1
|
Griffett K, Hayes M, Bedia-Diaz G, Appourchaux K, Sanders R, Boeckman MP, Koelblen T, Zhang J, Schulman IG, Elgendy B, Burris TP. Antihyperlipidemic Activity of Gut-Restricted LXR Inverse Agonists. ACS Chem Biol 2022; 17:1143-1154. [PMID: 35417135 DOI: 10.1021/acschembio.2c00057] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Hyperlipidemia and increased circulating cholesterol levels are associated with increased cardiovascular disease risk. The liver X receptors (LXRs) are regulators of de novo lipogenesis and cholesterol transport and have been validated as potential therapeutic targets for the treatment of atherosclerosis. However, efforts to develop LXR agonists to reduce cardiovascular diseases have failed due to poor clinical outcomes-associated increased hepatic lipogenesis and elevated low-density lipoprotein (LDL) cholesterol (C). Here, we report that LXR inverse agonists are effective in lowering plasma LDL cholesterol and triglycerides in several models of hyperlipidemia, including the Ldlr null mouse model of atherosclerosis. Mechanistic studies demonstrate that LXR directly regulates the expression of Soat2 enzyme in the intestine, which is directly responsible for the re-uptake or excretion of circulating lipids. Oral administration of a gut-specific LXR inverse agonist leads to reduction of Soat2 expression in the intestine and effectively lowers circulating LDL cholesterol and triglyceride levels without modulating LXR target genes in the periphery. In summary, our studies highlight the therapeutic potential of the gut-restricted molecules to treat hyperlipidemia and atherosclerosis through the intestinal LXR-Soat2 axis.
Collapse
Affiliation(s)
- Kristine Griffett
- Department of Anatomy, Physiology and Pharmacology, Auburn University College of Veterinary Medicine, Auburn, Alabama 36849, United States
| | - Matthew Hayes
- University of Florida Genetics Institute, Gainesville, Florida 32610, United States
| | - Gonzalo Bedia-Diaz
- Center for Clinical Pharmacology, Washington University School of Medicine and St. Louis College of Pharmacy, St. Louis, Missouri 63110, United States
| | - Kevin Appourchaux
- Center for Clinical Pharmacology, Washington University School of Medicine and St. Louis College of Pharmacy, St. Louis, Missouri 63110, United States
| | - Ryan Sanders
- University of Florida Genetics Institute, Gainesville, Florida 32610, United States
| | - Michael P. Boeckman
- Center for Clinical Pharmacology, Washington University School of Medicine and St. Louis College of Pharmacy, St. Louis, Missouri 63110, United States
| | - Thomas Koelblen
- University of Florida Genetics Institute, Gainesville, Florida 32610, United States
| | - Jinsong Zhang
- Department of Pharmacology & Physiology, Saint Louis University School of Medicine, St. Louis, Missouri 63104, United States
| | - Ira G. Schulman
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia 22903, United States
| | - Bahaa Elgendy
- Center for Clinical Pharmacology, Washington University School of Medicine and St. Louis College of Pharmacy, St. Louis, Missouri 63110, United States
| | - Thomas P. Burris
- University of Florida Genetics Institute, Gainesville, Florida 32610, United States
| |
Collapse
|
2
|
Russo-Savage L, Schulman IG. Liver X receptors and liver physiology. Biochim Biophys Acta Mol Basis Dis 2021; 1867:166121. [PMID: 33713792 DOI: 10.1016/j.bbadis.2021.166121] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Revised: 02/26/2021] [Accepted: 03/01/2021] [Indexed: 12/29/2022]
Abstract
The liver x receptors LXRα (NR1H3) and LXRβ (NR1H2) are members of the nuclear hormone receptor superfamily of ligand dependent transcription factors that regulate transcription in response to the direct binding of cholesterol derivatives. Studies using genetic knockouts and synthetic ligands have defined the LXRs as important modulators of lipid homeostasis throughout the body. This review focuses on the control of cholesterol and fatty acid metabolism by LXRs in the liver and how modifying LXR activity can influence the pathology of liver diseases.
Collapse
Affiliation(s)
- Lillian Russo-Savage
- Department of Pharmacology, University of Virginia, School of Medicine, United States of America
| | - Ira G Schulman
- Department of Pharmacology, University of Virginia, School of Medicine, United States of America.
| |
Collapse
|
3
|
Belorusova AY, Evertsson E, Hovdal D, Sandmark J, Bratt E, Maxvall I, Schulman IG, Åkerblad P, Lindstedt EL. Structural analysis identifies an escape route from the adverse lipogenic effects of liver X receptor ligands. Commun Biol 2019; 2:431. [PMID: 31799433 PMCID: PMC6874530 DOI: 10.1038/s42003-019-0675-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 11/04/2019] [Indexed: 02/08/2023] Open
Abstract
Liver X receptors (LXRs) are attractive drug targets for cardiovascular disease treatment due to their role in regulating cholesterol homeostasis and immunity. The anti-atherogenic properties of LXRs have prompted development of synthetic ligands, but these cause major adverse effects-such as increased lipogenesis-which are challenging to dissect from their beneficial activities. Here we show that LXR compounds displaying diverse functional responses in animal models induce distinct receptor conformations. Combination of hydrogen/deuterium exchange mass spectrometry and multivariate analysis allowed identification of LXR regions differentially correlating with anti-atherogenic and lipogenic activities of ligands. We show that lipogenic compounds stabilize active states of LXRα and LXRβ while the anti-atherogenic expression of the cholesterol transporter ABCA1 is associated with the ligand-induced stabilization of LXRα helix 3. Our data indicates that avoiding ligand interaction with the activation helix 12 while engaging helix 3 may provide directions for development of ligands with improved therapeutic profiles.
Collapse
Affiliation(s)
- Anna Y. Belorusova
- Medicinal Chemistry, Respiratory, Inflammation and Autoimmunity, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Emma Evertsson
- Medicinal Chemistry, Respiratory, Inflammation and Autoimmunity, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Daniel Hovdal
- Preclinical and Translational PK & PKPD, Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Jenny Sandmark
- Structure, Biophysics & Fragment Based Lead Generation, Discovery Sciences, R&D, AstraZeneca, Gothenburg, Sweden
| | - Emma Bratt
- Medicinal Chemistry, Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Ingela Maxvall
- Translational Science and Experimental Medicine, Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D AstraZeneca, Gothenburg, Sweden
| | - Ira G. Schulman
- Department of Pharmacology, University of Virginia, Charlottesville, VA USA
| | - Peter Åkerblad
- Bioscience Heart Failure, Cardiovascular, Renal and Metabolism, Biopharmaceuticals R&D AstraZeneca, Gothenburg, Sweden
- Present Address: Albireo Pharma, Gothenburg, Sweden
| | - Eva-Lotte Lindstedt
- Early Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| |
Collapse
|
4
|
Czimmerer Z, Daniel B, Horvath A, Rückerl D, Nagy G, Kiss M, Peloquin M, Budai MM, Cuaranta-Monroy I, Simandi Z, Steiner L, Nagy B, Poliska S, Banko C, Bacso Z, Schulman IG, Sauer S, Deleuze JF, Allen JE, Benko S, Nagy L. The Transcription Factor STAT6 Mediates Direct Repression of Inflammatory Enhancers and Limits Activation of Alternatively Polarized Macrophages. Immunity 2018; 48:75-90.e6. [PMID: 29343442 PMCID: PMC5772169 DOI: 10.1016/j.immuni.2017.12.010] [Citation(s) in RCA: 154] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Revised: 11/09/2017] [Accepted: 12/11/2017] [Indexed: 11/29/2022]
Abstract
The molecular basis of signal-dependent transcriptional activation has been extensively studied in macrophage polarization, but our understanding remains limited regarding the molecular determinants of repression. Here we show that IL-4-activated STAT6 transcription factor is required for the direct transcriptional repression of a large number of genes during in vitro and in vivo alternative macrophage polarization. Repression results in decreased lineage-determining transcription factor, p300, and RNA polymerase II binding followed by reduced enhancer RNA expression, H3K27 acetylation, and chromatin accessibility. The repressor function of STAT6 is HDAC3 dependent on a subset of IL-4-repressed genes. In addition, STAT6-repressed enhancers show extensive overlap with the NF-κB p65 cistrome and exhibit decreased responsiveness to lipopolysaccharide after IL-4 stimulus on a subset of genes. As a consequence, macrophages exhibit diminished inflammasome activation, decreased IL-1β production, and pyroptosis. Thus, the IL-4-STAT6 signaling pathway establishes an alternative polarization-specific epigenenomic signature resulting in dampened macrophage responsiveness to inflammatory stimuli. IL-4-activated STAT6 acts as a transcriptional repressor in macrophages IL-4-STAT6-repressed enhancers associate with reduced LDTF and p300 binding Inflammatory responsiveness of the IL-4-repressed enhancers is attenuated IL-4 limits the LPS-induced inflammasome activation, IL-1β production, and pyroptosis
Collapse
Affiliation(s)
- Zsolt Czimmerer
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Bence Daniel
- Sanford-Burnham-Prebys Medical Discovery Institute, 6400 Sanger Road, Orlando, FL 32827, USA
| | - Attila Horvath
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Dominik Rückerl
- Faculty of Biology, Medicine and Health, School of Biological Sciences, University of Manchester, Manchester, UK
| | - Gergely Nagy
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary; MTA-DE "Lendület" Immunogenomics Research Group, University of Debrecen, Debrecen, Hungary
| | - Mate Kiss
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Matthew Peloquin
- Sanford-Burnham-Prebys Medical Discovery Institute, 6400 Sanger Road, Orlando, FL 32827, USA
| | - Marietta M Budai
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Ixchelt Cuaranta-Monroy
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Zoltan Simandi
- Sanford-Burnham-Prebys Medical Discovery Institute, 6400 Sanger Road, Orlando, FL 32827, USA
| | - Laszlo Steiner
- UD-Genomed Medical Genomic Technologies Ltd., Debrecen, Hungary
| | - Bela Nagy
- Department of Laboratory Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Szilard Poliska
- Genomic Medicine and Bioinformatic Core Facility, Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Csaba Banko
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Zsolt Bacso
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Ira G Schulman
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA
| | - Sascha Sauer
- Otto Warburg Laboratory, Max Planck Institute for Molecular Genetics, Berlin, Germany; CU Systems Medicine, University of Würzburg, Würzburg, Germany; Max Delbrück Center for Molecular Medicine (BIMSB and BIH), Berlin, Germany
| | | | - Judith E Allen
- Faculty of Biology, Medicine and Health, School of Biological Sciences, University of Manchester, Manchester, UK
| | - Szilvia Benko
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Laszlo Nagy
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary; Sanford-Burnham-Prebys Medical Discovery Institute, 6400 Sanger Road, Orlando, FL 32827, USA; MTA-DE "Lendület" Immunogenomics Research Group, University of Debrecen, Debrecen, Hungary.
| |
Collapse
|
5
|
Adamson SE, Polanowska-Grabowska R, Marqueen K, Griffiths R, Angdisen J, Breevoort SR, Schulman IG, Leitinger N. Deficiency of Dab2 (Disabled Homolog 2) in Myeloid Cells Exacerbates Inflammation in Liver and Atherosclerotic Plaques in LDLR (Low-Density Lipoprotein Receptor)-Null Mice-Brief Report. Arterioscler Thromb Vasc Biol 2018; 38:1020-1029. [PMID: 29599136 DOI: 10.1161/atvbaha.117.310467] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 03/06/2018] [Indexed: 02/05/2023]
Abstract
OBJECTIVE Inflammatory macrophages promote the development of atherosclerosis. We have identified the adaptor protein Dab2 (disabled homolog 2) as a regulator of phenotypic polarization in macrophages. The absence of Dab2 in myeloid cells promotes an inflammatory phenotype, but the impact of myeloid Dab2 deficiency on atherosclerosis has not been shown. APPROACH AND RESULTS To determine the role of myeloid Dab2 in atherosclerosis, Ldlr-/- mice were reconstituted with either Dab2-positive or Dab2-deficient bone marrow and fed a western diet. Consistent with our previous finding that Dab2 inhibits NFκB (nuclear factor κ-light-chain-enhancer of activated B cells) signaling in macrophages, Ldlr-/- mice reconstituted with Dab2-deficient bone marrow had increased systemic inflammation as evidenced by increased serum IL-6 (interleukin-6) levels and increased inflammatory cytokine expression levels in liver. Serum lipid levels were significantly lower in Ldlr-/- mice reconstituted with Dab2-deficient bone marrow, and further examination of livers from these mice revealed drastically increased inflammatory tissue damage and massive infiltration of immune cells. Surprisingly, the atherosclerotic lesion burden in Ldlr-/- mice reconstituted with Dab2-deficient bone marrow was decreased compared with Ldlr-/- mice reconstituted with wild-type bone marrow. Further analysis of aortic root sections revealed increased macrophage content and evidence of increased apoptosis in lesions from Ldlr-/- mice reconstituted with Dab2-deficient bone marrow but no difference in collagen or α-smooth muscle actin content. CONCLUSIONS Dab2 deficiency in myeloid cells promotes inflammation in livers and atherosclerotic plaques in a mouse model of atherosclerosis. Nevertheless, decreased serum lipids as a result of massive inflammatory liver damage may preclude an appreciable increase in atherosclerotic lesion burden in mice reconstituted with Dab2-deficient bone marrow.
Collapse
Affiliation(s)
- Samantha E Adamson
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.).,Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville (S.E.A., R.P.-G., R.G., N.L.)
| | - Renata Polanowska-Grabowska
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.).,Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville (S.E.A., R.P.-G., R.G., N.L.)
| | - Kathryn Marqueen
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.)
| | - Rachael Griffiths
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.).,Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville (S.E.A., R.P.-G., R.G., N.L.)
| | - Jerry Angdisen
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.)
| | - Sarah R Breevoort
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.)
| | - Ira G Schulman
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.)
| | - Norbert Leitinger
- From the Department of Pharmacology (S.E.A., R.P.-G., K.M., R.G., J.A., S.R.B., I.G.S., N.L.) .,Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville (S.E.A., R.P.-G., R.G., N.L.)
| |
Collapse
|
6
|
Abstract
The response of immune cells to pathogens is often associated with changes in the flux through basic metabolic pathways. Indeed, in many cases changes in metabolism appear to be necessary for a robust immune response. The Liver X receptors (LXRs) are members of the nuclear hormone receptor superfamily that regulate gene networks controlling cholesterol and lipid metabolism. In immune cells, particularly in macrophages, LXRs also inhibit proinflammatory gene expression. This Review will highlight recent studies that connect LXR-dependent control of lipid metabolism to regulation of the immune response.
Collapse
Affiliation(s)
- Ira G Schulman
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, VA, USA
| |
Collapse
|
7
|
Gaykema RP, Newmyer BA, Ottolini M, Raje V, Warthen DM, Lambeth PS, Niccum M, Yao T, Huang Y, Schulman IG, Harris TE, Patel MK, Williams KW, Scott MM. Activation of murine pre-proglucagon-producing neurons reduces food intake and body weight. J Clin Invest 2017; 127:1031-1045. [PMID: 28218622 DOI: 10.1172/jci81335] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 12/30/2016] [Indexed: 12/14/2022] Open
Abstract
Peptides derived from pre-proglucagon (GCG peptides) act in both the periphery and the CNS to change food intake, glucose homeostasis, and metabolic rate while playing a role in anxiety behaviors and physiological responses to stress. Although the actions of GCG peptides produced in the gut and pancreas are well described, the role of glutamatergic GGC peptide-secreting hindbrain neurons in regulating metabolic homeostasis has not been investigated. Here, we have shown that chemogenetic stimulation of GCG-producing neurons reduces metabolic rate and food intake in fed and fasted states and suppresses glucose production without an effect on glucose uptake. Stimulation of GCG neurons had no effect on corticosterone secretion, body weight, or conditioned taste aversion. In the diet-induced obese state, the effects of GCG neuronal stimulation on gluconeogenesis were lost, while the food intake-lowering effects remained, resulting in reductions in body weight and adiposity. Our work suggests that GCG peptide-expressing neurons can alter feeding, metabolic rate, and glucose production independent of their effects on hypothalamic pituitary-adrenal (HPA) axis activation, aversive conditioning, or insulin secretion. We conclude that GCG neurons likely stimulate separate populations of downstream cells to produce a change in food intake and glucose homeostasis and that these effects depend on the metabolic state of the animal.
Collapse
|
8
|
Kick EK, Busch BB, Martin R, Stevens WC, Bollu V, Xie Y, Boren BC, Nyman MC, Nanao MH, Nguyen L, Plonowski A, Schulman IG, Yan G, Zhang H, Hou X, Valente MN, Narayanan R, Behnia K, Rodrigues AD, Brock B, Smalley J, Cantor GH, Lupisella J, Sleph P, Grimm D, Ostrowski J, Wexler RR, Kirchgessner T, Mohan R. Discovery of Highly Potent Liver X Receptor β Agonists. ACS Med Chem Lett 2016; 7:1207-1212. [PMID: 27994765 PMCID: PMC5150697 DOI: 10.1021/acsmedchemlett.6b00234] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Accepted: 09/27/2016] [Indexed: 12/13/2022] Open
Abstract
![]()
Introducing a uniquely substituted
phenyl sulfone into a series
of biphenyl imidazole liver X receptor (LXR) agonists afforded a dramatic
potency improvement for induction of ATP binding cassette transporters,
ABCA1 and ABCG1, in human whole blood. The agonist series demonstrated
robust LXRβ activity (>70%) with low partial LXRα agonist
activity (<25%) in cell assays, providing a window between desired
blood cell ABCG1 gene induction in cynomolgus monkeys and modest elevation
of plasma triglycerides for agonist 15. The addition
of polarity to the phenyl sulfone also reduced binding to the plasma
protein, human α-1-acid glycoprotein. Agonist 15 was selected for clinical development based on the favorable combination
of in vitro properties, excellent pharmacokinetic
parameters, and a favorable lipid profile.
Collapse
Affiliation(s)
| | - Brett B. Busch
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Richard Martin
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - William C. Stevens
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Venkataiah Bollu
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Yinong Xie
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Brant C. Boren
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Michael C. Nyman
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Max H. Nanao
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Lam Nguyen
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Artur Plonowski
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Ira G. Schulman
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | - Grace Yan
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Raju Mohan
- Exelixis Inc., 210 East Grand
Avenue, South San Francisco, California 94080, United States
| |
Collapse
|
9
|
Fond AM, Lee CS, Schulman IG, Kiss RS, Ravichandran KS. Apoptotic cells trigger a membrane-initiated pathway to increase ABCA1. J Clin Invest 2015; 125:2748-58. [PMID: 26075824 DOI: 10.1172/jci80300] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 05/12/2015] [Indexed: 01/15/2023] Open
Abstract
Macrophages clear millions of apoptotic cells daily and, during this process, take up large quantities of cholesterol. The membrane transporter ABCA1 is a key player in cholesterol efflux from macrophages and has been shown via human genetic studies to provide protection against cardiovascular disease. How the apoptotic cell clearance process is linked to macrophage ABCA1 expression is not known. Here, we identified a plasma membrane-initiated signaling pathway that drives a rapid upregulation of ABCA1 mRNA and protein. This pathway involves the phagocytic receptor brain-specific angiogenesis inhibitor 1 (BAI1), which recognizes phosphatidylserine on apoptotic cells, and the intracellular signaling intermediates engulfment cell motility 1 (ELMO1) and Rac1, as ABCA1 induction was attenuated in primary macrophages from mice lacking these molecules. Moreover, this apoptotic cell-initiated pathway functioned independently of the liver X receptor (LXR) sterol-sensing machinery that is known to regulate ABCA1 expression and cholesterol efflux. When placed on a high-fat diet, mice lacking BAI1 had increased numbers of apoptotic cells in their aortic roots, which correlated with altered lipid profiles. In contrast, macrophages from engineered mice with transgenic BAI1 overexpression showed greater ABCA1 induction in response to apoptotic cells compared with those from control animals. Collectively, these data identify a membrane-initiated pathway that is triggered by apoptotic cells to enhance ABCA1 within engulfing phagocytes and with functional consequences in vivo.
Collapse
|
10
|
Abstract
OBJECTIVE The ability of high-density lipoprotein (HDL) particles to accept cholesterol from peripheral cells, such as lipid-laden macrophages, and to transport cholesterol to the liver for catabolism and excretion in a process termed reverse cholesterol transport (RCT) is thought to underlie the beneficial cardiovascular effects of elevated HDL. The liver X receptors (LXRs; LXRα and LXRβ) regulate RCT by controlling the efflux of cholesterol from macrophages to HDL and the excretion, catabolism, and absorption of cholesterol in the liver and intestine. Importantly, treatment with LXR agonists increases RCT and decreases atherosclerosis in animal models. Nevertheless, LXRs are expressed in multiple tissues involved in RCT, and their tissue-specific contributions to RCT are still not well defined. APPROACH AND RESULTS Using tissue-specific LXR deletions together with in vitro and in vivo assays of cholesterol efflux and fecal cholesterol excretion, we demonstrate that macrophage LXR activity is neither necessary nor sufficient for LXR agonist-stimulated RCT. In contrast, the ability of LXR agonists primarily acting in the intestine to increase HDL mass and HDL function seems to underlie the ability of LXR agonists to stimulate RCT in vivo. CONCLUSIONS We demonstrate that activation of LXR in macrophages makes little or no contribution to LXR agonist-stimulated RCT. Unexpectedly, our studies suggest that the ability of macrophages to efflux cholesterol to HDL in vivo is not regulated by macrophage activity but is primarily determined by the quantity and functional activity of HDL.
Collapse
Affiliation(s)
- Sarah R Breevoort
- From the Department of Pharmacology, University of Virginia, Charlottesville
| | - Jerry Angdisen
- From the Department of Pharmacology, University of Virginia, Charlottesville
| | - Ira G Schulman
- From the Department of Pharmacology, University of Virginia, Charlottesville.
| |
Collapse
|
11
|
Affiliation(s)
- Irena D Ignatova
- From the Department of Pharmacology, University of Virginia Health System, Charlottesville
| | | |
Collapse
|
12
|
Ignatova ID, Angdisen J, Moran E, Schulman IG. Differential regulation of gene expression by LXRs in response to macrophage cholesterol loading. Mol Endocrinol 2013; 27:1036-47. [PMID: 23686114 DOI: 10.1210/me.2013-1051] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The ability of cells to precisely control gene expression in response to intracellular and extracellular signals plays an important role in both normal physiology and in pathological settings. For instance, the accumulation of excess cholesterol by macrophages initiates a genetic response mediated by the liver X receptors (LXRs)-α (NR1H3) and LXRβ (NR1H2), which facilitates the transport of cholesterol out of cells to high-density lipoprotein particles. Studies using synthetic LXR agonists have also demonstrated that macrophage LXR activation simultaneously induces a second network of genes that promotes fatty acid and triglyceride synthesis that may support the detoxification of excess free cholesterol by storage in the ester form. We now show that treatment of human THP-1 macrophages with endogenous or synthetic LXR ligands stimulates both transcriptional and posttranscriptional pathways that result in the selective recruitment of the LXRα subtype to LXR-regulated promoters. Interestingly, when human or mouse macrophages are loaded with cholesterol under conditions that mimic the development of atherogenic macrophage foam cells, a selective LXR response is generated that induces genes mediating cholesterol transport but does not coordinately regulate genes involved in fatty acid synthesis. The gene-selective response to cholesterol loading occurs, even in the presence of LXRα binding to the promoter of the gene encoding the sterol regulatory element-binding protein-1c, the master transcriptional regulator of fatty acid synthesis. The ability of promoter bound LXRα to recruit RNA polymerase to the sterol regulatory element-binding protein-1c promoter, however, appears to be ligand selective.
Collapse
Affiliation(s)
- Irena D Ignatova
- Department of Pharmacology, University of Virginia, 1300 Jefferson Park Avenue, PO Box 800735, Charlottesville, Virginia 22908, USA.
| | | | | | | |
Collapse
|
13
|
Abstract
Macrophages orchestrate the inflammatory response in inflamed tissues, and recent work indicates that these cells can alter their phenotypes and functions accordingly in response to changes in the microenvironment. Initial work in models of cardiovascular disease used immunologic markers to characterize macrophage phenotypes present in atherosclerotic plaque, and these studies have lately been extended through the use of markers that are more specific for atherosclerosis and metabolic disease. Together, these studies have led to a novel view of the function of macrophages in the development of atherosclerosis that suggests dynamic plasticity. Understanding this plasticity and the ensuing macrophage heterogeneity could lead to novel strategies of pharmacological intervention to combat chronic inflammation in metabolic diseases. Most importantly, revealing the functional characteristics of individual macrophage phenotypes will lead to a better understanding of their contribution to lesion development and plaque stability.
Collapse
Affiliation(s)
- Norbert Leitinger
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908-0735, USA.
| | | |
Collapse
|
14
|
Zhang Y, Breevoort SR, Angdisen J, Fu M, Schmidt DR, Holmstrom SR, Kliewer SA, Mangelsdorf DJ, Schulman IG. Liver LXRα expression is crucial for whole body cholesterol homeostasis and reverse cholesterol transport in mice. J Clin Invest 2012; 122:1688-99. [PMID: 22484817 DOI: 10.1172/jci59817] [Citation(s) in RCA: 149] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Accepted: 02/22/2012] [Indexed: 12/15/2022] Open
Abstract
Liver X receptors (LXRα and LXRβ) are important regulators of cholesterol and lipid metabolism, and their activation has been shown to inhibit cardiovascular disease and reduce atherosclerosis in animal models. Small molecule agonists of LXR activity are therefore of great therapeutic interest. However, the finding that such agonists also promote hepatic lipogenesis has led to the idea that hepatic LXR activity is undesirable from a therapeutic perspective. To investigate whether this might be true, we performed gene targeting to selectively delete LXRα in hepatocytes. Liver-specific deletion of LXRα in mice substantially decreased reverse cholesterol transport, cholesterol catabolism, and cholesterol excretion, revealing the essential importance of hepatic LXRα for whole body cholesterol homeostasis. Additionally, in a pro-atherogenic background, liver-specific deletion of LXRα increased atherosclerosis, uncovering an important function for hepatic LXR activity in limiting cardiovascular disease. Nevertheless, synthetic LXR agonists still elicited anti-atherogenic activity in the absence of hepatic LXRα, indicating that the ability of agonists to reduce cardiovascular disease did not require an increase in cholesterol excretion. Furthermore, when non-atherogenic mice were treated with synthetic LXR agonists, liver-specific deletion of LXRα eliminated the detrimental effect of increased plasma triglycerides, while the beneficial effect of increased plasma HDL was unaltered. In sum, these observations suggest that therapeutic strategies that bypass the liver or limit the activation of hepatic LXRs should still be beneficial for the treatment of cardiovascular disease.
Collapse
Affiliation(s)
- Yuan Zhang
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Cheng F, Theodorescu D, Schulman IG, Lee JK. In vitro transcriptomic prediction of hepatotoxicity for early drug discovery. J Theor Biol 2011; 290:27-36. [PMID: 21884709 DOI: 10.1016/j.jtbi.2011.08.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [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] [Received: 05/27/2011] [Revised: 07/27/2011] [Accepted: 08/11/2011] [Indexed: 01/08/2023]
Abstract
Liver toxicity (hepatotoxicity) is a critical issue in drug discovery and development. Standard preclinical evaluation of drug hepatotoxicity is generally performed using in vivo animal systems. However, only a small number of preselected compounds can be examined in vivo due to high experimental costs. A more efficient yet accurate screening technique that can identify potentially hepatotoxic compounds in the early stages of drug development would thus be valuable. Here, we develop and apply a novel genomic prediction technique for screening hepatotoxic compounds based on in vitro human liver cell tests. Using a training set of in vivo rodent experiments for drug hepatotoxicity evaluation, we discovered common biomarkers of drug-induced liver toxicity among six heterogeneous compounds. This gene set was further triaged to a subset of 32 genes that can be used as a multi-gene expression signature to predict hepatotoxicity. This multi-gene predictor was independently validated and showed consistently high prediction performance on five test sets of in vitro human liver cell and in vivo animal toxicity experiments. The predictor also demonstrated utility in evaluating different degrees of toxicity in response to drug concentrations, which may be useful not only for discerning a compound's general hepatotoxicity but also for determining its toxic concentration.
Collapse
Affiliation(s)
- Feng Cheng
- Department of Biophysics, University of Virginia, Charlottesville, VA, USA.
| | | | | | | |
Collapse
|
16
|
Schulman IG. Nuclear receptors as drug targets for metabolic disease. Adv Drug Deliv Rev 2010; 62:1307-15. [PMID: 20655343 DOI: 10.1016/j.addr.2010.07.002] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Revised: 07/06/2010] [Accepted: 07/14/2010] [Indexed: 01/02/2023]
Abstract
Nuclear hormone receptors comprise a superfamily of ligand-activated transcription factors that control development, differentiation, and homeostasis. Over the last 15 years a growing number of nuclear receptors have been identified that coordinate genetic networks regulating lipid metabolism and energy utilization. Several of these receptors directly sample the levels of metabolic intermediates including fatty acids and cholesterol derivatives and use this information to regulate the synthesis, transport, and breakdown of the metabolite of interest. In contrast, other family members sense metabolic activity via the presence or absence of interacting proteins. The ability of these nuclear receptors to impact metabolism will be discussed and the challenges facing drug discovery efforts for this class of targets will be highlighted.
Collapse
|
17
|
Bischoff ED, Daige CL, Petrowski M, Dedman H, Pattison J, Juliano J, Li AC, Schulman IG. Non-redundant roles for LXRalpha and LXRbeta in atherosclerosis susceptibility in low density lipoprotein receptor knockout mice. J Lipid Res 2010; 51:900-6. [PMID: 20388921 DOI: 10.1194/jlr.m900096] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The liver X receptors LXRalpha and LXRbeta play critical roles in maintaining lipid homeostasis by functioning as transcription factors that regulate genetic networks controlling the transport, catabolism, and excretion of cholesterol. The studies described in this report examine the individual anti-atherogenic activity of LXRalpha and LXRbeta and determine the ability of each subtype to mediate the biological response to LXR agonists. Utilizing individual knockouts of LXRalpha and LXRbeta in the Ldlr(-/-) background, we demonstrate that LXRalpha has a dominant role in limiting atherosclerosis in vivo. Functional studies in macrophages indicate that LXRalpha is required for a robust response to LXR ligands, whereas LXRbeta functions more strongly as a repressor. Furthermore, selective knockout of LXRalpha in hematopoietic cells and rescue experiments indicate that the anti-atherogenic activity of this LXR subtype is not restricted to macrophages. These studies indicate that LXRalpha plays a selective role in limiting atherosclerosis in response to hyperlipidemia.
Collapse
|
18
|
Bischoff ED, Daige CL, Petrowski M, Dedman H, Pattison J, Juliano J, Li AC, Schulman IG. Non-redundant roles for LXRα and LXRβ in atherosclerosis susceptibility in low density lipoprotein receptor knockout mice. J Lipid Res 2010. [DOI: 10.1194/jlr.m900096-jlr200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
|
19
|
Abstract
The worldwide epidemic of metabolic disease indicates that a better understanding of the pathways contributing to the pathogenesis of this constellation of diseases need to be determined. Nuclear hormone receptors comprise a superfamily of ligand-activated transcription factors that control development, differentiation, and metabolism. Over the last 15 years a growing number of nuclear receptors have been identified that coordinate genetic networks regulating lipid metabolism and energy utilization. Several of these receptors directly sample the levels of metabolic intermediates and use this information to regulate the synthesis, transport, and breakdown of the metabolite of interest. In contrast, other family members sense metabolic activity via the presence or absence of interacting proteins. The ability of these nuclear receptors to impact metabolism and inflammation will be discussed and the potential of each receptor subfamily to serve as drug targets for metabolic disease will be highlighted.
Collapse
Affiliation(s)
- Huey-Jing Huang
- Department of Biology, Exelixis Inc., 4757 Nexus Centre Drive, San Diego, California 92121, USA
| | | |
Collapse
|
20
|
Abstract
The farnesoid X receptor (FXR; NR1H4) is an intracellular bile acid-sensing transcription factor that plays a critical role in the regulation of synthesis and transport of bile acids as well as lipid metabolism. Although the reciprocal relationship between bile acid and triglyceride levels is well known, the mechanism underlying this link is not clearly defined. In this study, we demonstrate that FXR regulates the expression of at least two secreted factors, complement component C3 and FGF15, the rat ortholog of FGF19, known to influence lipid metabolism. The analysis of the human complement C3 gene reveals the presence of functional FXR response elements in the proximal promoter of C3. Furthermore, rats given a single dose of an FXR agonist exhibit an increase in the plasma concentration of complement C3 protein. These studies demonstrate a mechanism by which FXR, a nuclear receptor with a limited tissue expression pattern, regulates secretion of factors that ultimately can affect lipid metabolism in an endocrine or paracrine manner.
Collapse
MESH Headings
- Animals
- Base Sequence
- Bile Acids and Salts/metabolism
- Binding Sites
- Blotting, Northern
- Blotting, Western
- Caco-2 Cells
- Cell Line
- Cell Line, Tumor
- Cell Membrane/metabolism
- Cell Nucleus/metabolism
- Complement C3/biosynthesis
- Complement C3/genetics
- DNA Primers/chemistry
- DNA, Complementary/metabolism
- DNA-Binding Proteins/metabolism
- Electrophoresis, Polyacrylamide Gel
- Fibroblast Growth Factors/metabolism
- Genes, Reporter
- Genetic Complementation Test
- Humans
- Ligands
- Lipid Metabolism
- Luciferases/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Models, Genetic
- Molecular Sequence Data
- Mucous Membrane/pathology
- Oligonucleotides/chemistry
- Promoter Regions, Genetic
- RNA, Messenger/metabolism
- Rats
- Rats, Inbred F344
- Receptors, Cytoplasmic and Nuclear
- Reverse Transcriptase Polymerase Chain Reaction
- Time Factors
- Transcription Factors/metabolism
- Transfection
- Triglycerides/metabolism
Collapse
Affiliation(s)
- Jiali Li
- Department of Biology, X-Ceptor Therapeutics Inc., San Diego, California 92121, USA
| | | | | | | |
Collapse
|
21
|
Abstract
Members of the nuclear hormone receptor superfamily function as ligand-activated transcription factors to regulate genetic networks controlling cell growth and differentiation, inflammatory responses, and metabolism. The ability to modulate nuclear receptor-dependent gene expression with small molecules has made the superfamily a favored target for drug discovery. Not surprisingly, small molecules that regulate receptor activity are currently used to treat a number of human disorders. Over the last 10 years, the availability of a common platform of functional assays suitable for any nuclear receptor has facilitated the identification of endogenous and synthetic ligands that have been used as tools to uncover previously unanticipated endocrine signaling pathways. Recent progress in understanding the molecular basis for ligand-dependent gene regulation suggests that a new era of "designer" ligands with tissue- and/or gene-selective activity will quickly be upon us.
Collapse
Affiliation(s)
- Ira G Schulman
- X-Ceptor Therapeutics, 4756 Nexus Center Drive, Suite 200, San Diego, CA 92121 USA.
| | | |
Collapse
|
22
|
Levin N, Bischoff ED, Daige CL, Thomas D, Vu CT, Heyman RA, Tangirala RK, Schulman IG. Macrophage Liver X Receptor Is Required for Antiatherogenic Activity of LXR Agonists. Arterioscler Thromb Vasc Biol 2005; 25:135-42. [PMID: 15539622 DOI: 10.1161/01.atv.0000150044.84012.68] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [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: 11/16/2022]
Abstract
Objective—
Complications of atherosclerotic cardiovascular disease due to elevated blood cholesterol levels are the major cause of death in the Western world. The liver X receptors, LXRα and LXRβ (LXRs), are ligand-dependent transcription factors that act as cholesterol sensors and coordinately control transcription of genes involved in cholesterol and lipid homeostasis as well as macrophage inflammatory gene expression. LXRs regulate cholesterol balance through activation of ATP-binding cassette transporters that promote cholesterol transport and excretion from the liver, intestine, and macrophage. Although LXR agonists are known to delay progression of atherosclerosis in mouse models, their ability to abrogate preexisting cardiovascular disease by inducing regression and stabilization of established atherosclerotic lesions has not been addressed.
Methods and Results—
We demonstrate that LXR agonist treatment increases ATP-binding cassette transporter expression within preexisting atherosclerotic lesions, resulting in regression of these lesions as well as remodeling from vulnerable to stable lesions and a reduction in macrophage content. Further, using macrophage-selective LXR-deficient mice created by bone marrow transplantation, we provide the first evidence that macrophage LXR expression is necessary for the atheroprotective actions of an LXR agonist.
Conclusions—
These data substantiate that drugs targeting macrophage LXR activity may offer therapeutic benefit in the treatment of atherosclerotic cardiovascular disease.
Collapse
Affiliation(s)
- Nancy Levin
- X-Ceptor Therapeutics Inc, San Diego, Calif 92121, USA
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Willy PJ, Murray IR, Qian J, Busch BB, Stevens WC, Martin R, Mohan R, Zhou S, Ordentlich P, Wei P, Sapp DW, Horlick RA, Heyman RA, Schulman IG. Regulation of PPARgamma coactivator 1alpha (PGC-1alpha) signaling by an estrogen-related receptor alpha (ERRalpha) ligand. Proc Natl Acad Sci U S A 2004; 101:8912-7. [PMID: 15184675 PMCID: PMC428446 DOI: 10.1073/pnas.0401420101] [Citation(s) in RCA: 150] [Impact Index Per Article: 7.5] [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: 02/27/2004] [Indexed: 02/07/2023] Open
Abstract
Peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator 1alpha (PGC-1alpha) is a transcriptional coactivator that is a key component in the regulation of energy production and utilization in metabolic tissues. Recent work has identified PGC-1alpha as a strong coactivator of the orphan nuclear receptor estrogen-related receptor alpha (ERRalpha), implicating ERRalpha as a potential mediator of PGC-1alpha action. To understand the role of ERRalpha in PGC-1alpha signaling, a parallel approach of high-throughput screening and gene-expression analysis was used to identify ERRalpha small-molecule regulators and target genes. We report here the identification of a potent and selective ERRalpha inverse agonist that interferes effectively with PGC-1alpha/ERRalpha-dependent signaling. This inverse agonist inhibits the constitutive activity of ERRalpha in both biochemical and cell-based assays. Also, we demonstrate that monoamine oxidase B is an ERRalpha target gene whose expression is regulated by PGC-1alpha and ERRalpha and inhibited by the ERRalpha inverse agonist. The discovery of potent and selective ERRalpha modulators and their effect on PGC-1alpha signaling provides mechanistic insight into gene regulation by PGC-1alpha. These findings validate ERRalpha as a promising therapeutic target in the treatment of metabolic disorders, including diabetes and obesity.
Collapse
MESH Headings
- Animals
- Base Sequence
- Cell Line
- Cell Line, Tumor
- Chlorocebus aethiops
- Fluorescence Polarization
- Gene Expression
- HeLa Cells
- Heat-Shock Proteins/antagonists & inhibitors
- Heat-Shock Proteins/metabolism
- Humans
- Ligands
- Mice
- Molecular Sequence Data
- Monoamine Oxidase/biosynthesis
- Monoamine Oxidase/genetics
- Mutation
- Nitriles/chemistry
- Nitriles/pharmacology
- Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
- Promoter Regions, Genetic/genetics
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Cytoplasmic and Nuclear/physiology
- Receptors, Estrogen/agonists
- Receptors, Estrogen/genetics
- Receptors, Estrogen/metabolism
- Receptors, Estrogen/physiology
- Recombinant Proteins/agonists
- Recombinant Proteins/genetics
- Recombinant Proteins/metabolism
- Signal Transduction
- Thiazoles/chemistry
- Thiazoles/pharmacology
- Transcription Factors/antagonists & inhibitors
- Transcription Factors/metabolism
- Transfection
- ERRalpha Estrogen-Related Receptor
Collapse
Affiliation(s)
- Patricia J Willy
- Department of Biology, X-Ceptor Therapeutics, Inc., San Diego, CA 92121, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Mootha VK, Handschin C, Arlow D, Xie X, St Pierre J, Sihag S, Yang W, Altshuler D, Puigserver P, Patterson N, Willy PJ, Schulman IG, Heyman RA, Lander ES, Spiegelman BM. Erralpha and Gabpa/b specify PGC-1alpha-dependent oxidative phosphorylation gene expression that is altered in diabetic muscle. Proc Natl Acad Sci U S A 2004; 101:6570-5. [PMID: 15100410 PMCID: PMC404086 DOI: 10.1073/pnas.0401401101] [Citation(s) in RCA: 529] [Impact Index Per Article: 26.5] [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: 12/31/2022] Open
Abstract
Recent studies have shown that genes involved in oxidative phosphorylation (OXPHOS) exhibit reduced expression in skeletal muscle of diabetic and prediabetic humans. Moreover, these changes may be mediated by the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha). By combining PGC-1alpha-induced genome-wide transcriptional profiles with a computational strategy to detect cis-regulatory motifs, we identified estrogen-related receptor alpha (Erralpha) and GA repeat-binding protein alpha as key transcription factors regulating the OXPHOS pathway. Interestingly, the genes encoding these two transcription factors are themselves PGC-1alpha-inducible and contain variants of both motifs near their promoters. Cellular assays confirmed that Erralpha and GA-binding protein a partner with PGC-1alpha in muscle to form a double-positive-feedback loop that drives the expression of many OXPHOS genes. By using a synthetic inhibitor of Erralpha, we demonstrated its key role in PGC-1alpha-mediated effects on gene regulation and cellular respiration. These results illustrate the dissection of gene regulatory networks in a complex mammalian system, elucidate the mechanism of PGC-1alpha action in the OXPHOS pathway, and suggest that Erralpha agonists may ameliorate insulin-resistance in individuals with type 2 diabetes mellitus.
Collapse
Affiliation(s)
- Vamsi K Mootha
- The Eli and Edythe L. Broad Institute, Massachusetts Institute of Technology and Harvard University, Cambridge, MA 02139-1561, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
25
|
Wagner BL, Valledor AF, Shao G, Daige CL, Bischoff ED, Petrowski M, Jepsen K, Baek SH, Heyman RA, Rosenfeld MG, Schulman IG, Glass CK. Promoter-specific roles for liver X receptor/corepressor complexes in the regulation of ABCA1 and SREBP1 gene expression. Mol Cell Biol 2003; 23:5780-9. [PMID: 12897148 PMCID: PMC166346 DOI: 10.1128/mcb.23.16.5780-5789.2003] [Citation(s) in RCA: 188] [Impact Index Per Article: 9.0] [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: 12/22/2022] Open
Abstract
Liver X receptors (LXRs) regulate the expression of genes involved in cholesterol and fatty acid homeostasis, including the genes for ATP-binding cassette transporter A1 (ABCA1) and sterol response element binding protein 1 (SREBP1). Loss of LXR leads to derepression of the ABCA1 gene in macrophages and the intestine, while the SREBP1c gene remains transcriptionally silent. Here we report that high-density-lipoprotein (HDL) cholesterol levels are increased in LXR-deficient mice, suggesting that derepression of ABCA1 and possibly other LXR target genes in selected tissues is sufficient to result in enhanced HDL biogenesis at the whole-body level. We provide several independent lines of evidence indicating that the repressive actions of LXRs are dependent on interactions with the nuclear receptor corepressor (NCoR) and the silencing mediator of retinoic acid and thyroid hormone receptors (SMRT). While dissociation of NCoR and SMRT results in derepression of the ABCA1 gene in macrophages, it is not sufficient for derepression of the SREBP1c gene. These findings reveal differential requirements for corepressors in the regulation of genes involved in cholesterol and fatty acid homeostasis and raise the possibility that these interactions may be exploited to develop synthetic ligands that selectively modulate LXR actions in vivo.
Collapse
|
26
|
Pircher PC, Kitto JL, Petrowski ML, Tangirala RK, Bischoff ED, Schulman IG, Westin SK. Farnesoid X receptor regulates bile acid-amino acid conjugation. J Biol Chem 2003; 278:27703-11. [PMID: 12754200 DOI: 10.1074/jbc.m302128200] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.3] [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: 11/06/2022] Open
Abstract
The farnesoid X receptor (FXR; NR1H4) regulates bile acid and lipid homeostasis by acting as an intracellular bile acid-sensing transcription factor. Several identified FXR target genes serve critical roles in the synthesis and transport of bile acids as well as in lipid metabolism. Here we used Affymetrix micro-array and Northern analysis to demonstrate that two enzymes involved in conjugation of bile acids to taurine and glycine, namely bile acid-CoA synthetase (BACS) and bile acid-CoA: amino acid N-acetyltransferase (BAT) are induced by FXR in rat liver. Analysis of the human BACS and BAT genes revealed the presence of functional response elements in the proximal promoter of BACS and in the intronic region between exons 1 and 2 of the BAT gene. The response elements resemble the consensus FXR binding site consisting of two nuclear receptor half-sites organized as an inverted repeat and separated by a single nucleotide (IR-1). These response elements directly bind FXR/retinoid X receptor (RXR) heterodimers and confer the activity of FXR ligands in transient transfection experiments. Further mutational analysis confirms that the IR-1 sequence of the BACS and BAT genes mediate transactivation by FXR/RXR heterodimers. Finally, Fisher rats treated with the synthetic FXR ligand GW4064 clearly show increased transcript levels of both the BACS and BAT mRNA. These studies demonstrate a mechanism by which FXR regulates bile acid amidation, a critical component of the enterohepatic circulation of bile acids.
Collapse
Affiliation(s)
- Parinaz C Pircher
- Department of Biology, X-Ceptor Therapeutics Inc., San Diego, California 92121, USA
| | | | | | | | | | | | | |
Collapse
|
27
|
Muscat GEO, Wagner BL, Hou J, Tangirala RK, Bischoff ED, Rohde P, Petrowski M, Li J, Shao G, Macondray G, Schulman IG. Regulation of cholesterol homeostasis and lipid metabolism in skeletal muscle by liver X receptors. J Biol Chem 2002; 277:40722-8. [PMID: 12193599 DOI: 10.1074/jbc.m206681200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [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: 11/06/2022] Open
Abstract
Recent studies have identified the liver X receptors (LXRalpha and LXRbeta) as important regulators of cholesterol and lipid metabolism. Although originally identified as liver-enriched transcription factors, LXRs are also expressed in skeletal muscle, a tissue that accounts for approximately 40% of human total body weight and is the major site of glucose utilization and fatty acid oxidation. Nevertheless, no studies have yet addressed the functional role of LXRs in muscle. In this work we utilize a combination of in vivo and in vitro analysis to demonstrate that LXRs can functionally regulate genes involved in cholesterol metabolism in skeletal muscle. Furthermore we show that treatment of muscle cells in vitro with synthetic agonists of LXR increases the efflux of intracellular cholesterol to extracellular acceptors such as high density lipoprotein, thus identifying this tissue as a potential important regulator of reverse cholesterol transport and high density lipoprotein levels. Additionally we demonstrate that LXRalpha and a subset of LXR target genes are induced during myogenesis, suggesting a role for LXR-dependent signaling in the differentiation process.
Collapse
Affiliation(s)
- George E O Muscat
- X-Ceptor Therapeutics, Inc., 4757 Nexus Centre Drive, San Diego, CA 92121, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Tangirala RK, Bischoff ED, Joseph SB, Wagner BL, Walczak R, Laffitte BA, Daige CL, Thomas D, Heyman RA, Mangelsdorf DJ, Wang X, Lusis AJ, Tontonoz P, Schulman IG. Identification of macrophage liver X receptors as inhibitors of atherosclerosis. Proc Natl Acad Sci U S A 2002; 99:11896-901. [PMID: 12193651 PMCID: PMC129365 DOI: 10.1073/pnas.182199799] [Citation(s) in RCA: 374] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Recent studies have identified the liver X receptors (LXR alpha and LXR beta) as important regulators of cholesterol metabolism and transport. LXRs control transcription of genes critical to a range of biological functions including regulation of high density lipoprotein cholesterol metabolism, hepatic cholesterol catabolism, and intestinal sterol absorption. Although LXR activity has been proposed to be critical for physiologic lipid metabolism and transport, direct evidence linking LXR signaling pathways to the pathogenesis of cardiovascular disease has yet to be established. In this study bone marrow transplantations were used to selectively eliminate macrophage LXR expression in the context of murine models of atherosclerosis. Our results demonstrate that LXRs are endogenous inhibitors of atherogenesis. Additionally, elimination of LXR activity in bone marrow-derived cells mimics many aspects of Tangier disease, a human high density lipoprotein deficiency, including aberrant regulation of cholesterol transporter expression, lipid accumulation in macrophages, splenomegaly, and increased atherosclerosis. These results identify LXRs as targets for intervention in cardiovascular disease.
Collapse
|
29
|
Osburn DL, Shao G, Seidel HM, Schulman IG. Ligand-dependent degradation of retinoid X receptors does not require transcriptional activity or coactivator interactions. Mol Cell Biol 2001; 21:4909-18. [PMID: 11438648 PMCID: PMC87210 DOI: 10.1128/mcb.21.15.4909-4918.2001] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [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: 01/09/2023] Open
Abstract
Cells utilize ubiquitin-mediated proteolysis to regulate the activity of numerous proteins involved in signal transduction, cell cycle control, and transcriptional regulation. For a number of transcription factors, there appears to be a direct correlation between transcriptional activity and protein instability, suggesting that cells use targeted destruction as one method to down-regulate or attenuate gene expression. In this report we demonstrate that retinoid X receptors (RXRs) which function as versatile mediators of nuclear hormone-dependent gene expression are marked for destruction upon binding agonist ligands. Interestingly, when RXR serves as a heterodimeric partner for retinoic acid (RAR) or thyroid hormone (TR) receptors, binding of agonists by RAR or TR leads to degradation of both the transcriptionally active RAR or TR subunits as well as the transcriptionally inactive RXR subunit. Furthermore, using a series of mutants in the ligand-dependent activation domain (activation function 2), we demonstrate that agonist-stimulated degradation of RXR does not require corepressor release, coactivator binding, or transcriptional activity. Taken together, the data suggest a model for targeted destruction of transcription factors based on structural or conformational signals as opposed to functional coupling with gene transcription.
Collapse
Affiliation(s)
- D L Osburn
- Nuclear Receptor Discovery, Ligand Pharmaceuticals, San Diego, California 92121, USA
| | | | | | | |
Collapse
|
30
|
Abstract
Binding of agonists to nuclear receptors results in a conformational change in receptor structure that promotes interaction between activated receptors and coactivators. Receptor-coactivator interactions are mediated by the agonist-dependent formation of a hydrophobic pocket on the part of receptors, and short leucine-rich sequences termed LxxLL motifs or nuclear receptor boxes present in coactivators. RXR-PPARgamma (retinoid X receptor-peroxisome proliferator-activated receptor-gamma) heterodimers play important roles in adipocyte and macrophage differentiation and have been implicated as therapeutic targets in diabetes, atherosclerosis, and cancer. Analysis of interactions between RXR-PPARgamma heterodimers and coactivator nuclear receptor boxes suggests that RXR and PPARgamma can distinguish among coactivators by recognizing distinct structural features of nuclear receptor boxes. The results also indicate that coactivator choice by RXR is mediated by three nonconserved amino acids of the nuclear receptor box. The ability of an optimized seven-amino acid nuclear receptor box to specifically interact with RXR and function as a selective inhibitor suggests the coactivator-binding pocket may serve as a new target for drug discovery.
Collapse
Affiliation(s)
- G Shao
- Nuclear Receptor Discovery, Ligand Pharmaceuticals, Inc., San Diego, California 92121, USA
| | | | | |
Collapse
|
31
|
Schulman IG, Shao G, Heyman RA. Transactivation by retinoid X receptor-peroxisome proliferator-activated receptor gamma (PPARgamma) heterodimers: intermolecular synergy requires only the PPARgamma hormone-dependent activation function. Mol Cell Biol 1998; 18:3483-94. [PMID: 9584188 PMCID: PMC108929 DOI: 10.1128/mcb.18.6.3483] [Citation(s) in RCA: 148] [Impact Index Per Article: 5.7] [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: 02/07/2023] Open
Abstract
The ability of DNA sequence-specific transcription factors to synergistically activate transcription is a common property of genes transcribed by RNA polymerase II. The present work characterizes a unique form of intermolecular transcriptional synergy between two members of the nuclear hormone receptor superfamily. Heterodimers formed between peroxisome proliferator-activated receptor gamma (PPARgamma), an adipocyte-enriched member of the superfamily required for adipogenesis, and retinoid X receptors (RXRs) can activate transcription in response to ligands specific for either subunit of the dimer. Simultaneous treatment with ligands specific for both PPARgamma and RXR has a synergistic effect on the transactivation of reporter genes and on adipocyte differentiation in cultured cells. Mutation of the PPARgamma hormone-dependent activation domain (named tauc or AF-2) inhibits the ability of RXR-PPARgamma heterodimers to respond to ligands specific for either subunit. In contrast, the ability of RXR- and PPARgamma-specific ligands to synergize does not require the hormone-dependent activation domain of RXR. The results of in vitro and in vivo experiments indicate that binding of ligands to RXR alters the conformation of the dimerization partner, PPARgamma, and modulates the activity of the heterodimer in a manner independent of the RXR hormone-dependent activation domain.
Collapse
Affiliation(s)
- I G Schulman
- Department of Retinoid Research, Ligand Pharmaceuticals, San Diego, California 92121, USA.
| | | | | |
Collapse
|
32
|
Schulman IG, Evans RM. Retinoid receptors in development and disease. Leukemia 1997; 11 Suppl 3:376-7. [PMID: 9209395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Nuclear receptors comprise a large family of ligand-dependent transcription factors that display considerable specificity in and selectivity in regulating the genetic programs they ultimately influence. The response to retinoic acid (RA) is mediated by two families of transcription factors which include the retinoic acids receptors (RARs) and the retinoid X receptors (RXRs). In human acute promyelocytic leukemia (APL), RAR alpha becomes an activated oncogene as a consequence of its fusion to the PML locus. Because patients with APL can be induced into remission with high dose RA therapy, we propose that PML-RAR is a new class of dominant negative oncogene that disrupts a structure that includes at least five other proteins. This mega-complex, referred to as a "POD", is disrupted in leukemic cells expressing the oncoprotein and is reassembled following high dose RA therapy in both cell culture an in patients.
Collapse
|
33
|
Abstract
Regulation of gene expression via allosteric control of transcription is one of the fundamental concepts of molecular biology. Studies in prokaryotes have illustrated that binding of small molecules or ligands to sequence-specific transcription factors can produce conformational changes at a distance from the binding site. These ligand-induced changes can dramatically alter the DNA binding and/or trans-activation abilities of the target transcription factors. In this work, analysis of trans-activation by members of the steroid and thyroid hormone receptor superfamily identifies a unique form of allosteric control, the phantom ligand effect. Binding of a novel ligand (LG100754) to one subunit (RXR) of a heterodimeric transcription factor results in a linked conformational change in the second noncovalently bound subunit of the heterodimer (RAR). This conformational change results in both the dissociation of corepressors and association of coactivators in a fashion mediated by the activation function of the non-liganded subunit. Without occupying the RAR hormone binding pocket, binding of LG100754 to RXR mimics exactly the effects observed when hormone is bound to RAR. Thus, LG100754 behaves as a phantom ligand.
Collapse
Affiliation(s)
- I G Schulman
- The Salk Institute for Biological Sciences, La Jolla, California 92037, USA
| | | | | | | |
Collapse
|
34
|
Lala DS, Mukherjee R, Schulman IG, Koch SS, Dardashti LJ, Nadzan AM, Croston GE, Evans RM, Heyman RA. Activation of specific RXR heterodimers by an antagonist of RXR homodimers. Nature 1996; 383:450-3. [PMID: 8837780 DOI: 10.1038/383450a0] [Citation(s) in RCA: 137] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Retinoid X receptor (RXR) plays a central role in the regulation of many intracellular receptor signalling pathways and can mediate ligand-dependent transcription, acting as a homodimer or as a heterodimer. Here we identify an antagonist towards RXR homodimers which also functions as an agonist when RXR is paired as a heterodimer to specific partners, including peroxisome proliferator-activated receptor and retinoic acid receptor. This dimer-selective ligand confers differential interactions on the transcription machinery: the antagonist promotes association with TAF110 (TATA-binding protein (TBP)-associated factor 110) and the co-repressor SMRT, but not with TBP, and these properties are distinct from pure RXR agonists. This unique class of RXR ligands will provide a means to control distinct target genes at the level of transcription and allow the development of retinoids with a new pharmacological action.
Collapse
Affiliation(s)
- D S Lala
- Department of Retinoid Research, New Leads Ligand Pharmaceuticals, San Diego, California 92121, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Abstract
The nuclear receptor superfamily includes receptors for steroids, retinoids, thyroid hormone and vitamin D, as well as many related proteins. An important feature of the action of the lipophilic hormones and vitamins is that the maintenance of homeostatic function requires both intrinsic positive and negative regulation. Here we provide in vitro and in vivo evidence that identifies the CREB-binding protein (CBP) and its homologue P300 (refs 6,7) as cofactors mediating nuclear-receptor-activated gene transcription. The role of CBP/P300 in the transcriptional response to cyclic AMP, phorbol esters, serum, the lipophilic hormones and as the target of the E1A oncoprotein suggests they may serve as integrators of extracellular and intracellular signalling pathways.
Collapse
Affiliation(s)
- D Chakravarti
- The Gene Expression Laboratory, the Howard Hughes Medical Institute, La Jolla, California 92037, USA
| | | | | | | | | | | | | | | |
Collapse
|
36
|
Schulman IG, Juguilon H, Evans RM. Activation and repression by nuclear hormone receptors: hormone modulates an equilibrium between active and repressive states. Mol Cell Biol 1996; 16:3807-13. [PMID: 8668198 PMCID: PMC231377 DOI: 10.1128/mcb.16.7.3807] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.8] [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: 02/01/2023] Open
Abstract
Transactivation-defective retinoid X and thyroid hormone receptors have been used to examine mechanisms of hormonal activation. Activation and repression of transcription by retinoid X and thyroid hormone receptors are shown to be mediated by physically distinct and functionally independent regions of the hormone binding domain. Nevertheless, the ability of receptors to respond to hormone requires communication between both functional domains. Deletion of the hormone-dependent transactivation function of the retinoid X receptor, the common subunit of heterodimeric nuclear receptors, significantly impairs hormone-dependent transcription by retinoic acid, thyroid hormone, and vitamin D receptors. The results indicate that receptors do not exist in static off and on conformations but that hormone alters an equilibrium between inactive and active states.
Collapse
Affiliation(s)
- I G Schulman
- Howard Hughes Medical Institute, Salk Institute for Biological Studies, La Jolla, California 92037, USA
| | | | | |
Collapse
|
37
|
Schulman IG, Chakravarti D, Juguilon H, Romo A, Evans RM. Interactions between the retinoid X receptor and a conserved region of the TATA-binding protein mediate hormone-dependent transactivation. Proc Natl Acad Sci U S A 1995; 92:8288-92. [PMID: 7667283 PMCID: PMC41142 DOI: 10.1073/pnas.92.18.8288] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The retinoid X receptor (RXR) participates in a wide array of hormonal signaling pathways, either as a homodimer or as a heterodimer, with other members of the steroid and thyroid hormone receptor superfamily. In this report the ligand-dependent transactivation function of RXR has been characterized, and the ability of RXR to interact with components of the basal transcription machinery has been examined. In vivo and in vitro experiments indicate the RXR ligand-binding domain makes a direct, specific, and ligand-dependent contact with a highly conserved region of the TATA-binding protein. The ability of mutations that reduce ligand-dependent transcription by RXR to disrupt the RXR-TATA-binding protein interaction in vivo and in vitro suggests that RXR makes direct contact with the basal transcription machinery to achieve activation.
Collapse
Affiliation(s)
- I G Schulman
- Salk Institute for Biological Studies, La Jolla, CA 92037, USA
| | | | | | | | | |
Collapse
|
38
|
Abstract
A system to detect a minimal function of Saccharomyces cerevisiae centromeres in vivo has been developed. Centromere DNA mutants have been examined and found to be active in a plasmid copy number control assay in the absence of segregation. The experiments allow the identification of a minimal centromere unit, CDE III, independently of its ability to mediate chromosome segregation. Centromere-mediated plasmid copy number control correlates with the ability of CDE III to assemble a DNA-protein complex. Cells forced to maintain excess copies of CDE III exhibit increased loss of a nonessential artificial chromosome. Thus, segregationally impaired centromeres can have negative effects in trans on chromosome segregation. The use of a plasmid copy number control assay has allowed assembly steps preceding chromosome segregation to be defined.
Collapse
Affiliation(s)
- I G Schulman
- Department of Biology, University of North Carolina, Chapel Hill 27599-3280
| | | |
Collapse
|
39
|
Schulman IG, Wang TT, Stargell LA, Gorovsky MA, Allis CD. Cell-cell interactions trigger the rapid induction of a specific high mobility group-like protein during early stages of conjugation in Tetrahymena. Dev Biol 1991; 143:248-57. [PMID: 1991550 DOI: 10.1016/0012-1606(91)90075-e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Conjugation in Tetrahymena represents an ordered developmental pathway which represents the sexual phase of the ciliate life cycle. This pathway is initiated when starved cells of opposite mating types are mixed and are allowed to make a series of cell-cell contacts (a period termed costimulation) which lead to the formation of mating pairs. Here, we demonstrate that two previously described abundant high mobility group (HMG)-like proteins, HMG B and HMG C, whose synthesis appeared to be coordinately regulated in vegetative cells, are not required during the same stages of conjugation. The level of mRNA for both HMG B and HMG C is high during vegetative growth and during the development of new macronuclei. However, specific induction of HMG B mRNA is observed soon after cells of opposite mating types are mixed. Thus, the genes which encode HMG B and HMG C in Tetrahymena can be controlled independently or coordinately. Nuclear run-on experiments show that a significant factor underlying the rapid induction of HMG B message early in the sexual cycle is an increase in the transcriptional activity of the HMG B gene. Experiments are presented which show that this induction of HMG B message requires protein synthesis and is dependent upon the cell-cell contacts made during costimulation. Essentially all of the HMG B protein, which is newly synthesized during this period, is targeted to parental macronuclei where it serves an as yet undetermined function(s).
Collapse
Affiliation(s)
- I G Schulman
- Department of Biology, Syracuse University, New York 13244-1220
| | | | | | | | | |
Collapse
|
40
|
Roth SY, Schulman IG, Richman R, Cook RG, Allis CD. Characterization of phosphorylation sites in histone H1 in the amitotic macronucleus of Tetrahymena during different physiological states. J Cell Biol 1988; 107:2473-82. [PMID: 3204116 PMCID: PMC2115643 DOI: 10.1083/jcb.107.6.2473] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Histone H1 is highly phosphorylated in transcriptionally active, amitotic macronuclei of Tetrahymena during vegetative growth. However, the level of H1 phosphorylation changes dramatically in response to different physiological conditions. H1 is hyperphosphorylated in response to heat shock and during prezygotic stages of conjugation. Conversely, H1 is largely dephosphorylated during prolonged starvation and during elimination of parental macronuclei during conjugation. Mapping of phosphorylation sites within H1 indicates that phosphorylation occurs at multiple sites in the amino-terminal portion of the molecule, predominantly at threonine residues. Two of these sites have been identified by compositional analyses and microsequencing of tryptic peptides. Interestingly, two major sites contain the sequence Thr-Pro-Val-Lys similar to that contained in the sites recognized by growth-associated histone kinase in other organisms. No new sites are detected during the hyperphosphorylation of H1 which occurs during heat shock or in early stages of conjugation, and no sites are preferentially dephosphorylated during starvation or later stages of conjugation. Therefore, changes in the overall level of H1 phosphorylation, as opposed to phosphorylation or dephosphorylation at particular sites, appear to be important in the regulation of chromatin structure under these physiological conditions. Further, since no cell division or DNA replication occurs under these conditions, changes in the level of H1 phosphorylation are best correlated to changes in gene expression during heat shock, starvation, and conjugation. We suggest that, at least in Tetrahymena, H1 hyperphosphorylation is used as a rapid and transient mechanism for the cessation of transcription under conditions of cellular stress.
Collapse
Affiliation(s)
- S Y Roth
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030
| | | | | | | | | |
Collapse
|
41
|
Roth SY, Schulman IG, Cook RG, Allis CD. The complete amino acid sequence of an HMG-like protein isolated from the macronucleus of Tetrahymena. Nucleic Acids Res 1987; 15:8112. [PMID: 3671074 PMCID: PMC306334 DOI: 10.1093/nar/15.19.8112] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Affiliation(s)
- S Y Roth
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030
| | | | | | | |
Collapse
|
42
|
Abstract
Previous studies have described the existence of high mobility group (HMG)-like proteins in macronuclei of the ciliated protozoan, Tetrahymena thermophila (Hamana, K., and K. Iwai, 1979, J. Biochem. [Tokyo], 69:1097-1111; Levy-Wilson, B., M. S. Denker, and E. Ito, 1983, Biochemistry, 22:1715-1721). In this report, two of these proteins, LG-1 and LG-2, have been further characterized. Polyclonal antibodies raised against LG-1 and LG-2 fail to cross react with each other or any other macronuclear polypeptide in immunoblotting analyses. As well, LG-1 and LG-2 antibodies do not react with calf thymus, chicken, or yeast HMG proteins. Consistent with these results, a 47 amino-terminal sequence of LG-1 has been determined that shows limited homology to both calf thymus HMGs 1 and 2 and HMGs 14 and 17. Two internal sequences of V8 protease-generated peptides from LG-2 have been determined, and these do not share any homology to the LG-1 sequence or any other sequenced HMG proteins. Comparison of the partial sequences of LG-1 and LG-2 with the complete amino acid sequence of the Tetrahymena histone H1 (Wu, M., C. D. Allis, R. Richman, R. G. Cook, and M. A. Gorovsky, 1986, Proc. Natl. Acad. Sci. USA, 83:8674-8678) rules out the possibility that LG-1 and LG-2 are proteolytically derived from H1, the other major macronuclear perchloric acid-soluble protein. Interestingly, however, both LG-1 and LG-2 are efficiently extracted from macronuclei by elutive intercalation (Schröter, H., G. Maier, H. Ponsting, and A. Nordheim, 1985, Embo (Eur. Mol. Biol. Organ.) J., 4:3867-3872), suggesting that both may share yet undetermined properties with HMGs 14 and 17 of higher eukaryotes. Examination of the pattern of LG-1 and LG-2 synthesis during the sexual phase of the life cycle, conjugation, demonstrates that the synthesis of LG-1 and LG-2 is coordinately increased from basal levels during the differentiation of new macronuclei (7-13 h), suggesting that both of these proteins play a role in determining a macronuclear phenotype. However, a specific induction of LG-2 synthesis is detected in early stages of conjugation (meiotic prophase, 1-4 h), leading to maximal synthesis of LG-2 at 3 h. Interestingly, the early induction of LG-2 synthesis closely parallels the hyperphosphorylation of histone H1. Taken together, these data suggest that LG-1 and LG-2 are not strongly related to each other or to higher eukaryotic HMG proteins.(ABSTRACT TRUNCATED AT 400 WORDS)
Collapse
|
43
|
Chicoine LG, Schulman IG, Richman R, Cook RG, Allis CD. Nonrandom utilization of acetylation sites in histones isolated from Tetrahymena. Evidence for functionally distinct H4 acetylation sites. J Biol Chem 1986; 261:1071-6. [PMID: 3080415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Macro- and micronuclei of the ciliated protozoan Tetrahymena thermophila afford a unique opportunity to study histone acetylation under conditions where postsynthetic "transcription"-related acetylation and synthetic "deposition"-related acetylation are nonoverlapping. Recent studies have demonstrated that at least two general systems of acetylation operate in Tetrahymena. One is postsynthetic, macronuclear specific, and may be related to gene expression in that nucleus (Vavra, K. J., Allis, C. D., and Gorovsky, M. A. (1982) J. Biol. Chem. 257, 2591-2598). The other is synthetic, common to macro- and micronuclei, and is likely related to histone deposition during replication (Allis, C. D., Chicoine, L. G., Richman, R., and Schulman, I. G. (1985a) Proc. Natl. Acad. Sci. U. S. A., 82, 8048-8052). A unique feature of H3 and H4 in Tetrahymena is that neither are blocked at their amino termini. We have exploited this fact as well as the resolving capability of acid-urea gel electrophoresis and current microsequencing techniques to examine whether utilization of different NH2-terminal acetylation sites is random or nonrandom during the progression toward high acetylation states. Of the four acetylation sites which have been identified in H4 (in Tetrahymena these are lysines at positions 4, 7, 11, and 15), we find that lysine 7 is the exclusive site of postsynthetic acetylation in populations of monoacetylated H4 isolated from macronuclei. This site is retained in populations of diacetylated H4, which are acetylated exclusively at lysines 4 and 7. Our data also suggest that there is some preference for using lysine 11 (as compared to 15) as the third site of acetylation in triacetylated molecules. The data demonstrate that the postsynthetic acetylation-deacetylation process is surprisingly nonrandom for H4 in Tetrahymena macronuclei. We have also investigated the same question with macronuclear H3 (which contains acetylation sites at lysines 9, 14, 18, and 23). Our data demonstrate that unlike H4, lysines at position 9 or 14 are likely to be utilized as sites of acetylation within a population of monoacetylated H3. Both of these acetylation sites are retained in diacetylated H3 which suggests that if site 9 is used initially as the site of monoacetylation, 14 is used secondarily (and vice versa). Our data show, moreover, that there is a preference for utilizing lysine 18 as the third acetylation site (in triacetylated H3). Thus, these data show that H3 is also acetylated in a nonrandom fashion in macronuclei. Finally, we have determined which acetylation sites are utilized in macro- or micronuclear H4 when it is undergoing active synthesis and deposition.(ABSTRACT TRUNCATED AT 400 WORDS)
Collapse
|
44
|
Chicoine LG, Schulman IG, Richman R, Cook RG, Allis CD. Nonrandom utilization of acetylation sites in histones isolated from Tetrahymena. Evidence for functionally distinct H4 acetylation sites. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(17)36054-4] [Citation(s) in RCA: 51] [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] [Indexed: 10/22/2022] Open
|
45
|
Allis CD, Chicoine LG, Richman R, Schulman IG. Deposition-related histone acetylation in micronuclei of conjugating Tetrahymena. Proc Natl Acad Sci U S A 1985; 82:8048-52. [PMID: 3865215 PMCID: PMC391439 DOI: 10.1073/pnas.82.23.8048] [Citation(s) in RCA: 104] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Macro- and micronuclei of the ciliated protozoan, Tetrahymena thermophila, afford a unique opportunity to study histone acetylation under conditions where acetylation associated with the regulation of transcription and acetylation associated with the deposition of histones on the DNA are separable. In this study we demonstrate that histone H3 and histone H4 synthesized in young (5 hr) conjugating Tetrahymena are deposited into micronuclei in acetylated forms. Most of the newly synthesized histone H3 migrates as a monoacetylated form while essentially all of the new histone H4 is deposited as a diacetylated species. Since micronuclei replicate rapidly during this stage of the life cycle, but are transcriptionally inactive, these data suggest that histone acetylation is related functionally to histone deposition and chromatin assembly. Pulse-chase experiments show that micronuclei also contain a butyrate-sensitive deacetylase activity(ies) which operates to remove the deposition-related acetate groups from newly synthesized and deposited H3 and H4. This enzymatic activity probably contributes to the steady state level of micronuclear histone acetylation that is low or nonexistent. Thus, evidence is emerging for at least two independent systems of histone acetylation in Tetrahymena. The first system is specific to macronuclei and may be related to gene expression. The second system is common to macro- or micronuclear histones (H3 and H4) and may be related to histone deposition during DNA replication.
Collapse
|