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FXYD3 Expression Predicts Poor Prognosis in Renal Cell Carcinoma with Immunosuppressive Tumor Microenvironment. Cancers (Basel) 2022; 14:cancers14153596. [PMID: 35892856 PMCID: PMC9330147 DOI: 10.3390/cancers14153596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2022] [Revised: 07/15/2022] [Accepted: 07/17/2022] [Indexed: 11/17/2022] Open
Abstract
Simple Summary FXYD3 belongs to the protein-coding gene family associated with Na+/K+-ATPase enzymes and chloride ion channels. Recently, the biological role of FXYD3 has been reported in multiple cancers. Nevertheless, the prognostic value of FXYD3 expression has been undiscovered in clear renal cell carcinoma (KIRC). In this study, we assessed the datasets from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) dataset (GSE29609). We found the FXYD3 high KIRC patients had distinct clinical characteristics, including hypoxia and poor overall survival. Furthermore, the algorithms discovered that FXYD3 mRNA levels were associated with tumor purity, multiple types of the tumor infiltrating lymphocytes (TILs) and several genes related to T cell exhaustion. In conclusion, FXYD3 predicts a poor prognosis associated with hypoxia, pro-tumor TILs, and T cell exhaustion in KIRC. Abstract FXYD3 is a protein-coding gene, belonging to the FXYD protein family associated with Na+/K+-ATPase enzymes and chloride ion channels. Accumulating evidence suggests the biological role of FXYD3 in multiple cancers. However, the prognostic value of FXYD3 expression in clear renal cell carcinoma (KIRC) is unclear. Therefore, we evaluated the clinical data with tumor-infiltrating lymphocytes (TILs) and immunoinhibitory gene expression data using The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) dataset (GSE29609). First, the FXYD3 high KIRC patients had distinct clinical characteristics, including age, sex, disease stage, histological grade, and hypoxia-related gene expressions. Next, FXYD3 gene expression was correlated with poor overall survival in both TCGA and GSE29609 cohorts. The ESTIMATE algorithm revealed that higher FXYD3 mRNA levels were associated with increased infiltration of immune cells and tumor purity. Moreover, the FXYD3 high KIRC tissue harbored increased TILs such as B cells, CD8+ T cells, and M1 macrophage, whereas NK cells and neutrophils were decreased. In addition, we showed FXYD3 was co-expressed with several immunoinhibitory genes related to T cell exhaustion such as LGALS9, CTLA4, BTLA, PDCD1, and LAG3. In conclusion, FXYD3 is an unfavorable prognostic biomarker associated with hypoxia, pro-tumor TILs, and T cell exhaustion.
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Yap JQ, Seflova J, Sweazey R, Artigas P, Robia SL. FXYD proteins and sodium pump regulatory mechanisms. J Gen Physiol 2021; 153:211866. [PMID: 33688925 PMCID: PMC7953255 DOI: 10.1085/jgp.202012633] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 02/03/2021] [Indexed: 12/12/2022] Open
Abstract
The sodium/potassium-ATPase (NKA) is the enzyme that establishes gradients of sodium and potassium across the plasma membrane. NKA activity is tightly regulated for different physiological contexts through interactions with single-span transmembrane peptides, the FXYD proteins. This diverse family of regulators has in common a domain containing a Phe-X-Tyr-Asp (FXYD) motif, two conserved glycines, and one serine residue. In humans, there are seven tissue-specific FXYD proteins that differentially modulate NKA kinetics as appropriate for each system, providing dynamic responsiveness to changing physiological conditions. Our understanding of how FXYD proteins contribute to homeostasis has benefitted from recent advances described in this review: biochemical and biophysical studies have provided insight into regulatory mechanisms, genetic models have uncovered remarkable complexity of FXYD function in integrated physiological systems, new posttranslational modifications have been identified, high-resolution structural studies have revealed new details of the regulatory interaction with NKA, and new clinical correlations have been uncovered. In this review, we address the structural determinants of diverse FXYD functions and the special roles of FXYDs in various physiological systems. We also discuss the possible roles of FXYDs in protein trafficking and regulation of non-NKA targets.
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Affiliation(s)
- John Q Yap
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Jaroslava Seflova
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Ryan Sweazey
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
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Chen X, Ding L, Kong D, Zhao X, Liao L, Zhang Y, Li F, Liu R. FXYD6 overexpression in HBV-related hepatocellular carcinoma with cirrhosis. Open Life Sci 2020; 15:259-266. [PMID: 33817214 PMCID: PMC7874599 DOI: 10.1515/biol-2020-0027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 02/11/2020] [Accepted: 02/11/2020] [Indexed: 11/22/2022] Open
Abstract
Objective The aim of this study was to investigate the expression of FXYD domain-containing
ion transport regulator 6 (FXYD6) mRNA and protein in hepatitis B virus
(HBV)-related hepatocellular carcinoma (HCC) tissues with cirrhosis, the
corresponding paracancerous tissues and the normal liver tissues, and to explore
the clinical significance of FXYD6 expression in HBV-related HCC with
cirrhosis. Methods The FXYD6 mRNA and protein were examined by semi-quantitative reverse
transcription polymerase chain reaction and immunohistochemistry,
respectively. Results The FXYD6 mRNA in HBV-related HCC tissues was significantly higher than that in
the cirrhosis tissues or that in the normal liver tissues. The positive expression
rate of FXYD6 protein was statistically higher in HBV-related HCC tissues than
that in HBV-related cirrhosis or that in normal liver tissues. There was no
significant correlation between the expression of FXYD6 protein and gender, age,
histological differentiation, tumor diameter, tumor number, integrity of tumor
capsule or not and alpha fetoprotein (AFP) concentration in serum, but the protein
expression was associated with microvascular invasion, pathological stage, and
early recurrence after operation within 1 year. Conclusion FXYD6 might be involved in hepatocyte carcinogenesis and tumor progression in
HBV-related HCC with cirrhosis and indicated a poor prognosis.
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Affiliation(s)
- Xiongfei Chen
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Lishuang Ding
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Deshuai Kong
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Xiulei Zhao
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Lili Liao
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Yaomin Zhang
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Fengshan Li
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
| | - Ruhai Liu
- Department of Hepatobiliary and Pancreatic Surgery, Cangzhou Central Hospital, 16 Xinhuaxi Road, Yunhe District, Cangzhou, 061001, P. R. China
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Abnormal Scn1b and Fxyd1 gene expression in the pulled-through ganglionic colon may influence functional outcome in patients with Hirschsprung's disease. Pediatr Surg Int 2019; 35:9-14. [PMID: 30386899 DOI: 10.1007/s00383-018-4370-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 10/18/2018] [Indexed: 02/07/2023]
Abstract
PURPOSE Smooth muscle cells are electrically coupled to ICC and PDGFRα+ cells, to regulate smooth muscle contraction. Recent studies have reported that the voltage-gated sodium channel type 1β (Scn1b), and the chloride channel subunit, Fxyd1, are highly expressed by both ICC and PDGFRα+ cells in the mouse colon. We designed this study to investigate the expression of the Scn1b and Fxyd1 genes in the normal human colon and in HSCR. METHODS HSCR tissue specimens (n = 6) were collected at the time of pull-through surgery, while control samples were obtained at the time of colostomy closure in patients with imperforate anus (n = 6). qRT-PCR analysis was undertaken to quantify Scn1b and Fxyd1 gene expression, and immunolabelling of Scn1b and Fxyd1 proteins were visualized using confocal microscopy. RESULTS qRT-PCR analysis revealed significant downregulation of Scn1b and Fxyd1 genes in both aganglionic and ganglionic HSCR specimens compared to controls (p < 0.05). Confocal microscopy revealed a reduction in Scn1b and Fxyd1 protein expression in both aganglionic and ganglionic HSCR colon compared to controls. CONCLUSION Scn1b and Fxyd1 expression was significantly downregulated in HSCR colon. These results add to mounting evidence suggesting that the pulled-through ganglionic segment of bowel in these patients is abnormal, despite the presence of ganglion cells.
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Yoneda JS, Scanavachi G, Sebinelli HG, Borges JC, Barbosa LRS, Ciancaglini P, Itri R. Multimeric species in equilibrium in detergent-solubilized Na,K-ATPase. Int J Biol Macromol 2016; 89:238-45. [PMID: 27109755 DOI: 10.1016/j.ijbiomac.2016.04.058] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Revised: 04/19/2016] [Accepted: 04/20/2016] [Indexed: 12/29/2022]
Abstract
In this work, we find an equilibrium between different Na,K-ATPase (NKA) oligomeric species solubilized in a non-ionic detergent C12E8 by means of Dynamic Light Scattering (DLS), Analytical Ultracentrifugation (AUC), Small Angle X-ray Scattering (SAXS), Spectrophotometry (absorption at 280/350nm) and enzymatic activity assay. The NKA sample after chromatography purification presented seven different populations as identified by AUC, with monomers and tetramers amounting to ∼55% of the total protein mass in solution. These two species constituted less than 40% of the total protein mass after increasing the NKA concentration. Removal of higher-order oligomer/aggregate species from the NKA solution using 220nm-pore filter resulted in an increase of the specific enzymatic activity. Nevertheless, the enzyme forms new large aggregates over an elapsed time of 20h. The results thus point out that C12E8-solubilized NKA is in a dynamic equilibrium of monomers, tetramers and high-order oligomers/subunit aggregates. These latter have low or null activity. High amount of detergent leads to the dissociation of NKA into smaller aggregates with no enzymatic activity.
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Affiliation(s)
- Juliana Sakamoto Yoneda
- Instituto de Física da Universidade de São Paulo, IF USP, 05508-090 São Paulo, Brazil; Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, FFCLRP USP, 14040-901 Ribeirão Preto, SP, Brazil
| | - Gustavo Scanavachi
- Instituto de Física da Universidade de São Paulo, IF USP, 05508-090 São Paulo, Brazil
| | - Heitor Gobbi Sebinelli
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, FFCLRP USP, 14040-901 Ribeirão Preto, SP, Brazil
| | - Júlio Cesar Borges
- Instituto de Química de São Carlos, IQSC-USP, 13560-970 São Carlos, SP, Brazil
| | - Leandro R S Barbosa
- Instituto de Física da Universidade de São Paulo, IF USP, 05508-090 São Paulo, Brazil
| | - Pietro Ciancaglini
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, FFCLRP USP, 14040-901 Ribeirão Preto, SP, Brazil
| | - Rosangela Itri
- Instituto de Física da Universidade de São Paulo, IF USP, 05508-090 São Paulo, Brazil.
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Shattock MJ, Ottolia M, Bers DM, Blaustein MP, Boguslavskyi A, Bossuyt J, Bridge JHB, Chen-Izu Y, Clancy CE, Edwards A, Goldhaber J, Kaplan J, Lingrel JB, Pavlovic D, Philipson K, Sipido KR, Xie ZJ. Na+/Ca2+ exchange and Na+/K+-ATPase in the heart. J Physiol 2015; 593:1361-82. [PMID: 25772291 PMCID: PMC4376416 DOI: 10.1113/jphysiol.2014.282319] [Citation(s) in RCA: 145] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 10/30/2014] [Indexed: 12/17/2022] Open
Abstract
This paper is the third in a series of reviews published in this issue resulting from the University of California Davis Cardiovascular Symposium 2014: Systems approach to understanding cardiac excitation–contraction coupling and arrhythmias: Na+ channel and Na+ transport. The goal of the symposium was to bring together experts in the field to discuss points of consensus and controversy on the topic of sodium in the heart. The present review focuses on cardiac Na+/Ca2+ exchange (NCX) and Na+/K+-ATPase (NKA). While the relevance of Ca2+ homeostasis in cardiac function has been extensively investigated, the role of Na+ regulation in shaping heart function is often overlooked. Small changes in the cytoplasmic Na+ content have multiple effects on the heart by influencing intracellular Ca2+ and pH levels thereby modulating heart contractility. Therefore it is essential for heart cells to maintain Na+ homeostasis. Among the proteins that accomplish this task are the Na+/Ca2+ exchanger (NCX) and the Na+/K+ pump (NKA). By transporting three Na+ ions into the cytoplasm in exchange for one Ca2+ moved out, NCX is one of the main Na+ influx mechanisms in cardiomyocytes. Acting in the opposite direction, NKA moves Na+ ions from the cytoplasm to the extracellular space against their gradient by utilizing the energy released from ATP hydrolysis. A fine balance between these two processes controls the net amount of intracellular Na+ and aberrations in either of these two systems can have a large impact on cardiac contractility. Due to the relevant role of these two proteins in Na+ homeostasis, the emphasis of this review is on recent developments regarding the cardiac Na+/Ca2+ exchanger (NCX1) and Na+/K+ pump and the controversies that still persist in the field.
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Affiliation(s)
- Michael J Shattock
- King's College London BHF Centre of Excellence, The Rayne Institute, St Thomas' Hospital, London, SE1 7EH, UK
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7
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Yoneda JS, Rigos CF, de Lourenço TFA, Sebinelli HG, Ciancaglini P. Na,K-ATPase reconstituted in ternary liposome: the presence of cholesterol affects protein activity and thermal stability. Arch Biochem Biophys 2014; 564:136-41. [PMID: 25286376 DOI: 10.1016/j.abb.2014.09.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2014] [Revised: 09/12/2014] [Accepted: 09/26/2014] [Indexed: 01/27/2023]
Abstract
Differential scanning calorimetry (DSC) was applied to investigate the effect of cholesterol on the thermotropic properties of the lipid membrane (DPPC and DPPE). The thermostability and unfolding of solubilized and reconstituted Na,K-ATPase in DPPC:DPPE:cholesterol-liposomes was also studied to gain insight into the role of cholesterol in the Na,K-ATPase modulation of enzyme function and activity. The tertiary system (DPPC:DPPE:cholesterol) (molar ratio DPPC:DPPE equal 1:1) when cholesterol content was increased from 0% up to 40% results in a slight decrease in the temperature of transition and enthalpy, and an increase in width. We observed that, without heating treatment, at 37°C, the activity was higher for 20mol% cholesterol. However, thermal inactivation experiments showed that the enzyme activity loss time depends on the cholesterol membrane content. The unfolding of the enzyme incorporated to liposomes of DPPC:DPPE (1:1mol) with different cholesterol contents, ranging from 0% to 40% mol was also studied by DSC. Some differences between the thermograms indicate that the presence of lipids promotes a conformational change in protein structure and this change is enough to change the way Na,K-ATPase thermally unfolds.
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Affiliation(s)
- Juliana Sakamoto Yoneda
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil
| | - Carolina Fortes Rigos
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil
| | | | - Heitor Gobbi Sebinelli
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil
| | - Pietro Ciancaglini
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil.
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Li Y, Zhang X, Xu S, Ge J, Liu J, Li L, Fang G, Meng Y, Zhang H, Sun X. Expression and clinical significance of FXYD3 in endometrial cancer. Oncol Lett 2014; 8:517-522. [PMID: 25013464 PMCID: PMC4081380 DOI: 10.3892/ol.2014.2170] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 04/10/2014] [Indexed: 11/23/2022] Open
Abstract
FXYD3 expression is upregulated in numerous cancer cell types. The present study compared the FXDY3 expression in normal endometrium, premalignant lesion and endometrial cancer tissue samples, and investigated the correlation between FXDY3 expression and clinicopathological features. FXYD3 expression was analyzed by streptavidin-peroxidase immunohistochemistry in 21 normal endometrial tissue samples, 18 atypical endometrial hyperplasia samples and 50 tissues obtained from patients diagnosed with endometrial cancer. The percentage of FXYD3-positive cell expression in the normal endometrium, atypical hyperplasia and endometrial cancer tissues samples was 0, 22, and 26%, respectively. The differences between the atypical hyperplasia and endometrial cancer groups were statistically significant when compared with the normal group (P=0.007 and P=0.037, respectively). There was no significant difference between the atypical hyperplasia and endometrial cancer groups. The percentage of FXYD3-positive cells correlated with the fertility frequency (P<0.05). In conclusion, FXYD3 is a potential biomarker for endometrial cancer, and its upregulation may be an early event in endometrial carcinoma progression. In addition, FXYD3 expression in endometrial carcinoma correlates with fertility frequency.
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Affiliation(s)
- Yifei Li
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Xia Zhang
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Shuwen Xu
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Jing Ge
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Jing Liu
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Lin Li
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Guiying Fang
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Yali Meng
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Hongzhen Zhang
- Department of Obstetrics and Gynecology, First Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China
| | - Xiaofeng Sun
- Department of Oncology, Institute of Clinical and Experimental Medicine, Country Council of Östergötland, University of Linköping, Linköping 58185, Sweden
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Gong XM, Ding Y, Yu J, Yao Y, Marassi FM. Structure of the Na,K-ATPase regulatory protein FXYD2b in micelles: implications for membrane-water interfacial arginines. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:299-306. [PMID: 24794573 DOI: 10.1016/j.bbamem.2014.04.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/19/2014] [Accepted: 04/23/2014] [Indexed: 01/06/2023]
Abstract
FXYD2 is a membrane protein responsible for regulating the function of the Na,K-ATPase in mammalian kidney epithelial cells. Here we report the structure of FXYD2b, one of two splice variants of the protein, determined by NMR spectroscopy in detergent micelles. Solid-state NMR characterization of the protein embedded in phospholipid bilayers indicates that several arginine side chains may be involved in hydrogen bond interactions with the phospholipid polar head groups. The structure and the NMR data suggest that FXYD2b could regulate the Na,K-ATPase by modulating the effective membrane surface electrostatics near the ion binding sites of the pump.
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Affiliation(s)
- Xiao-Min Gong
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Yi Ding
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Jinghua Yu
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Yong Yao
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Francesca M Marassi
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
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Cirri E, Kirchner C, Becker S, Katz A, Karlish SJ, Apell HJ. Surface charges of the membrane crucially affect regulation of Na,K-ATPase by phospholemman (FXYD1). J Membr Biol 2013; 246:967-79. [PMID: 24105627 DOI: 10.1007/s00232-013-9600-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 09/24/2013] [Indexed: 01/02/2023]
Abstract
The human α1/His10-β1 isoform of Na,K-ATPase has been reconstituted as a complex with and without FXYD1 into proteoliposomes of various lipid compositions in order to study the effect of the regulatory subunit on the half-saturating Na⁺ concentration (K(½)) of Na⁺ ions for activation of the ion pump. It has been shown that the fraction of negatively charged lipid in the bilayer crucially affects the regulatory properties. At low concentrations of the negatively charged lipid DOPS (<10 %), FXYD1 increases K(½) of Na⁺ ions for activation of the ion pump. Phosphorylation of FXYD1 by protein kinase A at Ser68 abrogates this effect. Conversely, for proteoliposomes made with high concentrations of DOPS (>10 %), little or no effect of FXYD1 on the K(½) of Na⁺ ions is observed. Depending on ionic strength and lipid composition of the proteoliposomes, FXYD1 can alter the K(½) of Na⁺ ions by up to twofold. We propose possible molecular mechanisms to explain the regulatory effects of FXYD1 and the influence of charged lipid and protein phosphorylation. In particular, the positively charged C-terminal helix of FXYD1 appears to be highly mobile and may interact with the cytoplasmic N domain of the α-subunit, the interaction being strongly affected by phosphorylation at Ser68 and the surface charge of the membrane.
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Affiliation(s)
- Erica Cirri
- Department of Biology and Graduate School of Chemical Biology, University of Konstanz, 78464, Constance, Germany
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11
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Regulation of the cardiac Na(+) pump by palmitoylation of its catalytic and regulatory subunits. Biochem Soc Trans 2013; 41:95-100. [PMID: 23356265 DOI: 10.1042/bst20120269] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The Na+/K+-ATPase (Na+ pump) is the principal consumer of ATP in multicellular organisms. In the heart, the Na+ gradient established by the pump is essential for all aspects of cardiac function, and appropriate regulation of the cardiac Na+ pump is therefore crucial to match cardiac output to the physiological requirements of an organism. The cardiac pump is a multi-subunit enzyme, consisting of a catalytic α-subunit and regulatory β- and FXYD subunits. All three subunits may become palmitoylated, although the functional outcome of these palmitoylation events is incompletely characterized to date. Interestingly, both β- and FXYD subunits may be palmitoylated or glutathionylated at the same cysteine residues. These competing chemically distinct post-translational modifications may mediate functionally different effects on the cardiac pump. In the present article, we review the cellular events that control the balance between these modifications, and discuss the likely functional effects of pump subunit palmitoylation.
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12
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Fuller W, Tulloch LB, Shattock MJ, Calaghan SC, Howie J, Wypijewski KJ. Regulation of the cardiac sodium pump. Cell Mol Life Sci 2012; 70:1357-80. [PMID: 22955490 PMCID: PMC3607738 DOI: 10.1007/s00018-012-1134-y] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 07/27/2012] [Accepted: 08/13/2012] [Indexed: 01/24/2023]
Abstract
In cardiac muscle, the sarcolemmal sodium/potassium ATPase is the principal quantitative means of active transport at the myocyte cell surface, and its activity is essential for maintaining the trans-sarcolemmal sodium gradient that drives ion exchange and transport processes that are critical for cardiac function. The 72-residue phosphoprotein phospholemman regulates the sodium pump in the heart: unphosphorylated phospholemman inhibits the pump, and phospholemman phosphorylation increases pump activity. Phospholemman is subject to a remarkable plethora of post-translational modifications for such a small protein: the combination of three phosphorylation sites, two palmitoylation sites, and one glutathionylation site means that phospholemman integrates multiple signaling events to control the cardiac sodium pump. Since misregulation of cytosolic sodium contributes to contractile and metabolic dysfunction during cardiac failure, a complete understanding of the mechanisms that control the cardiac sodium pump is vital. This review explores our current understanding of these mechanisms.
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Affiliation(s)
- W Fuller
- Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine Dentistry and Nursing, University of Dundee, Dundee, UK.
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13
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Walker MB, King BL, Paigen K. Clusters of ancestrally related genes that show paralogy in whole or in part are a major feature of the genomes of humans and other species. PLoS One 2012; 7:e35274. [PMID: 22563380 PMCID: PMC3338513 DOI: 10.1371/journal.pone.0035274] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Accepted: 03/14/2012] [Indexed: 11/22/2022] Open
Abstract
Arrangements of genes along chromosomes are a product of evolutionary processes, and we can expect that preferable arrangements will prevail over the span of evolutionary time, often being reflected in the non-random clustering of structurally and/or functionally related genes. Such non-random arrangements can arise by two distinct evolutionary processes: duplications of DNA sequences that give rise to clusters of genes sharing both sequence similarity and common sequence features and the migration together of genes related by function, but not by common descent [1], [2], [3]. To provide a background for distinguishing between the two, which is important for future efforts to unravel the evolutionary processes involved, we here provide a description of the extent to which ancestrally related genes are found in proximity. Towards this purpose, we combined information from five genomic datasets, InterPro, SCOP, PANTHER, Ensembl protein families, and Ensembl gene paralogs. The results are provided in publicly available datasets (http://cgd.jax.org/datasets/clustering/paraclustering.shtml) describing the extent to which ancestrally related genes are in proximity beyond what is expected by chance (i.e. form paraclusters) in the human and nine other vertebrate genomes, as well as the D. melanogaster, C. elegans, A. thaliana, and S. cerevisiae genomes. With the exception of Saccharomyces, paraclusters are a common feature of the genomes we examined. In the human genome they are estimated to include at least 22% of all protein coding genes. Paraclusters are far more prevalent among some gene families than others, are highly species or clade specific and can evolve rapidly, sometimes in response to environmental cues. Altogether, they account for a large portion of the functional clustering previously reported in several genomes.
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Affiliation(s)
| | - Benjamin L. King
- The Jackson Laboratory, Bar Harbor, Maine, United States of America
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, United States of America
| | - Kenneth Paigen
- The Jackson Laboratory, Bar Harbor, Maine, United States of America
- * E-mail:
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14
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First crystal structures of Na+,K+-ATPase: new light on the oldest ion pump. Structure 2012; 19:1732-8. [PMID: 22153495 DOI: 10.1016/j.str.2011.10.016] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Revised: 10/20/2011] [Accepted: 10/21/2011] [Indexed: 11/21/2022]
Abstract
Na(+),K(+)-adenosine triphosphatase (NKA) is the first P-type ion translocating adenosine triphosphatase (ATPase) ever identified, and the significance of this class of proteins was highlighted by the 1997 Nobel Prize in Chemistry awarded to Jens C. Skou for the discovery in 1957. More than half a century passed between the initial identification and the publication of a high-resolution crystal structure of NKA. Although the new crystal structures provided many surprises and insights, structural biology on this system remains challenging, as NKA is a very difficult protein to crystallize. Here we explain the reasons behind the challenges, introduce a mechanism that governs the function, and summarize current knowledge of NKA structure in comparison with another member of the P-type ATPase family, Ca(2+)-ATPase.
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15
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Tulloch LB, Howie J, Wypijewski KJ, Wilson CR, Bernard WG, Shattock MJ, Fuller W. The inhibitory effect of phospholemman on the sodium pump requires its palmitoylation. J Biol Chem 2011; 286:36020-36031. [PMID: 21868384 DOI: 10.1074/jbc.m111.282145] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (PLM), the principal sarcolemmal substrate for protein kinases A and C in the heart, regulates the cardiac sodium pump. We investigated post-translational modifications of PLM additional to phosphorylation in adult rat ventricular myocytes (ARVM). LC-MS/MS of tryptically digested PLM immunoprecipitated from ARVM identified cysteine 40 as palmitoylated in some peptides, but no information was obtained regarding the palmitoylation status of cysteine 42. PLM palmitoylation was confirmed by immunoprecipitating PLM from ARVM loaded with [(3)H]palmitic acid and immunoblotting following streptavidin affinity purification from ARVM lysates subjected to fatty acyl biotin exchange. Mutagenesis identified both Cys-40 and Cys-42 of PLM as palmitoylated. Phosphorylation of PLM at serine 68 by PKA in ARVM or transiently transfected HEK cells increased its palmitoylation, but PKA activation did not increase the palmitoylation of S68A PLM-YFP in HEK cells. Wild type and unpalmitoylatable PLM-YFP were all correctly targeted to the cell surface membrane, but the half-life of unpalmitoylatable PLM was reduced compared with wild type. In cells stably expressing inducible PLM, PLM expression inhibited the sodium pump, but PLM did not inhibit the sodium pump when palmitoylation was inhibited. Hence, palmitoylation of PLM controls its turnover, and palmitoylated PLM inhibits the sodium pump. Surprisingly, phosphorylation of PLM enhances its palmitoylation, probably through the enhanced mobility of the phosphorylated intracellular domain increasing the accessibility of cysteines for the palmitoylating enzyme, with interesting theoretical implications. All FXYD proteins have conserved intracellular cysteines, so FXYD protein palmitoylation may be a universal means to regulate the sodium pump.
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Affiliation(s)
- Lindsay B Tulloch
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Jacqueline Howie
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Krzysztof J Wypijewski
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Catherine R Wilson
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - William G Bernard
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Michael J Shattock
- Cardiovascular Division, The Rayne Institute, St. Thomas' Hospital, King's College London, London SE1 7EH, United Kingdom
| | - William Fuller
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom.
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16
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Song Q, Pallikkuth S, Bossuyt J, Bers DM, Robia SL. Phosphomimetic mutations enhance oligomerization of phospholemman and modulate its interaction with the Na/K-ATPase. J Biol Chem 2011; 286:9120-6. [PMID: 21220422 DOI: 10.1074/jbc.m110.198036] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Na/K-ATPase (NKA) activity is dynamically regulated by an inhibitory interaction with a small transmembrane protein, phospholemman (PLM). Inhibition is relieved upon PLM phosphorylation. Phosphorylation may alter how PLM interacts with NKA and/or itself, but details of these interactions are unknown. To address this, we quantified FRET between PLM and its regulatory target NKA in live cells. Phosphorylation of PLM was mimicked by mutation S63E (PKC site), S68E (PKA/PKC site), or S63E/S68E. The dependence of FRET on protein expression in live cells yielded information about the structure and binding affinity of the PLM-NKA regulatory complex. PLM phosphomimetic mutations altered the quaternary structure of the regulatory complex and reduced the apparent affinity of the PLM-NKA interaction. The latter effect was likely due to increased oligomerization of PLM phosphomimetic mutants, as suggested by PLM-PLM FRET measurements. Distance constraints obtained by FRET suggest that phosphomimetic mutations slightly alter the oligomer quaternary conformation. Photon-counting histogram measurements revealed that the major PLM oligomeric species is a tetramer. We conclude that phosphorylation of PLM increases its oligomerization into tetramers, decreases its binding to NKA, and alters the structures of both the tetramer and NKA regulatory complex.
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Affiliation(s)
- Qiujing Song
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153, USA
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17
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Hughes E, Whittaker CAP, Barsukov IL, Esmann M, Middleton DA. A study of the membrane association and regulatory effect of the phospholemman cytoplasmic domain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:1021-31. [PMID: 21130070 DOI: 10.1016/j.bbamem.2010.11.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Revised: 11/18/2010] [Accepted: 11/22/2010] [Indexed: 10/18/2022]
Abstract
Phospholemman (PLM) is a single-span transmembrane protein belonging to the FXYD family of proteins. PLM (or FXYD1) regulates the Na,K-ATPase (NKA) ion pump by altering its affinity for K(+) and Na(+) and by reducing its hydrolytic activity. Structural studies of PLM in anionic detergent micelles have suggested that the cytoplasmic domain, which alone can regulate NKA, forms a partial helix which is stabilized by interactions with the charged membrane surface. This work examines the membrane affinity and regulatory function of a 35-amino acid peptide (PLM(38-72)) representing the PLM cytoplasmic domain. Isothermal titration calorimetry and solid-state NMR measurements confirm that PLM(38-72) associates strongly with highly anionic phospholipid membranes, but the association is weakened substantially when the negative surface charge is reduced to a more physiologically relevant environment. Membrane interactions are also weakened when the peptide is phosphorylated at S68, one of the substrate sites for protein kinases. PLM(38-72) also lowers the maximal velocity of ATP hydrolysis (V(max)) by NKA, and phosphorylation of the peptide at S68 gives rise to a partial recovery of V(max). These results suggest that the PLM cytoplasmic domain populates NKA-associated and membrane-associated states in dynamic equilibrium and that phosphorylation may alter the position of the equilibrium. Interestingly, peptides representing the cytoplasmic domains of two other FXYD proteins, Mat-8 (FXYD3) and CHIF (FXYD4), have little or no interaction with highly anionic phospholipid membranes and have no effect on NKA function. This suggests that the functional and physical properties of PLM are not conserved across the entire FXYD family.
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Affiliation(s)
- Eleri Hughes
- School of Biological Sciences, University of Liverpool, Liverpool L69 7ZB, UK
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18
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Translocation of Pseudomonas aeruginosa from the intestinal tract is mediated by the binding of ExoS to an Na,K-ATPase regulator, FXYD3. Infect Immun 2010; 78:4511-22. [PMID: 20805335 DOI: 10.1128/iai.00428-10] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The intestinal tract is considered the most important reservoir of Pseudomonas aeruginosa in intensive care units (ICUs). Gut colonization by P. aeruginosa underlies the development of invasive infections such as gut-derived sepsis. Intestinal colonization by P. aeruginosa is associated with higher ICU mortality rates. The translocation of endogenous P. aeruginosa from the colonized intestinal tract is an important pathogenic phenomenon. Here we identify bacterial and host proteins associated with bacterial penetration through the intestinal epithelial barrier. We first show by comparative genomic hybridization analysis that the exoS gene, encoding the type III effector protein, ExoS, was specifically detected in a clinical isolate that showed higher virulence in silkworms following midgut injection. We further show using a silkworm oral infection model that exoS is required both for virulence and for bacterial translocation from the midgut to the hemolymph. Using a bacterial two-hybrid screen, we show that the mammalian factor FXYD3, which colocalizes with and regulates the function of Na,K-ATPase, directly binds ExoS. A pulldown assay revealed that ExoS binds to the transmembrane domain of FXYD3, which also interacts with Na,K-ATPase. Na,K-ATPase controls the structure and barrier function of tight junctions in epithelial cells. Collectively, our results suggest that ExoS facilitates P. aeruginosa penetration through the intestinal epithelial barrier by binding to FXYD3 and thereby impairing the defense function of tight junctions against bacterial penetration.
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19
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Okudela K, Yazawa T, Ishii J, Woo T, Mitsui H, Bunai T, Sakaeda M, Shimoyamada H, Sato H, Tajiri M, Ogawa N, Masuda M, Sugimura H, Kitamura H. Down-regulation of FXYD3 expression in human lung cancers: its mechanism and potential role in carcinogenesis. THE AMERICAN JOURNAL OF PATHOLOGY 2009; 175:2646-56. [PMID: 19893046 DOI: 10.2353/ajpath.2009.080571] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
FXYD3 is a FXYD-containing Na,K-ATPase ion channel regulator first identified as a protein overexpressed in murine breast tumors initiated by oncogenic ras or neu. However, our preliminary study revealed that FXYD3 expression was down-regulated in oncogenic KRAS-transduced airway epithelial cells. This contradiction led us to investigate the role of FXYD3 in carcinogenesis of the lung. FXYD3 mRNA and protein levels were lower in most of the lung cancer cell lines than in either the noncancerous lung tissue or airway epithelial cells. Protein levels were also lower in a considerable proportion of primary lung cancers than in nontumoral airway epithelia; FXYD3 expression levels decreased in parallel with the dedifferentiation process. Also, a somatic point mutation, g55c (D19H), was found in one cell line. Forced expression of the wild-type FXYD3, but not the mutant, restored the well-demarcated distribution of cortical actin in cancer cells that had lost FXYD3 expression, suggesting FXYD3 plays a role in the maintenance of cytoskeletal integrity. However, no association between FXYD3 expression and its promoter's methylation status was observed. Therefore, inactivation of FXYD3 through a gene mutation or unknown mechanism could be one cause of the atypical shapes of cancer cells and play a potential role in the progression of lung cancer.
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Affiliation(s)
- Koji Okudela
- Department of Pathology, Yokohama City University Graduate School of Medicine, Kanazawa-Ku, Yokohama, Japan
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20
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Kim HJ, Howell SC, Van Horn WD, Jeon YH, Sanders CR. Recent Advances in the Application of Solution NMR Spectroscopy to Multi-Span Integral Membrane Proteins. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2009; 55:335-360. [PMID: 20161395 PMCID: PMC2782866 DOI: 10.1016/j.pnmrs.2009.07.002] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Affiliation(s)
- Hak Jun Kim
- Korea Polar Research Institute, Korea Ocean Research and Development Institute, Incheon, 406-840, Korea
| | - Stanley C. Howell
- Department of Biochemistry, Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232-8725, USA
| | - Wade D. Van Horn
- Department of Biochemistry, Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232-8725, USA
| | - Young Ho Jeon
- Center for Magnetic Resonance, Korea Basic Research Institute, Daejon, 305-333, Korea
| | - Charles R. Sanders
- Department of Biochemistry, Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, TN, 37232-8725, USA
- Corresponding Author: ; phone: 615-936-3756; fax: 615-936-2211
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21
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Mukhopadhyay R, Miao X, Shealy P, Valafar H. Efficient and accurate estimation of relative order tensors from lambda-maps. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 198:236-247. [PMID: 19345125 PMCID: PMC4071621 DOI: 10.1016/j.jmr.2009.02.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2008] [Revised: 02/17/2009] [Accepted: 02/27/2009] [Indexed: 05/25/2023]
Abstract
The rapid increase in the availability of RDC data from multiple alignment media in recent years has necessitated the development of more sophisticated analyses that extract the RDC data's full information content. This article presents an analysis of the distribution of RDCs from two media (2D-RDC data), using the information obtained from a lambda-map. This article also introduces an efficient algorithm, which leverages these findings to extract the order tensors for each alignment medium using unassigned RDC data in the absence of any structural information. The results of applying this 2D-RDC analysis method to synthetic and experimental data are reported in this article. The relative order tensor estimates obtained from the 2D-RDC analysis are compared to order tensors obtained from the program REDCAT after using assignment and structural information. The final comparisons indicate that the relative order tensors estimated from the unassigned 2D-RDC method very closely match the results from methods that require assignment and structural information. The presented method is successful even in cases with small datasets. The results of analyzing experimental RDC data for the protein 1P7E are presented to demonstrate the potential of the presented work in accurately estimating the principal order parameters from RDC data that incompletely sample the RDC space. In addition to the new algorithm, a discussion of the uniqueness of the solutions is presented; no more than two clusters of distinct solutions have been shown to satisfy each lambda-map.
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22
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Hallows KR, Wang H, Edinger RS, Butterworth MB, Oyster NM, Li H, Buck J, Levin LR, Johnson JP, Pastor-Soler NM. Regulation of epithelial Na+ transport by soluble adenylyl cyclase in kidney collecting duct cells. J Biol Chem 2009; 284:5774-83. [PMID: 19126549 DOI: 10.1074/jbc.m805501200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Alkalosis impairs the natriuretic response to diuretics, but the underlying mechanisms are unclear. The soluble adenylyl cyclase (sAC) is a chemosensor that mediates bicarbonate-dependent elevation of cAMP in intracellular microdomains. We hypothesized that sAC may be an important regulator of Na(+) transport in the kidney. Confocal images of rat kidney revealed specific immunolocalization of sAC in collecting duct cells, and immunoblots confirmed sAC expression in mouse cortical collecting duct (mpkCCD(c14)) cells. These cells exhibit aldosterone-stimulated transepithelial Na(+) currents that depend on both the apical epithelial Na(+) channel (ENaC) and basolateral Na(+),K(+)-ATPase. RNA interference-mediated 60-70% knockdown of sAC expression comparably inhibited basal transepithelial short circuit currents (I(sc)) in mpkCCD(c14) cells. Moreover, the sAC inhibitors KH7 and 2-hydroxyestradiol reduced I(sc) in these cells by 50-60% within 30 min. 8-Bromoadenosine-3',5'-cyclic-monophosphate substantially rescued the KH7 inhibition of transepithelial Na(+) current. Aldosterone doubled ENaC-dependent I(sc) over 4 h, an effect that was abolished in the presence of KH7. The sAC contribution to I(sc) was unaffected with apical membrane nystatin-mediated permeabilization, whereas the sAC-dependent Na(+) current was fully inhibited by basolateral ouabain treatment, suggesting that the Na(+),K(+)-ATPase, rather than ENaC, is the relevant transporter target of sAC. Indeed, neither overexpression of sAC nor treatment with KH7 modulated ENaC currents in Xenopus oocytes. ATPase and biotinylation assays in mpkCCD(c14) cells demonstrated that sAC inhibition decreases catalytic activity rather than surface expression of the Na(+),K(+)-ATPase. In summary, these results suggest that sAC regulates both basal and agonist-stimulated Na(+) reabsorption in the kidney collecting duct, acting to enhance Na(+),K(+)-ATPase activity.
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Affiliation(s)
- Kenneth R Hallows
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15621, USA.
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23
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Miao X, Mukhopadhyay R, Valafar H. Estimation of relative order tensors, and reconstruction of vectors in space using unassigned RDC data and its application. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 194:202-11. [PMID: 18692422 PMCID: PMC2669903 DOI: 10.1016/j.jmr.2008.07.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 06/27/2008] [Accepted: 07/02/2008] [Indexed: 05/11/2023]
Abstract
Advances in NMR instrumentation and pulse sequence design have resulted in easier acquisition of Residual Dipolar Coupling (RDC) data. However, computational and theoretical analysis of this type of data has continued to challenge the international community of investigators because of their complexity and rich information content. Contemporary use of RDC data has required a-priori assignment, which significantly increases the overall cost of structural analysis. This article introduces a novel algorithm that utilizes unassigned RDC data acquired from multiple alignment media (nD-RDC, n3) for simultaneous extraction of the relative order tensor matrices and reconstruction of the interacting vectors in space. Estimation of the relative order tensors and reconstruction of the interacting vectors can be invaluable in a number of endeavors. An example application has been presented where the reconstructed vectors have been used to quantify the fitness of a template protein structure to the unknown protein structure. This work has other important direct applications such as verification of the novelty of an unknown protein and validation of the accuracy of an available protein structure model in drug design. More importantly, the presented work has the potential to bridge the gap between experimental and computational methods of structure determination.
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Affiliation(s)
- Xijiang Miao
- Computer Science and Engineering, Swearingen Engineering Center, University of South Carolina, Columbia, SC 29308, USA
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