Synergistic Transcriptional Activation of HumanAcyl-coenzyme A: Cholesterol Acyltransterase-1 Gene by Interferon-γ and All-trans-Retinoic Acid THP-1 Cells

Abstract

cytokine that exerts many pro-atherosclerotic effects in vivo, causes up-regulation of ACAT-1 mRNA in human blood monocyte-derived macrophages and macrophage-like cells but not in other cell types. To examine the molecular nature of this observation, we identified within the ACAT-1 P1 promoter a 159-base pair core region. This region contains 4 Sp1 elements and an IFN-␥ activated sequence (GAS) that overlaps with the second Sp1 element. In the monocytic cell line THP-1 cell, the combination of IFN-␥ and all-trans-retinoic acid (a known differentiation agent) enhances the ACAT-1 P1 promoter but not the P7 promoter. Additional experiments showed that all-trans-retinoic acid causes large induction of the transcription factor STAT1, while IFN-␥ causes activation of STAT1 such that it binds to the GAS/Sp1 site in the ACAT-1 P1 promoter. Our work provides a molecular mechanism to account for the effect of IFN-␥ in causing transcriptional activation of ACAT-1 in macrophage-like cells. ACAT1 is an intracellular enzyme responsible for catalyzing the intracellular formation of cholesteryl esters from cholesterol and long-chain fatty acyl-coenzyme A (1). In mammals, two ACAT genes have been identified (2-5). In adult human tissues, ACAT-1 is the major enzyme present in various tissues, including macrophages, liver (hepatocytes and Kupffer cells), and adrenal gland (6, 7). ACAT-1 is also present in the intestine; however, the major enzyme involved in the intestinal cholesterol absorption may be ACAT-2, which is mainly located in the apical region of the intestinal villi (7). The relative tissue distributions of ACAT-1 and ACAT-2 in mice and monkeys are not entirely consistent with those found in humans (8, 9) raising the possibility that the distribution of the two ACATs in various tissues may be species dependent. In macrophages and other cell types, a dynamic cholesterol-cholesteryl ester cycle exist; the formation of intracellular cholesteryl esters is catalyzed by ACAT-1, while the hydrolysis of cholesteryl esters is catalyzed by the enzyme neutral cholesteryl ester hydrolase (10, 11). The net accumulation of intracellular cholesteryl esters is affected at the substrate level, as well as at the levels of the enzymes ACAT and neutral cholesteryl ester hydrolase (12)(13)(14). The main mode of sterol-specific regulation of ACAT-1 has been identified at the post-translational level, involving allosteric regulation by its substrate cholesterol (1, 15). On the other hand, the cellular and molecular nature of non-sterolmediated ACAT-1 regulation remains largely unknown. Recently, using mouse macrophage-derived foam cells, Panousis and Zuckerman (12) reported that IFN-␥ increased the cellular cholesteryl ester content and reduced high density lipoproteinmediated cholesterol efflux; its cellular effects were attributed to its ability to increase ACAT-1 message (12) and to induce down-regulation of the Tangier Disease gene (the ABC1 transporter) (16). In the current work, we showed that IFN-␥ increased ACAT-1 message and protein ...

Synergistic induction of the MUC4 mucin gene by interferon-γ and retinoic acid in human pancreatic tumour cells involves a reprogramming of signalling pathways

“…While STAT-1 induction by IFNg is partially repressed by RA (red dotted line), the upregulation of TGFb-2 by RA is inhibited by IFNg. The dotted blue line depicts a presumptive pathway (Ulloa et al, 1999) (our unpublished data) that may account for the inhibition of TGFb-2 expression, which leads to the attenuation of the TGFb-2-dependent pathway (dotted green arrow) the one hand, IFNg and RA are naturally occurring biological agents with proven cell growth inhibitory and/or differentiating properties (Ho, 1985;Windbichler et al, 1996;Widschwendter et al, 1997;Chelbi-Alix and Pelicano, 1999;Guzhova et al, 2001;Yang et al, 2001;Hu et al, 2002). Moreover, our recent studies have indicated a differential expression of IFNg in pancreatic tumours, as opposed to the lack of detection in the normal pancreas (Andrianifahanana et al, 2005).…”

“…Interestingly, IFNg and RA are well known for their ability to evoke a synergistic effect, which generally leads to an enhanced induction of target gene(s) and an exacerbation of the associated biological response(s). The impact of this synergism has been observed in a wide range of malignant tumour cell types, including breast, oral, neuroblastoma, leukemic and renal cancer cells (Ho, 1985;Windbichler et al, 1996;Widschwendter et al, 1997;Guzhova et al, 2001;Yang et al, 2001;Hu et al, 2002), but has remained largely unexplored in pancreatic tumour cells and, therefore, raises important questions.…”

Acyl-Coenzyme A:Cholesterol Acyltransferase 2 (ACAT2) Is Induced in Monocyte-Derived Macrophages: In Vivo and In Vitro Studies

“…signals elicited under various pathophysiologic conditions. The signals that up-regulate the expressions of ACAT1 in monocytes-derived macrophage include steroid hormones such as dexamethasone, interferon-␥, and vitamin D 3 Maung et al, 2001;Panousis and Zuckerman, 2000;Yang et al, 2001). In the future, it will be interesting to find out whether these or other agents can up-regulate the ACAT2 expression in macrophages.…”

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

“…We have produced the polyclonal antibody DM58 that specifically recognize the 56-kDa ACAT1 but not the 50-kDa ACAT1. Using antibodies DM58 and DM10 (which recognize both the 50-kDa ACAT1 and the 56-kDa ACAT1) as tools in parallel Western blots, thus far we are able to demonstrate the presence of the 56-kDa ACAT1 protein in PMA-activated THP-1 macrophages, and in human monocyte-derived macrophages; these cells express relatively abundant ACAT1 messages (33), (34). The 56-kDa ACAT1 may also be present in other human tissues and cells, and we are currently investigating this possibility in our laboratories.…”