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Shi H, Chen Y, Li Y, Chen L, Wang H, Yang C, Ding L, Ju H. Hierarchical Fluorescence Imaging Strategy for Assessment of the Sialylation Level of Lipid Rafts on the Cell Membrane. Anal Chem 2021; 93:14643-14650. [PMID: 34698497 DOI: 10.1021/acs.analchem.1c02738] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Glycosylation is one of the most ubiquitous and complicated modifications of proteins and lipids. The revelation of glycosylation-mediated regulation mechanisms of biological processes relies critically on the tools that can reflect the spatial heterogeneity of cell surface glycans, for example, distinguishing glycans exhibited in lipid raft or nonraft domains. To achieve simultaneous visualization of raft and raft-harbored glycans on the cell surface, we combine specific raft recognition, glycan chemoselective labeling, and DNA dynamic hybridization techniques to develop a hierarchical fluorescence imaging strategy using N-acetyl-neuraminic acid (Sia) as the model sugar. We fabricate a raft probe and Sia probe for rafts and Sia, respectively. After specifically anchoring the two probes on the cell surface, the raft probe can be cyclically utilized to turn on the fluorescence of the Sia probe, only residing in rafts, via a proximity cascade DNA reaction. The duplex imaging capability for spatially relevant levels of biological structures enables the revelation of the reason for raft-confined Sia variation in different biological processes. Thus, this work provides an elegant and powerful tool for interrogation of the glycan regulation mechanisms on raft composition, organization, and functions and also contributes to the development of raft-carried glycoconjugate-based theranostic techniques.
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Affiliation(s)
- Huifang Shi
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Younan Chen
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Yiran Li
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Liusheng Chen
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Haiqi Wang
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Chen Yang
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Lin Ding
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
| | - Huangxian Ju
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Chemistry and Biomedicine Innovation Center, Nanjing University, Nanjing 210023, People's Republic of China
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2
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Peterson RJ, Koval M. Above the Matrix: Functional Roles for Apically Localized Integrins. Front Cell Dev Biol 2021; 9:699407. [PMID: 34485286 PMCID: PMC8414885 DOI: 10.3389/fcell.2021.699407] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 07/23/2021] [Indexed: 12/14/2022] Open
Abstract
Integrins are transmembrane proteins that are most typically thought of as integrating adhesion to the extracellular matrix with intracellular signaling and cell regulation. Traditionally, integrins are found at basolateral and lateral cell surfaces where they facilitate binding to the ECM and intercellular adhesion through cytosolic binding partners that regulate organization of actin microfilaments. However, evidence is accumulating that integrins also are apically localized, either endogenously or due to an exogenous stimulus. Apically localized integrins have been shown to regulate several processes by interacting with proteins such as connexins, tight junction proteins, and polarity complex proteins. Integrins can also act as receptors to mediate endocytosis. Here we review these newly appreciated roles for integrins localized to the apical cell surface.
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Affiliation(s)
- Raven J Peterson
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA, United States
| | - Michael Koval
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA, United States.,Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, United States
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3
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Increased plasmin-mediated proteolysis of L1CAM in a mouse model of idiopathic normal pressure hydrocephalus. Proc Natl Acad Sci U S A 2021; 118:2010528118. [PMID: 34380733 PMCID: PMC8379912 DOI: 10.1073/pnas.2010528118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Idiopathic normal pressure hydrocephalus (iNPH) is the most common form of adult-onset hydrocephalus, but its etiology is poorly understood. Symptoms develop in previously normal individuals and include gait difficulty, incontinence, and dementia. We recently reported that 15% of iNPH patients harbor heterozygous loss-of-function deletions in CWH43, which encodes a protein that modifies other cell membrane proteins. Mice harboring CWH43 deletions develop hydrocephalus and gait dysfunction. Mutations affecting the L1CAM adhesion protein cause developmental brain abnormalities and hydrocephalus from birth. Here, we show that CWH43 deletion leads to L1CAM hypoglycosylation, decreased L1CAM association with lipid microdomains, increased plasmin-mediated L1CAM cleavage, and decreased L1CAM expression. Thus, decreased L1CAM expression appears to occur in adult-onset iNPH and congenital hydrocephalus. Idiopathic normal pressure hydrocephalus (iNPH) is a common neurological disorder that is characterized by enlarged cerebral ventricles, gait difficulty, incontinence, and dementia. iNPH usually develops after the sixth decade of life in previously asymptomatic individuals. We recently reported that loss-of-function deletions in CWH43 lead to the development of iNPH in a subgroup of patients, but how this occurs is poorly understood. Here, we show that deletions in CWH43 decrease expression of the cell adhesion molecule, L1CAM, in the brains of CWH43 mutant mice and in human HeLa cells harboring a CWH43 deletion. Loss-of-function mutations in L1CAM are a common cause of severe neurodevelopmental defects that include congenital X-linked hydrocephalus. Mechanistically, we find that CWH43 deletion leads to decreased N-glycosylation of L1CAM, decreased association of L1CAM with cell membrane lipid microdomains, increased L1CAM cleavage by plasmin, and increased shedding of cleaved L1CAM in the cerebrospinal fluid. CWH43 deletion also decreased L1CAM nuclear translocation, suggesting decreased L1CAM intracellular signaling. Importantly, the increase in L1CAM cleavage occurred primarily in the ventricular and subventricular zones where brain CWH43 is most highly expressed. Thus, CWH43 deletions may contribute to adult-onset iNPH by selectively downregulating L1CAM in the ventricular and subventricular zone.
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4
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Geng X, Zhang S, He J, Ma A, Li Y, Li M, Zhou H, Chen G, Yang B. The urea transporter UT-A1 plays a predominant role in a urea-dependent urine-concentrating mechanism. J Biol Chem 2020; 295:9893-9900. [PMID: 32461256 PMCID: PMC7380188 DOI: 10.1074/jbc.ra120.013628] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 05/22/2020] [Indexed: 12/12/2022] Open
Abstract
Urea transporters are a family of urea-selective channel proteins expressed in multiple tissues that play an important role in the urine-concentrating mechanism of the mammalian kidney. Previous studies have shown that knockout of urea transporter (UT)-B, UT-A1/A3, or all UTs leads to urea-selective diuresis, indicating that urea transporters have important roles in urine concentration. Here, we sought to determine the role of UT-A1 in the urine-concentrating mechanism in a newly developed UT-A1-knockout mouse model. Phenotypically, daily urine output in UT-A1-knockout mice was nearly 3-fold that of WT mice and 82% of all-UT-knockout mice, and the UT-A1-knockout mice had significantly lower urine osmolality than WT mice. After 24-h water restriction, acute urea loading, or high-protein (40%) intake, UT-A1-knockout mice were unable to increase urine-concentrating ability. Compared with all-UT-knockout mice, the UT-A1-knockout mice exhibited similarly elevated daily urine output and decreased urine osmolality, indicating impaired urea-selective urine concentration. Our experimental findings reveal that UT-A1 has a predominant role in urea-dependent urine-concentrating mechanisms, suggesting that UT-A1 represents a promising diuretic target.
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Affiliation(s)
- Xiaoqiang Geng
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Shun Zhang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Jinzhao He
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Ang Ma
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Yingjie Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Min Li
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Hong Zhou
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Guangping Chen
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Baoxue Yang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China
- Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Beijing, China
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5
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Su H, Ye C, Sands JM, Zhang C. E3 ligase MDM2 mediates urea transporter-A1 ubiquitination under either constitutive or stimulatory conditions. Am J Physiol Renal Physiol 2019; 317:F1331-F1341. [PMID: 31509007 PMCID: PMC6879931 DOI: 10.1152/ajprenal.00316.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Revised: 08/27/2019] [Accepted: 08/31/2019] [Indexed: 11/22/2022] Open
Abstract
Posttranslational modifications are essential for the regulation of urea transporter-A1 (UT-A1), among which ubiquitination is a rather attractive and complex issue. Previously, our group reported that murine double minute 2 (MDM2) is one of the E3 ubiquitin ligases for UT-A1, and, later, we showed that ubiquitination contributes to the subcellular trafficking and stability of UT-A1. In the present study, we discovered that MDM2 interacts with UT-A1 in an AP50 (a component of the clathrin-coated pit)-dependent manner. However, their binding is irrelevant to the phosphorylatory status of UT-A1. Next, our findings indicated that MDM2 decreases the stability of either total or membrane UT-A1. On the cell membrane, MDM2 and ubiquitinated UT-A1 are both distributed in the lipid raft domain, and their linkage is obviously enhanced under forskolin (FSK) stimulation. In line with these results, in the diabetic rat, not only MDM2 but also ubiquitinated UT-A1 are intensified. Also, in vitro high glucose and angiotensin II play similar roles as FSK does on the association of MDM2 with UT-A1. In conclusion, MDM2 binds with UT-A1 and mediates its ubiquitination and degradation in an AP50-dependent manner, and their binding capacity is strengthened under FSK and diabetic milieu.
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Affiliation(s)
- Hua Su
- Department of Nephrology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Chen Ye
- Department of Nephrology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jeff M Sands
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
| | - Chun Zhang
- Department of Nephrology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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6
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Recabarren-Leiva D, Alarcón M. New insights into the gene expression associated to amyotrophic lateral sclerosis. Life Sci 2018; 193:110-123. [DOI: 10.1016/j.lfs.2017.12.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2017] [Revised: 12/01/2017] [Accepted: 12/10/2017] [Indexed: 12/11/2022]
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7
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Abstract
Three neurodegenerative diseases [Amyotrophic Lateral Sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD)] have many characteristics like pathological mechanisms and genes. In this sense some researchers postulate that these diseases share the same alterations and that one alteration in a specific protein triggers one of these diseases. Analyses of gene expression may shed more light on how to discover pathways, pathologic mechanisms associated with the disease, biomarkers and potential therapeutic targets. In this review, we analyze four microarrays related to three neurodegenerative diseases. We will systematically examine seven genes (CHN1, MDH1, PCP4, RTN1, SLC14A1, SNAP25 and VSNL1) that are altered in the three neurodegenerative diseases. A network was built and used to identify pathways, miRNA and drugs associated with ALS, AD and PD using Cytoscape software an interaction network based on the protein interactions of these genes. The most important affected pathway is PI3K-Akt signalling. Thirteen microRNAs (miRNA-19B1, miRNA-107, miRNA-124-1, miRNA-124-2, miRNA-9-2, miRNA-29A, miRNA-9-3, miRNA-328, miRNA-19B2, miRNA-29B2, miRNA-124-3, miRNA-15A and miRNA-9-1) and four drugs (Estradiol, Acetaminophen, Resveratrol and Progesterone) for new possible treatments were identified.
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Affiliation(s)
| | - Marcelo Alarcón
- Department of Clinical Biochemistry and Immunohematology, Faculty of Health Sciences, Universidad de Talca, Talca 3460000, Chile; Interdisciplinary Excellence Research Program on Healthy Aging (PIEI-ES), Universidad de Talca, Talca 3460000, Chile.
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8
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Hou R, Alemozaffar M, Yang B, Sands JM, Kong X, Chen G. Identification of a Novel UT-B Urea Transporter in Human Urothelial Cancer. Front Physiol 2017; 8:245. [PMID: 28503151 PMCID: PMC5409228 DOI: 10.3389/fphys.2017.00245] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Accepted: 04/07/2017] [Indexed: 02/01/2023] Open
Abstract
The urea transporter UT-B is widely expressed and has been studied in erythrocyte, kidney, brain and intestines. Interestingly, UT-B gene has been found more abundant in bladder than any other tissue. Recently, gene analyses demonstrate that SLC14A1 (UT-B) gene mutations are associated with bladder cancer, suggesting that urea transporter UT-B may play an important role in bladder carcinogenesis. In this study, we examined UT-B expression in bladder cancer with human primary bladder cancer tissues and cancer derived cell lines. Human UT-B has two isoforms. We found that normal bladder expresses long form of UT-B2 but was lost in 8 of 24 (33%) or significantly downregulated in 16 of 24 (67%) of primary bladder cancer patients. In contrast, the short form of UT-B1 lacking exon 3 was detected in 20 bladder cancer samples. Surprisingly, a 24-nt in-frame deletion in exon 4 in UT-B1 (UT-B1Δ24) was identified in 11 of 20 (55%) bladder tumors. This deletion caused a functional defect of UT-B1. Immunohistochemistry revealed that UT-B protein levels were significantly decreased in bladder cancers. Western blot analysis showed a weak UT-B band of 40 kDa in some tumors, consistent with UT-B1 gene expression detected by RT-PCR. Interestingly, bladder cancer associate UT-B1Δ24 was barely sialylated, reflecting impaired glycosylation of UT-B1 in bladder tumors. In conclusion, SLC14A1 gene and UT-B protein expression are significantly changed in bladder cancers. The aberrant UT-B expression may promote bladder cancer development or facilitate carcinogenesis induced by other carcinogens.
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Affiliation(s)
- Ruida Hou
- Department of Urology, China-Japan Union Hospital, Jilin UniversityChangchun, China.,Department of Physiology, Emory University School of MedicineAtlanta, GA, USA
| | | | - Baoxue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking UniversityBeijing, China
| | - Jeff M Sands
- Department of Physiology, Emory University School of MedicineAtlanta, GA, USA.,Renal Division Department of Medicine, Emory University School of MedicineAtlanta, GA, USA
| | - Xiangbo Kong
- Department of Urology, China-Japan Union Hospital, Jilin UniversityChangchun, China
| | - Guangping Chen
- Department of Physiology, Emory University School of MedicineAtlanta, GA, USA.,Renal Division Department of Medicine, Emory University School of MedicineAtlanta, GA, USA
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9
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Thomson RB, Thomson CL, Aronson PS. N-glycosylation critically regulates function of oxalate transporter SLC26A6. Am J Physiol Cell Physiol 2016; 311:C866-C873. [PMID: 27681177 DOI: 10.1152/ajpcell.00171.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 09/22/2016] [Indexed: 11/22/2022]
Abstract
The brush border Cl--oxalate exchanger SLC26A6 plays an essential role in mediating intestinal secretion of oxalate and is crucial for the maintenance of oxalate homeostasis and the prevention of hyperoxaluria and calcium oxalate nephrolithiasis. Previous in vitro studies have suggested that SLC26A6 is heavily N-glycosylated. N-linked glycosylation is known to critically affect folding, trafficking, and function in a wide variety of integral membrane proteins and could therefore potentially have a critical impact on SLC26A6 function and subsequent oxalate homeostasis. Through a series of enzymatic deglycosylation studies we confirmed that endogenously expressed mouse and human SLC26A6 are indeed glycosylated, that the oligosaccharides are principally attached via N-glycosidic linkage, and that there are tissue-specific differences in glycosylation. In vitro cell culture experiments were then used to elucidate the functional significance of the addition of the carbohydrate moieties. Biotinylation studies of SLC26A6 glycosylation mutants indicated that glycosylation is not essential for cell surface delivery of SLC26A6 but suggested that it may affect the efficacy with which it is trafficked and maintained in the plasma membrane. Functional studies of transfected SLC26A6 demonstrated that glycosylation at two sites in the putative second extracellular loop of SLC26A6 is critically important for chloride-dependent oxalate transport and that enzymatic deglycosylation of SLC26A6 expressed on the plasma membrane of intact cells strongly reduced oxalate transport activity. Taken together, these studies indicated that oxalate transport function of SLC26A6 is critically dependent on glycosylation and that exoglycosidase-mediated deglycosylation of SLC26A6 has the capacity to profoundly modulate SLC26A6 function.
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Affiliation(s)
- R Brent Thomson
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
| | - Claire L Thomson
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
| | - Peter S Aronson
- Section of Nephrology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
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10
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Qian X, Sands JM, Song X, Chen G. Modulation of kidney urea transporter UT-A3 activity by alpha2,6-sialylation. Pflugers Arch 2016; 468:1161-1170. [PMID: 26972907 PMCID: PMC4945389 DOI: 10.1007/s00424-016-1802-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 02/16/2016] [Accepted: 02/23/2016] [Indexed: 10/22/2022]
Abstract
Two urea transporters, UT-A1 and UT-A3, are expressed in the kidney terminal inner medullary collecting duct (IMCD) and are important for the production of concentrated urine. UT-A1, as the largest isoform of all UT-A urea transporters, has gained much attention and been extensively studied; however, the role and the regulation of UT-A3 are less explored. In this study, we investigated UT-A3 regulation by glycosylation modification. A site-directed mutagenesis verified a single glycosylation site in UT-A3 at Asn279. Loss of the glycosylation reduced forskolin-stimulated UT-A3 cell membrane expression and urea transport activity. UT-A3 has two glycosylation forms, 45 and 65 kDa. Using sugar-specific binding lectins, the UT-A3 glycosylation profile was examined. The 45-kDa form was pulled down by lectin concanavalin A (Con A) and Galant husnivalis lectin (GNL), indicating an immature glycan with a high amount of mannose (Man), whereas the 65-kDa form is a mature glycan composed of acetylglucosamine (GlcNAc) and poly-N-acetyllactosame (poly-LacNAc) that was pulled down by wheat germ agglutinin (WGA) and tomato lectin, respectively. Interestingly, the mature form of UT-A3 glycan contains significant amounts of sialic acid. We explored the enzymes responsible for directing UT-A3 sialylation. Sialyltransferase ST6GalI, but not ST3GalIV, catabolizes UT-A3 α2,6-sialylation. Activation of protein kinase C (PKC) by PDB treatment promoted UT-A3 glycan sialylation and membrane surface expression. The PKC inhibitor chelerythrine blocks ST6GalI-induced UT-A3 sialylation. Increased sialylation by ST6GalI increased UT-A3 protein stability and urea transport activity. Collectively, our study reveals a novel mechanism of UT-A3 regulation by ST6GalI-mediated sialylation modification that may play an important role in kidney urea reabsorption and the urinary concentrating mechanism.
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Affiliation(s)
- Xiaoqian Qian
- Department of Physiology, Emory University, Atlanta, GA 30322, USA
- Cardiovascular Center, the 4 affiliated hospital, Harbin Medical University, Heilongjiang 150001, China
| | - Jeff M. Sands
- Department of Physiology, Emory University, Atlanta, GA 30322, USA
- Renal Division, Department of Medicine, Emory University, Atlanta, GA 30322, USA
| | - Xiang Song
- Cardiovascular Center, the 4 affiliated hospital, Harbin Medical University, Heilongjiang 150001, China
| | - Guangping Chen
- Department of Physiology, Emory University, Atlanta, GA 30322, USA
- Renal Division, Department of Medicine, Emory University, Atlanta, GA 30322, USA
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11
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Toyoda Y, Takada T, Miyata H, Ishikawa T, Suzuki H. Regulation of the Axillary Osmidrosis-Associated ABCC11 Protein Stability by N-Linked Glycosylation: Effect of Glucose Condition. PLoS One 2016; 11:e0157172. [PMID: 27281343 PMCID: PMC4900533 DOI: 10.1371/journal.pone.0157172] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Accepted: 05/25/2016] [Indexed: 01/09/2023] Open
Abstract
ATP-binding cassette C11 (ABCC11) is a plasma membrane protein involved in the transport of a variety of lipophilic anions. ABCC11 wild-type is responsible for the high-secretion phenotypes in human apocrine glands, such as that of wet-type ear wax, and the risk of axillary osmidrosis. We have previously reported that mature ABCC11 is a glycoprotein containing two N-linked glycans at Asn838 and Asn844. However, little is known about the role of N-linked glycosylation in the regulation of ABCC11 protein. In the current study, we investigated the effects of N-linked glycosylation on the protein level and localization of ABCC11 using polarized Madin-Darby canine kidney II cells. When the N-linked glycosylation in ABCC11-expressing cells was chemically inhibited by tunicamycin treatment, the maturation of ABCC11 was suppressed and its protein level was significantly decreased. Immunoblotting analyses demonstrated that the protein level of the N-linked glycosylation-deficient mutant (N838Q and N844Q: Q838/844) was about half of the ABCC11 wild-type level. Further biochemical studies with the Q838/844 mutant showed that this glycosylation-deficient ABCC11 was degraded faster than wild-type probably due to the enhancement of the MG132-sensitive protein degradation pathway. Moreover, the incubation of ABCC11 wild-type-expressing cells in a low-glucose condition decreased mature, glycosylated ABCC11, compared with the high-glucose condition. On the other hand, the protein level of the Q838/844 mutant was not affected by glucose condition. These results suggest that N-linked glycosylation is important for the protein stability of ABCC11, and physiological alteration in glucose may affect the ABCC11 protein level and ABCC11-related phenotypes in humans, such as axillary osmidrosis.
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Affiliation(s)
- Yu Toyoda
- Department of Pharmacy, The University of Tokyo Hospital, Tokyo, Japan
- * E-mail:
| | - Tappei Takada
- Department of Pharmacy, The University of Tokyo Hospital, Tokyo, Japan
| | - Hiroshi Miyata
- Department of Pharmacy, The University of Tokyo Hospital, Tokyo, Japan
| | | | - Hiroshi Suzuki
- Department of Pharmacy, The University of Tokyo Hospital, Tokyo, Japan
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12
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Chen M, Cai H, Klein JD, Laur O, Chen G. Dexamethasone increases aquaporin-2 protein expression in ex vivo inner medullary collecting duct suspensions. Front Physiol 2015; 6:310. [PMID: 26578982 PMCID: PMC4630297 DOI: 10.3389/fphys.2015.00310] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 10/14/2015] [Indexed: 12/25/2022] Open
Abstract
Aquaporin-2 (AQP2) is the vasopressin-regulated water channel that controls renal water reabsorption and plays an important role in the maintenance of body water homeostasis. Excessive glucocorticoid as often seen in Cushing's syndrome causes water retention. However, whether and how glucocorticoid regulates AQP2 remains unclear. In this study, we examined the direct effect of dexamethasone on AQP2 protein expression and activity. Dexamethasone increased AQP2 protein abundance in rat inner medullary collecting duct (IMCD) suspensions. This was confirmed in HEK293 cells transfected with AQP2 cDNA. Cell surface protein biotinylation showed an increase of dexamethasone-induced cell membrane AQP2 expression and this effect was blocked by glucocorticoid receptor antagonist RU486. Functionally, dexamethasone treatment of oocytes injected with an AQP2 cRNA increased water transport activity as judged by cell rupture time in a hypo-osmotic solution (66 ± 13 s in dexamethasone vs. 101 ± 11 s in control, n = 15). We further found that dexamethasone treatment reduced AQP2 protein degradation, which could result in an increase of AQP2 protein. Interestingly, dexamethasone promoted cell membrane AQP2 moving to less buoyant lipid raft submicrodomains. Taken together, our data demonstrate that dexamethasone promotes AQP2 protein expression and increases water permeability mainly via inhibition of AQP2 protein degradation. The increase in AQP2 activity promotes water reabsorption, which may contribute to glucocorticoid-induced water retention and hypertension.
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Affiliation(s)
- Minguang Chen
- Division of Nephrology, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University Wenzhou, China ; Department of Physiology, Emory University School of Medicine Atlanta, GA, USA
| | - Hui Cai
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA ; Renal Division, Department of Medicine, Emory University School of Medicine Atlanta, GA, USA
| | - Janet D Klein
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA ; Renal Division, Department of Medicine, Emory University School of Medicine Atlanta, GA, USA
| | - Oskar Laur
- Department of Microbiology and Immunology, Emory University School of Medicine Atlanta, GA, USA
| | - Guangping Chen
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA ; Renal Division, Department of Medicine, Emory University School of Medicine Atlanta, GA, USA
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13
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Qian X, Li X, Ilori TO, Klein JD, Hughey RP, Li CJ, Alli AA, Guo Z, Yu P, Song X, Chen G. RNA-seq analysis of glycosylation related gene expression in STZ-induced diabetic rat kidney inner medulla. Front Physiol 2015; 6:274. [PMID: 26483702 PMCID: PMC4590316 DOI: 10.3389/fphys.2015.00274] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2015] [Accepted: 09/17/2015] [Indexed: 12/30/2022] Open
Abstract
The UT-A1 urea transporter is crucial to the kidney's ability to generate concentrated urine. Native UT-A1 from kidney inner medulla (IM) is a heavily glycosylated protein with two glycosylation forms of 97 and 117 kDa. In diabetes, UT-A1 protein abundance, particularly the 117 kD isoform, is significantly increased corresponding to an increased urea permeability in perfused IM collecting ducts, which plays an important role in preventing the osmotic diuresis caused by glucosuria. However, how the glycan carbohydrate structure change and the glycan related enzymes regulate kidney urea transport activity, particularly under diabetic condition, is largely unknown. In this study, using sugar-specific binding lectins, we found that the carbohydrate structure of UT-A1 is changed with increased amounts of sialic acid, fucose, and increased glycan branching under diabetic conditions. These changes were accompanied by altered UT-A1 association with the galectin proteins, β-galactoside glycan binding proteins. To explore the molecular basis of the alterations of glycan structures, the highly sensitive next generation sequencing (NGS) technology, Illumina RNA-seq, was employed to analyze genes involved in the process of UT-A1 glycosylation using streptozotocin (STZ)—induced diabetic rat kidney. Differential gene expression analysis combining with quantitative PCR revealed that expression of a number of important glycosylation related genes were changed under diabetic conditions. These genes include the glycosyltransferase genes Mgat4a, the sialylation enzymes St3gal1 and St3gal4 and glycan binding protein galectin-3, -5, -8, and -9. In contrast, although highly expressed in kidney IM, the glycosyltransferase genes Mgat1, Mgat2, and fucosyltransferase Fut8, did not show any changes. Conclusions: In diabetes, not only is UT-A1 protein abundance increased but the protein's glycan structure is also significantly changed. UT-A1 protein becomes highly sialylated, fucosylated and branched. Consistently, a number of crucial glycosylation related genes are changed under diabetic conditions. The alteration of these genes may contribute to changes in the UT-A1 glycan structure and therefore modulate kidney urea transport activity and alleviate osmotic diuresis caused by glucosuria in diabetes.
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Affiliation(s)
- Xiaoqian Qian
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA ; Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University Harbin, China
| | - Xuechen Li
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA
| | - Titilayo O Ilori
- Renal Division, Department of Medicine, Emory University School of Medicine Atlanta, GA, USA
| | - Janet D Klein
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA ; Renal Division, Department of Medicine, Emory University School of Medicine Atlanta, GA, USA
| | - Rebecca P Hughey
- Renal-Electrolyte Division and Department of Cell Biology and Physiology, Department of Medicine, University of Pittsburgh School of Medicine Pittsburgh, PA, USA
| | - Cong-Jun Li
- Bovine Functional Genomics Laboratory, United States Department of Agriculture - Agricultural Research Service Beltsville, MD, USA
| | - Abdel A Alli
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA
| | - Zhengyu Guo
- Department of Electrical and Computer Engineering, TEES-AgriLife Center for Bioinformatics and Genomic Systems Engineering, Texas A&M University College Station, TX, USA
| | - Peng Yu
- Department of Electrical and Computer Engineering, TEES-AgriLife Center for Bioinformatics and Genomic Systems Engineering, Texas A&M University College Station, TX, USA
| | - Xiang Song
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University Harbin, China
| | - Guangping Chen
- Department of Physiology, Emory University School of Medicine Atlanta, GA, USA ; Renal Division, Department of Medicine, Emory University School of Medicine Atlanta, GA, USA
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14
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Glycosylation of solute carriers: mechanisms and functional consequences. Pflugers Arch 2015; 468:159-76. [PMID: 26383868 DOI: 10.1007/s00424-015-1730-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/19/2015] [Accepted: 08/21/2015] [Indexed: 12/21/2022]
Abstract
Solute carriers (SLCs) are one of the largest groups of multi-spanning membrane proteins in mammals and include ubiquitously expressed proteins as well as proteins with highly restricted tissue expression. A vast number of studies have addressed the function and organization of SLCs as well as their posttranslational regulation, but only relatively little is known about the role of SLC glycosylation. Glycosylation is one of the most abundant posttranslational modifications of animal proteins and through recent advances in our understanding of protein-glycan interactions, the functional roles of SLC glycosylation are slowly emerging. The purpose of this review is to provide a concise overview of the aspects of glycobiology most relevant to SLCs, to discuss the roles of glycosylation in the regulation and function of SLCs, and to outline the major open questions in this field, which can now be addressed given major technical advances in this and related fields of study in recent years.
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15
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Extracellular Vesicles from Ovarian Carcinoma Cells Display Specific Glycosignatures. Biomolecules 2015; 5:1741-61. [PMID: 26248080 PMCID: PMC4598773 DOI: 10.3390/biom5031741] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2015] [Revised: 06/22/2015] [Accepted: 07/28/2015] [Indexed: 12/19/2022] Open
Abstract
Cells release vesicles to the extracellular environment with characteristic nucleic acid, protein, lipid, and glycan composition. Here we have isolated and characterized extracellular vesicles (EVs) and total cell membranes (MBs) from ovarian carcinoma OVMz cells. EVs were enriched in specific markers, including Tsg101, CD63, CD9, annexin-I, and MBs contained markers of cellular membrane compartments, including calnexin, GRASP65, GS28, LAMP-1, and L1CAM. The glycoprotein galectin-3 binding protein (LGALS3BP) was strongly enriched in EVs and it contained sialylated complex N-glycans. Lectin blotting with a panel of lectins showed that EVs had specific glycosignatures relative to MBs. Furthermore, the presence of glycoproteins bearing complex N-glycans with α2,3-linked sialic acid, fucose, bisecting-GlcNAc and LacdiNAc structures, and O-glycans with the T-antigen were detected. The inhibition of N-glycosylation processing from high mannose to complex glycans using kifunensine caused changes in the composition of EVs and induced a decrease of several glycoproteins. In conclusion, the results showed that glycosignatures of EVs were specific and altered glycosylation within the cell affected the composition and/or dynamics of EVs release. Furthermore, the identified glycosignatures of EVs could provide novel biomarkers for ovarian cancer.
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16
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Karlsson I, Zhou X, Thomas R, Smith AT, Bonner MY, Bakshi P, Banga AK, Bowen JP, Qabaja G, Ford SL, Ballard MD, Petersen KS, Li X, Chen G, Ogretmen B, Zhang J, Watkins EB, Arnold RS, Arbiser JL. Solenopsin A and analogs exhibit ceramide-like biological activity. Vasc Cell 2015; 7:5. [PMID: 26015865 PMCID: PMC4443652 DOI: 10.1186/s13221-015-0030-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Accepted: 04/21/2015] [Indexed: 11/23/2022] Open
Abstract
BACKGROUND (-)-Solenopsin A is a piperidine alkaloid that is a component of the venom of the fire ant Solenopsis invicta. Previously, we have demonstrated that solenopsin exhibit anti-angiogenic activity and downregulate phosphoinositol-3 kinase (PI3K) in the p53 deficient renal cell carcinoma cell line 786-O. Solenopsin has structural similarities to ceramide, a major endogenous regulator of cell signaling and cancer therapy induced apoptosis. METHODS Different analogs of solenopsin were synthesized in order to explore structure-activity relationships. The anti-proliferative effect of solenopsin and analogs was tested on six different cell lines, including three tumor cell lines, two normal cutaneous cell lines, and one immortalized hyperproliferative cell line. FRET-based reporters were used to study the affect of solenopsin and analogs on Akt activity and PDK1 activation and sucrose density gradient fractionation was performed to examine recruitment of PTEN to membrane rafts. Western-blotting was used to evaluate the affect of solenopsin and analogs on the Akt and the MAPK 44/42 pathways in three different tumor cell lines. Measurement of cellular oxygen consumption rate together with autophagy staining was performed to study mitochondrial function. Finally, the affect of solenopsin and analogs on ROS production was investigated. RESULTS In this paper we demonstrate that solenopsin analogs with potent anti-proliferative effects can be synthesized from inexpensive dimethylpyridines. To determine whether solenopsin and analogs act as ceramide analogs, we examined the effect of solenopsin and analogs on two stereotypic sites of ceramide activity, namely at lipid rafts and mitochondria. We found that native solenopsin, (-)-solenopsin A, inhibits functional Akt activity and PDK1 activation in lipid rafts in a similar fashion as ceramide. Both cis and trans analogs of solenopsin reduce mitochondrial oxygen consumption, increase reactive oxygen, and kill tumor cells with elevated levels of Akt phosphorylation. However, only solenopsin induces mitophagy, like ceramide. CONCLUSIONS The requirements for ceramide induced mitophagy and inhibition of Akt activity and PDK1 activation in lipid rafts are under strict stereochemical control. The naturally occurring (-)-solenopsin A mimic some of the functions of ceramide and may be therapeutically useful in the treatment of hyperproliferative and malignant disorders of the skin, even in the presence of elevated levels of Akt.
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Affiliation(s)
- Isabella Karlsson
- />Department of Dermatology, Emory University School of Medicine, Atlanta, GA USA
| | - Xin Zhou
- />Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Raquela Thomas
- />Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC USA
| | - Allorie T Smith
- />Department of Pharmaceutical Sciences, School of Pharmacy, Union University, Jackson, TN USA
| | - Michael Y Bonner
- />Department of Dermatology, Emory University School of Medicine, Atlanta, GA USA
| | - Pooja Bakshi
- />Center for Drug Design, Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA USA
| | - Ajay K Banga
- />Center for Drug Design, Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA USA
| | - J Phillip Bowen
- />Center for Drug Design, Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA USA
| | - Ghassan Qabaja
- />Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA
| | - Shavon L Ford
- />Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA
| | - Matthew D Ballard
- />Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA
| | - Kimberly S Petersen
- />Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA
| | - Xuechen Li
- />Department of Physiology and Renal Division, Emory University School of Medicine, Atlanta, GA USA
| | - Guangping Chen
- />Department of Physiology and Renal Division, Emory University School of Medicine, Atlanta, GA USA
| | - Besim Ogretmen
- />Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC USA
| | - Jin Zhang
- />Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - E Blake Watkins
- />Department of Pharmaceutical Sciences, School of Pharmacy, Union University, Jackson, TN USA
| | - Rebecca S Arnold
- />Department of Urology, Emory University School of Medicine, Atlanta, GA USA
| | - Jack L Arbiser
- />Department of Dermatology, Emory University School of Medicine, Atlanta, GA USA
- />Atlanta Veterans Administration Hospital, and Winship Cancer Institute, Emory University, Atlanta, GA USA
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17
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Muthusamy S, Malhotra P, Hosameddin M, Dudeja AK, Borthakur S, Saksena S, Gill RK, Dudeja PK, Alrefai WA. N-glycosylation is essential for ileal ASBT function and protection against proteases. Am J Physiol Cell Physiol 2015; 308:C964-71. [PMID: 25855079 DOI: 10.1152/ajpcell.00023.2015] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 04/07/2015] [Indexed: 12/22/2022]
Abstract
The bile acid transporter ASBT is a glycoprotein responsible for active absorption of bile acids. Inhibiting ASBT function and bile acid absorption is an attractive approach to lower plasma cholesterol and improve glucose imbalance in diabetic patients. Deglycosylation of ASBT was shown to decrease its function. However, the exact roles of N-glycosylation of ASBT, and how it affects its function, is not known. Current studies investigated the roles of N-glycosylation in ASBT protein stability and protection against proteases utilizing HEK-293 cells stably transfected with ASBT-V5 fusion protein. ASBT-V5 protein was detected as two bands with molecular mass of ~41 and ~35 kDa. Inhibition of glycosylation by tunicamycin significantly decreased ASBT activity and shifted ASBT bands to ~30 kDa, representing a deglycosylated protein. Treatment of total cellular lysates with PNGase F or Endo H glycosidases showed that the upper 41-kDa band represents a fully mature N-acetylglucosamine-rich glycoprotein and the lower 35-kDa band represents a mannose-rich core glycoprotein. Studies with the glycosylation deficient ASBT mutant (N10Q) showed that the N-glycosylation is not essential for ASBT targeting to plasma membrane. However, mature glycosylation significantly increased the half-life and protected ASBT protein from digestion with trypsin. Incubating the cells with high glucose (25 mM) for 48 h increased mature glycosylated ASBT along with an increase in its function. These results unravel novel roles for N-glycosylation of ASBT and suggest that high levels of glucose alter the composition of the glycan and may contribute to the increase in ASBT function in diabetes mellitus.
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Affiliation(s)
- Saminathan Muthusamy
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Pooja Malhotra
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Mobashir Hosameddin
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Amish K Dudeja
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Sujata Borthakur
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Seema Saksena
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Ravinder K Gill
- Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Pradeep K Dudeja
- Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; and Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - Waddah A Alrefai
- Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois; and Division of Gastroenterology and Hepatology, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois
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18
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Li X, Yang B, Chen M, Klein JD, Sands JM, Chen G. Activation of protein kinase C-α and Src kinase increases urea transporter A1 α-2, 6 sialylation. J Am Soc Nephrol 2015; 26:926-34. [PMID: 25300290 PMCID: PMC4378103 DOI: 10.1681/asn.2014010026] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 07/18/2014] [Indexed: 11/03/2022] Open
Abstract
The urea transporter A1 (UT-A1) is a glycosylated protein with two glycoforms: 117 and 97 kD. In diabetes, the increased abundance of the heavily glycosylated 117-kD UT-A1 corresponds to an increase of kidney tubule urea permeability. We previously reported that diabetes not only causes an increase of UT-A1 protein abundance but also, results in UT-A1 glycan changes, including an increase of sialic acid content. Because activation of the diacylglycerol (DAG)-protein kinase C (PKC) pathway is elevated in diabetes and PKC-α regulates UT-A1 urea transport activity, we explored the role of PKC in UT-A1 glycan sialylation. We found that activation of PKC specifically promotes UT-A1 glycan sialylation in both UT-A1-MDCK cells and rat kidney inner medullary collecting duct suspensions, and inhibition of PKC activity blocks high glucose-induced UT-A1 sialylation. Overexpression of PKC-α promoted UT-A1 sialylation and membrane surface expression. Conversely, PKC-α-deficient mice had significantly less sialylated UT-A1 compared with wild-type mice. Furthermore, the effect of PKC-α-induced UT-A1 sialylation was mainly mediated by Src kinase but not Raf-1 kinase. Functionally, increased UT-A1 sialylation corresponded with enhanced urea transport activity. Thus, our results reveal a novel mechanism by which PKC regulates UT-A1 function by increasing glycan sialylation through Src kinase pathways, which may have an important role in preventing the osmotic diuresis caused by glucosuria under diabetic conditions.
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Affiliation(s)
- Xuechen Li
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China; and
- Department of Physiology and
| | - Baoxue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University, Beijing, China; and
| | | | - Janet D. Klein
- Department of Physiology and
- Renal Division, Department of Medicine, Emory University, Atlanta, Georgia
| | - Jeff M. Sands
- Department of Physiology and
- Renal Division, Department of Medicine, Emory University, Atlanta, Georgia
| | - Guangping Chen
- Department of Physiology and
- Renal Division, Department of Medicine, Emory University, Atlanta, Georgia
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19
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Liu BC, Yang LL, Lu XY, Song X, Li XC, Chen G, Li Y, Yao X, Humphrey DR, Eaton DC, Shen BZ, Ma HP. Lovastatin-Induced Phosphatidylinositol-4-Phosphate 5-Kinase Diffusion from Microvilli Stimulates ROMK Channels. J Am Soc Nephrol 2014; 26:1576-87. [PMID: 25349201 DOI: 10.1681/asn.2013121326] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 08/25/2014] [Indexed: 12/13/2022] Open
Abstract
We recently showed that lovastatin attenuates cyclosporin A (CsA)-induced damage of cortical collecting duct (CCD) principal cells by reducing intracellular cholesterol. Previous studies showed that, in cell expression models or artificial membranes, exogenous cholesterol directly inhibits inward rectifier potassium channels, including Kir1.1 (Kcnj1; the gene locus for renal outer medullary K(+) [ROMK1] channels). Therefore, we hypothesized that lovastatin might stimulate ROMK1 by reducing cholesterol in CCD cells. Western blots showed that mpkCCDc14 cells express ROMK1 channels with molecular masses that approximate the molecular masses of ROMK1 in renal tubules detected before and after treatment with DTT. Confocal microscopy showed that ROMK1 channels were not in the microvilli, where cholesterol-rich lipid rafts are located, but rather, the planar regions of the apical membrane of mpkCCDc14 cells. Furthermore, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], an activator of ROMK channels, was detected mainly in the microvilli under resting conditions along with the kinase responsible for PI(4,5)P2 synthesis, phosphatidylinositol-4-phosphate 5-kinase, type I γ [PI(4)P5K I γ], which may explain the low basal open probability and increased sensitivity to tetraethylammonium observed here for this channel. Notably, lovastatin induced PI(4)P5K I γ diffusion into planar regions and elevated PI(4,5)P2 and ROMK1 open probability in these regions through a cholesterol-associated mechanism. However, exogenous cholesterol alone did not induce these effects. These results suggest that lovastatin stimulates ROMK1 channels, at least in part, by inducing PI(4,5)P2 synthesis in planar regions of the renal CCD cell apical membrane, suggesting that lovastatin could reduce cyclosporin-induced nephropathy and associated hyperkalemia.
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Affiliation(s)
- Bing-Chen Liu
- Departments of Radiology and Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and
| | - Li-Li Yang
- Departments of Radiology and Department of Physiology and Molecular Imaging Center, Harbin Medical University, Harbin, Heilongjiang, China; and
| | - Xiao-Yu Lu
- Departments of Radiology and Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and
| | - Xiang Song
- Cardiology, Fourth Hospital of Harbin Medical University, Harbin, Heilongjiang, China; Department of Physiology and
| | | | | | - Yichao Li
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | - Xincheng Yao
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama
| | | | - Douglas C Eaton
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
| | - Bao-Zhong Shen
- Departments of Radiology and Molecular Imaging Center, Harbin Medical University, Harbin, Heilongjiang, China; and
| | - He-Ping Ma
- Department of Physiology and Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
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20
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Abstract
Urea and urea transporters (UT) are critical to the production of concentrated urine and hence in maintaining body fluid balance. The UT-A1 urea transporter is the major and most important UT isoform in the kidney. Native UT-A1, expressed in the terminal inner medullary collecting duct (IMCD) epithelial cells, is a glycosylated protein with two glycoforms of 117 and 97 kDa. Vasopressin is the major hormone in vivo that rapidly increases urea permeability in the IMCD through increases in phosphorylation and apical plasma-membrane accumulation of UT-A1. The cell signaling pathway for vasopressin-mediated UT-A1 phosphorylation and activity involves two cAMP-dependent signaling pathways: protein kinase A (PKA) and exchange protein activated by cAMP (Epac). In this chapter, we will discuss UT-A1 regulation by phosphorylation, ubiquitination, and glycosylation.
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Affiliation(s)
- Guangping Chen
- Department of Physiology, and Renal Division Department of Medicine, Emory University School of Medicine, Whitehead Research Building Room 605N, 615 Michael Street, Atlanta, GA, 30322, USA,
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21
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Abstract
UT-A and UT-B families of urea transporters consist of multiple isoforms that are subject to regulation of both acutely and by long-term measures. This chapter provides a brief overview of the expression of the urea transporter forms and their locations in the kidney. Rapid regulation of UT-A1 results from the combination of phosphorylation and membrane accumulation. Phosphorylation of UT-A1 has been linked to vasopressin and hyperosmolality, although through different kinases. Other acute influences on urea transporter activity are ubiquitination and glycosylation, both of which influence the membrane association of the urea transporter, again through different mechanisms. Long-term regulation of urea transport is most closely associated with the environment that the kidney experiences. Low-protein diets may influence the amount of urea transporter available. Conditions of osmotic diuresis, where urea concentrations are low, will prompt an increase in urea transporter abundance. Although adrenal steroids affect urea transporter abundance, conflicting reports make conclusions tenuous. Urea transporters are upregulated when P2Y2 purinergic receptors are decreased, suggesting a role for these receptors in UT regulation. Hypercalcemia and hypokalemia both cause urine concentration deficiencies. Urea transporter abundances are reduced in aging animals and animals with angiotensin-converting enzyme deficiencies. This chapter will provide information about both rapid and long-term regulation of urea transporters and provide an introduction into the literature.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine and Department of Physiology, Emory University School of Medicine, WMB Room 3319B, 1639 Pierce Drive, NE, Atlanta, GA, 30322, USA,
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22
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Su H, Chen M, Sands JM, Chen G. Activation of the cAMP/PKA pathway induces UT-A1 urea transporter monoubiquitination and targets it for lysosomal degradation. Am J Physiol Renal Physiol 2013; 305:F1775-82. [PMID: 24133116 PMCID: PMC3882448 DOI: 10.1152/ajprenal.00393.2013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 10/16/2013] [Indexed: 11/22/2022] Open
Abstract
Regulation of urea transporter UT-A1 in the kidney is important for the urinary concentrating mechanism. We previously reported that activation of the cAMP/PKA pathway by forskolin (FSK) leads to UT-A1 ubiquitination, endocytosis, and degradation. In this study, we discovered that FSK-induced UT-A1 ubiquitination is monoubiquitination as judged by immunoblotting with specific ubiquitin antibodies to the different linkages of the ubiquitin chain. UT-A1 monoubiquitination induced by FSK was processed mainly on the cell plasma membrane. Monoubiquitination facilitates UT-A1 endocytosis, and internalized UT-A1 is accumulated in the early endosome. Inhibition of ubiquitination by E1 ubiquitin-activating enzyme inhibitor PYR-41 significantly reduced FSK-induced UT-A1 endocytosis and degradation. Interestingly, FSK-stimulated UT-A1 degradation occurs through a lysosomal protein degradation system. We further found that the PKA phosphorylation sites of UT-A1 at Ser486 and Ser499 are required for FSK-induced UT-A1 monoubiquitination. The physiological significance was confirmed using rat kidney inner medullary collecting duct suspensions, which showed that vasopressin treatment promotes UT-A1 ubiquitination. We conclude that unlike under basal conditions in which UT-A1 is subject to polyubiquitination and proteasome-mediated protein degradation, activation of UT-A1 by FSK induces UT-A1 monoubiquitination and protein lysosomal degradation.
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Affiliation(s)
- Hua Su
- Dept. of Physiology, Emory Univ. School of Medicine, Whitehead Research Bldg. Rm. 615, 615 Michael St., Atlanta, GA 30322.
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23
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Sánchez-Tena S, Vizán P, Dudeja P, Centelles J, Cascante M. Green tea phenolics inhibit butyrate-induced differentiation of colon cancer cells by interacting with monocarboxylate transporter 1. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1832:2264-70. [PMID: 23994611 PMCID: PMC4889458 DOI: 10.1016/j.bbadis.2013.08.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 07/24/2013] [Accepted: 08/20/2013] [Indexed: 12/16/2022]
Abstract
Diet has a significant impact on colorectal cancer and both dietary fiber and plant-derived compounds have been independently shown to be inversely related to colon cancer risk. Butyrate (NaB), one of the principal products of dietary fiber fermentation, induces differentiation of colon cancer cell lines by inhibiting histone deacetylases (HDACs). On the other hand, (-)-epicatechin (EC) and (-)-epigallocatechin gallate (EGCG), two abundant phenolic compounds of green tea, have been shown to exhibit antitumoral properties. In this study we used colon cancer cell lines to study the cellular and molecular events that take place during co-treatment with NaB, EC and EGCG. We found that (i) polyphenols EC and EGCG fail to induce differentiation of colon adenocarcinoma cell lines; (ii) polyphenols EC and EGCG reduce NaB-induced differentiation; (iii) the effect of the polyphenols is specific for NaB, since differentiation induced by other agents, such as trichostatin A (TSA), was unaltered upon EC and EGCG treatment, and (iv) is independent of the HDAC inhibitory activity of NaB. Also, (v) polyphenols partially reduce cellular NaB; and (vi) on a molecular level, reduction of cellular NaB uptake by polyphenols is achieved by impairing the capacity of NaB to relocalize its own transporter (monocarboxylate transporter 1, MCT1) in the plasma membrane. Our findings suggest that beneficial effects of NaB on colorectal cancer may be reduced by green tea phenolic supplementation. This valuable information should be of assistance in choosing a rational design for more effective diet-driven therapeutic interventions in the prevention or treatment of colorectal cancer.
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Affiliation(s)
- S. Sánchez-Tena
- Department of Biochemistry and Molecular Biology, IBUB, Faculty of Biology, Universitat de Barcelona and Unit Associated with CSIC, 08028 Barcelona, Spain
- Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain
| | - P. Vizán
- Department of Biochemistry and Molecular Biology, IBUB, Faculty of Biology, Universitat de Barcelona and Unit Associated with CSIC, 08028 Barcelona, Spain
| | - P.K. Dudeja
- Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago and Jesse Brown VA Medical Center, Chicago, IL 60612, USA
| | - J.J. Centelles
- Department of Biochemistry and Molecular Biology, IBUB, Faculty of Biology, Universitat de Barcelona and Unit Associated with CSIC, 08028 Barcelona, Spain
- Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain
| | - M. Cascante
- Department of Biochemistry and Molecular Biology, IBUB, Faculty of Biology, Universitat de Barcelona and Unit Associated with CSIC, 08028 Barcelona, Spain
- Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), 08036 Barcelona, Spain
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24
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Su H, Liu B, Fröhlich O, Ma H, Sands JM, Chen G. Small GTPase Rab14 down-regulates UT-A1 urea transport activity through enhanced clathrin-dependent endocytosis. FASEB J 2013; 27:4100-7. [PMID: 23796783 PMCID: PMC4046183 DOI: 10.1096/fj.13-229294] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 06/11/2013] [Indexed: 11/11/2022]
Abstract
The UT-A1 urea transporter plays an important role in the urinary concentration mechanism. However, the molecular mechanisms regarding UT-A1 trafficking, endocytosis, and degradation are still unclear. In this study, we identified the small GTPase Rab14 as a binding partner to the C terminus of UT-A1 in a yeast 2-hybrid assay. Interestingly, UT-A1 binding is preferential for the GDP-bound inactive form of Rab14. Coinjection of Rab14 in Xenopus oocytes results in a decrease of UT-A1 urea transport activity, suggesting that Rab14 acts as a negative regulator of UT-A1. We subsequently found that Rab14 reduces the cell membrane expression of UT-A1, as evidenced by cell surface biotinylation. This effect is blocked by chlorpromazine, an inhibitor of the clathrin-mediated endocytic pathway, but not by filipin, an inhibitor of the caveolin-mediated endocytic pathway. In kidney, Rab14 is mainly expressed in IMCD epithelial cells with a pattern identical to UT-A1 expression. Consistent with its role in participating in clathrin-mediated endocytosis, Rab14 localizes in nonlipid raft microdomains and codistributes with Rab5, a marker of the clathrin-mediated endocytic pathway. Taken together, our study suggests that Rab14, as a novel UT-A1 partner, may have an important regulatory function for UT-A1 urea transport activity in the kidney inner medulla.
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Affiliation(s)
- Hua Su
- 1Department of Physiology, Emory University School of Medicine, 615 Michael St., Atlanta, GA 30322, USA.
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25
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Chen G. New advances in urea transporter UT-A1 membrane trafficking. Int J Mol Sci 2013; 14:10674-82. [PMID: 23698785 PMCID: PMC3676860 DOI: 10.3390/ijms140510674] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 05/09/2013] [Accepted: 05/09/2013] [Indexed: 01/23/2023] Open
Abstract
The vasopressin-regulated urea transporter UT-A1, expressed in kidney inner medullary collecting duct (IMCD) epithelial cells, plays a critical role in the urinary concentrating mechanisms. As a membrane protein, the function of UT-A1 transport activity relies on its presence in the plasma membrane. Therefore, UT-A1 successfully trafficking to the apical membrane of the polarized epithelial cells is crucial for the regulation of urea transport. This review summarizes the research progress of UT-A1 regulation over the past few years, specifically on the regulation of UT-A1 membrane trafficking by lipid rafts, N-linked glycosylation and a group of accessory proteins.
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Affiliation(s)
- Guangping Chen
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA.
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26
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Shayakul C, Clémençon B, Hediger MA. The urea transporter family (SLC14): physiological, pathological and structural aspects. Mol Aspects Med 2013; 34:313-22. [PMID: 23506873 DOI: 10.1016/j.mam.2012.12.003] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 12/12/2012] [Indexed: 11/27/2022]
Abstract
Urea transporters (UTs) belonging to the solute carrier 14 (SLC14) family comprise two genes with a total of eight isoforms in mammals, UT-A1 to -A6 encoded by SLC14A2 and UT-B1 to -B2 encoded by SLC14A1. Recent efforts have been directed toward understanding the molecular and cellular mechanisms involved in the regulation of UTs using transgenic mouse models and heterologous expression systems, leading to important new insights. Urea uptake by UT-A1 and UT-A3 in the kidney inner medullary collecting duct and by UT-B1 in the descending vasa recta for the countercurrent exchange system are chiefly responsible for medullary urea accumulation in the urinary concentration process. Vasopressin, an antidiuretic hormone, regulates UT-A isoforms via the phosphorylation and trafficking of the glycosylated transporters to the plasma membrane that occurs to maintain equilibrium with the exocytosis and ubiquitin-proteasome degradation pathways. UT-B isoforms are also important in several cellular functions, including urea nitrogen salvaging in the colon, nitric oxide pathway modulation in the hippocampus, and the normal cardiac conduction system. In addition, genomic linkage studies have revealed potential additional roles for SLC14A1 and SLC14A2 in hypertension and bladder carcinogenesis. The precise role of UT-A2 and presence of the urea recycling pathway in normal kidney are issues to be further explored. This review provides an update of these advances and their implications for our current understanding of the SLC14 UTs.
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Affiliation(s)
- Chairat Shayakul
- Renal Unit, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
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27
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Klein JD, Blount MA, Sands JM. Molecular mechanisms of urea transport in health and disease. Pflugers Arch 2012; 464:561-72. [PMID: 23007461 PMCID: PMC3514661 DOI: 10.1007/s00424-012-1157-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Revised: 09/05/2012] [Accepted: 09/06/2012] [Indexed: 10/27/2022]
Abstract
In the late 1980s, urea permeability measurements produced values that could not be explained by paracellular transport or lipid phase diffusion. The existence of urea transport proteins were thus proposed and less than a decade later, the first urea transporter was cloned. The family of urea transporters has two major subgroups, designated SLC14A1 (or UT-B) and Slc14A2 (or UT-A). UT-B and UT-A gene products are glycoproteins located in various extra-renal tissues however, a majority of the resulting isoforms are found in the kidney. The UT-B (Slc14A1) urea transporter was originally isolated from erythrocytes and two isoforms have been reported. In kidney, UT-B is located primarily in the descending vasa recta. The UT-A (Slc14A2) urea transporter yields six distinct isoforms, of which three are found chiefly in the kidney medulla. UT-A1 and UT-A3 are found in the inner medullary collecting duct (IMCD), while UT-A2 is located in the thin descending limb. These transporters are crucial to the kidney's ability to concentrate urine. The regulation of urea transporter activity in the IMCD involves acute modification through phosphorylation and subsequent movement to the plasma membrane. UT-A1 and UT-A3 accumulate in the plasma membrane in response to stimulation by vasopressin or hypertonicity. Long-term regulation of the urea transporters in the IMCD involves altering protein abundance in response to changes in hydration status, low protein diets, or adrenal steroids. Urea transporters have been studied using animal models of disease including diabetes mellitus, lithium intoxication, hypertension, and nephrotoxic drug responses. Exciting new genetically engineered mouse models are being developed to study these transporters.
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Affiliation(s)
- Janet D Klein
- Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA
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28
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Kim YS, Ahn YH, Song KJ, Kang JG, Lee JH, Jeon SK, Kim HC, Yoo JS, Ko JH. Overexpression and β-1,6-N-acetylglucosaminylation-initiated aberrant glycosylation of TIMP-1: a "double whammy" strategy in colon cancer progression. J Biol Chem 2012; 287:32467-78. [PMID: 22859303 DOI: 10.1074/jbc.m112.370064] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
There has been ongoing debate over whether tissue inhibitor of metalloproteinase-1 (TIMP-1) is pro- or anti-oncogenic. We confirmed that TIMP-1 reinforced cell proliferation in an αvβ3 integrin-dependent manner and conferred resistance against cytotoxicity triggered by TNF-α and IL-2 in WiDr colon cancer cells. The cell-proliferative effects of TIMP-1 contributed to clonogenicity and tumor growth during the onset and early phase of tumor formation in vivo and in vitro. However, mass-produced TIMP-1 impeded further tumor growth by tightly inhibiting the activities of collagenases, which are critical for tumor growth and malignant transformation. Tumor cells could overcome this impasse by overexpression of N-acetylglucosaminyltransferase V, which deteriorates TIMP-1 into an aberrant glycoform. The aberrant glycoform of TIMP-1 was responsible for the mitigated inhibition of collagenases. The outbalanced activities of collagenases can degrade the basement membrane and the interstitial matrix, which act as a physical barrier for tumor growth and progression more efficiently. The concomitant overexpression of TIMP-1 and N-acetylglucosaminyltransferase V enabled WiDr cells to show a higher tumor growth rate as well as more malignant behaviors in a three-dimensional culture system.
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Affiliation(s)
- Yong-Sam Kim
- Cancer Biomarkers Development Research Center, Korea Research Institute of Bioscience and Biotechnology, 125 Gwahak-ro, Yuseong-gu, Daejeon, South Korea
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29
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Hughey RP. The sweet side of urea transporters. Am J Physiol Renal Physiol 2012; 303:F375-6. [PMID: 22573383 DOI: 10.1152/ajprenal.00250.2012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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30
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Su H, Carter CB, Fröhlich O, Cummings RD, Chen G. Glycoforms of UT-A3 urea transporter with poly-N-acetyllactosamine glycosylation have enhanced transport activity. Am J Physiol Renal Physiol 2012; 303:F201-8. [PMID: 22535801 PMCID: PMC3404584 DOI: 10.1152/ajprenal.00140.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 04/23/2012] [Indexed: 11/22/2022] Open
Abstract
Urea transporters UT-A1 and UT-A3 are both expressed in the kidney inner medulla. However, the function of UT-A3 remains unclear. Here, we found that UT-A3, which comprises only the NH(2)-terminal half of UT-A1, has a higher urea transport activity than UT-A1 in the oocyte and that this difference was associated with differences in N-glycosylation. Heterologously expressed UT-A3 is fully glycosylated with two glycoforms of 65 and 45 kDa. By contrast, UT-A1 expressed in HEK293 cells and oocytes exhibits only a 97-kDa glycosylation form. We further found that N-glycans of UT-A3 contain a large amount of poly-N-acetyllactosamine. This highly glycosylated UT-A3 is more stable and is enriched in lipid raft domains on the cell membrane. Kifunensine, an inhibitor of α-mannosidase that inhibits N-glycan processing beyond high-mannose-type N-glycans, significantly reduced UT-A3 urea transport activity. We then examined the native UT-A1 and UT-A3 glycosylation states from kidney inner medulla and found the ratio of 65 to 45 kDa in UT-A3 is higher than that of 117 to 97 kDa in UT-A1. The highly stable expression of highly glycosylated UT-A3 on the cell membrane in kidney inner medulla suggests that UT-A3 may have an important function in urea reabsorption.
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Affiliation(s)
- Hua Su
- Renal Division, Emory University School of Medicine, 1639 Pierce Dr., Atlanta, GA 30322, USA
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31
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Cipriani P, Kim SL, Klein JD, Sim JH, von Bergen TN, Blount MA. The role of nitric oxide in the dysregulation of the urine concentration mechanism in diabetes mellitus. Front Physiol 2012; 3:176. [PMID: 22685437 PMCID: PMC3368392 DOI: 10.3389/fphys.2012.00176] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Accepted: 05/14/2012] [Indexed: 11/13/2022] Open
Abstract
Uncontrolled diabetes mellitus results in osmotic diuresis. Diabetic patients have lowered nitric oxide (NO) which may exacerbate polyuria. We examined how lack of NO affects the transporters involved in urine concentration in diabetic animals. Diabetes was induced in rats by streptozotocin. Control and diabetic rats were given L-NAME for 3 weeks. Urine osmolality, urine output, and expression of urea and water transporters and the Na-K-2Cl cotransporter were examined. Predictably, diabetic rats presented with polyuria (increased urine volume and decreased urine osmolality). Although metabolic parameters of control rats were unaffected by L-NAME, treated diabetic rats produced 30% less urine and osmolality was restored. UT-A1 and UT-A3 were significantly increased in diabetic rat inner medulla. While L-NAME treatment alone did not alter UT-A1 or UT-A3 abundance, absence of NO prevented the upregulation of both transporters in diabetic rats. Similarly, AQP2 and NKCC2 abundance was increased in diabetic animals however, expression of these transporters were unchanged by L-NAME treatment of diabetes. Increased expression of the concentrating transporters observed in diabetic rats provides a compensatory mechanism to decrease solute loss despite persistent glycosuria. Our studies found that although diabetic-induced glycosylation remained increased, total protein expression was decreased to control levels in diabetic rats treated with L-NAME. While the role of NO in urine concentration remains unclear, lowered NO associated with diabetes may be deleterious to the transporters’ response to the subsequent osmotic diuresis.
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Affiliation(s)
- Penelope Cipriani
- Renal Division, Department of Medicine, Emory University Atlanta, GA, USA
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Xu G, Su H, Carter CB, Fröhlich O, Chen G. Depolymerization of cortical actin inhibits UT-A1 urea transporter endocytosis but promotes forskolin-stimulated membrane trafficking. Am J Physiol Cell Physiol 2012; 302:C1012-8. [PMID: 22262062 PMCID: PMC3330733 DOI: 10.1152/ajpcell.00440.2011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Accepted: 01/17/2012] [Indexed: 11/22/2022]
Abstract
The cytoskeleton participates in many aspects of transporter protein regulation. In this study, by using yeast two-hybrid screening, we identified the cytoskeletal protein actin as a binding partner with the UT-A1 urea transporter. This suggests that actin plays a role in regulating UT-A1 activity. Actin specifically binds to the carboxyl terminus of UT-A1. A serial mutation study shows that actin binding to UT-A1's carboxyl terminus was abolished when serine 918 was mutated to alanine. In polarized UT-A1-MDCK cells, cortical filamentous (F) actin colocalizes with UT-A1 at the apical membrane and the subapical cytoplasm. In the cell surface, both actin and UT-A1 are distributed in the lipid raft microdomains. Disruption of the F-actin cytoskeleton by latrunculin B resulted in UT-A1 accumulation in the cell membrane as measured by biotinylation. This effect was mainly due to inhibition of UT-A1 endocytosis in both clathrin and caveolin-mediated endocytic pathways. In contrast, actin depolymerization facilitated forskolin-stimulated UT-A1 trafficking to the cell surface. Functionally, depolymerization of actin by latrunculin B significantly increased UT-A1 urea transport activity in an oocyte expression system. Our study shows that cortical F-actin not only serves as a structural protein, but directly interacts with UT-A1 and plays an important role in controlling UT-A1 cell surface expression by affecting both endocytosis and trafficking, therefore regulating UT-A1 bioactivity.
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Affiliation(s)
- Gang Xu
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
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