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Cryo-EM structure of human bile salts exporter ABCB11. Cell Res 2020; 30:623-625. [PMID: 32203132 DOI: 10.1038/s41422-020-0302-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Accepted: 03/04/2020] [Indexed: 11/08/2022] Open
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Roma MG, Barosso IR, Miszczuk GS, Crocenzi FA, Pozzi EJS. Dynamic Localization of Hepatocellular Transporters: Role in Biliary Excretion and Impairment in Cholestasis. Curr Med Chem 2019; 26:1113-1154. [DOI: 10.2174/0929867325666171205153204] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 09/06/2017] [Accepted: 09/07/2017] [Indexed: 12/25/2022]
Abstract
Bile flow generation is driven by the vectorial transfer of osmotically active compounds from sinusoidal blood into a confined space, the bile canaliculus. Hence, localization of hepatocellular transporters relevant to bile formation is crucial for bile secretion. Hepatocellular transporters are localized either in the plasma membrane or in recycling endosomes, from where they can be relocated to the plasma membrane on demand, or endocytosed when the demand decreases. The balance between endocytic internalization/ exocytic targeting to/from this recycling compartment is therefore the main determinant of the hepatic capability to generate bile, and to dispose endo- and xenobiotics. Furthermore, the exacerbated endocytic internalization is a common pathomechanisms in both experimental and human cholestasis; this results in bile secretory failure and, eventually, posttranslational transporter downregulation by increased degradation. This review summarizes the proposed structural mechanisms accounting for this pathological condition (e.g., alteration of function, localization or expression of F-actin or F-actin/transporter cross-linking proteins, and switch to membrane microdomains where they can be readily endocytosed), and the mediators implicated (e.g., triggering of “cholestatic” signaling transduction pathways). Lastly, we discussed the efficacy to counteract the cholestatic failure induced by transporter internalization of a number of therapeutic experimental approaches based upon the use of compounds that trigger exocytic targetting of canalicular transporters (e.g., cAMP, tauroursodeoxycholate). This therapeutics may complement treatments aimed to transcriptionally improve transporter expression, by affording proper localization and membrane stability to the de novo synthesized transporters.
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Affiliation(s)
- Marcelo G. Roma
- Instituto de Fisiologia Experimental (IFISE) - Facultad de Ciencias Bioquimicas y Farmaceuticas (CONICET - U.N.R.), S2002LRL, Rosario, Argentina
| | - Ismael R. Barosso
- Instituto de Fisiologia Experimental (IFISE) - Facultad de Ciencias Bioquimicas y Farmaceuticas (CONICET - U.N.R.), S2002LRL, Rosario, Argentina
| | - Gisel S. Miszczuk
- Instituto de Fisiologia Experimental (IFISE) - Facultad de Ciencias Bioquimicas y Farmaceuticas (CONICET - U.N.R.), S2002LRL, Rosario, Argentina
| | - Fernando A. Crocenzi
- Instituto de Fisiologia Experimental (IFISE) - Facultad de Ciencias Bioquimicas y Farmaceuticas (CONICET - U.N.R.), S2002LRL, Rosario, Argentina
| | - Enrique J. Sánchez Pozzi
- Instituto de Fisiologia Experimental (IFISE) - Facultad de Ciencias Bioquimicas y Farmaceuticas (CONICET - U.N.R.), S2002LRL, Rosario, Argentina
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Kubitz R, Dröge C, Kluge S, Stross C, Walter N, Keitel V, Häussinger D, Stindt J. Autoimmune BSEP disease: disease recurrence after liver transplantation for progressive familial intrahepatic cholestasis. Clin Rev Allergy Immunol 2016; 48:273-84. [PMID: 25342496 DOI: 10.1007/s12016-014-8457-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Severe cholestasis may result in end-stage liver disease with the need of liver transplantation (LTX). In children, about 10 % of LTX are necessary because of cholestatic liver diseases. Apart from bile duct atresia, three types of progressive familial intrahepatic cholestasis (PFIC) are common causes of severe cholestasis in children. The three subtypes of PFIC are defined by the involved genes: PFIC-1, PFIC-2, and PFIC-3 are due to mutations of P-type ATPase ATP8B1 (familial intrahepatic cholestasis 1, FIC1), the ATP binding cassette transporter ABCB11 (bile salt export pump, BSEP), or ABCB4 (multidrug resistance protein 3, MDR3), respectively. All transporters are localized in the canalicular membrane of hepatocytes and together mediate bile salt and phospholipid transport. In some patients with PFIC-2 disease, recurrence has been observed after LTX, which mimics a PFIC phenotype. It could be shown by several groups that inhibitory anti-BSEP antibodies emerge, which most likely cause disease recurrence. The prevalence of severe BSEP mutations (e.g., splice site and premature stop codon mutations) is very high in this group of patients. These mutations often result in the complete absence of BSEP, which likely accounts for an insufficient auto-tolerance against BSEP. Although many aspects of this "new" disease are not fully elucidated, the possibility of anti-BSEP antibody formation has implications for the pre- and posttransplant management of PFIC-2 patients. This review will summarize the current knowledge including diagnosis, pathomechanisms, and management of "autoimmune BSEP disease."
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Affiliation(s)
- Ralf Kubitz
- Department of Gastroenterology, Hepatology and Infectious Diseases, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany,
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Bachour-El Azzi P, Sharanek A, Burban A, Li R, Guével RL, Abdel-Razzak Z, Stieger B, Guguen-Guillouzo C, Guillouzo A. Comparative Localization and Functional Activity of the Main Hepatobiliary Transporters in HepaRG Cells and Primary Human Hepatocytes. Toxicol Sci 2015; 145:157-68. [PMID: 25690737 DOI: 10.1093/toxsci/kfv041] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The role of hepatobiliary transporters in drug-induced liver injury remains poorly understood. Various in vivo and in vitro biological approaches are currently used for studying hepatic transporters; however, appropriate localization and functional activity of these transporters are essential for normal biliary flow and drug transport. Human hepatocytes (HHs) are considered as the most suitable in vitro cell model but erratic availability and inter-donor functional variations limit their use. In this work, we aimed to compare localization of influx and efflux transporters and their functional activity in differentiated human HepaRG hepatocytes with fresh HHs in conventional (CCHH) and sandwich (SCHH) cultures. All tested influx and efflux transporters were correctly localized to canalicular [bile salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2), multidrug resistance protein 1 (MDR1), and MDR3] or basolateral [Na(+)-taurocholate co-transporting polypeptide (NTCP) and MRP3] membrane domains and were functional in all models. Contrary to other transporters, NTCP and BSEP were less abundant and active in HepaRG cells, cellular uptake of taurocholate was 2.2- and 1.4-fold and bile excretion index 2.8- and 2.6-fold lower, than in SCHHs and CCHHs, respectively. However, when taurocholate canalicular efflux was evaluated in standard and divalent cation-free conditions in buffers or cell lysates, the difference between the three models did not exceed 9.3%. Interestingly, cell imaging showed higher bile canaliculi contraction/relaxation activity in HepaRG hepatocytes and larger bile canaliculi networks in SCHHs. Altogether, our results bring new insights in mechanisms involved in bile acids accumulation and excretion in HHs and suggest that HepaRG cells represent a suitable model for studying hepatobiliary transporters and drug-induced cholestasis.
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Affiliation(s)
- Pamela Bachour-El Azzi
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Ahmad Sharanek
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Audrey Burban
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Ruoya Li
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Rémy Le Guével
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Ziad Abdel-Razzak
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Bruno Stieger
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - Christiane Guguen-Guillouzo
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | - André Guillouzo
- *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland *Inserm UMR991, Foie, Métabolismes et Cancer, Rennes, France; Université de Rennes 1, Rennes, France, Université Libanaise, EDST-PRASE and EDST-AZM-center-LBA3B, Beirut, Lebanon, Biopredic International, Saint Grégoire, France, ImPACcell, SFR Biosit, Université de Rennes 1, Rennes, France and Department of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
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Soroka CJ, Boyer JL. Biosynthesis and trafficking of the bile salt export pump, BSEP: therapeutic implications of BSEP mutations. Mol Aspects Med 2014; 37:3-14. [PMID: 23685087 PMCID: PMC3784619 DOI: 10.1016/j.mam.2013.05.001] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Revised: 04/25/2013] [Accepted: 05/07/2013] [Indexed: 12/17/2022]
Abstract
The bile salt export pump (BSEP, ABCB11) is the primary transporter of bile acids from the hepatocyte to the biliary system. This rate-limiting step in bile formation is essential to the formation of bile salt dependent bile flow, the enterohepatic circulation of bile acids, and the digestion of dietary fats. Mutations in BSEP are associated with cholestatic diseases such as progressive familial intrahepatic cholestasis type 2 (PFIC2), benign recurrent intrahepatic cholestasis type 2 (BRIC2), drug-induced cholestasis, and intrahepatic cholestasis of pregnancy. Development of clinical therapies for these conditions necessitates a clear understanding of the cell biology of biosynthesis, trafficking, and transcriptional and translational regulation of BSEP. This chapter will focus on the molecular and cell biological aspects of this critical hepatic membrane transporter.
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Affiliation(s)
- Carol J Soroka
- Yale University School of Medicine, Department of Internal Medicine, New Haven, CT 06520, United States.
| | - James L Boyer
- Yale University School of Medicine, Department of Internal Medicine, New Haven, CT 06520, United States.
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Abstract
Bile is a unique and vital aqueous secretion of the liver that is formed by the hepatocyte and modified down stream by absorptive and secretory properties of the bile duct epithelium. Approximately 5% of bile consists of organic and inorganic solutes of considerable complexity. The bile-secretory unit consists of a canalicular network which is formed by the apical membrane of adjacent hepatocytes and sealed by tight junctions. The bile canaliculi (∼1 μm in diameter) conduct the flow of bile countercurrent to the direction of portal blood flow and connect with the canal of Hering and bile ducts which progressively increase in diameter and complexity prior to the entry of bile into the gallbladder, common bile duct, and intestine. Canalicular bile secretion is determined by both bile salt-dependent and independent transport systems which are localized at the apical membrane of the hepatocyte and largely consist of a series of adenosine triphosphate-binding cassette transport proteins that function as export pumps for bile salts and other organic solutes. These transporters create osmotic gradients within the bile canalicular lumen that provide the driving force for movement of fluid into the lumen via aquaporins. Species vary with respect to the relative amounts of bile salt-dependent and independent canalicular flow and cholangiocyte secretion which is highly regulated by hormones, second messengers, and signal transduction pathways. Most determinants of bile secretion are now characterized at the molecular level in animal models and in man. Genetic mutations serve to illuminate many of their functions.
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Affiliation(s)
- James L Boyer
- Department of Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut, USA.
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The bile salt export pump (BSEP) in health and disease. Clin Res Hepatol Gastroenterol 2012; 36:536-53. [PMID: 22795478 DOI: 10.1016/j.clinre.2012.06.006] [Citation(s) in RCA: 128] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Revised: 05/29/2012] [Accepted: 06/06/2012] [Indexed: 02/04/2023]
Abstract
The bile salt export pump (BSEP) is the major transporter for the secretion of bile acids from hepatocytes into bile in humans. Mutations of BSEP are associated with cholestatic liver diseases of varying severity including progressive familial intrahepatic cholestasis type 2 (PFIC-2), benign recurrent intrahepatic cholestasis type 2 (BRIC-2) and genetic polymorphisms are linked to intrahepatic cholestasis of pregnancy (ICP) and drug-induced liver injury (DILI). Detailed analysis of these diseases has considerably increased our knowledge about physiology and pathophysiology of bile secretion in humans. This review focuses on expression, localization, and function, short- and long-term regulation of BSEP as well as diseases association and treatment options for BSEP-associated diseases.
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Boaglio AC, Zucchetti AE, Toledo FD, Barosso IR, Sánchez Pozzi EJ, Crocenzi FA, Roma MG. ERK1/2 and p38 MAPKs are complementarily involved in estradiol 17ß-D-glucuronide-induced cholestasis: crosstalk with cPKC and PI3K. PLoS One 2012; 7:e49255. [PMID: 23166621 PMCID: PMC3498151 DOI: 10.1371/journal.pone.0049255] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 10/04/2012] [Indexed: 12/17/2022] Open
Abstract
Objective The endogenous, cholestatic metabolite estradiol 17ß-d-glucuronide (E217G) induces endocytic internalization of the canalicular transporters relevant to bile formation, Bsep and Mrp2. We evaluated here whether MAPKs are involved in this effect. Design ERK1/2, JNK1/2, and p38 MAPK activation was assessed by the increase in their phosphorylation status. Hepatocanalicular function was evaluated in isolated rat hepatocyte couplets (IRHCs) by quantifying the apical secretion of fluorescent Bsep and Mrp2 substrates, and in isolated, perfused rat livers (IPRLs), using taurocholate and 2,4-dinitrophenyl-S-glutathione, respectively. Protein kinase participation in E217G-induced secretory failure was assessed by co-administering selective inhibitors. Internalization of Bsep/Mrp2 was assessed by confocal microscopy and image analysis. Results E217G activated all kinds of MAPKs. The PI3K inhibitor wortmannin prevented ERK1/2 activation, whereas the cPKC inhibitor Gö6976 prevented p38 activation, suggesting that ERK1/2 and p38 are downstream of PI3K and cPKC, respectively. The p38 inhibitor SB203580 and the ERK1/2 inhibitor PD98059, but not the JNK1/2 inhibitor SP600125, partially prevented E217G-induced changes in transporter activity and localization in IRHCs. p38 and ERK1/2 co-inhibition resulted in additive protection, suggesting complementary involvement of these MAPKs. In IPRLs, E217G induced endocytosis of canalicular transporters and a rapid and sustained decrease in bile flow and biliary excretion of Bsep/Mrp2 substrates. p38 inhibition prevented this initial decay, and the internalization of Bsep/Mrp2. Contrarily, ERK1/2 inhibition accelerated the recovery of biliary secretion and the canalicular reinsertion of Bsep/Mrp2. Conclusions cPKC/p38 MAPK and PI3K/ERK1/2 signalling pathways participate complementarily in E217G-induced cholestasis, through internalization and sustained intracellular retention of canalicular transporters, respectively.
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Affiliation(s)
| | | | | | | | | | - Fernando A. Crocenzi
- Institute of Experimental Physiology, National Scientific and Technical Research Council/National University of Rosario, Rosario, Argentina
- * E-mail: (FAC); (MGR)
| | - Marcelo G. Roma
- Institute of Experimental Physiology, National Scientific and Technical Research Council/National University of Rosario, Rosario, Argentina
- * E-mail: (FAC); (MGR)
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Keitel V, Burdelski M, Vojnisek Z, Schmitt L, Häussinger D, Kubitz R. De novo bile salt transporter antibodies as a possible cause of recurrent graft failure after liver transplantation: a novel mechanism of cholestasis. Hepatology 2009; 50:510-7. [PMID: 19642168 DOI: 10.1002/hep.23083] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Progressive familial intrahepatic cholestasis type 2 (PFIC-2) is caused by mutations of the bile salt export pump (BSEP [ABCB11]), an ATP-binding cassette (ABC)-transporter exclusively expressed at the canalicular membrane of hepatocytes. An absence of BSEP from the canalicular membrane causes cholestasis and leads to liver cirrhosis, which may necessitate liver transplantation in early childhood. We report on the first case of a child with PFIC-2 suffering from repeated posttransplant recurrence of progressive intrahepatic cholestasis due to autoantibodies against BSEP. These antibodies occurred after transplantation and were detected in the patient's serum and at the canalicular membrane of two consecutive liver transplants. The antibodies were reactive toward the first extracellular loop of BSEP, were of high affinity, and inhibited transport activity of BSEP, thus causing severe cholestasis. The patient had three homozygous, missense changes in the BSEP gene. Their combination resulted in the complete absence of BSEP, which explains the lack of tolerance, a prerequisite of autoantibody formation toward BSEP. The findings illustrate a novel disease mechanism due to a new class of functionally relevant autoantibodies resulting in cholestasis and subsequent liver failure.
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Affiliation(s)
- Verena Keitel
- Department of Gastroenterology, Heinrich-Heine-University of Düsseldorf, Moorenstrasse 5, D-40225 Düsseldorf, Germany
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Mitchell KAP, Szabo G, de S Otero A. Direct binding of cytosolic NDP kinases to membrane lipids is regulated by nucleotides. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:469-76. [PMID: 19146889 DOI: 10.1016/j.bbamcr.2008.12.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2008] [Revised: 11/30/2008] [Accepted: 12/03/2008] [Indexed: 11/19/2022]
Abstract
In spite of their complete lack of any structural features that characterize membrane proteins, cytosolic nucleoside-diphosphate kinases (NDPKs) have been found repeatedly to associate with membranes. In some instances the recruitment of cytosolic NDPKs to membranes was attributed to interactions with peripheral or integral membrane proteins, but in many cases the mechanism underlying the association of NDPKs with membranes remained unknown. We show here that cytosolic NDPKs bind directly to membrane lipids in a dynamic process that is controlled by its substrates, nucleoside tri- and diphosphates, and can be fully reconstituted with chemically defined, protein-free phospholipids and recombinant NDPK, or with purified NDPK. Our results uncover a novel mechanism for the reversible targeting of soluble NDPKs to membranes, where they may act as a reservoir of high energy phosphate, supporting the operation of membrane-based processes that utilize nucleotides other than ATP, such as intracellular traffic and phospholipid biosynthesis.
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Affiliation(s)
- Kimberly A P Mitchell
- Department of Molecular Physiology and Biological Physics, University of Virginia Medical School, P.O. Box 800736, Charlottesville, VA 22908-0736, USA
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Roma MG, Crocenzi FA, Mottino AD. Dynamic localization of hepatocellular transporters in health and disease. World J Gastroenterol 2008; 14:6786-801. [PMID: 19058304 PMCID: PMC2773873 DOI: 10.3748/wjg.14.6786] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Vesicle-based trafficking of hepatocellular transporters involves delivery of the newly-synthesized carriers from the rough endoplasmic reticulum to either the plasma membrane domain or to an endosomal, submembrane compartment, followed by exocytic targeting to the plasma membrane. Once delivered to the plasma membrane, the transporters usually undergo recycling between the plasma membrane and the endosomal compartment, which usually serves as a reservoir of pre-existing transporters available on demand. The balance between exocytic targeting and endocytic internalization from/to this recycling compartment is therefore a chief determinant of the overall capability of the liver epithelium to secrete bile and to detoxify endo and xenobiotics. Hence, it is a highly regulated process. Impaired regulation of this balance may lead to abnormal localization of these transporters, which results in bile secretory failure due to endocytic internalization of key transporters involved in bile formation. This occurs in several experimental models of hepatocellular cholestasis, and in most human cholestatic liver diseases. This review describes the molecular bases involved in the biology of the dynamic localization of hepatocellular transporters and its regulation, with a focus on the involvement of signaling pathways in this process. Their alterations in different experimental models of cholestasis and in human cholestatic liver disease are reviewed. In addition, the causes explaining the pathological condition (e.g. disorganization of actin or actin-transporter linkers) and the mediators involved (e.g. activation of cholestatic signaling transduction pathways) are also discussed. Finally, several experimental therapeutic approaches based upon the administration of compounds known to stimulate exocytic insertion of canalicular transporters (e.g. cAMP, tauroursodeoxycholate) are described.
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Norouziyan F, Shen WC, Hamm-Alvarez SF. Tyrphostin A8 stimulates a novel trafficking pathway of apically endocytosed transferrin through Rab11-enriched compartments in Caco-2 cells. Am J Physiol Cell Physiol 2007; 294:C7-21. [PMID: 17959726 DOI: 10.1152/ajpcell.00372.2006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The potential application of transferrin receptors as delivery vehicles for transport of macromolecular drugs across intestinal epithelial cells is limited by several factors, including the low level of transferrin receptor-mediated transcytosis, particularly in the apical-to-basolateral direction. The GTPase inhibitor, AG10 (tyrphostin A8), has been shown previously to increase the apical-to-basolateral transcytosis of transferrin in Caco-2 cells. However, the mechanism of the increased transcytosis has not been established. In this report, the effect of AG10 on the trafficking of endocytosed transferrin among different endosomal compartments as well as the involvement of Rab11 in the intracellular trafficking of transferrin was investigated. Confocal microscopy studies showed a high level of colocalization of FITC-transferrin with Rab5 and Rab11 in Caco-2 cells pulsed at 16 degrees C and 37 degrees C, which indicated the presence of apically endocytosed FITC-transferrin in early endosomes and apical recycling endosomes at 16 degrees C and 37 degrees C, respectively. The effect of AG10 on the accumulation of transferrin within different endosomal compartment was studied, and an increase in the transcytosis and recycling of internalized (125)I-labeled transferrin, as well as a decrease in cell-associated (125)I-labeled transferrin, was observed in AG10-treated Caco-2 cells pulsed at 37 degrees C for 30 min and chased for 30 min. Moreover, confocal microscopy showed that FITC-transferrin exhibited an increased level of colocalization with Rab11, but not with Rab5, in the presence of AG10. These results suggest an effect of AG10 on the later steps of transferrin receptor trafficking, which are involved in subsequent recycling, and possibly transcytosis, of endocytosed transferrin in Caco-2 cells.
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Affiliation(s)
- Fariba Norouziyan
- Department of Pharmacology and Pharmaceutical Sciences, University of Southern California, Los Angeles, California 90033, USA
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Wüstner D. Quantification of polarized trafficking of transferrin and comparison with bulk membrane transport in hepatic cells. Biochem J 2006; 400:267-80. [PMID: 16879100 PMCID: PMC1652827 DOI: 10.1042/bj20060626] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Transport of the recycling marker transferrin was analysed in polarized hepatic HepG2 cells using quantitative fluorescence microscopy and mathematical modelling. A detailed map and kinetic model for transport of transferrin in hepatic cells was developed. Fluorescent transferrin was found to be transported sequentially through basolateral SE (sorting endosomes) to a SAC/ARC (subapical compartment/apical recycling compartment). DiI (di-indocarbocyanine) lipid probes of different acyl chain length (DiIC12 and DiIC16) co-localized with transferrin in basolateral SE and in the SAC/ARC. By kinetic comparison of hepatic transport of transferrin and labelled HDL (high-density lipoprotein), it is shown that transport of transferrin from SE to the SAC/ARC follows a default pathway together with HDL. Kinetic modelling of fluorescence data provides an identical half-time for SE-to-SAC/ARC transport of transferrin and fluorescent HDL (t(1/2)=4.2 min). Fluorescent transferrin was found to recycle with a half-time of t(1/2)=12.9 min from the SAC/ARC to the basolateral cell surface of HepG2 cells. In contrast with HDL, targeting of labelled transferrin from the SAC/ARC to the apical biliary canaliculus was negligible. The results indicate that transport from basolateral hepatic SE to the SAC/ARC represents a bulk flow process and that polarized sorting occurs mainly at the level of the SAC/ARC.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
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14
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Tradtrantip L, Boyer JL, Suksamrarn A, Piyachaturawat P. Differential effects of hydroxyacetophenone analogues on the transcytotic vesicular pathway in rat liver. Eur J Pharmacol 2006; 547:152-9. [PMID: 16945364 DOI: 10.1016/j.ejphar.2006.07.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2006] [Revised: 06/08/2006] [Accepted: 07/13/2006] [Indexed: 10/24/2022]
Abstract
Insertion of transporter proteins into the apical canalicular membrane via vesicular transport is one of several choleretic mechanisms. Based on different choleretic activities of hydroxyacetophenone analogues including 4-mono; 2,6-di and 2,4,6-trihydroxy-acetophenone (MHA, DHA and THA), the present study aims to determine if these compounds stimulated vesicular transport in hepatocytes. Hydroxyacetophenone was continuously infused into the duodenum of the bile fistula rat. Bile flow rate was allowed to stabilize and then followed by an intraportal injection of horseradish peroxidase, a marker of the transcytotic vesicle pathway. MHA which stimulates bile acid independent flow, showed a dose-dependent increase in both the early (paracellular) and late (transcellular) peak of horseradish peroxidase excretion in bile. THA, which stimulates both bile acid dependent flow and bile acid independent flow, did not alter the pattern of horseradish peroxidase excretion into bile. However, DHA, which is more hydrophobic and increases only bile acid dependent flow, decreased the late peak. The stimulating effects of MHA on bile flow and horseradish peroxidase excretion were markedly inhibited by colchicine, suggesting that its choleretic action involves stimulation of exocytosis, as well as increase in paracellular permeability. In contrast, the lack of a stimulatory effect of THA and DHA on biliary horseradish peroxidase excretion suggested that their choleretic action is not associated with vesicular exocytosis. These results demonstrate a variable effect of hydroxyacetophenones on the transcytotic vesicular pathway reflecting different choleretic mechanisms and therapeutic potential.
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Affiliation(s)
- Lukmanee Tradtrantip
- Department of Physiology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok, Thailand
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15
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Wang W, Soroka CJ, Mennone A, Rahner C, Harry K, Pypaert M, Boyer JL. Radixin is required to maintain apical canalicular membrane structure and function in rat hepatocytes. Gastroenterology 2006; 131:878-84. [PMID: 16952556 PMCID: PMC1820831 DOI: 10.1053/j.gastro.2006.06.013] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Accepted: 06/02/2006] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS Ezrin-radixin-moesin proteins are cross-linkers between the plasma membrane and actin filaments. Radixin, the dominant ezrin-radixin-moesin protein in hepatocytes, has been reported to selectively tether multidrug-resistance-associated protein 2 to the apical canalicular membrane. However, it remains to be determined if this is its primary function. METHODS An adenovirus-mediated short interfering RNA (siRNA) was used to down-regulate radixin expression in collagen sandwich-cultured rat hepatocytes and morphologic and functional changes were characterized quantitatively. RESULTS In control cultures, an extensive bile canalicular network developed with properly localized apical and basolateral transporters that provided for functional excretion of fluorescent cholephiles into the bile canalicular lumina. siRNA-induced suppression of radixin was associated with a marked reduction in the canalicular membrane structure as observed by differential interference contrast microscopy and F-actin staining, in contrast to control cells exposed to adenovirus encoding scrambled siRNA. Indirect immunofluorescence showed that apical transporters (multidrug-resistance-associated protein 2, bile salt export pump, and multidrug-resistance protein 1) dissociated from their normal location at the apical membrane and were found largely associated with Rab11-containing endosomes. Localization of the basolateral membrane transporter, organic anion transporting polypeptide 2 (Oatp2), was not affected. Consistent with this dislocation of apical transporters, the biliary excretion of glutathione-methylfluorescein and cholylglycylamido-fluorescein was decreased significantly in the radixin-deficient cells, but not in the control siRNA cells. CONCLUSIONS Radixin is essential for maintaining the polarized targeting and/or retaining of canalicular membrane transporters and is a critical determinant of the overall structure and function of the apical membrane of hepatocytes.
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Affiliation(s)
- Wei Wang
- Liver Center, Yale University School of Medicine, New Haven, Connecticut 06520-8019, USA
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16
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Dombrowski F, Stieger B, Beuers U. Tauroursodeoxycholic acid inserts the bile salt export pump into canalicular membranes of cholestatic rat liver. J Transl Med 2006; 86:166-74. [PMID: 16344857 DOI: 10.1038/labinvest.3700371] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Ursodeoxycholic acid exerts anticholestatic effects in chronic cholestatic liver disease in humans as well as in experimental animal models of cholestasis. Its taurine conjugate, TUDCA, was recently shown to stimulate insertion of the apical conjugate export pump, Mrp2 (ABCC2), into canalicular membranes of rat hepatocytes made cholestatic by exposure to taurolithocholic acid (TLCA). The aim of this immunoelectronmicroscopic study was to test whether TLCA and TUDCA modulate the canalicular density of the other key apical transporter, the bile salt export pump, Bsep (ABCB11), in a similar way. Immunoelectronmicroscopic analysis of Bsep density on canalicular membranes, microvilli, and pericanalicular area of hepatocytes was performed in rat liver tissue prepared after liver perfusion with bile acids or carrier medium only. TLCA (10 micromol/l for 50 min) decreased Bsep density in canalicular membranes to 31% of controls (P<0.05) when bile flow was reduced to 35% of controls (P<0.05). Concomitantly, Bsep density in a 1 microm pericanalicular zone increased to 202% (P<0.05) indicating effective retrieval of Bsep from the canalicular membrane induced by TLCA. Coadministration of TUDCA (25 micromol/l) led to a 3.2-fold increase of Bsep density in canalicular membranes equal to control liver (P<0.05 vs TLCA) in association with a 3.8-fold increase of bile flow (P<0.05 vs TLCA). Stimulation of apical membrane insertion of key transporters like the bile salt export pump, Bsep, and-as previously shown-the conjugate export pump, Mrp2, may contribute to the anticholestatic action of UDCA amides in cholestatic conditions.
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Affiliation(s)
- Frank Dombrowski
- Department of Pathology, University of Magdeburg, Magdeburg, Germany
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17
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Gradilone SA, Tietz PS, Splinter PL, Marinelli RA, LaRusso NF. Expression and subcellular localization of aquaporin water channels in the polarized hepatocyte cell line, WIF-B. BMC PHYSIOLOGY 2005; 5:13. [PMID: 16109175 PMCID: PMC1208912 DOI: 10.1186/1472-6793-5-13] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Accepted: 08/18/2005] [Indexed: 12/12/2022]
Abstract
Background Recent data suggest that canalicular bile secretion involves selective expression and coordinated regulation of aquaporins (AQPs), a family of water channels proteins. In order to further characterize the role of AQPs in this process, an in vitro cell system with retained polarity and expression of AQPs and relevant solute transporters involved in bile formation is highly desirable. The WIF-B cell line is a highly differentiated and polarized rat hepatoma/human fibroblast hybrid, which forms abundant bile canalicular structures. This cell line has been reported to be a good in vitro model for studying hepatocyte polarity. Results Using RT-PCR, immunoblotting and confocal immunofluorescence, we showed that WIF-B cells express the aquaporin water channels that facilitate the osmotically driven water movements in the liver, i.e. AQP8, AQP9, and AQP0; as well as the key solute transporters involved in the generation of canalicular osmotic gradients, i.e., the bile salt export pump Bsep, the organic anion transporter Mrp2 and the chloride bicarbonate exchanger AE2. The subcellular localization of the AQPs and the solute transporters in WIF-B cells was similar to that in freshly isolated rat hepatocytes and in intact liver. Immunofluorescent costaining studies showed intracellular colocalization of AQP8 and AE2, suggesting the possibility that these transporters are expressed in the same population of pericanalicular vesicles. Conclusion The hepatocyte cell line WIF-B retains the expression and subcellular localization of aquaporin water channels as well as key solute transporters for canalicular bile secretion. Thus, these cells can work as a valuable tool for regulatory and mechanistic studies of the biology of bile formation.
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Affiliation(s)
- Sergio A Gradilone
- Instituto de Fisiología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, 2000 Rosario, Santa Fe, Argentina
| | - Pamela S Tietz
- Center for Basic Research in Digestive Diseases. Mayo Medical School, Clinic and Foundation, Rochester, MN, USA
| | - Patrick L Splinter
- Center for Basic Research in Digestive Diseases. Mayo Medical School, Clinic and Foundation, Rochester, MN, USA
| | - Raúl A Marinelli
- Instituto de Fisiología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, 2000 Rosario, Santa Fe, Argentina
| | - Nicholas F LaRusso
- Center for Basic Research in Digestive Diseases. Mayo Medical School, Clinic and Foundation, Rochester, MN, USA
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18
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Affiliation(s)
- Raúl A Marinelli
- Instituto de Fisiología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Santa Fe, Argentina.
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19
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Hoekstra D, Tyteca D, van IJzendoorn SCD. The subapical compartment: a traffic center in membrane polarity development. J Cell Sci 2005; 117:2183-92. [PMID: 15126620 DOI: 10.1242/jcs.01217] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Spatially separated apical and basolateral plasma membrane domains that have distinct functions and molecular compositions are a characteristic feature of epithelial cell polarity. The subapical compartment (SAC), also known as the common endosome (CE), where endocytic pathways from both surfaces merge, plays a crucial role in the maintenance and probably the biogenesis of these distinct membrane domains. Although differences in morphology are apparent, the same principal features of a SAC can be distinguished in different types of epithelial cells. As polarity develops, the compartment acquires several distinct machineries that, in conjunction with the cytoskeleton, are necessary for polarized trafficking. Disrupting trafficking via the SAC and hence bypassing its sorting machinery, as occurs upon actin depolymerization, leads to mis-sorting of apical and basolateral molecules, thereby compromising the development of polarity. The structural and functional integrity of the compartment in part depends on microtubules. Moreover, the acquisition of a particular set of Rab proteins, including Rab11 and Rab3, appears to be crucial in regulating molecular sorting and vesicular transport relevant both to recycling to either plasma membrane domain and to de novo assembly of the apical domain. Furthermore, subcompartmentalization of the SAC appears to be key to its various functions.
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Affiliation(s)
- Dick Hoekstra
- Department of Membrane Cell Biology, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
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20
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Affiliation(s)
- Lin Wang
- The Yale Liver Center, Yale University School of Medicine, New Haven, CT, USA.
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21
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Affiliation(s)
- M Sawkat Anwer
- Department of Biomedical Sciences, Tufts University School of Veterinary Medicine, 200 Westboro Road, N. Grafton, MA 01536, USA.
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22
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Crocenzi FA, Mottino AD, Cao J, Veggi LM, Pozzi EJS, Vore M, Coleman R, Roma MG. Estradiol-17beta-D-glucuronide induces endocytic internalization of Bsep in rats. Am J Physiol Gastrointest Liver Physiol 2003; 285:G449-59. [PMID: 12702498 DOI: 10.1152/ajpgi.00508.2002] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Endocytic internalization of the multidrug resistance-associated protein 2 (Mrp2) was previously suggested to be involved in estradiol-17beta-D-glucuronide (E217G)-induced cholestasis. Here we evaluated in the rat whether a similar phenomenon occurs with the bile salt export pump (Bsep) and the ability of DBcAMP to prevent it. E217G (15 micromol/kg i.v.) impaired bile salt (BS) output and induced Bsep internalization, as assessed by confocal microscopy and Western blotting. Neither cholestasis nor Bsep internalization occurred in TR- rats lacking Mrp2. DBcAMP (20 micromol/kg i.v.) partially prevented the decrease in bile flow and BS output and substantially prevented E217G-induced Bsep internalization. In hepatocyte couplets, E217G (50 microM) diminished canalicular accumulation of a fluorescent BS and decreased Bsep-associated fluorescence in the canalicular membrane; DBcAMP (10 microM) fully prevented both effects. In conclusion, our results suggest that changes in Bsep localization are involved in E217G-induced impairment of bile flow and BS transport and that DBcAMP prevents this effect by stimulating insertion of canalicular transporter-containing vesicles. Mrp2 is required for E217G to induce its harmful effect.
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Affiliation(s)
- Fernando A Crocenzi
- Instituto de Fisiología Experimental, Universidad Nacional de Rosario, Argentina
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23
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Gerk PM, Vore M. Regulation of expression of the multidrug resistance-associated protein 2 (MRP2) and its role in drug disposition. J Pharmacol Exp Ther 2002; 302:407-15. [PMID: 12130697 DOI: 10.1124/jpet.102.035014] [Citation(s) in RCA: 151] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The multidrug resistance protein 2 (MRP2; ABCC2) is an ATP-binding cassette transporter accepting a diverse range of substrates, including glutathione, glucuronide, and sulfate conjugates of many endo- and xenobiotics. MRP2 generally performs excretory or protective roles, and it is expressed on the apical domain of hepatocytes, enterocytes of the proximal small intestine, and proximal renal tubular cells, as well as in the brain and the placenta. MRP2 is regulated at several levels, including membrane retrieval and reinsertion, translation, and transcription. In addition to transport of conjugates, MRP2 transports cancer chemotherapeutics, uricosurics, antibiotics, leukotrienes, glutathione, toxins, and heavy metals. Several mutagenesis studies have described critical residues for substrate binding and various naturally occurring mutations that eliminate MRP2 expression or function. MRP2 is important clinically as it modulates the pharmacokinetics of many drugs, and its expression and activity are also altered by certain drugs and disease states.
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Affiliation(s)
- Phillip M Gerk
- Graduate Center for Toxicology, University of Kentucky, Room 306, Health Science Building, Lexington, KY 40536-0305, USA
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24
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Huebert RC, Splinter PL, Garcia F, Marinelli RA, LaRusso NF. Expression and localization of aquaporin water channels in rat hepatocytes. Evidence for a role in canalicular bile secretion. J Biol Chem 2002; 277:22710-7. [PMID: 11932260 DOI: 10.1074/jbc.m202394200] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Although bile formation requires that large volumes of water be rapidly transported across liver epithelia, including hepatocytes, the molecular mechanisms by which water is secreted into bile are obscure. The aquaporins are a family of 10 channel-forming, integral membrane proteins of approximately 28 kDa numbered 0-9 that allow water to rapidly traverse epithelial barriers in several organs including kidney, eye, and brain. We found transcripts of three of 10 aquaporins in hepatocytes (aquaporin 8 aquaporin 9 > aquaporin 0) by reverse transcription-polymerase chain reaction and quantitative ribonuclease protection assays; immunohistochemistry confirmed the presence of these three proteins in liver. Immunoblots of subcellular fractions of hepatocytes showed enrichment of aquaporins 0 and 8 in microsomes and canalicular plasma membranes; aquaporin 9 was enriched only in basolateral plasma membranes. Immunofluorescence of hepatocyte couplets confirmed the intracellular/canalicular localization of aquaporins 0 and 8 and the basolateral localization of aquaporin 9. Upon exposure of couplets to a choleretic stimulus (i.e. dibutyryl cAMP), aquaporin 8 redistributed to the canalicular plasma membrane; the subcellular distributions of aquaporins 0 and 9 were unaffected. In addition, exposure of couplets to dibutyryl cAMP caused an increase in canalicular water transport in the presence and absence of an osmotic gradient, an effect that was blocked by aquaporin inhibitors. These results provide evidence that aquaporins are present in hepatocytes and that aquaporins are involved in agonist-stimulated canalicular bile secretion.
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Affiliation(s)
- Robert C Huebert
- Center for Basic Research in Digestive Diseases, Mayo Medical School, Clinic and Foundation, Rochester, Minnesota 55905, USA
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25
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Abstract
New insights into the regulation of hepatobiliary transport proteins have provided the basis for a better understanding of the pathogenesis of cholestatic liver diseases. Mutations of transporter genes can cause hereditary cholestatic syndromes, the study of which has shed much light on the basic mechanisms of bile secretion and cholestasis. Important new studies have been published about the pathogenesis, clinical features, and treatment of primary biliary cirrhosis, primary sclerosing cholangitis, cholestasis of pregnancy, total parenteral nutrition-induced cholestasis, and drug-induced cholestasis.
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Affiliation(s)
- M Trauner
- Division of Gastroenterology and Hepatology, Department of Internal Medicine, Karl Franzens University School of Medicine, Graz, Austria
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26
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García F, Kierbel A, Larocca MC, Gradilone SA, Splinter P, LaRusso NF, Marinelli RA. The water channel aquaporin-8 is mainly intracellular in rat hepatocytes, and its plasma membrane insertion is stimulated by cyclic AMP. J Biol Chem 2001; 276:12147-52. [PMID: 11278499 DOI: 10.1074/jbc.m009403200] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected an N-glycosylated band of approximately 34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt(2)cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt(2)cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt(2)cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.
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Affiliation(s)
- F García
- Instituto de Fisiologia Experimental, Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET), Universidad Nacional de Rosario, Rosario, Santa Fe, Argentina 2000
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27
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Olson AL, Trumbly AR, Gibson GV. Insulin-mediated GLUT4 translocation is dependent on the microtubule network. J Biol Chem 2001; 276:10706-14. [PMID: 11278355 DOI: 10.1074/jbc.m007610200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The GLUT4 facilitative glucose transporter is recruited to the plasma membrane by insulin. This process depends primarily on the exocytosis of a specialized pool of vesicles containing GLUT4 in their membranes. The mechanism of GLUT4 vesicle exocytosis in response to insulin is not understood. To determine whether GLUT4 exocytosis is dependent on intact microtubule network, we measured insulin-mediated GLUT4 exocytosis in 3T3-L1 adipocytes in which the microtubule network was depolymerized by pretreatment with nocodazole. Insulin-mediated GLUT4 translocation was inhibited by more than 80% in nocodazole-treated cells. Phosphorylation of insulin receptor substrate 1 (IRS-1), activation of IRS-1 associated phosphatidylinositide 3-kinase, and phosphorylation of protein kinase B/Akt-1 were not inhibited by nocodazole treatment indicating that the microtubule network was not required for proximal insulin signaling. An intact microtubule network is specifically required for insulin-mediated GLUT4 translocation since nocodazole treatment did not affect insulin-mediated GLUT1 translocation or adipsin secretion. By using in vitro microtubule binding, we demonstrated that both GLUT4 vesicles and IRS-1 bind specifically to microtubules, implicating microtubules in both insulin signaling and GLUT4 translocation. Vesicle binding to microtubules was not mediated through direct binding of GLUT4 or insulin-responsive aminopeptidase to microtubules. A model microtubule-dependent translocation of GLUT4 is proposed.
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Affiliation(s)
- A L Olson
- Department of Biochemistry and Molecular Biology, the University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190, USA.
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28
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Maier O, Aït Slimane T, Hoekstra D. Membrane domains and polarized trafficking of sphingolipids. Semin Cell Dev Biol 2001; 12:149-61. [PMID: 11292381 DOI: 10.1006/scdb.2000.0232] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The plasma membrane of polarized cells consists of distinct domains, the apical and basolateral membrane, that are characterized by a distinct lipid and protein content. Apical protein transport is largely mediated by (glyco)sphingolipid--cholesterol enriched membrane microdomains, so called rafts. In addition changes in the direction of polarized sphingolipid transport appear instrumental in cell polarity development. Knowledge is therefore required of the mechanisms that mediate sphingolipid sorting and the complexity of the trafficking pathways that are involved in polarized transport of both sphingolipids and proteins. Here we summarize specific biophysical properties that underly mechanisms relevant to sphingolipid sorting, cargo recruitment and polarized trafficking, and discuss the central role of a subapical compartment, SAC or common endosome (CE), as a major intracellular site involved in polarized sorting of sphingolipids, and in development and maintenance of membrane polarity.
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Affiliation(s)
- O Maier
- Department of Membrane Cell Biology, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
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29
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Rahner C, Stieger B, Landmann L. Apical endocytosis in rat hepatocytes In situ involves clathrin, traverses a subapical compartment, and leads to lysosomes. Gastroenterology 2000; 119:1692-707. [PMID: 11113091 DOI: 10.1053/gast.2000.20233] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND & AIMS This study demonstrates and characterizes apical (canalicular) endocytic pathways in hepatocytes in situ. METHODS Endocytic markers were administered by retrograde infusion through the common bile duct. Colocalization with proteins that are specific for various endocytic compartments was performed on stacks of deconvoluted confocal immunofluorescence images. The subcellular distribution of marker proteins was assessed by electron microscopy (EM). RESULTS Bulk-phase, as well as membrane-associated markers, were internalized readily at the apical cell pole. At the EM level, marker was found initially in 60-100-nm tubulovesicular structures and 150-200-nm cup-shaped vesicles, whereas multivesicular bodies and lysosomes became labeled after longer time intervals. Apical endocytosis involved clathrin and delivered marker to late endosomes (rab7(+), cathepsin D(+)), as well as lysosomes (rab7(-), cathepsin D(+)). Simultaneous labeling of the basolateral endocytic route resulted in overlap of both pathways in the late endosomal and lysosomal compartments. In addition, apical endocytosis involved a subapical compartment (endolyn-78(+), rab11(+), polymeric IgA receptor [pIgA-R(+)]) that is passed by the transcytotic route, thus constituting a crossroads. pIgA-R immunoreactivity, probably reflecting the cleaved receptor fragment, was associated with apical endocytic marker and colocalized with clathrin and later with cathepsin D. CONCLUSIONS Apical endocytosis involves coated pits/vesicles, leads to a subapical compartment, and plays a role in the retrieval of canalicular plasma membrane components for lysosomal degradation.
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Affiliation(s)
- C Rahner
- Department of Anatomy, University of Basel, Basel, Switzerland
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30
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Kipp H, Arias IM. Newly synthesized canalicular ABC transporters are directly targeted from the Golgi to the hepatocyte apical domain in rat liver. J Biol Chem 2000; 275:15917-25. [PMID: 10748167 DOI: 10.1074/jbc.m909875199] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Newly synthesized canalicular ectoenzymes and a cell adhesion molecule (cCAM105) have been shown to traffic from the Golgi to the basolateral plasma membrane, from where they transcytose to the apical bile canalicular domain. It has been proposed that all canalicular proteins are targeted via this indirect route in hepatocytes. We studied the membrane targeting of rat canalicular proteins by in vivo [(35)S]methionine metabolic labeling followed by preparation of highly purified Golgi membranes and canalicular (CMVs) and sinusoidal/basolateral (SMVs) membrane vesicles and subsequent immunoprecipitation. In particular, we compared membrane targeting of newly synthesized canalicular ABC (ATP-binding cassette) transporters MDR1, MDR2, and SPGP (sister of P-glycoprotein) with that of cCAM105. Significant differences were observed in metabolic pulse-chase labeling experiments with regard to membrane targeting of these apical proteins. After a chase time of 15 min, cCAM105 appeared exclusively in SMVs, peaked at 1 h, and progressively declined thereafter. In CMVs, cCAM105 was first detected after 1 h and subsequently increased for 3 h. This findings confirm the transcytotic targeting of cCAM105 reported in earlier studies. In contrast, at no time point investigated were MDR1, MDR2, and SPGP detected in SMVs. In CMVs, MDR1 and MDR2 appeared after 30 min, whereas SPGP appeared after 2 h of labeling. In Golgi membranes, each of the ABC transporters peaked at 30 min and was virtually absent thereafter. These data suggest rapid, direct targeting of newly synthesized MDR1 and MDR2 from the Golgi to the bile canaliculus and transient sequestering of SPGP in an intracellular pool en route from the Golgi to the apical plasma membrane. This study provides biochemical evidence for direct targeting of newly synthesized apical ABC transporters from the Golgi to the bile canaliculus in vivo.
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Affiliation(s)
- H Kipp
- Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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