1
|
Rungratanawanich W, Ballway JW, Wang X, Won KJ, Hardwick JP, Song BJ. Post-translational modifications of histone and non-histone proteins in epigenetic regulation and translational applications in alcohol-associated liver disease: Challenges and research opportunities. Pharmacol Ther 2023; 251:108547. [PMID: 37838219 DOI: 10.1016/j.pharmthera.2023.108547] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 09/30/2023] [Accepted: 10/05/2023] [Indexed: 10/16/2023]
Abstract
Epigenetic regulation is a process that takes place through adaptive cellular pathways influenced by environmental factors and metabolic changes to modulate gene activity with heritable phenotypic variations without altering the DNA sequences of many target genes. Epigenetic regulation can be facilitated by diverse mechanisms: many different types of post-translational modifications (PTMs) of histone and non-histone nuclear proteins, DNA methylation, altered levels of noncoding RNAs, incorporation of histone variants, nucleosomal positioning, chromatin remodeling, etc. These factors modulate chromatin structure and stability with or without the involvement of metabolic products, depending on the cellular context of target cells or environmental stimuli, such as intake of alcohol (ethanol) or Western-style high-fat diets. Alterations of epigenetics have been actively studied, since they are frequently associated with multiple disease states. Consequently, explorations of epigenetic regulation have recently shed light on the pathogenesis and progression of alcohol-associated disorders. In this review, we highlight the roles of various types of PTMs, including less-characterized modifications of nuclear histone and non-histone proteins, in the epigenetic regulation of alcohol-associated liver disease (ALD) and other disorders. We also describe challenges in characterizing specific PTMs and suggest future opportunities for basic and translational research to prevent or treat ALD and many other disease states.
Collapse
Affiliation(s)
- Wiramon Rungratanawanich
- Section of Molecular Pharmacology and Toxicology, National Institute on Alcohol Abuse and Alcoholism, 9000 Rockville Pike, Bethesda, MD 20892, USA
| | - Jacob W Ballway
- Section of Molecular Pharmacology and Toxicology, National Institute on Alcohol Abuse and Alcoholism, 9000 Rockville Pike, Bethesda, MD 20892, USA
| | - Xin Wang
- Department of Neurosurgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | - Kyoung-Jae Won
- Department of Computational Biomedicine, Cedars-Sinai Medical Center, West Hollywood, CA, 90069, USA
| | - James P Hardwick
- Department of Integrative Medical Sciences, Northeast Ohio Medical University, Rootstown, OH 44272, USA.
| | - Byoung-Joon Song
- Section of Molecular Pharmacology and Toxicology, National Institute on Alcohol Abuse and Alcoholism, 9000 Rockville Pike, Bethesda, MD 20892, USA.
| |
Collapse
|
2
|
Ganjayi MS, Brown AM, Baumann CW. Longitudinal assessment of strength and body composition in a mouse model of chronic alcohol-related myopathy. ALCOHOL, CLINICAL & EXPERIMENTAL RESEARCH 2023; 47:1653-1664. [PMID: 37431705 DOI: 10.1111/acer.15149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 06/28/2023] [Accepted: 07/03/2023] [Indexed: 07/12/2023]
Abstract
BACKGROUND Excessive, chronic alcohol consumption can result in muscle atrophy and weakness (i.e., alcoholic myopathy) that impairs the quality of life. However, the precise mechanisms responsible for ethanol's detrimental impact on skeletal muscle have not been fully elucidated, in part due because the time course of disease development and progression are not well established. Therefore, we examined muscle strength and body composition longitudinally using an established preclinical mouse model of chronic alcoholic myopathy. METHODS To establish a time course of chronic alcoholic myopathy, we fed High Drinking in the Dark (HDID) female mice (n = 7) 20% ethanol for ~32 weeks (following a 2-week ethanol ramping period). We assessed in vivo isometric contractility of the left ankle dorsiflexor and lean mass via NMR every 4 weeks. Outcomes were compared with age-matched control HDID mice that did not consume ethanol (n = 8). RESULTS At study completion, mice who consumed ethanol were 12% weaker than control mice (p = 0.015). Compared to baseline, consuming ethanol resulted in an acute transient reduction in dorsiflexion torque at Week 4 (p = 0.032) that was followed by a second, more sustained reduction at Week 20 (p < 0.001). Changes in lean mass paralleled those of dorsiflexor torque, with ~40% of the variance in dorsiflexor torque being explained by the variance in lean mass of the ethanol group (p < 0.001). Dorsiflexor torque normalized to lean mass (mN·m/g lean mass) did not differ between the ethanol and control groups from Weeks 4 to 32 (p ≥ 0.498). CONCLUSIONS These results indicate that reductions in muscle mass and strength due to chronic, excessive ethanol intake are dynamic, not necessarily linear, processes. Moreover, the findings confirm that ethanol-induced weakness is primarily driven by muscle atrophy (i.e., loss of muscle quantity). Future studies should consider how chronic alcoholic myopathy develops and progresses rather than identifying changes after it has been diagnosed.
Collapse
Affiliation(s)
- Muni Swamy Ganjayi
- Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio, USA
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio, USA
| | - Austin M Brown
- Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio, USA
- Honors Tutorial College, Ohio University, Athens, Ohio, USA
| | - Cory W Baumann
- Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio, USA
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio, USA
| |
Collapse
|
3
|
Bogenpohl JW, Smith ML, Farris SP, Dumur CI, Lopez MF, Becker HC, Grant KA, Miles MF. Cross-Species Co-analysis of Prefrontal Cortex Chronic Ethanol Transcriptome Responses in Mice and Monkeys. Front Mol Neurosci 2019; 12:197. [PMID: 31456662 PMCID: PMC6701453 DOI: 10.3389/fnmol.2019.00197] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 07/30/2019] [Indexed: 12/20/2022] Open
Abstract
Despite recent extensive genomic and genetic studies on behavioral responses to ethanol, relatively few new therapeutic targets for the treatment of alcohol use disorder have been validated. Here, we describe a cross-species genomic approach focused on identifying gene networks associated with chronic ethanol consumption. To identify brain mechanisms underlying a chronic ethanol consumption phenotype highly relevant to human alcohol use disorder, and to elucidate potential future therapeutic targets, we conducted a genomic study in a non-human primate model of chronic open-access ethanol consumption. Microarray analysis of RNA expression in anterior cingulate and subgenual cortices from rhesus macaques was performed across multiple cohorts of animals. Gene networks correlating with ethanol consumption or showing enrichment for ethanol-regulated genes were identified, as were major ethanol-related hub genes within these networks. A subsequent consensus module analysis was used to co-analyze monkey data with expression data from a chronic intermittent ethanol vapor-exposure and consumption model in C57BL/6J mice. Ethanol-related gene networks conserved between primates and rodents were enriched for genes involved in discrete biological functions, including; myelination, synaptic transmission, chromatin modification, Golgi apparatus function, translation, cellular respiration, and RNA processing. The myelin-related network, in particular, showed strong correlations with ethanol consumption behavior and displayed marked network reorganization between control and ethanol-drinking animals. Further bioinformatics analysis revealed that these networks also showed highly significant overlap with other ethanol-regulated gene sets. Altogether, these studies provide robust primate and rodent cross-species validation of gene networks associated with chronic ethanol consumption. Our results also suggest potential novel focal points for future therapeutic interventions in alcohol use disorder.
Collapse
Affiliation(s)
- James W Bogenpohl
- Department of Molecular Biology and Chemistry, Christopher Newport University, Newport News, VA, United States
| | - Maren L Smith
- Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA, United States
| | - Sean P Farris
- Waggoner Center for Alcohol and Addiction Research, University of Texas at Austin, Austin, TX, United States
| | - Catherine I Dumur
- Aurora Diagnostics-Sonic Healthcare, Bernhardt Laboratories, Jacksonville, FL, United States
| | - Marcelo F Lopez
- Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC, United States
| | - Howard C Becker
- Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC, United States
| | - Kathleen A Grant
- Department of Behavioral Neuroscience, Oregon Health and Science University, Portland, OR, United States.,Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science University, Beaverton, OR, United States
| | - Michael F Miles
- Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA, United States.,Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, United States.,Department of Neurology, Virginia Commonwealth University, Richmond, VA, United States.,VCU Alcohol Research Center, Virginia Commonwealth University, Richmond, VA, United States
| |
Collapse
|
4
|
Peana AT, Sánchez-Catalán MJ, Hipólito L, Rosas M, Porru S, Bennardini F, Romualdi P, Caputi FF, Candeletti S, Polache A, Granero L, Acquas E. Mystic Acetaldehyde: The Never-Ending Story on Alcoholism. Front Behav Neurosci 2017; 11:81. [PMID: 28553209 PMCID: PMC5425597 DOI: 10.3389/fnbeh.2017.00081] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 04/18/2017] [Indexed: 12/12/2022] Open
Abstract
After decades of uncertainties and drawbacks, the study on the role and significance of acetaldehyde in the effects of ethanol seemed to have found its main paths. Accordingly, the effects of acetaldehyde, after its systemic or central administration and as obtained following ethanol metabolism, looked as they were extensively characterized. However, almost 5 years after this research appeared at its highest momentum, the investigations on this topic have been revitalized on at least three main directions: (1) the role and the behavioral significance of acetaldehyde in different phases of ethanol self-administration and in voluntary ethanol consumption; (2) the distinction, in the central effects of ethanol, between those arising from its non-metabolized fraction and those attributable to ethanol-derived acetaldehyde; and (3) the role of the acetaldehyde-dopamine condensation product, salsolinol. The present review article aims at presenting and discussing prospectively the most recent data accumulated following these three research pathways on this never-ending story in order to offer the most up-to-date synoptic critical view on such still unresolved and exciting topic.
Collapse
Affiliation(s)
| | - María J. Sánchez-Catalán
- Department of Pharmacy, Pharmaceutical Technology and Parasitology, University of ValenciaValència, Spain
| | - Lucia Hipólito
- Department of Pharmacy, Pharmaceutical Technology and Parasitology, University of ValenciaValència, Spain
| | - Michela Rosas
- Department of Life and Environmental Sciences, University of CagliariCagliari, Italy
| | - Simona Porru
- Department of Life and Environmental Sciences, University of CagliariCagliari, Italy
| | | | - Patrizia Romualdi
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
| | - Francesca F. Caputi
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
| | - Sanzio Candeletti
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
| | - Ana Polache
- Department of Pharmacy, Pharmaceutical Technology and Parasitology, University of ValenciaValència, Spain
| | - Luis Granero
- Department of Pharmacy, Pharmaceutical Technology and Parasitology, University of ValenciaValència, Spain
| | - Elio Acquas
- Department of Life and Environmental Sciences, University of CagliariCagliari, Italy
- Centre of Excellence on Neurobiology of Addiction, University of CagliariCagliari, Italy
| |
Collapse
|
5
|
Caputi FF, Carboni L, Mazza D, Candeletti S, Romualdi P. Cocaine and ethanol target 26S proteasome activity and gene expression in neuroblastoma cells. Drug Alcohol Depend 2016; 161:265-75. [PMID: 26922280 DOI: 10.1016/j.drugalcdep.2016.02.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 01/26/2016] [Accepted: 02/05/2016] [Indexed: 10/22/2022]
Abstract
BACKGROUND Ethanol and cocaine are widely abused drugs triggering long-lasting changes in neuronal circuits and synaptic transmission through the regulation of enzyme activity and gene expression. Compelling evidence indicates that the ubiquitin-proteasome system plays a role in the molecular changes induced by addictive substances, impacting on several mechanisms implicated in abuse. The goal of these studies was to evaluate the effects of cocaine or ethanol on proteasome activity in neuroblastoma cells. Moreover, the gene expression of specific subunits was assessed. METHODS Chymotrypsin-like activity was measured after 2 h, 24 h, and 48 h exposure to 5 μM cocaine or 40 mM ethanol. Proteasome subunit transcripts were evaluated by qPCR at the same time-points. RESULTS Treatments modified proteasome function in opposite directions, since cocaine increased and ethanol reduced chymotrypsin-like activity. Interestingly, we observed gene expression alterations induced by these drugs. In the core particle, the β1 and α5 subunits were mainly up-regulated by cocaine, whereas α6 transcripts were mostly decreased. β2 and β5 did not change. Similarly, ethanol exposure generally increased β1 and α5 mRNAs. Moreover, the β2 subunit was significantly up-regulated by ethanol only. The β5 and α6 subunits were not altered. In the regulatory particle, Rpt3 was increased by cocaine exposure, whereas it was reduced by ethanol. No significant Rpn9 alterations were observed. CONCLUSIONS These findings support the notion that addictive substances regulate proteasome function, contributing to the dysregulations related to drug abuse since the availability of adequate subunit amounts is necessary for proper complex assembly and function.
Collapse
Affiliation(s)
- Francesca Felicia Caputi
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy.
| | - Lucia Carboni
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| | - Daria Mazza
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| | - Sanzio Candeletti
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| | - Patrizia Romualdi
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Irnerio 48, 40126 Bologna, Italy
| |
Collapse
|
6
|
Zhao Q, Qin CY, Zhao ZH, Fan YC, Wang K. Epigenetic modifications in hepatic stellate cells contribute to liver fibrosis. TOHOKU J EXP MED 2013; 229:35-43. [PMID: 23238615 DOI: 10.1620/tjem.229.35] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Liver fibrosis represents the final common pathway of virtually all types of chronic liver diseases, and it has been a major public health concern. Many genes have been demonstrated to be involved in the pathogenesis of liver fibrosis, while the mechanisms underlying gene regulation still needs further research. On the other hand, hepatic stellate cells (HSCs) are quiescent cells in the perisinusoidal space in liver. HSCs facilitate hepatocytes interactions via releasing soluble inflammatory factors and producing extracellular matrix. HSCs can be activated in response to liver injury, and they differentiate to myofibroblasts, which greatly contribute to the fibrogenesis process. Various epigenetic procedures, including DNA methylation, histone modification and formation of particular chromatin structure, play crucial roles in the gene transcriptional expression in HSCs, regulating various vital processes. For instance, epigenetic modulation on the peroxisome proliferator-activated receptor gamma (PPAR-γ) gene promoter accounts for HSC differentiation through interacting pathways. Aberrant expression of a series of histones and chemokines in activated HSCs can aggravate inflammation and oxidative stress, which in turn promotes differentiation of HSCs to myofibroblasts and enhances the whole fibrogenesis process. Degradation of extracellular matrix is also regulated through epigenetic modulation on matrix associated enzymes. Moreover, fibrosis-related epigenetic modifications in the parental generation may be inherited to their offspring. In this review, we firstly summarize the vital epigenetic modifications of fibrosis-related genes in HSCs, and highlight specific nucleic acid sequences and structures in gene promoters as important action sites, which may provide indicators for liver fibrosis diagnosis in the future.
Collapse
Affiliation(s)
- Qi Zhao
- Department of Hepatology, Qilu Hospital of Shandong University, Jinan, Shangdong, PR China.
| | | | | | | | | |
Collapse
|
7
|
Kharbanda KK, Bardag-Gorce F, Barve S, Molina PE, Osna NA. Impact of altered methylation in cytokine signaling and proteasome function in alcohol and viral-mediated diseases. Alcohol Clin Exp Res 2013; 37:1-7. [PMID: 22577887 PMCID: PMC3421055 DOI: 10.1111/j.1530-0277.2012.01840.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Accepted: 03/18/2012] [Indexed: 02/05/2023]
Abstract
Data from several laboratories have shown that ethanol (EtOH) feeding impairs many essential methylation reactions that contribute to alcoholic liver disease (ALD). EtOH is also a comorbid factor in the severity of hepatitis C virus-induced liver injury. The presence of viral proteins further exacerbates the methylation defects to disrupt multiple pathways that promote the pathogenesis of liver disease. This review is a compilation of presentations that linked the methylation reaction defects with proteasome inhibition, decreased antigen presentation, and impaired interferon (IFN) signaling in the hepatocytes and dysregulated TNFα expression in macrophages. Two therapeutic modalities, betaine and S-adenosylmethionine, can correct methylation defects to attenuate many EtOH-induced liver changes, as well as improve IFN signaling pathways, thereby overcoming viral treatment resistance.
Collapse
Affiliation(s)
- Kusum K. Kharbanda
- Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska, 68105, USA; Phone: 1-402-995-3752; Fax: +1-402-449-0604
- Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska, 68198, USA; Phone: 1-402-995-3735; Fax: +1-402-449-0604
- Corresponding author: Kusum K. Kharbanda, Ph.D., Research Service, Veterans Affairs, Nebraska-Western Iowa Health Care System, Omaha, Nebraska, 68105, USA Tel.:+1-402-995-3752; Fax: 1+402-449-0604;
| | - Fawzia Bardag-Gorce
- Department of Pathology, Los Angeles Biomedical Research Institute, Harbor UCLA Medical Center, 1124 W Carson St., Torrance, CA, 90502, USA; Phone: +1-310-222-1846; Fax: +1-310-222-3614
| | - Shirish Barve
- Department of Medicine and Alcohol Research Center, University of Louisville, Louisville, KY 40202, USA, Phone: +1-502-852-5245; Fax: +1-502-852-8927
| | - Patricia E. Molina
- Department of Physiology and Alcohol and Drug Abuse Center of Excellence, Department of Physiology, Louisiana State University Health Sciences Center, 1901 Perdido Street, Medical Education Building, New Orleans, LA 70112; Phone: 504-568-6187; Fax: 504-568-6158
| | - Natalia A. Osna
- Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, Nebraska, 68105, USA; Phone: 1-402-995-3752; Fax: +1-402-449-0604
- Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska, 68198, USA; Phone: 1-402-995-3735; Fax: +1-402-449-0604
| |
Collapse
|
8
|
Pashikanti S, Boissonneault GA, Cervantes-Laurean D. Ex vivo detection of histone H1 modified with advanced glycation end products. Free Radic Biol Med 2011; 50:1410-6. [PMID: 21315148 DOI: 10.1016/j.freeradbiomed.2011.01.034] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Revised: 01/14/2011] [Accepted: 01/24/2011] [Indexed: 10/18/2022]
Abstract
A number of oxidative stress agents cause DNA and protein damage, which may compromise genomic integrity. Whereas oxidant-induced DNA damage has been extensively studied, much less is known concerning the occurrence and fate of nuclear protein damage, particularly of proteins involved in the regulation and maintenance of chromatin structure. Protein damage may be caused by the formation of reactive carbonyl species such as glyoxal, which forms after lipid peroxide degradation. It may also result from degradation of early protein glycation adducts and from methylglyoxal, formed in the process of glycolytic intermediate degradation. Major adducts indicative of protein damage include the advanced glycation end product (AGE) carboxymethyllysine (CML) and argpyrimidine protein adducts. Thus, the formation of CML and argpyrimidine protein adducts represents potential biomarkers for nuclear protein damage deriving from a variety of sources. The purpose of this study was to identify and quantify AGE adducts formed in vivo in a nuclear protein, specifically histone H1, using CML and argpyrimidine as biomarkers. Histone H1 was isolated from calf thymus collected immediately after slaughter under conditions designed to minimize AGE formation before isolation. Using antibodies directed against oxidative protein adducts, we identified CML, argpyrimidine, and protein crosslinks present in the freshly isolated histone H1. Detailed mass spectroscopy analysis of histone H1 revealed the presence of two specific lysine residues modified by CML adducts. Our results strongly suggest that glycation of important nuclear protein targets such as histone H1 occurs in vivo and that these oxidative changes may alter chromatin structure, ultimately contributing to chronic changes associated with aging and diseases such as diabetes.
Collapse
Affiliation(s)
- Srinath Pashikanti
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57006, USA
| | | | | |
Collapse
|
9
|
Osna NA, White RL, Donohue TM, Beard MR, Tuma DJ, Kharbanda KK. Impaired methylation as a novel mechanism for proteasome suppression in liver cells. Biochem Biophys Res Commun 2010; 391:1291-6. [PMID: 20026058 PMCID: PMC2812660 DOI: 10.1016/j.bbrc.2009.12.074] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Accepted: 12/11/2009] [Indexed: 02/08/2023]
Abstract
The proteasome is a multi-catalytic protein degradation enzyme that is regulated by ethanol-induced oxidative stress; such suppression is attributed to CYP2E1-generated metabolites. However, under certain conditions, it appears that in addition to oxidative stress, other mechanisms are also involved in proteasome regulation. This study investigated whether impaired protein methylation that occurs during exposure of liver cells to ethanol, may contribute to suppression of proteasome activity. We measured the chymotrypsin-like proteasome activity in Huh7CYP cells, hepatocytes, liver cytosols and nuclear extracts or purified 20S proteasome under conditions that maintain or prevent protein methylation. Reduction of proteasome activity of hepatoma cell and hepatocytes by ethanol or tubercidin was prevented by simultaneous treatment with S-adenosylmethionine (SAM). Moreover, the tubercidin-induced decline in proteasome activity occurred in both nuclear and cytosolic fractions. In vitro exposure of cell cytosolic fractions or highly purified 20S proteasome to low SAM:S-adenosylhomocysteine (SAH) ratios in the buffer also suppressed proteasome function, indicating that one or more methyltransferase(s) may be associated with proteasomal subunits. Immunoblotting a purified 20S rabbit red cell proteasome preparation using methyl lysine-specific antibodies revealed a 25kDa proteasome subunit that showed positive reactivity with anti-methyl lysine. This reactivity was modified when 20S proteasome was exposed to differential SAM:SAH ratios. We conclude that impaired methylation of proteasome subunits suppressed proteasome activity in liver cells indicating an additional, yet novel mechanism of proteasome activity regulation by ethanol.
Collapse
Affiliation(s)
- Natalia A Osna
- Liver Study Unit, The Omaha Veterans Affairs (VA) Medical Center, Omaha, NE 68105, USA.
| | | | | | | | | | | |
Collapse
|