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Meng X, Zhou Y, Xu L, Hu L, Wang C, Tian X, Zhang X, Hao Y, Cheng B, Ma J, Wang L, Liu J, Xie R. O-GlcNAcylation Facilitates the Interaction between Keratin 18 and Isocitrate Dehydrogenases and Potentially Influencing Cholangiocarcinoma Progression. ACS CENTRAL SCIENCE 2024; 10:1065-1083. [PMID: 38799671 PMCID: PMC11117311 DOI: 10.1021/acscentsci.4c00163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 03/06/2024] [Accepted: 04/10/2024] [Indexed: 05/29/2024]
Abstract
Glycosylation plays a pivotal role in the intricate landscape of human cholangiocarcinoma (CCA), actively participating in key pathophysiological processes driving tumor progression. Among the various glycosylation modifications, O-linked β-N-acetyl-glucosamine modification (O-GlcNAcylation) emerges as a dynamic regulator influencing diverse tumor-associated biological activities. In this study, we employed a state-of-the-art chemical proteomic approach to analyze intact glycopeptides, unveiling the critical role of O-GlcNAcylation in orchestrating Keratin 18 (K18) and its interplay with tricarboxylic acid (TCA) cycle enzymes, specifically isocitrate dehydrogenases (IDHs), to propel CCA progression. Our findings shed light on the mechanistic intricacies of O-GlcNAcylation, revealing that site-specific modification of K18 on Ser 30 serves as a stabilizing factor, amplifying the expression of cell cycle checkpoints. This molecular event intricately fosters cell cycle progression and augments cellular growth in CCA. Notably, the interaction between O-GlcNAcylated K18 and IDHs orchestrates metabolic reprogramming by down-regulating citrate and isocitrate levels while elevating α-ketoglutarate (α-KG). These metabolic shifts further contribute to the overall tumorigenic potential of CCA. Our study thus expands the current understanding of protein O-GlcNAcylation and introduces a new layer of complexity to post-translational control over metabolism and tumorigenesis.
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Affiliation(s)
- Xiangfeng Meng
- State
Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Yue Zhou
- Department
of Gastroenterology, Nanjing Drum Tower Hospital, The Affiliated, Hospital of Nanjing University Medical School, Nanjing 210008, China
| | - Lei Xu
- Department
of Gastroenterology, Nanjing Drum Tower Hospital, The Affiliated, Hospital of Nanjing University Medical School, Nanjing 210008, China
| | - Limu Hu
- State
Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Changjiang Wang
- State
Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Xiao Tian
- State
Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Xiang Zhang
- Department
of Gastroenterology, Nanjing Drum Tower Hospital, The Affiliated, Hospital of Nanjing University Medical School, Nanjing 210008, China
| | - Yi Hao
- College
of
Chemistry and Molecular Engineering, Peking
University, Beijing 100871, China
| | - Bo Cheng
- School
of Pharmaceutical Sciences, Peking University, Beijing 100191, China
| | - Jing Ma
- State
Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210023, China
- Collaborative
Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210023, China
| | - Lei Wang
- Department
of Gastroenterology, Nanjing Drum Tower Hospital, The Affiliated, Hospital of Nanjing University Medical School, Nanjing 210008, China
| | - Jialin Liu
- State
Key Laboratory of Medical Proteomics, Beijing Proteome Research Center,
National Center for Protein Sciences (Beijing), Beijing Institute of Lifeomics, Beijing 102206, China
| | - Ran Xie
- State
Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210023, China
- Chemistry
and Biomedicine Innovation Center (ChemBIC), Nanjing University, Nanjing 210023, China
- Beijing
National Laboratory for Molecular Sciences, Beijing 100191, China
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2
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MacTaggart B, Kashina A. Posttranslational modifications of the cytoskeleton. Cytoskeleton (Hoboken) 2021; 78:142-173. [PMID: 34152688 DOI: 10.1002/cm.21679] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Revised: 06/13/2021] [Accepted: 06/16/2021] [Indexed: 12/12/2022]
Abstract
The cytoskeleton plays important roles in many essential processes at the cellular and organismal levels, including cell migration and motility, cell division, and the establishment and maintenance of cell and tissue architecture. In order to facilitate these varied functions, the main cytoskeletal components-microtubules, actin filaments, and intermediate filaments-must form highly diverse intracellular arrays in different subcellular areas and cell types. The question of how this diversity is conferred has been the focus of research for decades. One key mechanism is the addition of posttranslational modifications (PTMs) to the major cytoskeletal proteins. This posttranslational addition of various chemical groups dramatically increases the complexity of the cytoskeletal proteome and helps facilitate major global and local cytoskeletal functions. Cytoskeletal proteins undergo many PTMs, most of which are not well understood. Recent technological advances in proteomics and cell biology have allowed for the in-depth study of individual PTMs and their functions in the cytoskeleton. Here, we provide an overview of the major PTMs that occur on the main structural components of the three cytoskeletal systems-tubulin, actin, and intermediate filament proteins-and highlight the cellular function of these modifications.
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Affiliation(s)
- Brittany MacTaggart
- School of Veterinary Medicine, Department of Biomedical Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Anna Kashina
- School of Veterinary Medicine, Department of Biomedical Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Chatham JC, Zhang J, Wende AR. Role of O-Linked N-Acetylglucosamine Protein Modification in Cellular (Patho)Physiology. Physiol Rev 2020; 101:427-493. [PMID: 32730113 DOI: 10.1152/physrev.00043.2019] [Citation(s) in RCA: 157] [Impact Index Per Article: 39.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In the mid-1980s, the identification of serine and threonine residues on nuclear and cytoplasmic proteins modified by a N-acetylglucosamine moiety (O-GlcNAc) via an O-linkage overturned the widely held assumption that glycosylation only occurred in the endoplasmic reticulum, Golgi apparatus, and secretory pathways. In contrast to traditional glycosylation, the O-GlcNAc modification does not lead to complex, branched glycan structures and is rapidly cycled on and off proteins by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery, O-GlcNAcylation has been shown to contribute to numerous cellular functions, including signaling, protein localization and stability, transcription, chromatin remodeling, mitochondrial function, and cell survival. Dysregulation in O-GlcNAc cycling has been implicated in the progression of a wide range of diseases, such as diabetes, diabetic complications, cancer, cardiovascular, and neurodegenerative diseases. This review will outline our current understanding of the processes involved in regulating O-GlcNAc turnover, the role of O-GlcNAcylation in regulating cellular physiology, and how dysregulation in O-GlcNAc cycling contributes to pathophysiological processes.
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Affiliation(s)
- John C Chatham
- Division of Molecular and Cellular Pathology, Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama; and Birmingham Veterans Affairs Medical Center, Birmingham, Alabama
| | - Jianhua Zhang
- Division of Molecular and Cellular Pathology, Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama; and Birmingham Veterans Affairs Medical Center, Birmingham, Alabama
| | - Adam R Wende
- Division of Molecular and Cellular Pathology, Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama; and Birmingham Veterans Affairs Medical Center, Birmingham, Alabama
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Dmello C, Srivastava SS, Tiwari R, Chaudhari PR, Sawant S, Vaidya MM. Multifaceted role of keratins in epithelial cell differentiation and transformation. J Biosci 2019. [DOI: 10.1007/s12038-019-9864-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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5
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Zachara NE. Critical observations that shaped our understanding of the function(s) of intracellular glycosylation (O-GlcNAc). FEBS Lett 2018; 592:3950-3975. [PMID: 30414174 DOI: 10.1002/1873-3468.13286] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 10/30/2018] [Accepted: 10/31/2018] [Indexed: 12/30/2022]
Abstract
Almost 100 years after the first descriptions of proteins conjugated to carbohydrates (mucins), several studies suggested that glycoproteins were not restricted to the serum, extracellular matrix, cell surface, or endomembrane system. In the 1980s, key data emerged demonstrating that intracellular proteins were modified by monosaccharides of O-linked β-N-acetylglucosamine (O-GlcNAc). Subsequently, this modification was identified on thousands of proteins that regulate cellular processes as diverse as protein aggregation, localization, post-translational modifications, activity, and interactions. In this Review, we will highlight critical discoveries that shaped our understanding of the molecular events underpinning the impact of O-GlcNAc on protein function, the role that O-GlcNAc plays in maintaining cellular homeostasis, and our understanding of the mechanisms that regulate O-GlcNAc-cycling.
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Affiliation(s)
- Natasha E Zachara
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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The role of keratins in the digestive system: lessons from transgenic mouse models. Histochem Cell Biol 2018; 150:351-359. [PMID: 30039330 DOI: 10.1007/s00418-018-1695-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/17/2018] [Indexed: 01/17/2023]
Abstract
Keratins are the largest subfamily of intermediate filament proteins. They are either type I acidic or type II basic keratins. Keratins form obligate heteropolymer in epithelial cells and their expression patterns are tissue-specific. Studies have shown that keratin mutations are the cause of many diseases in humans or predispose humans to acquiring them. Using mouse models to study keratin-associated human diseases is critical, because they allow researchers to get a better understanding of these diseases and their progressions, and so many such studies have been conducted. Acknowledging the importance, researches with genetically modified mice expressing human disease-associated keratin mutants have been widely done. Numerous studies using keratin knockout mice, keratin-overexpressed mice, or transgenic mice expressing keratin mutants have been conducted. This review summarizes the mouse models that have been used to study type I and type II keratin expression in the digestive organs, namely, the liver, pancreas, and colon.
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Silibinin Ameliorates O-GlcNAcylation and Inflammation in a Mouse Model of Nonalcoholic Steatohepatitis. Int J Mol Sci 2018; 19:ijms19082165. [PMID: 30042374 PMCID: PMC6121629 DOI: 10.3390/ijms19082165] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 07/13/2018] [Accepted: 07/19/2018] [Indexed: 02/06/2023] Open
Abstract
The mechanisms underlying the progression to non-alcoholic steatohepatitis (NASH) remain to be elucidated. In the present study, we aimed to identify the proteins involved in the pathogenesis of liver tissue inflammation and to investigate the effects of silibinin, a natural polyphenolic flavonoid, on steatohepatitis. We performed comparative proteomic analysis using methionine and choline-deficient (MCD) diet-induced NASH model mice. Eighteen proteins were identified from the two-dimensional proteomic analysis, which are not only differentially expressed, but also significantly improved, by silibinin treatment. Interestingly, seven of these proteins, including keratin cytoskeletal 8 and 18, peroxiredoxin-4, and protein disulfide isomerase, are known to undergo GlcNAcylation modification, most of which are related to structural and stress-related proteins in NASH model animals. Thus, we primarily focused on how the GlcNAc modification of these proteins is involved in the progression to NASH. Remarkably, silibinin treatment alleviates the severity of hepatic inflammation along with O-GlcNAcylation in steatohepatitis. In particular, the reduction of inflammation by silibinin is due to the inhibition of the O-GlcNAcylation-dependent NF-κB-signaling pathway. Therefore, silibinin is a promising therapeutic agent for hyper-O-GlcNAcylation as well as NASH.
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8
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Abstract
A protein modification called O-linked glycosylation regulates the interactions between vimentin molecules under normal conditions, and the ability of Chlamydia bacteria to replicate after they infect cells.
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Affiliation(s)
- Natasha T Snider
- Department of Cell Biology and PhysiologyUniversity of North Carolina at Chapel HillChapel HillUnited States
| | - Nam-On Ku
- Interdisciplinary Program of Integrated OMICS Biomedical science, Graduate SchoolYonsei UniversitySeoulRepublic of Korea
| | - M Bishr Omary
- Department of Molecular & Integrative PhysiologyUniversity of Michigan Medical SchoolAnn ArborUnited States
- Department of MedicineUniversity of Michigan Medical SchoolAnn ArborUnited States
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10
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Kakade PS, Budnar S, Kalraiya RD, Vaidya MM. Functional Implications of O-GlcNAcylation-dependent Phosphorylation at a Proximal Site on Keratin 18. J Biol Chem 2016; 291:12003-13. [PMID: 27059955 DOI: 10.1074/jbc.m116.728717] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Indexed: 01/16/2023] Open
Abstract
Keratins 8/18 (K8/18) are phosphoglycoproteins and form the major intermediate filament network of simple epithelia. The three O-GlcNAcylation (Ser(29), Ser(30), and Ser(48)) and two phosphorylation (Ser(33) and Ser(52)) serine sites on K18 are well characterized. Both of these modifications have been reported to increase K18 solubility and regulate its filament organization. In this report, we investigated the site-specific interplay between these two modifications in regulating the functional properties of K18, like solubility, stability, and filament organization. An immortalized hepatocyte cell line (HHL-17) stably expressing site-specific single, double, and triple O-GlcNAc and phosphomutants of K18 were used to identify the site(s) critical for regulating these functions. Keratin 18 mutants where O-GlcNAcylation at Ser(30) was abolished (K18-S30A) exhibited reduced phosphorylation induced solubility, increased stability, defective filament architecture, and slower migration. Interestingly, K18-S30A mutants also showed loss of phosphorylation at Ser(33), a modification known to regulate the solubility of K18. Further to this, the K18 phosphomutant (K18-S33A) mimicked K18-S30A in its stability, filament organization, and cell migration. These results indicate that O-GlcNAcylation at Ser(30) promotes phosphorylation at Ser(33) to regulate the functional properties of K18 and also impact cellular processes like migration. O-GlcNAcylation and phosphorylation on the same or adjacent sites on most proteins antagonize each other in regulating protein functions. Here we report a novel, positive interplay between O-GlcNAcylation and phosphorylation at adjacent sites on K18 to regulate its fundamental properties.
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Affiliation(s)
- Poonam S Kakade
- From the Advanced Centre for Treatment, Research, and Education in Cancer (ACTREC), Tata Memorial Centre, Sector 22, Kharghar, Navi Mumbai 410210, India
| | - Srikanth Budnar
- From the Advanced Centre for Treatment, Research, and Education in Cancer (ACTREC), Tata Memorial Centre, Sector 22, Kharghar, Navi Mumbai 410210, India
| | - Rajiv D Kalraiya
- From the Advanced Centre for Treatment, Research, and Education in Cancer (ACTREC), Tata Memorial Centre, Sector 22, Kharghar, Navi Mumbai 410210, India
| | - Milind M Vaidya
- From the Advanced Centre for Treatment, Research, and Education in Cancer (ACTREC), Tata Memorial Centre, Sector 22, Kharghar, Navi Mumbai 410210, India
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11
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Snider NT, Omary MB. Assays for Posttranslational Modifications of Intermediate Filament Proteins. Methods Enzymol 2015; 568:113-38. [PMID: 26795469 DOI: 10.1016/bs.mie.2015.09.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Intermediate filament (IF) proteins are known to be regulated by a number of posttranslational modifications (PTMs). Phosphorylation is the best-studied IF PTM, whereas ubiquitination, sumoylation, acetylation, glycosylation, ADP-ribosylation, farnesylation, and transamidation are less understood in functional terms but are known to regulate specific IFs under various contexts. The number and diversity of IF PTMs is certain to grow along with rapid advances in proteomic technologies. Therefore, the need for a greater understanding of the implications of PTMs to the structure, organization, and function of the IF cytoskeleton has become more apparent with the increased availability of data from global profiling studies of normal and diseased specimens. This chapter will provide information on established methods for the isolation and monitoring of IF PTMs along with the key reagents that are necessary to carry out these experiments.
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Affiliation(s)
- Natasha T Snider
- Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, North Carolina, USA.
| | - M Bishr Omary
- Department of Molecular & Integrative Physiology, Department of Medicine, University of Michigan, Ann Arbor, Michigan, USA; VA Ann Arbor Healthcare System, Ann Arbor, Michigan, USA
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12
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Cieniewski-Bernard C, Lambert M, Dupont E, Montel V, Stevens L, Bastide B. O-GlcNAcylation, contractile protein modifications and calcium affinity in skeletal muscle. Front Physiol 2014; 5:421. [PMID: 25400587 PMCID: PMC4214218 DOI: 10.3389/fphys.2014.00421] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Accepted: 10/11/2014] [Indexed: 12/02/2022] Open
Abstract
O-GlcNAcylation, a generally undermined atypical protein glycosylation process, is involved in a dynamic and highly regulated interplay with phosphorylation. Akin to phosphorylation, O-GlcNAcylation is also involved in the physiopathology of several acquired diseases, such as muscle insulin resistance or muscle atrophy. Recent data underline that the interplay between phosphorylation and O-GlcNAcylation acts as a modulator of skeletal muscle contractile activity. In particular, the O-GlcNAcylation level of the phosphoprotein myosin light chain 2 seems to be crucial in the modulation of the calcium activation properties, and should be responsible for changes in calcium properties observed in functional atrophy. Moreover, since several key structural proteins are O-GlcNAc-modified, and because of the localization of the enzymes involved in the O-GlcNAcylation/de-O-GlcNAcylation process to the nodal Z disk, a role of O-GlcNAcylation in the modulation of the sarcomeric structure should be considered.
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Affiliation(s)
| | - Matthias Lambert
- Université Lille Lille, France ; EA4488, APMS, URePsss, Université de Lille 1 Villeneuve d'Ascq, France
| | - Erwan Dupont
- Université Lille Lille, France ; EA4488, APMS, URePsss, Université de Lille 1 Villeneuve d'Ascq, France
| | - Valérie Montel
- Université Lille Lille, France ; EA4488, APMS, URePsss, Université de Lille 1 Villeneuve d'Ascq, France
| | - Laurence Stevens
- Université Lille Lille, France ; EA4488, APMS, URePsss, Université de Lille 1 Villeneuve d'Ascq, France
| | - Bruno Bastide
- Université Lille Lille, France ; EA4488, APMS, URePsss, Université de Lille 1 Villeneuve d'Ascq, France
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14
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Chaiyawat P, Netsirisawan P, Svasti J, Champattanachai V. Aberrant O-GlcNAcylated Proteins: New Perspectives in Breast and Colorectal Cancer. Front Endocrinol (Lausanne) 2014; 5:193. [PMID: 25426101 PMCID: PMC4227529 DOI: 10.3389/fendo.2014.00193] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Accepted: 10/28/2014] [Indexed: 12/21/2022] Open
Abstract
Increasing glucose consumption is thought to provide an evolutionary advantage to cancer cells. Alteration of glucose metabolism in cancer influences various important metabolic pathways including the hexosamine biosynthesis pathway (HBP), a relatively minor branch of glycolysis. Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), an end product of HBP, is a sugar substrate used for classical glycosylation and O-GlcNAcylation, a post-translational protein modification implicated in a wide range of effects on cellular functions. Emerging evidence reveals that certain cellular proteins are abnormally O-GlcNAc modified in many kinds of cancers, indicating O-GlcNAcylation is associated with malignancy. Since O-GlcNAc rapidly on and off modifies in a similar time scale as in phosphorylation and these modifications may occur on proteins at either on the same or adjacent sites, it suggests that both modifications can work to regulate the cellular signaling pathways. This review describes the metabolic shifts related to the HBP, which are commonly found in most cancers. It also describes O-GlcNAc modified proteins identified in primary breast and colorectal cancer, as well as in the related cancer cell lines. Moreover, we also discuss the potential use of aberrant O-GlcNAcylated proteins as novel biomarkers of cancer.
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Affiliation(s)
- Parunya Chaiyawat
- Applied Biological Sciences Program, Chulabhorn Graduate Institute, Bangkok, Thailand
| | | | - Jisnuson Svasti
- Applied Biological Sciences Program, Chulabhorn Graduate Institute, Bangkok, Thailand
- Laboratory of Biochemistry, Chulabhorn Research Institute, Bangkok, Thailand
| | - Voraratt Champattanachai
- Applied Biological Sciences Program, Chulabhorn Graduate Institute, Bangkok, Thailand
- Laboratory of Biochemistry, Chulabhorn Research Institute, Bangkok, Thailand
- *Correspondence: Voraratt Champattanachai, Laboratory of Biochemistry, Chulabhorn Research Institute, 54 Kamphaeng Phet 6, Laksi, Bangkok 10210, Thailand e-mail:
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Phueaouan T, Chaiyawat P, Netsirisawan P, Chokchaichamnankit D, Punyarit P, Srisomsap C, Svasti J, Champattanachai V. Aberrant O-GlcNAc-modified proteins expressed in primary colorectal cancer. Oncol Rep 2013; 30:2929-36. [PMID: 24126823 DOI: 10.3892/or.2013.2794] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Accepted: 08/28/2013] [Indexed: 11/05/2022] Open
Abstract
O-GlcNAcylation is a post-translational modification of serine and threonine residues which is dynamically regulated by 2 enzymes; O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) that catalyze the addition and removal of a single N-acetylglucosamine (GlcNAc) molecule, respectively. This modification is thought to be a nutrient sensor in highly proliferating cells via the hexosamine biosynthesis pathway, a minor branch of glycolysis. Although emerging evidence suggests that O-GlcNAc modification is associated with many types of cancer, identification of O-GlcNAc-modified proteins and their role in cancer remain unexplored. In the present study, we demonstrated that O-GlcNAcylation is increased in primary colorectal cancer tissues, and that this augmentation is associated with an increased expression of OGT levels. Using 2-dimensional O-GlcNAc immunoblotting and LC-MS/MS analysis, 16 proteins were successfully identified and 8 proteins showed an increase in O-GlcNAcylation, including cytokeratin 18, heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNP A2/B1), hnRNP H, annexin A2, annexin A7, laminin-binding protein, α-tubulin and protein DJ-1. Among these identified proteins, annexin A2 was further confirmed to show overexpression of O-GlcNAc in all cancer samples. The results, therefore, indicate that aberrant O-GlcNAcylation of proteins is associated with colorectal cancer and that identification of O-GlcNAc-modified proteins may provide novel biomarkers of cancer.
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Affiliation(s)
- Thanong Phueaouan
- Applied Biological Sciences Program, Chulabhorn Graduate Institute, Bangkok, Thailand
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16
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Champattanachai V, Netsirisawan P, Chaiyawat P, Phueaouan T, Charoenwattanasatien R, Chokchaichamnankit D, Punyarit P, Srisomsap C, Svasti J. Proteomic analysis and abrogated expression of O-GlcNAcylated proteins associated with primary breast cancer. Proteomics 2013; 13:2088-99. [PMID: 23576270 DOI: 10.1002/pmic.201200126] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Revised: 02/20/2013] [Accepted: 03/26/2013] [Indexed: 02/06/2023]
Abstract
O-GlcNAcylation is a dynamic PTM of nuclear and cytoplasmic proteins, regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase, which catalyze the addition and removal of O-GlcNAc, respectively. This modification is associated with glucose metabolism, which plays important roles in many diseases including cancer. Although emerging evidence reveals that some tumor-associated proteins are O-GlcNAc modified, the total O-GlcNAcylation in cancer is still largely unexplored. Here, we demonstrate that O-GlcNAcylation was increased in primary breast malignant tumors, not in benign tumors and that this augmentation was associated with increased expression of OGT level. Using 2D O-GlcNAc immnoblotting and LC-MS/MS analysis, we successfully identified 29 proteins, with seven being uniquely O-GlcNAcylated or associated with O-GlcNAcylation in cancer. Of these identified proteins, some were related to the Warburg effect, including metabolic enzymes, proteins involved in stress responses and biosynthesis. In addition, proteins associated with RNA metabolism, gene expression, and cytoskeleton were highly O-GlcNAcylated or associated with O-GlcNAcylation. Moreover, OGT knockdown showed that decreasing O-GlcNAcylation was related to inhibition of the anchorage-independent growth in vitro. These data indicate that aberrant protein O-GlcNAcylation is associated with breast cancer. Abnormal modification of these O-GlcNAc-modified proteins might be one of the vital malignant characteristics of cancer.
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Majumdar D, Tiernan JP, Lobo AJ, Evans CA, Corfe BM. Keratins in colorectal epithelial function and disease. Int J Exp Pathol 2012; 93:305-18. [PMID: 22974212 DOI: 10.1111/j.1365-2613.2012.00830.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Keratins are the largest subgroup of intermediate filament proteins, which are an important constituent of the cellular cytoskeleton. The principally expressed keratins (K) of the intestinal epithelium are K8, K18 and K19. The specific keratin profile of a particular epithelium provides it with strength and integrity. In the colon, keratins have been shown to regulate electrolyte transport, likely by targeting ion transporters to their correct location in the colonocytes. Keratins are highly dynamic and are subject to post-translational modifications including phosphorylation, acetylation and glycosylation. These affect the filament dynamics and hence solubility of keratins and may contribute to protection against degradation. Keratin null mice (K8(-/-) ) develop colitis, and abnormal keratin mutations have been shown to be associated with inflammatory bowel disease (IBD). Abnormal expression of K7 and K20 has been noted in colitis-associated dysplasia and cancers. In sporadic colorectal cancers (CRCs) may be useful in predicting tumour prognosis; a low K20 expression is noted in CRCs with high microsatellite instability; and keratins have been noted as dysregulated in peri-adenomatous fields. Caspase-cleaved fragment of K18 (M30) in the serum of patients with CRC has been used as a marker of cancer load and to assess response to therapy. These data suggest an emerging importance of keratins in maintaining normal function of the gastrointestinal epithelium as well as being a marker of various colorectal diseases. This review will primarily focus on the biology of these proteins, physiological functions and alterations in IBD and CRCs.
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Affiliation(s)
- Debabrata Majumdar
- Molecular Gastroenterology Research Group, Academic Unit of Surgical Oncology, Department of Oncology, The Medical School, University of Sheffield, Sheffield, UK
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Drougat L, Olivier-Van Stichelen S, Mortuaire M, Foulquier F, Lacoste AS, Michalski JC, Lefebvre T, Vercoutter-Edouart AS. Characterization of O-GlcNAc cycling and proteomic identification of differentially O-GlcNAcylated proteins during G1/S transition. Biochim Biophys Acta Gen Subj 2012; 1820:1839-48. [PMID: 22967762 DOI: 10.1016/j.bbagen.2012.08.024] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Revised: 08/21/2012] [Accepted: 08/27/2012] [Indexed: 12/25/2022]
Abstract
BACKGROUND DNA replication represents a critical step of the cell cycle which requires highly controlled and ordered regulatory mechanisms to ensure the integrity of genome duplication. Among a plethora of elements, post-translational modifications (PTMs) ensure the spatiotemporal regulation of pivotal proteins orchestrating cell division. Despite increasing evidences showing that O-GlcNAcylation regulates mitotic events, the impact of this PTM in the early steps of the cell cycle remains poorly understood. METHODS AND RESULTS Quiescent MCF7 cells were stimulated by serum mitogens and cell cycle progression was determined by flow cytometry. The levels of O-GlcNAc modified proteins, O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA) were examined by Western blotting and OGA activity was measured during the progression of cells towards S phase. A global decrease in O-GlcNAcylation was observed at S phase entry, concomitantly to an increase in the activity of OGA. A combination of two-dimensional electrophoresis, Western blotting and mass spectrometry was then used to detect and identify cell cycle-dependent putative O-GlcNAcylated proteins. 58 cytoplasmic and nuclear proteins differentially O-GlcNAcylated through G1/S transition were identified and the O-GlcNAc variations of Cytokeratin 8, hnRNP K, Caprin-1, Minichromosome Maintenance proteins MCM3, MCM6 and MCM7 were validated by immunoprecipitation. CONCLUSIONS The dynamics of O-GlcNAc is regulated during G1/S transition and observed on key proteins involved in the cytoskeleton networks, mRNA processing, translation, protein folding and DNA replication. GENERAL SIGNIFICANCE Our results led us to propose that O-GlcNAcylation joins the PTMs that take part in the regulation of DNA replication initiation.
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Affiliation(s)
- Ludivine Drougat
- Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France
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19
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Rotty JD, Hart GW, Coulombe PA. Stressing the role of O-GlcNAc: linking cell survival to keratin modification. Nat Cell Biol 2010; 12:847-9. [PMID: 20811358 DOI: 10.1038/ncb0910-847] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mounting evidence suggests that keratin post-translational modifications are crucial for many cellular processes. Now, keratin 18 modified by the addition of an O-linked N-acetylglucosamine residue is shown to be as a critical effector of stress-responsive Akt signalling, providing an important link between keratin glycosylation and cell survival.
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20
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Ku NO, Toivola DM, Strnad P, Omary MB. Cytoskeletal keratin glycosylation protects epithelial tissue from injury. Nat Cell Biol 2010; 12:876-85. [PMID: 20729838 DOI: 10.1038/ncb2091] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Accepted: 07/27/2010] [Indexed: 12/25/2022]
Abstract
Keratins 8 and 18 (K8 and K18) are heteropolymeric intermediate filament phosphoglycoproteins of simple-type epithelia. Mutations in K8 and K18 predispose the affected individual to liver disease as they protect hepatocytes from apoptosis. K18 undergoes dynamic O-linked N-acetylglucosamine glycosylation at Ser 30, 31 and 49. We investigated the function of K18 glycosylation by generating mice that overexpress human K18 S30/31/49A substitution mutants that cannot be glycosylated (K18-Gly(-)), and compared the susceptibility of these mice to injury with wild-type and other keratin-mutant mice. K18-Gly(-) mice are more susceptible to liver and pancreatic injury and apoptosis induced by streptozotocin or to liver injury by combined N-acetyl-D-glucosaminidase inhibition and Fas administration. The enhanced apoptosis in the livers of mice that express K18-Gly(-) involves the inactivation of Akt1 and protein kinase Ctheta as a result of their site-specific hypophosphorylation. Akt1 binds to K8, which probably contributes to the reciprocal hyperglycosylation and hypophosphorylation of Akt1 that occurs on K18 hypoglycosylation, and leads to decreased Akt1 kinase activity. Therefore, K18 glycosylation provides a unique protective role in epithelial injury by promoting the phosphorylation and activation of cell-survival kinases.
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Affiliation(s)
- Nam-On Ku
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, 7744 Medical Science II, 1301 East Catherine Street, Ann Arbor, MI 48109-5622, USA.
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21
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Srikanth B, Vaidya MM, Kalraiya RD. O-GlcNAcylation determines the solubility, filament organization, and stability of keratins 8 and 18. J Biol Chem 2010; 285:34062-71. [PMID: 20729549 DOI: 10.1074/jbc.m109.098996] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Keratins 8 and 18 (K8/18) are intermediate filament proteins expressed specifically in simple epithelial tissues. Dynamic equilibrium of these phosphoglycoproteins in the soluble and filament pool is an important determinant of their cellular functions, and it is known to be regulated by site-specific phosphorylation. However, little is known about the role of dynamic O-GlcNAcylation on this keratin pair. Here, by comparing immortalized (Chang) and transformed hepatocyte (HepG2) cell lines, we have demonstrated that O-GlcNAcylation of K8/18 exhibits a positive correlation with their solubility (Nonidet P-40 extractability). Heat stress, which increases K8/18 solubility, resulted in a simultaneous increase in O-GlcNAc on these proteins. Conversely, increasing O-GlcNAc levels were associated with a concurrent increase in their solubility. This was also associated with a notable decrease in total cellular levels of K8/18. Unaltered levels of transcripts and the reduced half-life of K8 and K18 indicated their decreased stability on increasing O-GlcNAcylation. On the contrary, the K18 glycosylation mutant (K18 S29A/S30A/S48A) was notably more stable than the wild type K18 in Chang cells. The K18-O-GlcNAc mutant accumulated as aggregates upon stable expression, which possibly altered endogenous filament architecture. These results strongly indicate the involvement of O-GlcNAc on K8/18 in regulating their solubility and stability, which may have a bearing on the functions of these keratins.
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Affiliation(s)
- Budnar Srikanth
- Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Kharghar, Navi Mumbai 410210, India
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22
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Slawson C, Lakshmanan T, Knapp S, Hart GW. A mitotic GlcNAcylation/phosphorylation signaling complex alters the posttranslational state of the cytoskeletal protein vimentin. Mol Biol Cell 2008; 19:4130-40. [PMID: 18653473 DOI: 10.1091/mbc.e07-11-1146] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
O-linked beta-N-acetylglucosamine (O-GlcNAc) is a highly dynamic intracellular protein modification responsive to stress, hormones, nutrients, and cell cycle stage. Alterations in O-GlcNAc addition or removal (cycling) impair cell cycle progression and cytokinesis, but the mechanisms are not well understood. Here, we demonstrate that the enzymes responsible for O-GlcNAc cycling, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) are in a transient complex at M phase with the mitotic kinase Aurora B and protein phosphatase 1. OGT colocalized to the midbody during telophase with Aurora B. Furthermore, these proteins coprecipitated with each other in a late mitotic extract. The complex was stable under Aurora inhibition; however, the total cellular levels of O-GlcNAc were increased and the localization of OGT was decreased at the midbody after Aurora inhibition. Vimentin, an intermediate filament protein, is an M phase substrate for both Aurora B and OGT. Overexpression of OGT or OGA led to defects in mitotic phosphorylation on multiple sites, whereas OGT overexpression increased mitotic GlcNAcylation of vimentin. OGA inhibition caused a decrease in vimentin late mitotic phosphorylation but increased GlcNAcylation. Together, these data demonstrate that the O-GlcNAc cycling enzymes associate with kinases and phosphatases at M phase to regulate the posttranslational status of vimentin.
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Affiliation(s)
- Chad Slawson
- Department of Biological Chemistry, The Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
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23
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Hyder CL, Pallari HM, Kochin V, Eriksson JE. Providing cellular signposts - Post-translational modifications of intermediate filaments. FEBS Lett 2008; 582:2140-8. [DOI: 10.1016/j.febslet.2008.04.064] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2008] [Revised: 04/29/2008] [Accepted: 04/30/2008] [Indexed: 10/22/2022]
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24
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Gurcel C, Vercoutter-Edouart AS, Fonbonne C, Mortuaire M, Salvador A, Michalski JC, Lemoine J. Identification of new O-GlcNAc modified proteins using a click-chemistry-based tagging. Anal Bioanal Chem 2008; 390:2089-97. [DOI: 10.1007/s00216-008-1950-y] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2007] [Revised: 01/30/2008] [Accepted: 02/06/2008] [Indexed: 11/28/2022]
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25
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Cytokeratin fragments in the serum: their utility for the management of oral cancer. Oral Oncol 2008; 44:722-32. [PMID: 18203649 DOI: 10.1016/j.oraloncology.2007.10.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Revised: 10/30/2007] [Accepted: 10/31/2007] [Indexed: 11/23/2022]
Abstract
Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy and is a major cause of cancer morbidity and mortality worldwide. Oral cancer is the most predominant malignancy in the Indian subcontinent due to the widespread habits of chewing tobacco and related products. Patients with oral tumours have a high risk of early locoregional relapse. Early detection of disease progression remains a challenging task mainly due to the lack of adequate early prognostic markers. CEA, SCC Ag, CA-125, serum cytokeratin (CK) fragments, Cyfra 21-1 (CK 19), TPS (CK 18), TPA (CK 8, 18, and 19) etc. are being used as serum markers for the prediction of prognosis of various malignancies. This review presents the available literature on serum CK markers in different malignancies evaluates their utility in the management of oral cancer, and identifies the lacunae which need to be addressed to develop sensitive and specific assays for early detection of recurrence, prognosis, and treatment monitoring.
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26
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Tao GZ, Kirby C, Whelan SA, Rossi F, Bi X, MacLaren M, Gentalen E, O'Neill RA, Hart GW, Omary MB. Reciprocal keratin 18 Ser48 O-GlcNAcylation and Ser52 phosphorylation using peptide analysis. Biochem Biophys Res Commun 2006; 351:708-12. [PMID: 17084817 PMCID: PMC2692749 DOI: 10.1016/j.bbrc.2006.10.092] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2006] [Accepted: 10/19/2006] [Indexed: 12/19/2022]
Abstract
Phosphorylation and O-GlcNAcylation of keratin 18 (K18) are highly dynamic and involve primarily independent K18 populations. We used in vitro phosphorylation and O-GlcNAcylation of wild-type, phospho-Ser52, glyco-Ser48, and Ser-to-Ala mutant 17mer peptides (K18 amino acids 40-56), which include the major K18 glycosylation (Ser48) and phosphorylation (Ser52) sites, to address whether each modification blocks the other. The glyco-K18 peptide blocks Ser52 phosphorylation by protein kinase C, an in vivo K18 kinase, while the phospho-K18 peptide blocks its O-GlcNAcylation. Our findings support the reciprocity of these two post-translational modifications. Therefore, regulation of protein Ser/Thr phosphorylation and glycosylation at proximal sites can be interdependent and provides a potential mechanism of counter regulation.
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Affiliation(s)
- Guo-Zhong Tao
- Palo Alto VA Medical Center, Stanford University, Palo Alto, CA 94304, USA
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27
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Huq MDM, Khan SA, Park SW, Wei LN. Mapping of phosphorylation sites of nuclear corepressor receptor interacting protein 140 by liquid chromatography-tandem mass spectroscopy. Proteomics 2005; 5:2157-66. [PMID: 15846843 DOI: 10.1002/pmic.200401090] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Receptor interacting protein (RIP140) is a versatile coregulator for many nuclear receptors and transcription factors. Analysis by liqid chromatography tandem mass spectroscopy led to the identification of 11 phosphopeptides from tryptic digests of His6-RIP140 purified from Sf21 insect cells. No phosphopeptides were detected on RIP140 expressed in E. coli in a parallel experiment, suggesting that RIP140 phosphorylation occurred specifically only in eukaryotic cells. The tandem mass spectra of the precursor ions of the phosphopeptides were analyzed to map the exact phosphorylation sites on RIP140. All the phosphopeptides displayed intact phosphate containing y- or b-ion signals along with their beta-eliminated product ions, due to neutral loss of phosphoric acid. Phosphorylation occurred specifically on nine serine and a single threonine residues, including Ser-104, Thr-207, Ser-358, Ser-380, Ser-488, Ser-519, Ser-531, Ser-543, Ser-672, and Ser-1003. No tyrosine phosphorylation was found. These data suggested that the central region of RIP140, one major repressive domain, was extensively modified by phosphorylation. These phosphorylation sites can be the targets in future studies addressing post-translational modification of RIP140 with regards to its biological activities.
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Affiliation(s)
- M D Mostaqul Huq
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, 55455, USA
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28
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Barak V, Goike H, Panaretakis KW, Einarsson R. Clinical utility of cytokeratins as tumor markers. Clin Biochem 2005; 37:529-40. [PMID: 15234234 DOI: 10.1016/j.clinbiochem.2004.05.009] [Citation(s) in RCA: 230] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/04/2004] [Indexed: 12/22/2022]
Abstract
Cytokeratins, belonging to the intermediate filament (IF) protein family, are particularly useful tools in oncology diagnostics. At present, more than 20 different cytokeratins have been identified, of which cytokeratins 8, 18, and 19 are the most abundant in simple epithelial cells. Upon release from proliferating or apoptotic cells, cytokeratins provide useful markers for epithelial malignancies, distinctly reflecting ongoing cell activity. It appears that motifs in certain cytokeratins make them likely substrates for caspase degradation, and their subsequent release occurs during the intermediate events in apoptosis. The clinical value of determining soluble cytokeratin protein fragments in body fluids lies in the early detection of recurrence and the fast assessment of the efficacy of therapy response in epithelial cell carcinomas. The three most applied cytokeratin markers used in the clinic are tissue polypeptide antigen (TPA), tissue polypeptide specific antigen (TPS), and CYFRA 21-1. TPA is a broad spectrum test that measures cytokeratins 8, 18, and 19. TPS and CYFRA 21-1 assays are more specific and measure cytokeratin 18 and cytokeratin 19, respectively. By following patients with repeated testing during management, the oncologist may obtain critical information regarding the growth activity in symptomatic patients. Although their main use is to monitor treatment and evaluate response to therapy, early prognostic information particularly on tumor progression and metastasis formation is also provided for several types of cancers. Cytokeratin tumor markers can accurately predict disease status before conventional methods and offer a simple, noninvasive, cheap, and reliable tool for more efficient management.
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Affiliation(s)
- Vivian Barak
- Immunology Laboratory for Tumor Diagnosis, Oncology Department, Hadassah University Hospital, Jerusalem, Israel
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29
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Ku NO, Toivola DM, Zhou Q, Tao GZ, Zhong B, Omary MB. Studying simple epithelial keratins in cells and tissues. Methods Cell Biol 2004; 78:489-517. [PMID: 15646629 DOI: 10.1016/s0091-679x(04)78017-6] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Nam-On Ku
- Department of Medicine, Palo Alto VA Medical Center and Stanford University, Palo Alto, California 94304, USA
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30
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Kochin V, Pallari HM, Pant H, Eriksson JE. Approaches to Study Posttranslational Regulation of Intermediate Filament Proteins. Methods Cell Biol 2004; 78:373-409. [PMID: 15646626 DOI: 10.1016/s0091-679x(04)78014-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Affiliation(s)
- Vitaly Kochin
- Turku Centre for Biotechnology University of Turku, FIN-20521 Turku, Finland
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31
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Hatsell S, Medina L, Merola J, Haltiwanger R, Cowin P. Plakoglobin is O-glycosylated close to the N-terminal destruction box. J Biol Chem 2003; 278:37745-52. [PMID: 12847106 DOI: 10.1074/jbc.m301346200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Plakoglobin provides a key linkage in protein chains that connect desmosomal and classical cadherins to the cytoskeleton. It is also present in a significant cytosolic pool that has the capacity to impact on canonical Wnt signaling by competing for interaction with partner proteins of beta-catenin. The closely related protein, beta-catenin, is rapidly targeted for proteasomal degradation by phosphorylation of a "destruction box" within the N-terminal domain. Inhibition of this process forms the basis of Wnt signaling. This destruction box is also found in the N-terminal domain of plakoglobin. We report that plakoglobin is modified by the addition of O-GlcNAc at a single site in close proximity to the destruction box. O-GlcNAc modification has been proposed to counteract phosphorylation, provide protection from proteasomal degradation, mediate signal transduction, silence transcription, and regulate multimolecular protein assembly. This finding has potential implications for understanding the roles of plakoglobin.
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Affiliation(s)
- Sarah Hatsell
- Department of Cell Biology, New York University Medical School, New York, New York 10016, USA
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32
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Abstract
Beta-N-acetylglucosamine (O-GlcNAc) is a regulatory post-translational modification of nuclear and cytosolic proteins. The enzymes for its addition and removal have recently been cloned and partially characterized. While only about 80 mammalian proteins have been identified to date that carry this modification, it is clear that this represents just a small percentage of the modified proteins. O-GlcNAc has all the properties of a regulatory modification including being dynamic and inducible. The modification appears to modulate transcriptional and signal transduction events. There are also accruing data that O-GlcNAc plays a role in apoptosis and neurodegeneration. A working model is emerging that O-GlcNAc serves as a metabolic sensor that attenuates a cell's response to extracellular stimuli based on the energy state of the cell. In this review, we will focus on the enzymes that add/remove O-GlcNAc, the functional impact of O-GlcNAc modification, and the current working model for O-GlcNAc as a nutrient sensor.
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Affiliation(s)
- Lance Wells
- Department of Biological Chemistry, Johns Hopkins School of Medicine, 517 WBSB, 725 N. Wolfe St., Baltimore, MD 21205, USA
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33
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Affiliation(s)
- Natasha E Zachara
- The Department of Biological Chemistry, The Johns Hopkins University Medical School, Baltimore, Maryland 21205-2185, USA
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34
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Irvine AD, Rugg EL, Lane EB, Hoare S, Peret C, Hughes AE, Heagerty AH. Molecular confirmation of the unique phenotype of epidermolysis bullosa simplex with mottled pigmentation. Br J Dermatol 2001; 144:40-5. [PMID: 11167681 DOI: 10.1046/j.1365-2133.2001.03950.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND A distinctive subtype of epidermolysis bullosa simplex, with the additional feature of mottled pigmentation (EBS-MP), was initially characterized in a Swedish family in 1979, and seven further families have been reported. Features of EBS-MP that are observed in most affected patients include acral blistering early in childhood, mottled pigmentation distributed in a number of sites, focal punctate hyperkeratoses of the palms and soles, and dystrophic, thickened nails. The genetic basis of EBS-MP has been ascribed in five unrelated families to a heterozygous point mutation, P25L, in the non-helical V1 domain of K5. OBJECTIVES We report a clinical, ultrastructural and molecular study of two of the earliest families to be clinically characterized as EBS-MP. METHODS The P25L mutation was identified in all affected members of each of these families, bringing the total number of EBS-MP families with this mutation to seven. RESULTS This unusual recurrent mutation may uniquely cause EBS-MP. CONCLUSIONS While the exact molecular mechanisms by which this mutation causes epidermolysis, palmoplantar keratoderma and pigmentation remain elusive, we suggest possible molecular mechanisms through which the P25L substitution could cause this unusual phenotype.
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Affiliation(s)
- A D Irvine
- Department of Dermatology, The Hospital for Children, Great Ormond Street, London WC1N 3JH, UK.
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35
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Abstract
O-linked N-acetylglucosamine (O-GlcNAc) is a highly dynamic and abundant modification found on nuclear and cytoplasmic proteins of nearly all eukaryotes. O-GlcNAc addition is required for life at the single cell level and is analogous to protein phosphorylation in most respects. In a previous study (M.S. Jiang, G.W. Hart, A subpopulation of estrogen receptors are modified by O-linked N-acetylglucosamine. J. Biol. Chem. 270 (1997) 2421-2428), we demonstrated that a subpopulation of the murine estrogen receptor-alpha (mER-alpha) is modified by O-GlcNAc at Thr(575). Here we mutated mER-alpha to convert Thr(575) and Ser(576) to Val and Ala, respectively. Surprisingly, this glycosylation-site mutant is still extensively modified by O-GlcNAc. Analyses of glycopeptides identified two additional sites of modification on mER-alpha, at Ser(10) and Thr(50) near the N-terminus. The major glycosylation sites are within or near PEST regions, suggesting that O-GlcNAc may regulate mER-alpha turnover.
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Affiliation(s)
- X Cheng
- Department of Biological Chemistry, School of Medicine, Johns Hopkins University, 725 N Wolfe St., Baltimore, MD 21205-2185, USA
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36
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Mapping and Regulation of the Tumor-associated Epitope Recognized by Monoclonal Antibody RS-11. J Biol Chem 2000. [DOI: 10.1016/s0021-9258(19)61482-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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37
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Eriksson JE, Toivola DM, Sahlgren C, Mikhailov A, Härmälä-Braskén AS. Strategies to assess phosphoprotein phosphatase and protein kinase-mediated regulation of the cytoskeleton. Methods Enzymol 1998; 298:542-69. [PMID: 9751907 DOI: 10.1016/s0076-6879(98)98044-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- J E Eriksson
- Turku Centre for Biotechnology, University of Turku, Finland
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38
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Abstract
O-GlcNAcylation is a form of cytoplasmic and nuclear glycosylation that is found on many diverse proteins of the cell including RNA polymerase II and its associated transcription factors, cytoskeletal proteins, nucleoporins, viral proteins, heat shock proteins, tumor suppressors, and oncogenes. It involves the attachment of a single, unmodified N-acetylglucosaminyl residue O-glycosidically linked to the hydroxyl groups of serine and threonine moieties of proteins. It is a highly abundant and dynamic form of posttranslational modification that appears to modulate function in a manner similar to phosphorylation. All O-GlcNAc-containing proteins are phosphoproteins that are involved in the formation of multimeric complexes, suggesting that O-GlcNAc may play a role in mediating protein-protein interactions. O-GlcNAc sites resemble phosphorylation sites and in many cases the two modifications are mutually exclusive; therefore, O-GlcNAcylation may act as an antagonist of phosphorylation and help to mediate many essential functions of the cell.
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Affiliation(s)
- D M Snow
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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39
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Ku NO, Liao J, Omary MB. Phosphorylation of human keratin 18 serine 33 regulates binding to 14-3-3 proteins. EMBO J 1998; 17:1892-906. [PMID: 9524113 PMCID: PMC1170536 DOI: 10.1093/emboj/17.7.1892] [Citation(s) in RCA: 187] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Members of the 14-3-3 protein family bind the human intermediate filament protein keratin 18 (K18) in vivo, in a cell-cycle- and phosphorylation-dependent manner. We identified K18 Ser33 as an interphase phosphorylation site, which increases its phosphorylation during mitosis in cultured cells and regenerating liver, and as an in vitro cdc2 kinase phosphorylation site. Comparison of wild-type versus K18 Ser33-->Ala/Asp transfected cells showed that K18 Ser33 phosphorylation is essential for the association of K18 with 14-3-3 proteins, and plays a role in keratin organization and distribution. Mutation of another K18 major phosphorylation site (Ser52) or K18 glycosylation sites had no effect on the binding of K18 to 14-3-3 proteins. The K18 phospho-Ser33 motif is different from several 14-3-3-binding phosphomotifs already described. Antibodies that are specific to K18 phospho-Ser33 or phospho-Ser52 show that although Ser52 and Ser33 phosphorylated K18 molecules manifest partial colocalization, these phosphorylation events reside predominantly on distinct K18 molecules. Our results demonstrate a unique K18 phosphorylation site that is necessary but not sufficient for K18 binding to 14-3-3 proteins. This binding is likely to involve one or more mitotic events coupled to K18 Ser33 phosphorylation, and plays a role in keratin subcellular distribution. Physiological Ser52 or Ser33 phosphorylation on distinct K18 molecules suggests functional compartmentalization of these modifications.
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Affiliation(s)
- N O Ku
- VA Palo Alto Health Care System, 3801 Miranda Avenue, 154J, Palo Alto, CA 94304, USA
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40
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Abstract
Type I and II keratins help maintain the structural integrity of epithelial cells. Since apoptosis involves progressive cell breakdown, we examined its effect on human keratin polypeptides 8, 18, and 19 (K8, K18, K19) that are expressed in simple-type epithelia as noncovalent type I (K18, K19) and type II (K8) heteropolymers. Apoptosis induces rapid hyperphosphorylation of most known K8/18 phosphorylation sites and delayed formation of K18 and K19 stable fragments. In contrast, K8 is resistant to proteolysis and remains associated with the K18 fragments. Transfection of phosphorylation/glycosylation-mutant K8 and K18 does not alter fragment formation. The protein domains of the keratin fragments were determined using epitope-defined antibodies, and microsequencing indicated that K18 cleavage occurs at a conserved caspase-specific aspartic acid. The fragments are found preferentially within the detergent-insoluble pool and can be generated, in a phosphorylation-independent manner, by incubating keratins with caspase-3 or with detergent lysates of apoptotic cells but not with lysates of nonapoptotic cells. Our results indicate that type I keratins are targets of apoptosis-activated caspases, which is likely a general feature of keratins in most if not all epithelial cells undergoing apoptosis. Keratin hyperphosphorylation occurs early but does not render the keratins better substrates of the downstream caspases.
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Affiliation(s)
- N O Ku
- Veterans Administration Palo Alto Health Care System, Palo Alto, California 94304, USA
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Haltiwanger RS, Philipsberg GA. Mitotic arrest with nocodazole induces selective changes in the level of O-linked N-acetylglucosamine and accumulation of incompletely processed N-glycans on proteins from HT29 cells. J Biol Chem 1997; 272:8752-8. [PMID: 9079710 DOI: 10.1074/jbc.272.13.8752] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
O-Linked N-acetylglucosamine (O-GlcNAc) is a ubiquitous and abundant protein modification found on nuclear and cytoplasmic proteins. Several lines of evidence suggest that it is a highly dynamic modification and that the levels of this sugar on proteins may be regulated. Previous workers (Chou, C. F., and Omary, M. B. (1993) J. Biol. Chem. 268, 4465-4472) have shown that mitotic arrest with microtubule-destabilizing agents such as nocodazole causes an increase in the O-GlcNAc levels on keratins in the human colon cancer cell line HT29. We have sought to determine whether this increase in glycosylation is a general (i.e. occurring on many proteins) or a limited (i.e. occurring only on the keratins) process. A general increase would suggest that the microtubule-destabilizing agents were somehow affecting the enzymes responsible for addition and/or removal of O-GlcNAc. Our results suggest that the changes in O-GlcNAc induced by nocodazole are selective for the keratins. The levels of O-GlcNAc on other proteins, including the nuclear pore protein p62 and the transcription factor Sp1, are not significantly affected by this treatment. In agreement with these findings, nocodazole treatment caused no change in the activity of the enzymes responsible for addition or removal of O-GlcNAc as determined by direct in vitro assay. Interestingly, nocodazole treatment did cause a dramatic increase in modification of N-glycans with terminal GlcNAc residues on numerous proteins. Potential mechanisms for this and the change in glycosylation of the keratins are discussed.
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Affiliation(s)
- R S Haltiwanger
- Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, State University of New York, Stony Brook, New York 11794-5215, USA
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Ku NO, Omary MB. Phosphorylation of human keratin 8 in vivo at conserved head domain serine 23 and at epidermal growth factor-stimulated tail domain serine 431. J Biol Chem 1997; 272:7556-64. [PMID: 9054461 DOI: 10.1074/jbc.272.11.7556] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Dynamic phosphorylation is one mechanism that regulates the more than 20 keratin type I and II intermediate filament proteins in epithelial cells. The major type II keratin in "simple type" glandular epithelia is keratin 8 (K8). We used biochemical and mutational approaches to localize two major in vivo phosphorylation sites of human K8 to the head (Ser-23) and tail (Ser-431) domains. Since Ser-23 of K8 is highly conserved among all type II keratins, we also examined if the corresponding Ser-59 in stratified epithelial keratin 6e is phosphorylated. Mutation of K6e Ser-59 abolished its phosphorylation in 32PO4-labeled baby hamster kidney cell transfectants. With regard to K8 phosphorylation at Ser-431, it increases dramatically upon stimulation of cells with epidermal growth factor (EGF) or after mitotic arrest and is the major K8 phosphorylated residue after incubating K8 immunoprecipitates with mitogen-activated protein or cdc2 kinases. A monoclonal antibody that specifically recognizes phosphoserine 431-K8 manifests increased reactivity with K8 and recognizes reorganized K8/18 filaments after EGF stimulation. Our results suggest that in vivo serine phosphorylation of K8 and K6e within the conserved head domain motif is likely to reflect a conserved phosphorylation site of most if not all type II keratins. Furthermore, K8 Ser-431 phosphorylation occurs after EGF stimulation and during mitotic arrest and is likely to be mediated by mitogen-activated protein and cdc2 kinases, respectively.
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Affiliation(s)
- N O Ku
- Department of Medicine, Veterans Administration Palo Alto Health Care System, Palo Alto, California 94304, USA
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Haltiwanger RS, Busby S, Grove K, Li S, Mason D, Medina L, Moloney D, Philipsberg G, Scartozzi R. O-glycosylation of nuclear and cytoplasmic proteins: regulation analogous to phosphorylation? Biochem Biophys Res Commun 1997; 231:237-42. [PMID: 9070256 DOI: 10.1006/bbrc.1997.6110] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- R S Haltiwanger
- Department of Biochemistry and Cell Biology, State University of New York at Stony Brook 11794-5215, USA
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Abstract
Intermediate filament (IF) proteins, a large family of tissue specific proteins, undergo several posttranslational modifications, with phosphorylation being the most studied modification. IF protein phosphorylation is highly dynamic and involves the head and/or tail domains of these proteins, which are the domains that impart most of the structural heterogeneity and hence presumed tissue specific functions. Although the function of IF proteins remains poorly understood, several regulatory roles for IF protein phosphorylation have been identified or are emerging. Those roles include filament disassembly and reorganization, solubility, localization within specific cellular domains, association with other cytoplasmic or membrane associated proteins, protection against physiologic stress and mediation of tissue-specific functions. Understanding the mechanistic and functional aspects of IF protein phosphorylation is providing insights not only regarding the function of this modification, but also regarding the function of IF proteins.
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Affiliation(s)
- N O Ku
- VA Palo Alto Health Care System, CA 94304, USA
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Liao J, Ku NO, Omary MB. Two-dimensional gel analysis of glandular keratin intermediate filament phosphorylation. Electrophoresis 1996; 17:1671-6. [PMID: 8982599 DOI: 10.1002/elps.1150171104] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- J Liao
- VA Palo Alto Health Care System, CA, USA
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Dong DL, Xu ZS, Hart GW, Cleveland DW. Cytoplasmic O-GlcNAc modification of the head domain and the KSP repeat motif of the neurofilament protein neurofilament-H. J Biol Chem 1996; 271:20845-52. [PMID: 8702840 DOI: 10.1074/jbc.271.34.20845] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Neurofilaments, the major intermediate filaments in large myelinated neurons, are essential for specifying proper axonal caliber. Mammalian neurofilaments are obligate heteropolymers assembled from three polypeptides, neurofilament (NF)-H, NF-M, and NF-L, each of which undergoes phosphorylation at multiple sites. NF-M and NF-L are known to be modified by O-linked N-acetylglucosamine (O-GlcNAc) (Dong, D. L.-Y., Xu, Z.-S., Chevrier, M. R., Cotter, R. J., Cleveland, D. W., and Hart, G. W. (1993) J. Biol. Chem. 268, 16679-16687). Here we further report that NF-H is extensively modified by O-GlcNAc at Thr53, Ser54, and Ser56 in the head domain and, somewhat surprisingly, at multiple sites within the Lys-Ser-Pro repeat motif in the tail domain, a region in assembled neurofilaments known to be nearly stoichiometrically phosphorylated on each of the approximately 50 KSP repeats. Beyond the earlier identified sites on NF-M and NF-L, O-GlcNAc sites on Thr19 and Ser34 of NF-M and Ser34 and Ser48 of NF-L are also determined here, all of which are localized in head domain sequences critical for filament assembly. The proximity of O-GlcNAc and phosphorylation sites in both head and tail domains of each subunit indicates that these modifications may influence one another and play a role in filament assembly and network formation.
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Affiliation(s)
- D L Dong
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Ku NO, Michie SA, Soetikno RM, Resurreccion EZ, Broome RL, Oshima RG, Omary MB. Susceptibility to hepatotoxicity in transgenic mice that express a dominant-negative human keratin 18 mutant. J Clin Invest 1996; 98:1034-46. [PMID: 8770877 PMCID: PMC507520 DOI: 10.1172/jci118864] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Keratins 8 and 18 (K8/18) are intermediate filament phosphoglycoproteins that are expressed preferentially in simple-type epithelia. We recently described transgenic mice that express point-mutant human K18 (Ku, N.-O., S. Michie, R.G. Oshima, and M.B. Omary. 1995. J. Cell Biol. 131:1303-1314) and develop chronic hepatitis and hepatocyte fragility in association with hepatocyte keratin filament disruption. Here we show that mutant K18 expressing transgenic mice are highly susceptible to hepatotoxicity after acute administration of acetaminophen (400 mg/Kg) or chronic ingestion of griseofulvin (1.25% wt/wt of diet). The predisposition to hepatotoxicity results directly from the keratin mutation since nontransgenic or transgenic mice that express normal human K18 are more resistant. Hepatotoxicity was manifested by a significant difference in lethality, liver histopathology, and biochemical serum testing. Keratin glycosylation decreased in all griseofulvin-fed mice, whereas keratin phosphorylation increased dramatically preferentially in mice expressing normal K18. The phosphorylation increase in normal K18 after griseofulvin feeding appears to involve sites that are different to those that increase after partial hepatectomy. Our results indicate that hepatocyte intermediate filament disruption renders mice highly susceptible to hepatotoxicity, and raises the possibility that K18 mutations may predispose to drug hepatotoxicity. The dramatic phosphorylation increase in nonmutant keratins could provide survival advantage to hepatocytes.
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Affiliation(s)
- N O Ku
- Department of Medicine, VA Palo Alto Health Care System, California 94304, USA
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Liao J, Lowthert LA, Ku NO, Fernandez R, Omary MB. Dynamics of human keratin 18 phosphorylation: polarized distribution of phosphorylated keratins in simple epithelial tissues. J Biophys Biochem Cytol 1995; 131:1291-301. [PMID: 8522590 PMCID: PMC2120635 DOI: 10.1083/jcb.131.5.1291] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Phosphorylation of keratin polypeptides 8 and 18 (K8/18) and other intermediate filament proteins results in their reorganization in vitro and in vivo. In order to study functional aspects of human K18 phosphorylation, we generated and purified a polyclonal antibody (termed 3055) that specifically recognizes a major phosphorylation site (ser52) of human K18 but not dephosphorylated K18 or a ser52-->ala K18 mutant. Pulse-chase experiments followed by immunoprecipitation and peptide mapping of in vivo 32PO4-labeled K8/18 indicated that the overall phosphorylation turnover rate is faster for K18 versus K8, and that ser52 of K18 is a highly dynamic phosphorylation site. Isoelectric focusing of 32PO4 labeled K18 followed by immunoblotting with 3055 showed that the major phosphorylated K18 species contain ser52 phosphorylation but that some K18 molecules exist that are preferentially phosphorylated on K18 sites other than ser52. Immunoblotting of total cell lysates obtained from cells at different stages of the cell cycle showed that ser52 phosphorylation increases three to fourfold during the S and G2/M phases of the cell cycle. Immunofluorescence staining of cells at different stages of mitosis, using 3055 or other antibodies that recognize the total keratin pool, resulted in preferential binding of the 3055 antibody to the reorganized keratin fraction. Staining of human tissues or tissues from transgenic mice that express human K18 showed that the phospho-ser52 K18 species are located preferentially in the basolateral and apical domains in the liver and pancreas, respectively, but no preferential localization was noted in other simple epithelial organs examined. Our results support a model whereby phosphorylated intermediate filaments are localized in specific cellular domains depending on the tissue type and site(s) of phosphorylation. In addition, ser52 of human K18 is a highly dynamic phosphorylation site that undergoes modulation during the S and G2/M phases of the cell cycle in association with filament reorganization.
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Affiliation(s)
- J Liao
- VA Palo Alto Health Care System, California 94304, USA
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Ku NO, Michie S, Oshima RG, Omary MB. Chronic hepatitis, hepatocyte fragility, and increased soluble phosphoglycokeratins in transgenic mice expressing a keratin 18 conserved arginine mutant. J Cell Biol 1995; 131:1303-14. [PMID: 8522591 PMCID: PMC2120631 DOI: 10.1083/jcb.131.5.1303] [Citation(s) in RCA: 138] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The two major intermediate filament proteins in glandular epithelia are keratin polypeptides 8 and 18 (K8/18). To evaluate the function and potential disease association of K18, we examined the effects of mutating a highly conserved arginine (arg89) of K18. Expression of K18 arg89-->his/cys and its normal K8 partner in cultured cells resulted in punctate staining as compared with the typical filaments obtained after expression of wild-type K8/18. Generation of transgenic mice expressing human K18 arg89-->cys resulted in marked disruption of liver and pancreas keratin filament networks. The most prominent histologic abnormalities were liver inflammation and necrosis that appeared at a young age in association with hepatocyte fragility and serum transaminase elevation. These effects were caused by the mutation since transgenic mice expressing wild-type human K18 showed a normal phenotype. A relative increase in the phosphorylation and glycosylation of detergent solubilized K8/18 was also noted in vitro and in transgenic animals that express mutant K18. Our results indicate that the highly conserved arg plays an important role in glandular keratin organization and tissue fragility as already described for epidermal keratins. Phosphorylation and glycosylation alterations in the arg mutant keratins may account for some of the potential changes in the cellular function of these proteins. Mice expressing mutant K18 provide a novel animal model for human chronic hepatitis, and for studying the tissue specific function(s) of K8/18.
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Affiliation(s)
- N O Ku
- Department of Medicine, VA Palo Alto Health Care System, California 94304, USA
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