., New York, NY, USA.
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Lei L, Xiong Y, Chen J, Yang JB, Wang Y, Yang XY, Chang CCY, Song BL, Chang TY, Li BL. TNF-alpha stimulates the ACAT1 expression in differentiating monocytes to promote the CE-laden cell formation. J Lipid Res 2009; 50:1057-67. [PMID: 19189937 DOI: 10.1194/jlr.m800484-jlr200] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
High levels of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) are present in atherosclerotic lesions. TNF-alpha regulates expression of multiple genes involved in various stages of atherosclerosis, and it exhibits proatherosclerotic and antiatherosclerotic properties. ACAT catalyzes the formation of cholesteryl esters (CE) in monocytes/macrophages, and it promotes the foam cell formation at the early stage of atherosclerosis. We hypothesize that TNF-alpha may be involved in regulating the ACAT gene expression in monocytes/macrophages. In this article, we show that in cultured, differentiating human monocytes, TNF-alpha enhances the expression of the ACAT1 but not ACAT2 gene, increases the cholesteryl ester accumulation, and promotes the lipid-laden cell formation. Several other proinflammatory cytokines tested do not affect the ACAT1 gene expression. The stimulation effect is consistent with a receptor-dependent process, and is blocked by using nuclear factor-kappa B (NF-kappa B) inhibitors. A functional and unique NF-kappa B element located within the human ACAT1 gene proximal promoter is required to mediate the action of TNF-alpha. Our data demonstrate that TNF-alpha, through the NF-kappa B pathway, specifically enhances the expression of human ACAT1 gene to promote the CE-laden cell formation from the differentiating monocytes, and our data support the hypothesis that TNF-alpha is proatherosclerotic during early phase of lesion development.
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Affiliation(s)
- Lei Lei
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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Pramfalk C, Angelin B, Eriksson M, Parini P. Cholesterol regulates ACAT2 gene expression and enzyme activity in human hepatoma cells. Biochem Biophys Res Commun 2007; 364:402-9. [PMID: 17950700 DOI: 10.1016/j.bbrc.2007.10.028] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2007] [Accepted: 10/06/2007] [Indexed: 10/22/2022]
Abstract
Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the synthesis of cholesteryl esters from cholesterol and long-chain fatty acids. The two ACAT enzymes, ACAT1 and ACAT2, lack sterol regulatory elements in their promoters and have not been thought to be transcriptionally regulated by cellular cholesterol. However, Cynomolgus monkeys respond to high-cholesterol diet with increased hepatic ACAT2 mRNA expression. Also, a decrease in hepatic ACAT2 mRNA expression has been observed during statin treatment in humans. Thus, we hypothesized that cholesterol may exert transcriptional regulation on the human ACAT2 gene. To test this, we studied two human hepatoma cell lines (HuH7 and HepG2) under conditions of cholesterol loading or depletion and analyzed ACAT gene expression, enzymatic activity, and cellular cholesterol mass. We show a dose-dependent increase of ACAT2 mRNA expression, an increased enzymatic activity of ACAT2, and increased esterified cholesterol mass upon cholesterol loading. These results suggest that human ACAT2 is transcriptionally regulated by cholesterol.
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Affiliation(s)
- Camilla Pramfalk
- Division of Clinical Chemistry, Department of Laboratory Medicine, C1-74, Karolinska Institute at Karolinska University Hospital Huddinge, S-141 86 Stockholm, Sweden
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Song BL, Wang CH, Yao XM, Yang L, Zhang WJ, Wang ZZ, Zhao XN, Yang JB, Qi W, Yang XY, Inoue K, Lin ZX, Zhang HZ, Kodama T, Chang C, Liu YK, Chang TY, Li BL. Human acyl-CoA:cholesterol acyltransferase 2 gene expression in intestinal Caco-2 cells and in hepatocellular carcinoma. Biochem J 2006; 394:617-26. [PMID: 16274362 PMCID: PMC1383711 DOI: 10.1042/bj20051417] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2005] [Revised: 11/02/2005] [Accepted: 11/08/2005] [Indexed: 11/17/2022]
Abstract
Humans express two ACAT (acyl-CoA:cholesterol acyltransferase) genes, ACAT1 and ACAT2. ACAT1 is ubiquitously expressed, whereas ACAT2 is primarily expressed in intestinal mucosa and plays an important role in intestinal cholesterol absorption. To investigate the molecular mechanism(s) responsible for the tissue-specific expression of ACAT2, we identified five cis-elements within the human ACAT2 promoter, four for the intestinal-specific transcription factor CDX2 (caudal type homeobox transcription factor 2), and one for the transcription factor HNF1alpha (hepatocyte nuclear factor 1alpha). Results of luciferase reporter and electrophoretic mobility shift assays show that CDX2 and HNF1alpha exert a synergistic effect, enhancing the ACAT2 promoter activity through binding to these cis-elements. In undifferentiated Caco-2 cells, the ACAT2 expression is increased when exogenous CDX2 and/or HNF1alpha are expressed by co-transfection. In differentiated Caco-2 cells, the ACAT2 expression significantly decreases when the endogenous CDX2 or HNF1alpha expression is suppressed by using RNAi (RNA interference) technology. The expression levels of CDX2, HNF1alpha, and ACAT2 are all greatly increased when the Caco-2 cells differentiate to become intestinal-like cells. These results provide a molecular mechanism for the tissue-specific expression of ACAT2 in intestine. In normal adult human liver, CDX2 expression is not detectable and the ACAT2 expression is very low. In the hepatoma cell line HepG2 the CDX2 expression is elevated, accounting for its elevated ACAT2 expression. A high percentage (seven of fourteen) of liver samples from patients affected with hepatocellular carcinoma exhibited elevated ACAT2 expression. Thus, the elevated ACAT2 expression may serve as a new biomarker for certain form(s) of hepatocellular carcinoma.
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Key Words
- acyl-coa:cholesterol acyltransferase (acat2)
- caudal type homeobox transcription factor 2 (cdx2)
- hepatocyte nuclear factor 1α (hnf1α)
- intestine
- hepatocellular carcinoma (hcc)
- acat, acyl-coa:cholesterol acyltransferase
- afp, α-fetalprotein
- cdx2, caudal type homeobox transcription factor 2
- cldn2, claudin 2 gene
- dmem, dulbecco's modified eagle's medium
- emsa, electrophoretic mobility shift assay
- fbs, fetal bovine serum
- gapdh, glyceraldehyde-3-phosphate dehydrogenase
- hcc, hepatocellular carcinoma
- hnf1α, hepatocyte nuclear factor 1α
- lph, lactase-phlorizin hydrolase gene
- luc, luciferase reporter
- rnai, rna interference
- rt, reverse transcriptase
- ugt1a8–10, udp glucuronosyltransferase 1 family polypeptides a8–10 gene
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Affiliation(s)
- Bao-Liang Song
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Can-Hua Wang
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
- †Department of Biochemistry and Technology, Jiao Tong University, Shanghai 200030, China
| | - Xiao-Min Yao
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
- †Department of Biochemistry and Technology, Jiao Tong University, Shanghai 200030, China
| | - Li Yang
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Wen-Jing Zhang
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
- ‡Department of Biochemistry and Technology, East China University of Science and Technology, Shanghai 200237, China
| | - Zhen-Zhen Wang
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiao-Nan Zhao
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Jin-Bo Yang
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Wei Qi
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xin-Ying Yang
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Kenji Inoue
- §Laboratory for Systems Biology and Medicine, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan
| | - Zhi-Xin Lin
- †Department of Biochemistry and Technology, Jiao Tong University, Shanghai 200030, China
| | - Hui-Zhan Zhang
- ‡Department of Biochemistry and Technology, East China University of Science and Technology, Shanghai 200237, China
| | - Tatsuhiko Kodama
- §Laboratory for Systems Biology and Medicine, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan
| | | | - Yin-Kun Liu
- ¶Liver Cancer Institute of Zhong San Hospital, Fudan University, Shanghai 200031, China
| | - Ta-Yuan Chang
- ∥Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, U.S.A
| | - Bo-Liang Li
- *State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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He X, Lu Y, Saha N, Yang H, Heng CK. Acyl-CoA: cholesterol acyltransferase-2 gene polymorphisms and their association with plasma lipids and coronary artery disease risks. Hum Genet 2005; 118:393-403. [PMID: 16195894 DOI: 10.1007/s00439-005-0055-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2005] [Accepted: 08/09/2005] [Indexed: 10/25/2022]
Abstract
Acyl-CoA: cholesterol acyltransferase-2 (ACAT2), an intracellular cholesterol esterification enzyme found only in the intestine and liver, has been demonstrated to be associated with hypercholesterolemia and atherosclerosis in mice. To explore the possible impact of ACAT2 gene variants on CAD susceptibility and plasma lipid levels, three polymorphisms, 41A>G (Glu>Gly), 734C>T (Thr>Ile), and IVS4-57_58 ins48 bp (D/I), were genotyped in 809 CAD patients (CAD+) and 1,304 controls (CAD-) from three distinct Singaporean ethnic groups (1,228 Chinese, 367 Malays and 518 Indians). The 734T allele frequency was significantly lower in CAD+ (0.20) than CAD- (0.26) in Chinese (P=0.003) and I allele of D/I was significantly higher in CAD+ (0.17) than CAD- (0.10) in Indians (P=0.011). The 41G allele was significantly more frequent among normolipidemic (0.19) than dyslipidemic (0.13) individuals in Chinese (P=0.008). In normolipidemic females, 734C>T was associated with apoA1, apoB and lipoprotein (a) in Indians, and with apoA1 in Malays, whereas 41A>G is associated with total cholesterol in Indians. The 734C>T polymorphism was in almost complete linkage disequilibrium (LD) with the IVS4-57_58 ins48 bp and in very strong LD with 41A>G in all the three ethnic groups. In the normolipidemic females, the AG/CT had much higher apoB than AA/CC in Indians. We found that the three ACAT2 polymorphisms studied are associated with CAD risk and plasma lipid levels but their effects are not consistent across genders and ethnic groups.
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Affiliation(s)
- Xuelian He
- Department of Paediatrics, National University of Singapore, 5 Lower Kent Ridge Road, Singapore, 119074, Singapore
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Yao XM, Wang CH, Song BL, Yang XY, Wang ZZ, Qi W, Lin ZX, Chang CCY, Chang TY, Li BL. Two human ACAT2 mRNA variants produced by alternative splicing and coding for novel isoenzymes. Acta Biochim Biophys Sin (Shanghai) 2005; 37:797-806. [PMID: 16331323 DOI: 10.1111/j.1745-7270.2005.00118.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Acyl coenzyme A:cholesterol acyltransferase 2 (ACAT2) plays an important role in cholesterol absorption. Human ACAT2 is highly expressed in small intestine and fetal liver, but its expression is greatly diminished in adult liver. The full-length human ACAT2 mRNA encodes a protein, designated ACAT2a, with 522 amino acids. We have previously reported the organization of the human ACAT2 gene and the differentiation-dependent promoter activity in intestinal Caco-2 cells. In the current work, two human ACAT2 mRNA variants produced by alternative splicing are cloned and predicted to encode two novel ACAT2 isoforms, named ACAT2b and ACAT2c, with 502 and 379 amino acids, respectively. These mRNA variants differ from ACAT2a mRNA by lack of the exon 4 (ACAT2b mRNA) and exons 4-5 plus 8-9-10 (ACAT2c mRNA). Significantly, comparable amounts of the alternatively spliced ACAT2 mRNA variants were detected by RT-PCR, and Western blot analysis confirmed the presence of their corresponding proteins in human liver and intestinecells. Furthermore, phosphorylation and enzymatic activity analyses demonstrated that the novel isoenzymes ACAT2b and ACAT2c lacked the phosphorylatable site SLLD, and their enzymatic activities reduced to 25%-35% of that of ACAT2a. These evidences indicate that alternative splicing produces two human ACAT2 mRNA variants that encode the novel ACAT2 isoenzymes. Our findings might help to understand the regulation of the ACAT2 gene expression under certain physiological and pathological conditions.
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Affiliation(s)
- Xiao-Min Yao
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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Leon C, Hill JS, Wasan KM. Potential role of acyl-coenzyme A:cholesterol transferase (ACAT) Inhibitors as hypolipidemic and antiatherosclerosis drugs. Pharm Res 2005; 22:1578-88. [PMID: 16180116 DOI: 10.1007/s11095-005-6306-0] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2005] [Accepted: 06/03/2005] [Indexed: 11/29/2022]
Abstract
Acyl-coenzyme A:cholesterol transferase (ACAT) is an integral membrane protein localized in the endoplasmic reticulum. ACAT catalyzes the formation of cholesteryl esters from cholesterol and fatty acyl coenzyme A. The cholesteryl esters are stored as cytoplasmic lipid droplets inside the cell. This process is very important to the organism as high cholesterol levels have been associated with cardiovascular disease. In mammals, two ACAT genes have been identified, ACAT1 and ACAT2. ACAT1 is ubiquitous and is responsible for cholesteryl ester formation in brain, adrenal glands, macrophages, and kidneys. ACAT2 is expressed in the liver and intestine. The inhibition of ACAT activity has been associated with decreased plasma cholesterol levels by suppressing cholesterol absorption and by diminishing the assembly and secretion of apolipoprotein B-containing lipoproteins such as very low density lipoprotein (VLDL). ACAT inhibition also prevents the conversion of macrophages into foam cells in the arterial walls, a critical event in the development of atherosclerosis. This review paper will focus on the role of ACAT in cholesterol metabolism, in particular as a target to develop novel therapeutic agents to control hypercholesterolemia, atherosclerosis, and Alzheimer's disease.
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Affiliation(s)
- Carlos Leon
- Division of Pharmaceutics and Biopharmaceutics, Faculty of Pharmaceutical Sciences, The University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada
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Abstract
ACAT catalyzes the formation of cholesteryl esters from cholesterol and long-chain fatty acids. There are two known genes encoding the two ACAT enzymes, ACAT1 and ACAT2 (also known as Soat1 and Soat2). In adult humans, ACAT1 is present in most tissues, whereas ACAT2 is localized to enterocytes and hepatocytes. In this report, we elucidate the mechanisms that control the liver-specific expression of the human ACAT2 gene. We identified hepatic nuclear factor 1 (HNF1) as an important liver-specific trans-acting element for the human ACAT2 gene using the human hepatocellular carcinoma cell lines HuH7 and HepG2. Targeted deletion of the HNF1 binding site in the DNA sequence abolished not only the basal promoter function in HepG2 and HuH7 cells but also the induction of the ACAT2 promoter by HNF1. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that the transcription factors HNF1alpha and HNF1beta interact with this region in the human ACAT2 gene in vitro and in vivo. These data indicate that a) the identified HNF1 binding site serves as a positive regulator sequence, b) the binding site is functionally active both in vivo and in vitro, and c) the transcription factors HNF1alpha and HNF1beta, which bind to this site, play an important part in the regulation of the human ACAT2 promoter.
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Affiliation(s)
- Camilla Pramfalk
- Metabolism Unit, Center for Metabolism and Endocrinology, NOVUM, Karolinska Institutet at Karolinska University Hospital in Huddinge, S-141 86 Stockholm, Sweden
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16
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Allister EM, Pal S, Thomson AM, Helmerhorst E, Mamo JCL. Insulin decreases the secretion of apoB-100 from hepatic HepG2 cells but does not decrease the secretion of apoB-48 from intestinal CaCo-2 cells. J Biomed Sci 2004; 11:789-98. [PMID: 15591776 DOI: 10.1007/bf02254364] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2003] [Accepted: 05/20/2004] [Indexed: 11/25/2022] Open
Abstract
We compared the acute effect of insulin on the human colonic intestinal epithelial cell line CaCo-2 and the transformed human hepatic cell line HepG2. Over 24 h, 100 nM and 10 microM insulin significantly inhibited the secretion of apolipoprotein (apo) B-100 from HepG2 cells to 63 and 49% of control, respectively. Insulin had no effect on the secretion of apoB-48 from CaCo-2 cells. There was no effect of insulin on the cholesterol ester or free cholesterol concentrations in HepG2 or CaCo-2 cells. HepG2 and CaCo-2 cells bound insulin with high affinity, leading to similar stimulation of insulin receptor protein tyrosine kinase activation. Protein kinase C or mitogen-activated protein kinase activity in the presence or absence of insulin was not correlated with apoB-48 production in CaCo-2 cells. Therefore, insulin acutely decreases the secretion of apoB-100 in hepatic HepG2 cells, but does not acutely modulate the production or secretion of apoB-48 from CaCo-2 intestinal cells.
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Affiliation(s)
- Emma M Allister
- Department of Nutrition, Dietetics and Food Sciences, Curtin University of Technology, Perth, WA, Australia
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17
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Yang L, Lee O, Chen J, Chen J, Chang CCY, Zhou P, Wang ZZ, Ma HH, Sha HF, Feng JX, Wang Y, Yang XY, Wang L, Dong R, Ornvold K, Li BL, Chang TY. Human Acyl-Coenzyme A:Cholesterol Acyltransferase 1 (acat1) Sequences Located in Two Different Chromosomes (7 and 1) Are Required to Produce a Novel ACAT1 Isoenzyme with Additional Sequence at the N Terminus. J Biol Chem 2004; 279:46253-62. [PMID: 15319423 DOI: 10.1074/jbc.m408155200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
A rare form of human ACAT1 mRNA, containing the optional long 5'-untranslated region, is produced as a 4.3-kelonucleotide chimeric mRNA through a novel interchromosomal trans-splicing of two discontinuous RNAs transcribed from chromosomes 1 and 7. To investigate its function, we express the chimeric ACAT1 mRNA in Chinese hamster ovary cells and show that it can produce a larger ACAT1 protein, with an apparent molecular mass of 56 kDa on SDS-PAGE, in addition to the normal, 50-kDa ACAT1 protein, which is produced from the ACAT1 mRNAs without the optional long 5'-untranslated repeat. To produce the 56-kDa ACAT1, acat1 sequences located at both chromosomes 7 and 1 are required. The 56-kDa ACAT1 can be recognized by specific antibodies prepared against the predicted additional amino acid sequence located upstream of the N-terminal of the ACAT1(ORF). The translation initiation codon for the 56-kDa protein is GGC, which encodes for glycine, as deduced by mutation analysis and mass spectrometry. Similar to the 50-kDa protein, when expressed alone, the 56-kDa ACAT1 is located in the endoplasmic reticulum and is enzymatically active. The 56-kDa ACAT1 is present in native human cells, including human monocyte-derived macrophages. Our current results show that the function of the chimeric ACAT1 mRNA is to increase the ACAT enzyme diversity by producing a novel isoenzyme. To our knowledge, our result provides the first mammalian example that a trans-spliced mRNA produces a functional protein.
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Affiliation(s)
- Li Yang
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Rd., Shanghai 200031, China
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18
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Hori M, Satoh M, Furukawa K, Sakamoto YI, Hakamata H, Komohara Y, Takeya M, Sasaki Y, Miyazaki A, Horiuchi S. Acyl-coenzyme A:cholesterol acyltransferase-2 (ACAT-2) is responsible for elevated intestinal ACAT activity in diabetic rats. Arterioscler Thromb Vasc Biol 2004; 24:1689-95. [PMID: 15242859 DOI: 10.1161/01.atv.0000137976.88533.13] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Diabetes-induced dyslipidemia is seen in streptozotocin-induced diabetic rats. This is caused, in part, by elevated intestinal acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity. Because two ACAT isozymes (ACAT-1 and ACAT-2) were identified, in the present study we determined which ACAT isozyme was involved in the elevated intestinal ACAT activity in diabetic rats. METHODS AND RESULTS We cloned a full-length cDNA of rat ACAT-2. Its overexpression in ACAT-deficient AC29 cells demonstrated that the ACAT activity is derived from the cloned cDNA, and a 45-kDa protein of rat ACAT-2 cross-reacts with an anti-human ACAT-2 antibody. The tissue distribution of rat ACAT-2 mRNA revealed its restricted expression to liver and small intestine. Immunohistochemical analyses using an anti-human ACAT-2 antibody demonstrated that ACAT-2 is localized in villus-crypt axis of rat small intestine. The intestinal ACAT activity in diabetic rats was significantly immunodepleted by an anti-ACAT-2 antibody but not by an anti-ACAT-1 antibody. Finally, intestinal ACAT-2 in diabetic rats significantly increased at both protein and mRNA levels as compared with that in control rats. CONCLUSIONS Our data demonstrate that ACAT-2 isozyme is responsible for the increased intestinal ACAT activity of diabetic rats, suggesting an important role of ACAT-2 for dyslipidemia in diabetic patients. Diabetic rats exhibit dyslipidemia caused, in part, by elevated intestinal acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity. We determined which ACAT isozyme (ACAT-1 or ACAT-2) was involved in the elevated intestinal ACAT activity in diabetic rats. We demonstrated an important role of ACAT-2, implicating its involvement in dyslipidemia in diabetic patients.
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Affiliation(s)
- Masaharu Hori
- Department of Medical Biochemistry, Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan
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Smith JL, Rangaraj K, Simpson R, Maclean DJ, Nathanson LK, Stuart KA, Scott SP, Ramm GA, de Jersey J. Quantitative analysis of the expression of ACAT genes in human tissues by real-time PCR. J Lipid Res 2004; 45:686-96. [PMID: 14729857 DOI: 10.1194/jlr.m300365-jlr200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
ACAT (also called sterol o-acyltransferase) catalyzes the esterification of cholesterol by reaction with long-chain acyl-CoA derivatives and plays a pivotal role in the regulation of cholesterol homeostasis. Although two human ACAT genes termed ACAT-1 and ACAT-2 have been reported, prior research on differential tissue expression is qualitative and incomplete. We have developed a quantitative multiplex assay for each ACAT isoform after RT treatment of total RNA using TaqMan real-time quantitative PCR normalized to beta-actin in the same reaction tube. This enabled us to calculate the relative abundance of transcripts in several human tissues as an ACAT-2/ACAT-1 ratio. In liver (n = 17), ACAT-1 transcripts were on average 9-fold (range, 1.7- to 167-fold) more abundant than ACAT-2, whereas in duodenal samples (n = 10), ACAT-2 transcripts were on average 3-fold (range, 0.39- to 12.2-fold) more abundant than ACAT-1. ACAT-2 was detected for the first time in peripheral blood mononuclear cells. Interesting differences in ACAT-2 mRNA expression were evident in subgroup analysis of samples from different sources. These results demonstrate quantitatively that ACAT-1 transcripts predominate in human liver and ACAT-2 transcripts predominate in human duodenum and support the notion that ACAT-2 has an important regulatory role in liver and intestine.
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Affiliation(s)
- Jeffery L Smith
- Department of Biochemistry and Molecular Biology, University of Queensland, Brisbane 4072, Australia.
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20
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Hardy MP, Hertzog PJ, Owczarek CM. Multiple regions within the promoter of the murine Ifnar-2 gene confer basal and inducible expression. Biochem J 2002; 365:355-67. [PMID: 11939908 PMCID: PMC1222688 DOI: 10.1042/bj20020105] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2002] [Revised: 03/18/2002] [Accepted: 04/09/2002] [Indexed: 11/17/2022]
Abstract
The (murine) type I interferon (IFN) receptor, muIfnar-2, is expressed ubiquitously, and exists as both transmembrane and soluble forms. In the present study we show that the gene encoding muIfnar-2 spans approx. 33 kb on mouse chromosome 16, and consists of nine exons and eight introns. The three mRNA splice variants resulting in one transmembrane (muIfnar-2c) and two soluble (muIfnar-2a/2a') mRNA isoforms are generated by alternative RNA processing of the muIfnar-2 gene. Treatment of a range of murine cell lines with a combination of type I and II IFN showed that the muIfnar-2a and -2c mRNA isoforms were up-regulated independently of each other in L929 fibroblasts and hepa-1c1c7 hepatoma cells, but not in M1 myeloid leukaemia cells. Analysis of the 5' flanking region of muIfnar-2 using promoter-luciferase reporter constructs defined three regulatory regions: a region proximal to exon 1, conferring high basal expression, a distal region conferring inducible expression, and a negative regulatory region between the two. These data represent the first promoter analysis of a type I IFN receptor and, taken together with our previous data demonstrating high expression levels and dual biological functions for muIfnar-2a protein, suggests that the regulation of muIfnar-2 isoform expression may be an important way of modulating type I IFN responses.
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MESH Headings
- Alternative Splicing
- Amino Acid Sequence
- Animals
- Base Sequence
- Blotting, Northern
- Chromosome Mapping
- Chromosomes, Human, Pair 16
- Cloning, Molecular
- DNA, Complementary
- Exons
- Gene Expression Regulation/genetics
- Humans
- Introns
- Membrane Proteins
- Mice
- Promoter Regions, Genetic
- RNA, Messenger/genetics
- Receptor, Interferon alpha-beta
- Receptors, Interferon/genetics
- Regulatory Sequences, Nucleic Acid
- Sequence Homology, Amino Acid
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Affiliation(s)
- Matthew P Hardy
- Center for Functional Genomics and Human Disease, Monash Institute of Reproduction and Development, Monash University, Melbourne, Victoria 3168, Australia
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22
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Abstract
Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that produces cholesteryl esters in various tissues. In mammals, two ACAT genes (ACAT1 and ACAT2) have been identified. Together, these two enzymes are involved in storing cholesteryl esters as lipid droplets, in macrophage foam-cell formation, in absorbing dietary cholesterol, and in supplying cholesteryl esters as part of the core lipid for lipoprotein synthesis and assembly. The key difference in tissue distribution of ACAT1 and ACAT2 between humans, mice and monkeys is that, in adult human liver (including hepatocytes and bile duct cells), the major enzyme is ACAT1, rather than ACAT2. There is compelling evidence implicating a role for ACAT1 in macrophage foam-cell formation, and for ACAT2 in intestinal cholesterol absorption. However, further studies at the biochemical and cell biological levels are needed in order to clarify the functional roles of ACAT1 and ACAT2 in the VLDL or chylomicron synthesis/assembly process.
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Affiliation(s)
- T Y Chang
- Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
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