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Basiglio CL, Crocenzi FA, Sánchez Pozzi EJ, Roma MG. Oxidative Stress and Localization Status of Hepatocellular Transporters: Impact on Bile Secretion and Role of Signaling Pathways. Antioxid Redox Signal 2021; 35:808-831. [PMID: 34293961 DOI: 10.1089/ars.2021.0021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Significance: Most hepatopathies are primarily or secondarily cholestatic in nature. Oxidative stress (OS) is a frequent trait among them, and impairs the machinery to generate bile by triggering endocytic internalization of hepatocellular transporters, thus causing cholestasis. This is critical, since it leads to accelerated transporter degradation, which could explain the common post-transcriptional downregulation of transporter expression in human cholestatic diseases. Recent Advances: The mechanisms involved in OS-induced hepatocellular transporter internalization are being revealed. Filamentous actin (F-actin) cytoskeleton disorganization and/or detachment of crosslinking actin proteins that afford transporter stability have been characterized as causal factors. Activation of redox-sensitive signaling pathways leading to changes in phosphorylation status of these structures is involved, including Ca2+-mediated activation of "classical" and "novel" protein kinase C (PKC) isoforms or redox-signaling cascades downstream of NADPH oxidase. Critical Issues: Despite the well-known occurrence of hepatocellular transporter internalization in human hepatopathies, the cholestatic implications of this phenomenon have been overlooked. Accordingly, no specific treatment has been established in the clinical practice for its prevention/reversion. Future Directions: We need to improve our knowledge on the pro-oxidant triggering factors and the multiple signaling pathways that mediate this oxidative injury in each cholestatic hepatopathy, so as to envisage tailor-made therapeutic strategies for each case. Meanwhile, administration of antioxidants or heme oxygenase-1 induction to elevate the hepatocellular levels of the endogenous scavenger bilirubin are promising alternatives that need to be re-evaluated and implemented. They may complement current treatments in cholestasis aimed to enhance transcriptional carrier expression, by providing membrane stability to the newly synthesized carriers. Antioxid. Redox Signal. 35, 808-831.
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Affiliation(s)
- Cecilia L Basiglio
- Instituto de Fisiología Experimental (IFISE), Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, U.N.R., Rosario, Argentina
| | - Fernando A Crocenzi
- Instituto de Fisiología Experimental (IFISE), Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, U.N.R., Rosario, Argentina
| | - Enrique J Sánchez Pozzi
- Instituto de Fisiología Experimental (IFISE), Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, U.N.R., Rosario, Argentina
| | - Marcelo G Roma
- Instituto de Fisiología Experimental (IFISE), Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, U.N.R., Rosario, Argentina
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2
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Bonus M, Häussinger D, Gohlke H. Liver cell hydration and integrin signaling. Biol Chem 2021; 402:1033-1045. [PMID: 33915604 DOI: 10.1515/hsz-2021-0193] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 04/12/2021] [Indexed: 12/21/2022]
Abstract
Liver cell hydration (cell volume) is dynamic and can change within minutes under the influence of hormones, nutrients, and oxidative stress. Such volume changes were identified as a novel and important modulator of cell function. It provides an early example for the interaction between a physical parameter (cell volume) on the one hand and metabolism, transport, and gene expression on the other. Such events involve mechanotransduction (osmosensing) which triggers signaling cascades towards liver function (osmosignaling). This article reviews our own work on this topic with emphasis on the role of β1 integrins as (osmo-)mechanosensors in the liver, but also on their role in bile acid signaling.
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Affiliation(s)
- Michele Bonus
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany
| | - Dieter Häussinger
- Clinic for Gastroenterology, Hepatology, and Infectious Diseases, Heinrich Heine University Düsseldorf, Moorenstr. 5, D-40225 Düsseldorf, Germany
| | - Holger Gohlke
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany
- John von Neumann Institute for Computing (NIC), Jülich Supercomputing Centre (JSC), Wilhelm-Johnen-Str., D-52428 Jülich, Germany
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), and Institute of Bio- and Geosciences (IBG-4: Bioinformatics), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Str., D-52428 Jülich, Germany
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Engin A. Bile Acid Toxicity and Protein Kinases. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1275:229-258. [PMID: 33539018 DOI: 10.1007/978-3-030-49844-3_9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
If the bile acids reach to pathological concentrations due to cholestasis, accumulation of hydrophobic bile acids within the hepatocyte may result in cell death. Thus, hydrophobic bile acids induce apoptosis in hepatocytes, while hydrophilic bile acids increase intracellular adenosine 3',5'-monophosphate (cAMP) levels and activate mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways to protect hepatocytes from apoptosis.Two apoptotic pathways have been described in bile acids-induced death. Both are controlled by multiple protein kinase signaling pathways. In mitochondria-controlled pathway, caspase-8 is activated with death domain-independent manner, whereas, Fas-dependent classical pathway involves ligand-independent oligomerization of Fas.Hydrophobic bile acids dose-dependently upregulate the inflammatory response by further stimulating production of inflammatory cytokines. Death receptor-mediated apoptosis is regulated at the cell surface by the receptor expression, at the death-inducing signaling complex (DISC) by expression of procaspase-8, the death receptors Fas-associated death domain (FADD), and cellular FADD-like interleukin 1-beta (IL-1β)-converting enzyme (FLICE) inhibitory protein (cFLIP). Bile acids prevent cFLIP recruitment to the DISC and thereby enhance initiator caspase activation and lead to cholestatic apoptosis. At mitochondria, the expression of B-cell leukemia/lymphoma-2 (Bcl-2) family proteins contribute to apoptosis by regulating mitochondrial cytochrome c release via Bcl-2, Bcl-2 homology 3 (BH3) interacting domain death agonist (Bid), or Bcl-2 associated protein x (Bax). Fas receptor CD95 activation by hydrophobic bile acids is initiated by reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) signaling. However, activation of necroptosis by ligands of death receptors requires the kinase activity of receptor interacting protein1 (RIP1), which mediates the activation of RIP3 and mixed lineage kinase domain-like protein (MLKL). In this chapter, mainly the effect of protein kinases signal transduction on the mechanisms of hydrophobic bile acids-induced inflammation, apoptosis, necroptosis and necrosis are discussed.
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Affiliation(s)
- Atilla Engin
- Department of General Surgery, Faculty of Medicine, Gazi University, Ankara, Turkey.
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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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McKim JM, Willoughby JA, Blakemore WR, Weiner ML. Clarifying the confusion between poligeenan, degraded carrageenan, and carrageenan: A review of the chemistry, nomenclature, and in vivo toxicology by the oral route. Crit Rev Food Sci Nutr 2018; 59:3054-3073. [DOI: 10.1080/10408398.2018.1481822] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Zhou X, Naguro I, Ichijo H, Watanabe K. Mitogen-activated protein kinases as key players in osmotic stress signaling. Biochim Biophys Acta Gen Subj 2016; 1860:2037-52. [PMID: 27261090 DOI: 10.1016/j.bbagen.2016.05.032] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 05/21/2016] [Indexed: 11/29/2022]
Abstract
BACKGROUND Osmotic stress arises from the difference between intracellular and extracellular osmolality. It induces cell swelling or shrinkage as a consequence of water influx or efflux, which threatens cellular activities. Mitogen-activated protein kinases (MAPKs) play central roles in signaling pathways in osmotic stress responses, including the regulation of intracellular levels of inorganic ions and organic osmolytes. SCOPE OF REVIEW The present review summarizes the cellular osmotic stress response and the function and regulation of the vertebrate MAPK signaling pathways involved. We also describe recent findings regarding apoptosis signal-regulating kinase 3 (ASK3), a MAP3K member, to demonstrate its regulatory effects on signaling molecules beyond MAPKs. MAJOR CONCLUSIONS MAPKs are rapidly activated by osmotic stress and have diverse roles, such as cell volume regulation, gene expression, and cell survival/death. There is significant cell type specificity in the function and regulation of MAPKs. Based on its activity change during osmotic stress and its regulation of the WNK1-SPAK/OSR1 pathway, ASK3 is expected to play important roles in osmosensing mechanisms and cellular functions related to osmoregulation. GENERAL SIGNIFICANCE MAPKs are essential for various cellular responses to osmotic stress; thus, the identification of the upstream regulators of MAPK pathways will provide valuable clues regarding the cellular osmosensing mechanism, which remains elusive in mammals. The elucidation of in vivo MAPK functions is also important because osmotic stress in physiological and pathophysiological conditions often results from changes in the intracellular osmolality. These studies potentially contribute to the establishment of therapeutic strategies against diseases that accompany osmotic perturbation.
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Affiliation(s)
- Xiangyu Zhou
- Laboratory of Cell Signaling, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Isao Naguro
- Laboratory of Cell Signaling, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Hidenori Ichijo
- Laboratory of Cell Signaling, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Kengo Watanabe
- Laboratory of Cell Signaling, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Sommerfeld A, Mayer PGK, Cantore M, Häussinger D. Regulation of plasma membrane localization of the Na+-taurocholate cotransporting polypeptide (Ntcp) by hyperosmolarity and tauroursodeoxycholate. J Biol Chem 2015; 290:24237-54. [PMID: 26306036 DOI: 10.1074/jbc.m115.666883] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Indexed: 01/05/2023] Open
Abstract
In perfused rat liver, hepatocyte shrinkage induces a Fyn-dependent retrieval of the bile salt export pump (Bsep) and multidrug resistance-associated protein 2 (Mrp2) from the canalicular membrane (Cantore, M., Reinehr, R., Sommerfeld, A., Becker, M., and Häussinger, D. (2011) J. Biol. Chem. 286, 45014-45029) leading to cholestasis. However little is known about the effects of hyperosmolarity on short term regulation of the Na(+)-taurocholate cotransporting polypeptide (Ntcp), the major bile salt uptake system at the sinusoidal membrane of hepatocytes. The aim of this study was to analyze hyperosmotic Ntcp regulation and the underlying signaling events. Hyperosmolarity induced a significant retrieval of Ntcp from the basolateral membrane, which was accompanied by an activating phosphorylation of the Src kinases Fyn and Yes but not of c-Src. Hyperosmotic internalization of Ntcp was sensitive to SU6656 and PP-2, suggesting that Fyn mediates Ntcp retrieval from the basolateral membrane. Hyperosmotic internalization of Ntcp was also found in livers from wild-type mice but not in p47(phox) knock-out mice. Tauroursodeoxycholate (TUDC) and cAMP reversed hyperosmolarity-induced Fyn activation and triggered re-insertion of the hyperosmotically retrieved Ntcp into the membrane. This was associated with dephosphorylation of the Ntcp on serine residues. Insertion of Ntcp by TUDC was sensitive to the integrin inhibitory hexapeptide GRGDSP and inhibition of protein kinase A. TUDC also reversed the hyperosmolarity-induced retrieval of bile salt export pump from the canalicular membrane. These findings suggest a coordinated and oxidative stress- and Fyn-dependent retrieval of sinusoidal and canalicular bile salt transport systems from the corresponding membranes. Ntcp insertion was also identified as a novel target of β1-integrin-dependent TUDC action, which is frequently used in the treatment of cholestatic liver disease.
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Affiliation(s)
- Annika Sommerfeld
- From the Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University Düsseldorf, 40225 Düsseldorf, Germany
| | - Patrick G K Mayer
- From the Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University Düsseldorf, 40225 Düsseldorf, Germany
| | - Miriam Cantore
- From the Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University Düsseldorf, 40225 Düsseldorf, Germany
| | - Dieter Häussinger
- From the Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University Düsseldorf, 40225 Düsseldorf, Germany
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8
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Biosynthesis and trafficking of the bile salt export pump, BSEP: therapeutic implications of BSEP mutations. Mol Aspects Med 2013; 37:3-14. [PMID: 23685087 DOI: 10.1016/j.mam.2013.05.001] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [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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9
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Abstract
Bile acids (BAs) are not only facilitators participating in the absorption of dietary lipids and soluble vitamins, but are also important signaling molecules exerting versatile biophysiological effects. Three major signaling pathways, including the MAPK pathways, the nuclear hormone receptor farnesoid X receptor a-mediated pathways and the G protein-coupled receptor TGR5/M-BAR-mediated pathways, have been identified to be the targets of BAs. BAs, the biologically many-sided and toxic molecules, regulate the homeostasis of themselves via these signaling pathways. BAs also affect diverse metabolic status including glucose metabolism, lipid metabolism, energy expenditure, immunity and others. BAs and their related signaling mechanisms are attractive therapeutic targets of various diseases such as metabolic syndrome.
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Affiliation(s)
- Kohkichi Morimoto
- a Division of Endocrinology, Metabolism and Nephrology, Department of Internal Medicine, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
| | - Hiroshi Itoh
- a Division of Endocrinology, Metabolism and Nephrology, Department of Internal Medicine, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
- b Graduate School of Media and Governance, Faculty of Environment and Information Studies, Keio University, 5322 Endo, Fujisawa, Kanagawa 252-0882, Japan.
| | - Mitsuhiro Watanabe
- a Division of Endocrinology, Metabolism and Nephrology, Department of Internal Medicine, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
- b Graduate School of Media and Governance, Faculty of Environment and Information Studies, Keio University, 5322 Endo, Fujisawa, Kanagawa 252-0882, Japan.
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Mühlfeld S, Domanova O, Berlage T, Stross C, Helmer A, Keitel V, Häussinger D, Kubitz R. Short-term feedback regulation of bile salt uptake by bile salts in rodent liver. Hepatology 2012; 56:2387-97. [PMID: 22806967 DOI: 10.1002/hep.25955] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2012] [Accepted: 06/18/2012] [Indexed: 12/17/2022]
Abstract
UNLABELLED The sodium taurocholate cotransporting polypeptide (Ntcp) is the major bile salt uptake transporter at the sinusoidal membrane of hepatocytes. Short-term feedback regulation of Ntcp by primary bile salts has not yet been investigated in vivo. Subcellular localization of Ntcp was analyzed in Ntcp-transfected HepG2-cells by flow cytometry and in immunofluorescence images from tissue sections by a new automated image analysis method. Net bile salt uptake was investigated in perfused rat liver by a pulse chase technique. In Flag-Ntcp-EGFP (enhanced green fluorescent protein) expressing HepG2-cells, taurochenodeoxycholate (TCDC), but not taurocholate (TC), induced endocytosis of Ntcp. TCDC, but not TC, caused significant internalization of Ntcp in perfused rat livers, as shown by an increase in intracellular Ntcp immunoreactivity, whereas Bsep distribution remained unchanged. These results correlate with functional studies. Rat livers were continuously perfused with 100 μmol/L of TC. 25 μmol/L of TCDC, taurodeoxycholate (TDC), tauroursodeoxycholate (TUDC), or TC were added for 30 minutes, washed out, followed by a pulse of (3) [H]-TC. TCDC, but not TDC, TUDC, or TC significantly increased the amount of (3) [H]-TC in the effluent, indicating a reduced sinusoidal net TC uptake. This effect was sensitive to chelerythrine (protein kinase C inhibitor) and cypermethrin (protein phosphatase 2B inhibitor). Phosphoinositide 3-kinase (PI3K) inhibitors had an additive effect, whereas Erk1/2 (extracellular signal activated kinase 1/2), p38MAPK, protein phosphatase 1/2A (PP1/2A), and reactive oxygen species (ROS) were not involved. CONCLUSION TCDC regulates bile salt transport at the sinusoidal membrane by protein kinase C- and protein phosphatase 2B-mediated retrieval of Ntcp from the plasma membrane. During increased portal bile salt load this mechanism may adjust bile salt uptake along the acinus and protect periportal hepatocytes from harmful bile salt concentrations.
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Affiliation(s)
- Stefanie Mühlfeld
- Department of Gastroenterology, Hepatology and Infectious Diseases, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany
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Harnett CC, Guerin PJ, Furtak T, Gauthier ER. Control of late apoptotic events by the p38 stress kinase in L-glutamine-deprived mouse hybridoma cells. Cell Biochem Funct 2012; 31:417-26. [PMID: 23080342 DOI: 10.1002/cbf.2916] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 09/18/2012] [Accepted: 09/19/2012] [Indexed: 01/08/2023]
Abstract
L-Glutamine (Gln) starvation rapidly triggers apoptosis in Sp2/0-Ag14 (Sp2/0) murine hybridoma cells. Here, we report on the role played by the stress-activated kinase p38 mitogen-activated protein kinase (MAPK) in this process. p38 activation was detected 2 h after Gln withdrawal and, although treatment with the p38 inhibitor SB203580 did not prevent caspase activation in Gln-starved cells, it reduced the occurrence of both nuclear condensation/fragmentation and apoptotic body formation. Similarly, transfection of Sp2/0 cells with a dominant negative p38 MAPK reduced the incidence of nuclear pyknosis and apoptotic body formation following 2 h of Gln starvation. Gln withdrawal-induced apoptosis was blocked by the overexpression of the anti-apoptotic protein Bcl-xL or by the caspase inhibitor Z-VAD-fmk. Interestingly, Bcl-xL expression inhibited p38 activation, but Z-VAD-fmk treatment did not, indicating that activation of this MAPK occurs downstream of mitochondrial dysfunction and is independent of caspases. Moreover, the anti-oxidant N-acetyl-l-cysteine prevented p38 phosphorylation, showing that p38 activation is triggered by an oxidative stress. Altogether, our findings indicate that p38 MAPK does not contribute to the induction of apoptosis in Gln-starved Sp2/0 cells. Rather, Gln withdrawal leads to mitochondrial dysfunction, causing an oxidative stress and p38 activation, the latter contributing to the formation of late morphological features of apoptotic Sp2/0 cells.
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Affiliation(s)
- Curtis C Harnett
- Biomolecular Sciences Program, Laurentian University, Sudbury, ON, Canada
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Ma H, Xie Y, Zhao J, Ye B. Small molecule-enrichment analysis in response to osmotic stimuli in the intervertebral disc. GENETICS AND MOLECULAR RESEARCH 2012; 11:3668-75. [DOI: 10.4238/2012.october.9.2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Cantore M, Reinehr R, Sommerfeld A, Becker M, Häussinger D. The Src family kinase Fyn mediates hyperosmolarity-induced Mrp2 and Bsep retrieval from canalicular membrane. J Biol Chem 2011; 286:45014-29. [PMID: 22057277 PMCID: PMC3247936 DOI: 10.1074/jbc.m111.292896] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 10/23/2011] [Indexed: 12/17/2022] Open
Abstract
In perfused rat liver, hyperosmolarity induces Mrp2- (Kubitz, R., D'urso, D., Keppler, D., and Häussinger, D. (1997) Gastroenterology 113, 1438-1442) and Bsep retrieval (Schmitt, M., Kubitz, R., Lizun, S., Wettstein, M., and Häussinger, D. (2001) Hepatology 33, 509-518) from the canalicular membrane leading to cholestasis. The aim of this study was to elucidate the underlying signaling events. Hyperosmolarity-induced retrieval of Mrp2 and Bsep from the canalicular membrane in perfused rat liver was accompanied by an activating phosphorylation of the Src kinases Fyn and Yes but not of c-Src. Both hyperosmotic transporter retrieval and Src kinase activation were sensitive to apocynin (300 μmol/liter), N-acetylcysteine (NAC; 10 mmol/liter), and SU6656 (1 μmol/liter). Also PP-2 (250 nmol/liter), which inhibited hyperosmotic Fyn but not Yes activation, prevented hyperosmotic transporter retrieval from the canalicular membrane, suggesting that Fyn but not Yes mediates hyperosmotic Bsep and Mrp2 retrieval. Neither hyperosmotic Fyn activation nor Bsep/Mrp2 retrieval was observed in livers from p47(phox) knock-out mice. Hyperosmotic activation of JNKs was sensitive to apocynin and NAC but insensitive to SU6656 and PP-2, indicating that JNKs are not involved in transporter retrieval, as also evidenced by experiments using the JNK inhibitors L-JNKI-1 and SP6001255, respectively. Hyperosmotic transporter retrieval was accompanied by a NAC and Fyn knockdown-sensitive inhibition of biliary excretion of the glutathione conjugate of 1-chloro-2,4-dinitrobenzene in perfused rat liver and of cholyl-L-lysyl-fluorescein secretion into the pseudocanaliculi formed by hepatocyte couplets. Hyperosmolarity triggered an association between Fyn and cortactin and increased the amount of phosphorylated cortactin underneath the canalicular membrane. It is concluded that the hyperosmotic cholestasis is triggered by a NADPH oxidase-driven reactive oxygen species formation that mediates Fyn-dependent retrieval of the Mrp2 and Bsep from the canalicular membrane, which may involve an increased cortactin phosphorylation.
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Affiliation(s)
- Miriam Cantore
- From the Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University Düsseldorf, D-40225 Düsseldorf, Germany
| | - Roland Reinehr
- From the Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University Düsseldorf, D-40225 Düsseldorf, Germany
| | - Annika Sommerfeld
- From the Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University Düsseldorf, D-40225 Düsseldorf, Germany
| | - Martin Becker
- From the Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University Düsseldorf, D-40225 Düsseldorf, Germany
| | - Dieter Häussinger
- From the Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University Düsseldorf, D-40225 Düsseldorf, Germany
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Häussinger D, Reinehr R. Osmotic Regulation of Bile Acid Transport, Apoptosis and Proliferation in Rat Liver. Cell Physiol Biochem 2011; 28:1089-98. [DOI: 10.1159/000335845] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/03/2011] [Indexed: 01/04/2023] Open
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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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Abstract
Bile acids are not only important for the absorption of dietary lipids and fat soluble vitamins but are signalling molecules with diverse endocrine and paracrine functions. Bile acids regulate bile acid, lipid and glucose metabolism and modulate temperature and energy homeostasis. Furthermore, bile acids can not only promote cell proliferation and liver regeneration but can also induce programmed cell death. Bile acid functions are mediated through different pathways which comprise the activation of nuclear hormone receptors, of intracellular kinases and of the plasma membrane-bound, G-protein coupled bile acid receptor TGR5/Gpbar-1.
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Norenberg MD, Jayakumar AR, Rama Rao KV, Panickar KS. New concepts in the mechanism of ammonia-induced astrocyte swelling. Metab Brain Dis 2007; 22:219-34. [PMID: 17823859 DOI: 10.1007/s11011-007-9062-5] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
It is generally accepted that astrocyte swelling forms the major anatomic substrate of the edema associated with acute liver failure (ALF) and that ammonia represents a major etiological factor in its causation. The mechanisms leading to such swelling, however, remain elusive. Recent studies have invoked the role of oxidative stress in the mechanism of hepatic encephalopathy (HE), as well as in the brain edema related to ALF. This article summarizes the evidence for oxidative stress as a major pathogenetic factor in HE/ALF and discusses mechanisms that are triggered by oxidative stress, including the induction of the mitochondrial permeability transition (MPT) and activation of signaling kinases. We propose that a cascade of events initiated by ammonia-induced oxidative stress results in cell volume dysregulation leading to cell swelling/brain edema. Blockade of this cascade may provide novel therapies for the brain edema associated with ALF.
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Affiliation(s)
- M D Norenberg
- Veterans Affairs Medical Center, Miami, FL 33101, USA.
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Huang CC, Hall AC, Lim PH. Characterisation of three pathways for osmolyte efflux in human erythroleukemia cells. Life Sci 2007; 81:732-9. [PMID: 17698149 DOI: 10.1016/j.lfs.2007.07.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Revised: 06/22/2007] [Accepted: 07/04/2007] [Indexed: 01/01/2023]
Abstract
Cell volume decrease is a key step during differentiation of erythroid cells. This could arise from membrane transporter activation leading to a loss of cell osmolytes; however, the pathways involved are poorly understood. We have characterised Cl(-)-independent K(+) and (3)H-taurine efflux from the erythroleukemia cell line, K562. K(+) efflux (measured using (86)Rb(+)) from pre-loaded cells subjected to hypo-osmotic challenge demonstrated two phases, a rapid increase in K(+) efflux followed by a smaller slower increase. Swelling-activated taurine efflux only demonstrated a single phase. Both phases of K(+) efflux were significantly (P<0.05) blocked by anion channel inhibitor 5-nitro-2-(3-phenypropylamino)-benzoic acid (NPPB). However the antiestrogen, tamoxifen, only inhibited the slow late phase. The initial rapid phase had a higher IC(50) for NPPB inhibition than the slow phase, and was insensitive to protein kinases inhibitors KN-62, wortmannin and PD98059. For the slow K(+) efflux phase, the IC(50) for NPPB inhibition and the inhibition by KN-62, wortmannin, genistein or PD98059, were very similar to those measured for the hypo-osmotically-activated taurine efflux. With NPPB (100 microM) present, the slow K(+) efflux phase was further significantly decreased by the Ca(2+) chelator BAPTA-AM or by the Ca(2+)-activated K(+) channel blockers clotrimazole and charybdotoxin but not by apamin. Thus, at least 3 Cl(-)-independent pathways are involved: (a) a tamoxifen-sensitive and taurine-permeable anion channel; (b) a tamoxifen-insensitive and taurine-impermeable K(+) efflux pathway; and (c) a subtype of Ca(2+)-activated K(+) channel. Any or all of these could be involved in the cell volume decrease associated with differentiation in K562 cells.
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Affiliation(s)
- Chiun-Chien Huang
- Department of Physiology, Chung Shan Medical University, Taichung 40203, Taiwan, ROC.
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Capó-Aponte JE, Wang Z, Bildin VN, Iserovich P, Pan Z, Zhang F, Pokorny KS, Reinach PS. Functional and molecular characterization of multiple K-Cl cotransporter isoforms in corneal epithelial cells. Exp Eye Res 2007; 84:1090-103. [PMID: 17418819 PMCID: PMC2696115 DOI: 10.1016/j.exer.2007.02.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2006] [Revised: 12/19/2006] [Accepted: 02/06/2007] [Indexed: 11/20/2022]
Abstract
The dependence of regulatory volume decrease (RVD) activity on potassium-chloride cotransporter (KCC) isoform expression was characterized in corneal epithelial cells (CEC). During exposure to a 50% hypotonic challenge, the RVD response was larger in SV40-immortalized human CEC (HCEC) than in SV40-immortalized rabbit CEC (RCEC). A KCC inhibitor-[(dihydroindenyl)oxy] alkanoic acid (DIOA)-blocked RVD more in HCEC than RCEC. Under isotonic conditions, N-ethylmaleimide (NEM) produced KCC activation and transient cell shrinkage. Both of these changes were greater in HCEC than in RCEC. Immunoblot analysis of HCEC, RCEC, primary human CEC (pHCEC), and primary bovine CEC (BCEC) plasma membrane enriched fractions revealed KCC1, KCC3, and KCC4 isoform expression, whereas KCC2 was undetectable. During a hypotonic challenge, KCC1 membrane content increased more rapidly in HCEC than in RCEC. Such a challenge induced a larger increase and more transient p44/42MAPK activation in HCEC than RCEC. On the other hand, HCEC and RCEC p38MAPK phosphorylation reached peak activations at 2.5 and 15 min, respectively. Only in HCEC, pharmacological manipulation of KCC activity modified the hypotonicity-induced activation of p44/42MAPK, whereas p38MAPK phosphorylation was insensitive to such procedures in both cell lines. Larger increases in HCEC KCC1 membrane protein content correlated with their ability to undergo faster and more complete RVD. Furthermore, pharmacological activation of KCC increased p44/42MAPK phosphorylation in HCEC but not in RCEC, presumably a reflection of low KCC1 membrane expression in RCEC. These findings suggest that KCC1 plays a role in (i) maintaining isotonic steady-state cell volume homeostasis, (ii) recovery of isotonic cell volume after a hypotonic challenge through RVD, and (iii) regulating hypotonicity-induced activation of the p44/42MAPK signaling pathway required for cell proliferation.
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Affiliation(s)
- José E. Capó-Aponte
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, NY 10036, USA
| | - Zheng Wang
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, NY 10036, USA
| | - Victor N. Bildin
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, NY 10036, USA
| | - Pavel Iserovich
- Department of Ophthalmology, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA
| | - Zan Pan
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, NY 10036, USA
| | - Fan Zhang
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, NY 10036, USA
| | - Kathryn S. Pokorny
- The Institute of Ophthalmology & Visual Science, New Jersey Medical School, University of Medicine & Dentistry, Newark, NJ 07101, USA
| | - Peter S. Reinach
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, NY 10036, USA
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Abstract
Bile secretion by liver parenchymal cells is the result of vectorial transcellular transport of solutes and involves the coordinated action of transport proteins at the basolateral (sinusoidal) and apical (canalicular) membranes of the hepatocyte. A complex network of signals controls uptake and efflux transporters on a long- and a short-term timescale, including regulation at the level of gene transcription, protein translation and maturation, covalent modification, and dynamic localization of transporter proteins, as well as substrate availability. Evidence has shown that the hepatocellular hydration state exerts powerful control on the transcellular transport of solutes, such as conjugated bile acids and glucuronide and glutathione conjugates. This is of physiological significance because liver cell hydration is a dynamic parameter, which changes within minutes under the influence of hormones, nutrients, and oxidative stress. Thus, osmoregulation of bile formation is of physiological and pathophysiological interest.
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Affiliation(s)
- Ralf Kubitz
- Clinic of Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
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21
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Abstract
Changes in hepatocyte hydration are induced not only by ambient hypo- or hyperosmolarity, but also under isosmotic condition by hormones, substrates, and oxidative stress. The perfused rat liver is a well-established intact organ model with preservation of the three-dimensional hepatocyte anchoring to the extracellular matrix and/or adjacent cells, parenchymal cell polarity, liver cell heterogeneity, acinar construction, and gene expression gradients. Originally, data from the perfused rat liver indicated that changes of cell hydration independent of their origin critically contribute to the control of autophagic proteolysis and canalicular bile acid excretion. Meanwhile, the concept that cell hydration changes trigger signal transduction processes that control metabolism, gene expression, transport, and the susceptibility to stress is well accepted. This chapter summarizes evidence obtained from experiments with the perfused rat liver that integrins are osmosensors in the liver and thereby critically contribute to the Src- and MAP-kinase-dependent inhibition of autophagic proteolysis, stimulation of canalicular taurocholate excretion, and regulatory volume decrease as induced by hypoosmotic swelling. Moreover, integrin-dependent sensing of hepatocyte swelling is essential for signaling and proteolysis inhibition by insulin and glutamine. These findings define a novel role of integrins in insulin and glutamine signaling and set an example for mechanotransduction as an integral part of overall growth factor and nutrient signaling.
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Affiliation(s)
- Freimut Schliess
- Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany
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22
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Jayakumar AR, Panickar KS, Murthy CRK, Norenberg MD. Oxidative stress and mitogen-activated protein kinase phosphorylation mediate ammonia-induced cell swelling and glutamate uptake inhibition in cultured astrocytes. J Neurosci 2006; 26:4774-84. [PMID: 16672650 PMCID: PMC6674149 DOI: 10.1523/jneurosci.0120-06.2006] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Hepatic encephalopathy (HE) is a major neurological complication in patients with severe liver failure. Elevated levels of ammonia have been strongly implicated as a factor in HE, and astrocytes appear to be the primary target of its neurotoxicity. Mechanisms mediating key aspects of ammonia-induced astrocyte dysfunction such as cell swelling and inhibition of glutamate uptake are not clear. We demonstrated previously that cultured astrocytes exposed to ammonia increase free radical production. We now show that treatment with antioxidants significantly prevents ammonia-induced astrocyte swelling as well as glutamate uptake inhibition. Because one consequence of oxidative stress is the phosphorylation of mitogen-activated protein kinases (MAPKs), we investigated whether phosphorylation of MAPKs may mediate astrocyte dysfunction. Primary cultured astrocytes exposed to 5 mm NH4Cl for different time periods (1-72 h) significantly increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38(MAPK), and c-Jun N-terminal kinase (JNK) 1/2/3, which was inhibited by appropriate MAPK inhibitors 1, 4-diamino-2, 3-dicyano-1, 4-bis (2-aminophenylthio) butadiene (UO126; for ERK1/2), trans-1-(4-hydroxyclyclohexyl)-4-(4-fluorophenyl)-5-(2-methoxypyrimidin-4-yl)imidazole (SB 239063; for p38(MAPK)), and anthra[1,9-cd]pyrazol-6(2H)-one (SP600125; for JNK1/2/3), as well as by antioxidants. Kinase inhibitors partially or completely prevented astrocyte swelling. Although SB239063 and SP600125 significantly reversed glutamate uptake inhibition and ammonia-induced decline in glutamate-aspartate transporter protein levels, UO126 did not, indicating a differential effect of these kinases in ammonia-induced astrocyte swelling and glutamate transport impairment. These studies strongly suggest the involvement of oxidative stress and phosphorylation of MAPKs in the mechanism of ammonia-induced astrocyte dysfunction associated with ammonia neurotoxicity.
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Affiliation(s)
- A R Jayakumar
- Department of Pathology, University of Miami School of Medicine, Miami, Florida 33101, USA
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23
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Abstract
Alterations of cell volume induced by either aniso-osmotic environments or under the influence of hormones, concentrative amino acid uptake and oxidative stress were recognized as an independent signal contributing to the regulation of metabolism and gene expression. The regulation of cell function by hydration changes requires structures, which register fluctuations of cell hydration (osmosensing) and thereby activate intracellular signalling pathways towards effector sites (osmosignalling). Meanwhile, it is well established that osmosensing and signalling integrate into the overall context of hormone- and nutrient-induced signal transduction. Recent evidence suggests integrins to play a major role in osmosensing and signalling due to hepatocyte swelling. This review focuses on the role of integrins in sensing of hepatocyte swelling as triggered by hypo-osmolarity, glutamine and insulin and the relevance of integrin-dependent osmosignalling for inhibition of autophagic proteolysis, stimulation of canalicular bile acid excretion and regulatory volume decrease.
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Affiliation(s)
- D Häussinger
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany.
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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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25
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Häussinger D. Neural control of hepatic osmolytes and parenchymal cell hydration. ACTA ACUST UNITED AC 2004; 280:893-900. [PMID: 15382012 DOI: 10.1002/ar.a.20094] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Liver cell function is strongly influenced by cell hydration and osmolyte content via osmosensing and osmosignaling pathways. Electrical stimulation of hepatic nerves increases the hepatocellular hydration state via an alpha-adrenergic mechanism, promotes taurine release from parenchymal cells and myo-inositol release from hepatic stellate cells. Although changes in liver cell hydration and osmolyte content are known regulators of liver cell function, the functional relevance and integration of nerve-stimulation-dependent alterations of liver cell volume and osmolyte content in the overall hepatic response to towards signals from the nervous system remains to be established.
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Affiliation(s)
- Dieter Häussinger
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich Heine University, Düsseldorf, Germany.
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26
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Schmitt M, Horbach A, Kubitz R, Frilling A, Häussinger D. Disruption of hepatocellular tight junctions by vascular endothelial growth factor (VEGF): a novel mechanism for tumor invasion. J Hepatol 2004; 41:274-83. [PMID: 15288477 DOI: 10.1016/j.jhep.2004.04.035] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2003] [Revised: 04/10/2004] [Accepted: 04/26/2004] [Indexed: 12/13/2022]
Abstract
BACKGROUND/AIMS Vascular endothelial growth factor (VEGF) is expressed by many tumors, including hepatocellular carcinoma (HCC) and is involved in tumor angiogenesis. Little is known about its role for HCC infiltration into normal liver parenchyma. METHODS The effects of VEGF on the integrity of tight junctions were studied in HepG2 cells and human HCC by means of confocal laser scanning microscopy. RESULTS VEGF induced within 45 min a marked loss of pseudocanaliculi and disruption of occludin-delineated tight junctions. This effect of VEGF was mimicked by phorbol-12-myristate-13-acetate (PMA) and was sensitive to protein kinase C (PKC) inhibition by Gö6850. VEGF induced within 15 min the translocation of the PKC alpha-isoform to the plasma-membrane, but had no effect on the activity of Erks and p38(MAPK). Sections from surgically removed HCC showed expression of VEGF in the tumor and occludin disassembly in normal liver parenchyma next to the tumor. CONCLUSIONS VEGF induces disruption of tight junctions in a PKC-alpha dependent manner. In addition to its known angioneogenic properties, VEGF may promote HCC spreading into normal liver parenchyma. The data may provide another rationale for the use of VEGF antagonists for tumor therapy.
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Affiliation(s)
- Marcus Schmitt
- Department of Gastroenterology, Hepatology and Infectiology, Heinrich Heine University, Düsseldorf, Germany
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27
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d'Anglemont de Tassigny A, Souktani R, Ghaleh B, Henry P, Berdeaux A. Structure and pharmacology of swelling-sensitive chloride channels, I(Cl,swell). Fundam Clin Pharmacol 2004; 17:539-53. [PMID: 14703715 DOI: 10.1046/j.1472-8206.2003.00197.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Since several years, the interest for chloride channels and more particularly for the enigmatic swelling-activated chloride channel (I(Cl,swell)) is increasing. Despite its well-characterized electrophysiological properties, the I(Cl,swell) structure and pharmacology are not totally elucidated. These channels are involved in a variety of cell functions, such as cardiac rhythm, cell proliferation and differentiation, cell volume regulation and cell death through apoptosis. This review will consider different aspects regarding structure, electrophysiological properties, pharmacology, modulation and functions of these swelling-activated chloride channels.
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28
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Gatof D, Kilic G, Fitz JG. Vesicular exocytosis contributes to volume-sensitive ATP release in biliary cells. Am J Physiol Gastrointest Liver Physiol 2004; 286:G538-46. [PMID: 14604861 DOI: 10.1152/ajpgi.00355.2003] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Extracellular ATP is a potent autocrine/paracrine signal that regulates a broad range of liver functions through activation of purinergic receptors. In biliary epithelium, increases in cell volume stimulate ATP release through a phosphoinositide 3-kinase (PI3-kinase)-dependent mechanism. Because PI3-kinase also regulates vesicular exocytosis, the purpose of these studies was to determine whether volume-stimulated vesicular exocytosis contributes to cellular ATP release. In a human cholangiocarcinoma cell line, exocytosis was measured by using the plasma membrane marker FM1-43, whereas ATP release was assessed by using a luciferase-luciferin assay. Under basal conditions, cholangiocytes exhibited constitutive exocytosis at a rate of 1.6%/min, and low levels of extracellular ATP were detected at 48.2 arbitrary light units. Increases in cholangiocyte cell volume induced by hypotonic exposure resulted in a 10-fold increase in the rate of exocytosis and a robust 35-fold increase in ATP release. Both vesicular exocytosis and ATP release were proportional to cell volume, and both exhibited similar regulatory properties including: 1) dependence on intact PI3-kinase, 2) attenuation by inhibition of PKC, and 3) potentiation by activation of PKC before hypotonic exposure. These findings demonstrate that increases in cholangiocyte cell volume stimulate ATP release and vesicular exocytosis through similar regulatory paradigms. Functional interactions among cell volume, PKC, and PI3-kinase modulate exocytosis, thereby regulating ATP release and purinergic signaling in cholangiocytes. It is hypothesized that PKC is involved in the recruitment of a volume-sensitive vesicular pool to a readily releasable state.
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Affiliation(s)
- David Gatof
- Department of Medicine, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
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29
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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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30
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Kubitz R, Sütfels G, Kühlkamp T, Kölling R, Häussinger D. Trafficking of the bile salt export pump from the Golgi to the canalicular membrane is regulated by the p38 MAP kinase. Gastroenterology 2004; 126:541-53. [PMID: 14762791 DOI: 10.1053/j.gastro.2003.11.003] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS Bile secretion depends on the delivery and removal of transporter proteins to and from the canalicular membrane. Trafficking of the bile salt export pump (BSEP) to the canalicular membrane was investigated in HepG2 cells and rat hepatocytes. METHODS Subcellular localization of BSEP was determined by confocal laser scanning microscopy using different BSEP antibodies. RESULTS Ten percent of untreated HepG2 cells developed pseudocanaliculi, but only 15% of these pseudocanaliculi contained BSEP, which largely colocalized with the Golgi marker GM130. Cycloheximide, an inhibitor of protein translation, induced a microtubule- and p38(MAP) kinase-dependent decrease of Golgi-associated BSEP, accompanied by a more than 2-fold increase in BSEP-positive pseudocanaliculi. Also, tauroursodeoxycholate (TUDC), which activates p38(MAP) kinase (p38(MAPK), increased BSEP-positive pseudocanaliculi by more than 50% in rat sodium taurocholate cotransporting peptide (Ntcp)-transfected but not in untransfected HepG2 cells. The TUDC-dependent increase was sensitive to inhibitors of p38(MAPK) and microtubules and involved Ca(2+)-independent protein kinase C isoforms as suggested by its sensitivity to Gö6850 but insensitivity to Gö6976. In isolated rat hepatocytes with intact bile secretion, no colocalization of rat isoforms of the bile salt export pump (Bsep) and Golgi was found, but colocalization occurred after inhibition of p38(MAPK) and PKC, suggesting that Bsep trafficking to the canalicular membrane depends on the basal activity of these kinases in polarized cells. CONCLUSIONS p38(MAPK) regulates BSEP trafficking from the Golgi to the canalicular membrane, and the Golgi may serve as a BSEP pool in certain forms of cholestasis or when p38(MAPK) activity is inhibited. Activation of p38(MAPK) by TUDC can recruit Golgi-associated BSEP in line with its choleretic action.
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Affiliation(s)
- Ralf Kubitz
- Department of Gastroenterology, Hepatology, and Infectiology, Heinrch Heine University, Duesseldorf, Germany.
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Reinehr R, Häussinger D. Inhibition of bile salt-induced apoptosis by cyclic AMP involves serine/threonine phosphorylation of CD95. Gastroenterology 2004; 126:249-62. [PMID: 14699504 DOI: 10.1053/j.gastro.2003.09.044] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND AND AIMS Cyclic AMP (cAMP) inhibits bile salt-induced hepatocyte apoptosis; the underlying mechanisms are unclear. METHODS The effects of cAMP on taurolithocholate-3-sulfate-(TLCS)- or glycochenodesoxycholate (GCDC)-induced CD95 (Fas/APO-1) activation and apoptosis were studied in 24-hour cultured rat hepatocytes and in perfused rat liver. RESULTS TLCS induced a rapid oxidative stress response, c-Jun-N-terminal kinase (JNK) and epidermal growth factor (EGF) receptor (EGF-R) activation, subsequent EGF-R/CD95 association and CD95 tyrosine phosphorylation, CD95 membrane targeting, death-inducing signal complex (DISC) formation and hepatocyte apoptosis. None of these responses was triggered by cAMP; however, cAMP induced H89-sensitive serine/threonine phosphorylation of CD95. Similar data were obtained with GCDC, another proapoptotic bile acid. cAMP did not prevent the TLCS-induced oxidative stress response, JNK activation and EGF-R/CD95 association, however abolished EGF-R activation and subsequent CD95 tyrosine phosphorylation, CD95 membrane trafficking, and DISC formation in a H89-sensitive way. Also in presence of TLCS, cAMP induced rapid Ser/Thr phosphorylation of CD95 within 10 min. The effects of cAMP on the various steps of CD95 activation were also found in the intact perfused rat liver. Evidence is given that a cAMP-induced Ser/Thr phosphorylation favors internalization of CD95. CONCLUSIONS Inhibition of bile salt-induced apoptosis by cAMP involves both PKA-dependent Ser/Thr phosphorylation of the CD95 and inhibition of EGF-R activation, which results in an inhibition of CD95 tyrosine phosphorylation, CD95 membrane targeting, and DISC formation. CD95 regulation involves complex phosphorylations with CD95-tyrosine phosphorylation favoring CD95 membrane trafficking and DISC formation, whereas CD95 Ser/Thr phosphorylation inhibits these processes.
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Affiliation(s)
- Roland Reinehr
- Clinic for Gastroenterology, Heinrich-Heine-University, Düsseldorf, Germany
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32
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Abstract
Perturbations of cell hydration as provoked by changes in ambient osmolarity or under isoosmotic conditions by hormones, second messengers, intracellular substrate accumulation, or reactive oxygen intermediates critically contribute to the physiological regulation of cell function. In general an increase in cell hydration stimulates anabolic metabolism and proliferation and provides cytoprotection, whereas cellular dehydration leads to a catabolic situation and sensitizes cells to apoptotic stimuli. Insulin produces cell swelling by inducing a net K+ and Na+ accumulation inside the cell, which results from a concerted activation of Na+/H+ exchange, Na+/K+/2Cl- symport, and the Na+/K(+)-ATPase. In the liver, insulin-induced cell swelling is critical for stimulation of glycogen and protein synthesis as well as inhibition of autophagic proteolysis. These insulin effects can largely be mimicked by hypoosmotic cell swelling, pointing to a role of cell swelling as a trigger of signal transduction. This article discusses insulin-induced signal transduction upstream of swelling and introduces the hypothesis that cell swelling as a signal amplifyer represents an essential component in insulin signaling, which contributes to the full response to insulin at the level of signal transduction and function. Cellular dehydration impairs insulin signaling and may be a major cause of insulin resistance, which develops in systemic hyperosmolarity, nutrient deprivation, uremia, oxidative challenges, and unbalanced production of insulin-counteracting hormones. Hydration changes affect cell functions at multiple levels (such as transcriptom, proteom, phosphoproteom, and the metabolom) and a system biological approach may allow us to develop a more holistic view on the hydration dependence of insulin signaling in the future.
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Affiliation(s)
- Freimut Schliess
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany
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van der Wijk T, Tomassen SFB, Houtsmuller AB, de Jonge HR, Tilly BC. Increased vesicle recycling in response to osmotic cell swelling. Cause and consequence of hypotonicity-provoked ATP release. J Biol Chem 2003; 278:40020-5. [PMID: 12871943 DOI: 10.1074/jbc.m307603200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Osmotic swelling of Intestine 407 cells leads to an immediate increase in cell surface membrane area as determined using the fluorescent membrane dye FM 1-43. In addition, as measured by tetramethylrhodamine isothiocyanate (TRITC)-dextran uptake, a robust (>100-fold) increase in the rate of endocytosis was observed, starting after a discrete lag time of 2-3 min and lasting for approximately 10-15 min. The hypotonicity-induced increase in membrane surface area, like the cell swelling-induced release of ATP (Van der Wijk, T., De Jonge, H. R., and Tilly, B. C. (1999) Biochem. J. 343, 579-586), was diminished after 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester loading or cytochalasin B treatment. Uptake of TRITC-dextrans, however, was not affected. Treatment of the cells with the vesicle-soluble N-ethylmaleimide-sensitive factor attachment protein receptor-specific protease Clostridium botulinum toxin F not only nearly eliminated the hypotonicity-induced increase in membrane surface area but also strongly diminished the release of ATP, indicating the involvement of regulated exocytosis. Both the ATP hydrolase apyrase and the MEK inhibitor PD098059 diminished the osmotic swelling-induced increase in membrane surface area as well as the subsequent uptake of TRITC-dextrans. Taken together, the results indicate that extracellular ATP is required for the hypotonicity-induced vesicle recycling and suggest that a positive feedback loop, involving purinergic activation of the Erk-1/2 pathway, may contribute to the release of ATP from hypo-osmotically stimulated cells.
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Affiliation(s)
- Thea van der Wijk
- Department of Biochemistry, Erasmus University Medical Center, 3000DR Rotterdam, The Netherlands
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Reinehr R, Graf D, Häussinger D. Bile salt-induced hepatocyte apoptosis involves epidermal growth factor receptor-dependent CD95 tyrosine phosphorylation. Gastroenterology 2003; 125:839-53. [PMID: 12949729 DOI: 10.1016/s0016-5085(03)01055-2] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
BACKGROUND & AIMS Hydrophobic bile acids induce CD95-dependent hepatocyte apoptosis. METHODS The mechanisms of bile acid-induced CD95 activation were studied in 24-hour cultured rat hepatocytes, in situ-perfused rat livers, and livers from bile duct-ligated rats. RESULTS Within 1 minute, the proapoptotic bile salts taurolithocholate-3-sulfate and glycochenodeoxycholate induced oxidative stress and EGF receptor (EGF-R) tyrosine phosphorylation followed by rapid c-Jun-N-terminal kinase (JNK) activation. Thereafter, EGF-R associated with CD95 with subsequent CD95 tyrosine phosphorylation, CD95 membrane targeting, and death-inducing signal complex (DISC) formation. All of these responses were also triggered by taurochenodeoxycholate except that DISC formation only occurred in the presence of phosphatidylinositol 3-kinase inhibitors. No activation of EGF-R or CD95 was observed with tauroursodeoxycholate or taurocholate. Taurolithocholate-3-sulfate-induced EGF-R phosphorylation was sensitive to N-acetylcysteine (NAC) and genistein, whereas CD95/EGF-R association was inhibited by NAC, JNK, or protein kinase C inhibition but not by AG1478. However, the latter compound as well as NAC, genistein, inhibition of JNK, or protein kinase C inhibited CD95 tyrosine phosphorylation, membrane trafficking, and DISC formation. CONCLUSIONS Induction of apoptosis by hydrophobic bile salts involves EGF-R activation and EGF-R-dependent CD95 tyrosine phosphorylation, which triggers CD95 membrane targeting and Fas-associated death domain/caspase-8 recruitment. The latter step is apparently also controlled by phosphatidylinositol 3-kinase.
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Affiliation(s)
- Roland Reinehr
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düesseldorf, Germany
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vom Dahl S, Schliess F, Reissmann R, Görg B, Weiergräber O, Kocalkova M, Dombrowski F, Häussinger D. Involvement of integrins in osmosensing and signaling toward autophagic proteolysis in rat liver. J Biol Chem 2003; 278:27088-95. [PMID: 12721289 DOI: 10.1074/jbc.m210699200] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inhibition of autophagic proteolysis by hypoosmotic or amino acid-induced hepatocyte swelling requires osmosignaling toward p38MAPK; however, the upstream osmosensing and signaling events are unknown. These were studied in the intact perfused rat liver with a preserved in situ environment of hepatocytes. It was found that hypoosmotic hepatocyte swelling led to an activation of Src (but not FAK), Erks, and p38MAPK, which was prevented by the integrin inhibitory hexapeptide GRGDSP, but not its inactive analogue GRGESP. Src inhibition by PP-2 prevented hypoosmotic MAP kinase activation, indicating that the integrin/Src system is located upstream in the osmosignaling toward p38MAPK and Erks. Inhibition of the integrin/Src system by the RGD motif-containing peptide or PP-2 also prevented the inhibition of proteolysis and the decrease in autophagic vacuole volume, which is otherwise observed in response to hypoosmotic or glutamine/glycine-induced hepatocyte swelling. These inhibitors, however, did not affect swelling-independent proteolysis inhibition by phenylalanine. In line with a role of p38MAPK in triggering the volume regulatory decrease (RVD), PP-2 and the RGD peptide blunted RVD in response to hypoosmotic cell swelling. The data identify integrins and Src as upstream events in the osmosignaling toward MAP kinases, proteolysis, and RVD. They further point to a role of integrins as osmo- and mechanosensors in the intact liver, which may provide a link between cell volume and cell function.
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Affiliation(s)
- Stephan vom Dahl
- Division of Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Moorenstrasse 5, D-40225-Düsseldorf, Germany.
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Häussinger D, Kurz AK, Wettstein M, Graf D, Vom Dahl S, Schliess F. Involvement of integrins and Src in tauroursodeoxycholate-induced and swelling-induced choleresis. Gastroenterology 2003; 124:1476-87. [PMID: 12730886 DOI: 10.1016/s0016-5085(03)00274-9] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND & AIMS Stimulation of canalicular secretion by tauroursodeoxycholate (TUDC) involves dual activation of p38 mitogen-activated protein kinase (p38(MAPK)) and extracellular signal-regulated kinase (ERK). This study investigates the sensing and upstream signaling events of TUDC-induced choleresis. METHODS TUDC and hypo-osmolarity effects on protein kinase activities and taurocholate excretion were studied in perfused rat liver. RESULTS TUDC induced a rapid activation of focal adhesion kinase (FAK) and Src, as shown by an increase in Y418 phosphorylation and a decrease in Y529 phosphorylation of Src. Inhibition of Src by PP-2 abolished the TUDC-induced activation of p38(MAPK) but not of FAK and ERKs. An integrin-inhibitory peptide with an RGD motif blocked TUDC-induced FAK, Src, ERK, and p38(MAPK) activation, suggesting that integrin signaling toward FAK/Src is required for TUDC-induced MAPK activation. The RGD peptide and PP-2 also abolished the stimulation of taurocholate excretion in perfused rat liver in response to TUDC. Integrin-dependent Src activation was also identified as an upstream event in hypo-osmotic signaling toward MAPKs and choleresis. CONCLUSIONS TUDC-induced stimulation of canalicular taurocholate excretion involves integrin sensing, FAK, and Src activation as upstream events for dual MAPK activation. Integrins may also represent one long-searched sensor for cell hydration changes in response to hypo-osmolarity.
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Affiliation(s)
- Dieter Häussinger
- Department of Gastroenterology, Hepatology and Infectology, Universitätsklinikum Düsseldorf, Germany.
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Håversen LA, Baltzer L, Dolphin G, Hanson LA, Mattsby-Baltzer I. Anti-inflammatory activities of human lactoferrin in acute dextran sulphate-induced colitis in mice. Scand J Immunol 2003; 57:2-10. [PMID: 12542792 DOI: 10.1046/j.1365-3083.2003.01162.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In this study, we investigated the anti-inflammatory effects of orally administered human lactoferrin (hLF) and two peptides, based on the bactericidal region of hLF (HLD1 and HLD2), on the course of experimental colitis. Acute colitis was induced in C57Bl/6 mice by giving 5% dextran sulphate (DX) in the drinking water. The mice were killed after 2 or 7 days of DX exposure. The animals were given hLF or the peptides orally twice a day (2 mg/dose/mouse) during the DX exposure. In the control animals, the hLF or the peptides were replaced by bovine serum albumin or water. The appearance of occult blood in the faeces and macroscopic rectal bleeding were significantly delayed and partly reduced in the hLF-treated animals compared with the control animals. The shortening of the colon, a pathological effect of DX exposure, was significantly less pronounced in the hLF-treated group compared with the control group. Also, the interleukin-1beta (IL-1beta) levels in the blood were significantly diminished in this group after 2 days of DX exposure. A significantly lower crypt score was observed in the distal part of the colon in the hLF-treated group compared with the control group. Also, significantly reduced numbers of CD4 cells, F4/80-positive macrophages and tumour necrosis factor-alpha-producing cells were detected by immunohistochemistry in the distal colon of the hLF-treated animals compared with the control animals after 7 days of DX exposure. A reduction was also observed concerning the IL-10-producing cells in the middle colonic submucosa. The HLD1 and HLD2 treatment, which was carried out for 2 days, only gave results almost identical to those of hLF, concerning clinical parameters after the 2 days of DX exposure. An even stronger effect was observed for HLD2, regarding decreased occult blood in the faeces and colon length. Our results show that perorally given hLF mediates anti-inflammatory effects on the DX-induced acute colitis, and further suggest that the bactericidal region of the hLF molecule may be involved in these activities.
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Affiliation(s)
- L A Håversen
- Department of Clinical Bacteriology, University of Göteborg, Sweden.
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Moore AL, Roe MW, Melnick RF, Lidofsky SD. Calcium mobilization evoked by hepatocellular swelling is linked to activation of phospholipase Cgamma. J Biol Chem 2002; 277:34030-5. [PMID: 12167665 DOI: 10.1074/jbc.m205945200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recovery from swelling of hepatocytes and selected other epithelia is triggered by intracellular Ca(2+) release from the endoplasmic reticulum, which leads to fluid and electrolyte efflux through volume-sensitive K(+) and Cl(-) channels. The aim of this study was to determine the mechanisms responsible for swelling-mediated hepatocellular Ca(2+) mobilization. Swelling of HTC rat hepatoma cells, evoked by exposure to hypotonic medium, elicited transient increases in intracellular levels of inositol 1,4,5-trisphosphate (IP(3)) and cytosolic [Ca(2+)]. The latter was attenuated by inhibition of phospholipase C (PLC) with and by IP(3) receptor blockade with 2-aminoethoxydiphenyl borate, but it was unaffected by ryanodine, an inhibitor of intracellular Ca(2+)-induced Ca(2+) release channels. Hypotonic swelling was associated with a transient increase in tyrosine phosphorylation of PLCgamma, with kinetics that paralleled the increases in intracellular IP(3) levels and cytosolic [Ca(2+)]. Confocal imaging of HTC cells exposed to hypotonic medium revealed a swelling-induced association of tyrosine-phosphorylated PLCgamma with the plasma membrane. These findings suggest that activation of PLCgamma by hepatocellular swelling leads to the generation of IP(3) and stimulates discharge of Ca(2+) from the endoplasmic reticulum via activation of IP(3) receptors. By extension, these data support the concept that tyrosine phosphorylation of PLCgamma represents a critical step in adaptive responses to hepatocellular swelling.
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Affiliation(s)
- Ann L Moore
- Department of Medicine, University of Vermont College of Medicine, Burlington, VT 05401, USA
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Shen MR, Chou CY, Browning JA, Wilkins RJ, Ellory JC. Human cervical cancer cells use Ca2+ signalling, protein tyrosine phosphorylation and MAP kinase in regulatory volume decrease. J Physiol 2001; 537:347-62. [PMID: 11731569 PMCID: PMC2278960 DOI: 10.1111/j.1469-7793.2001.00347.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
1. This study was aimed at identifying the signalling pathways involved in the activation of volume-regulatory mechanisms of human cervical cancer cells. 2. Osmotic swelling of human cervical cancer cells induced a substantial increase in intracellular Ca2+ ([Ca2+]i) by the activation of Ca2+ entry across the cell membrane, as well as Ca2+ release from intracellular stores. This Ca2+ signalling was critical for the normal regulatory volume decrease (RVD) response. 3. The activation of swelling-activated ion and taurine transport was significantly inhibited by tyrosine kinase inhibitors (genistein and tyrphostin AG 1478) and potentiated by the tyrosine phosphatase inhibitor Na3VO4. However, the Src family of tyrosine kinases was not involved in regulation of the swelling-activated Cl- channel. 4. Cell swelling triggered mitogen-activated protein (MAP) kinase cascades leading to the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) and p38 kinase. The volume-responsive ERK1/ERK2 signalling pathway linked with the activation of K+ and Cl- channels, and taurine transport. However, the volume-regulatory mechanism was independent of the activation of p38 MAP kinase. 5. The phosphorylated ERK1/ERK2 expression following a hypotonic shock was up-regulated by protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and down-regulated by PKC inhibitor staurosporine. The response of ERK activation to hypotonicity also required Ca2+ entry and depended on tyrosine kinase and mitogen-activated/ERK-activating kinase (MEK) activity. 6. Considering the results overall, osmotic swelling promotes the activation of tyrosine kinase and ERK1/ERK2 and raises intracellular Ca2+, all of which play a crucial role in the volume-regulatory mechanism of human cervical cancer cells.
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Affiliation(s)
- M R Shen
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK
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Kim RD, Darling CE, Roth TP, Ricciardi R, Chari RS. Activator protein 1 activation following hypoosmotic stress in HepG2 cells is actin cytoskeleton dependent. J Surg Res 2001; 100:176-82. [PMID: 11592789 DOI: 10.1006/jsre.2001.6225] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND Following hypoosmotic stress-induced cell volume change, the actin cytoskeleton reorganizes itself. The role of this reorganization in the activation of the phosphatidylinositol 3-OH-kinase/protein kinase B/activator protein 1 (PI-3-K/PKB/AP-1) proliferative signaling cascade is unknown. Focal adhesion kinase (FAK) participates in the cytoskeleton-based activation of PI-3-K. We hypothesized that hypoosmotic stress-induced activation of PKB and AP-1 in HepG2 cells is dependent on an intact actin cytoskeleton and subsequent FAK phosphorylation. METHODS HepG2 cells were incubated for 1 h with or without 20 microM cytochalasin D, an actin disrupter, and were then exposed for up to 30 min to hypoosmotic medium (200 mOsm/L) to induce swelling. Tumor necrosis factor alpha (1.4 nM) and medium alone served as positive and negative controls, respectively. Western blots measured cytoplasmic phosphorylated or total FAK and PKB. EMSAs measured nuclear AP-1. All experiments were performed in triplicate. RESULTS Exposure to hypoosmotic stress resulted in activation of the following signaling messengers in a sequential fashion: (1) phosphorylation of FAK occurred by 2 min, (2) phosphorylation of PKB occurred by 10 min, (3) nuclear translocation of AP-1 occurred by 30 min. All three signaling events were abolished when these cells were pretreated with cytochalasin D. CONCLUSION Actin reorganization following hypoosmotic stress is essential for the FAK-mediated activation of the PI-3-K/PKB/AP-1 proliferative cascade. These data delineate a possible mechanism by which the cell swelling-induced cytoskeletal changes can initiate proliferative signal transduction in human liver cancer.
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Affiliation(s)
- R D Kim
- Department of Surgery, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA
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Häussinger D, Graf D, Weiergräber OH. Glutamine and cell signaling in liver. J Nutr 2001; 131:2509S-14S; discussion 2523S-4S. [PMID: 11533303 DOI: 10.1093/jn/131.9.2509s] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In the liver, glutamine plays an important role in ammonia detoxication and the regulation of pH homeostasis ("intercellular glutamine cycle"). In addition, this amino acid regulates liver metabolism and transport by mechanisms that cannot be attributed to its metabolism. Examples include the stimulation of protein and glycogen synthesis and bile acid secretion and the inhibition of proteolysis in liver. The major trigger for such effects is an increased hepatocyte hydration due to the cumulative uptake of glutamine into the cells, which activates osmosignaling pathways involving mitogen-activated protein kinases (MAPK). Glutamine- and hypoosmolarity-induced cell swelling activates extracellular signal-regulated kinases (ERK) and p38(MAPK). Activation of these MAPK results in an increased capacity of bile acid excretion into bile due to a rapid translocation of canalicular transport ATPases from a subcanalicular storage compartment to the canalicular membrane. Similarly, glutamine augments biliary excretion of cysteinyl leukotrienes in endotoxin-treated rat livers. Also, the antiproteolytic effect of glutamine is largely due to glutamine-induced cell swelling, which activates osmosignaling pathways. Here, the glutamine-induced p38(MAPK) activation mediates the inhibition of autophagic proteolysis at the level of autophagosome formation.
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Affiliation(s)
- D Häussinger
- Department of Gastroenterology, Hepatology and Infectiology, Heinrich Heine University, Düsseldorf, Germany.
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Kurz AK, Graf D, Schmitt M, Vom Dahl S, Häussinger D. Tauroursodesoxycholate-induced choleresis involves p38(MAPK) activation and translocation of the bile salt export pump in rats. Gastroenterology 2001; 121:407-19. [PMID: 11487550 DOI: 10.1053/gast.2001.26262] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND & AIMS Canalicular secretion of bile acids is stimulated by tauroursodesoxycholate (TUDC). This study investigates the underlying mechanisms. METHODS TUDC effects on mitogen-activated protein (MAP) kinases, taurocholate (TC) excretion, proteolysis, and the localization of the bile salt export pump (Bsep) were studied in rat hepatocytes and perfused liver. RESULTS TUDC induced a transient and concentration-dependent activation of p38(MAPK) and of extracellular signal-regulated kinase 2 (Erk-2), but not of c-Jun-N-terminal kinase (JNK). In perfused liver, TUDC concentrations of 20 micromol/L was sufficient to elicit the MAP kinase responses and TC choleresis. SB 202190, a specific inhibitor of p38(MAPK), had no effect on TUDC- induced Erk activation but abolished the stimulatory effect of TUDC on TC excretion in perfused liver, indicating the requirement of p38(MAPK) in addition to the reported Erk dependence for the choleretic response. TUDC-induced stimulation of TC excretion was accompanied by a p38(MAPK)-dependent insertion of subcanalicular immunoreactive Bsep into the canalicular membrane. In addition TUDC induced a p38(MAPK)-sensitive inhibition of proteolysis. CONCLUSIONS TUDC-induced stimulation of canalicular TC excretion involves a MAP kinase-dependent translocation of subcanalicular Bsep to the canalicular membrane. Dual activation of Erks and p38(MAPK) is required for the choleretic effect of both TUDC and hypo-osmotic cell swelling.
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Affiliation(s)
- A K Kurz
- Department of Gastroenterology, Hepatology and Infectiology, Medizinische Einrichtungen der Heinrich-Heine Universität Düsseldorf, Moorenstrasse 5, D-40225 Düsseldorf, Germany
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Schliess F, von Dahl S, Häussinger D. Insulin resistance induced by loop diuretics and hyperosmolarity in perfused rat liver. Biol Chem 2001; 382:1063-9. [PMID: 11530937 DOI: 10.1515/bc.2001.133] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Insulin-induced cell swelling was recently suggested to reflect an independent signal for metabolic insulin effects such as inhibition of hepatic proteolysis, which is transmitted at the level of autophagosome formation via p38MAPK activation [Häussinger et al., Gastroenterology 116 (1999), 921-935]. Here, the role of insulin-induced cell swelling in the overall context of insulin signalling towards proteolysis inhibition was studied in perfused rat liver. Loop diuretics and hyperosmolarity, which impair insulin-stimulated cell swelling, strongly blunt Erk-2 and p38MAPK activation as well as proteolysis inhibition by insulin, but are without effect on insulin-induced tyrosine phosphorylation of IR-beta and IRS-1. Inhibitors of phosphatidylinositol-3-kinase (PI3-kinase) also block insulin-induced cell swelling, MAP kinase activation and proteolysis inhibition, but the antiproteolytic response to hypoosmolarity remains unaffected. We suggest that PI3-kinase-mediated cell swelling induced by insulin is required to amplify the insulin signal to MAP kinases and thus proteolysis regulation. The perturbation of insulin-induced cell swelling may be of pathophysiological relevance for the development of insulin resistance in clinical situations associated with hyperosmotic dehydration and loop diuretic treatment.
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Affiliation(s)
- F Schliess
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany
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Kim RD, Stein GS, Chari RS. Impact of cell swelling on proliferative signal transduction in the liver. J Cell Biochem 2001; 83:56-69. [PMID: 11500954 DOI: 10.1002/jcb.1205] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Cellular swelling has emerged as an important initiator of metabolic and proliferative changes in various cells. Because of the unique regenerative capacity of the adult liver, researchers have delineated key intracellular signals that are activated following mitogens, injury, and partial hepatectomy. Although hepatocellular swelling is commonly observed following these regenerative stimuli, only recently has the relationship between cell volume increase and proliferative activity been investigated; to date, the data implicating cell volume increase with hepatocyte regeneration has been mostly indirect. Hepatocyte swelling has been demonstrated in various clinical scenarios from sepsis, hepatic resection, ischemia-reperfusion injury, glucocorticoid excess, and hyperinsulinemia. Using various in vivo and in vitro models of hepatocyte swelling, particularly hypo-osmotic stress, investigators have demonstrated changes in cellular structure: (1) cell membrane stretch, (2) cytoskeletal microtubule and microfilament reorganization, and (3) alterations in cytoskeletal-membrane complexes. Similar studies have demonstrated a causal relationship between cell volume increase and intracellular signals: (1) activation of cytoplasmic signaling cascades such as MAPKs, PI-3-K, and PKC, (2) activation of proliferative transcription factors NF-kappaB, AP-1, STATs, C/EBPs, and (3) transcription of metabolic and immediate early genes of regeneration. Through mechanotransduction, or the translation of physical changes to chemical signals, cell volume is a potent effector of these signaling events. Growing evidence demonstrates a link between these physical and chemical changes in the swelling-mediated growth in the liver.
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Affiliation(s)
- R D Kim
- Department of Surgery, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA
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Phosphoinositide 3-kinase-dependent Ras activation by tauroursodesoxycholate in rat liver. Biochem J 2001. [PMID: 10926845 DOI: 10.1042/0264-6021:3500207] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Ursodesoxycholic acid, widely used for the treatment of cholestatic liver disease, causes choleretic, anti-apoptotic and immunomodulatory effects. Here the effects on choleresis of its taurine conjugate tauroursodesoxycholate (TUDC), which is present in the enterohepatic circulation, were correlated with the activation of important elements of intracellular signal transduction in cultured rat hepatocytes and perfused rat liver. TUDC induced a time- and concentration-dependent activation of the small GTP-binding protein Ras and of phosphoinositide 3-kinase (PI 3-kinase) in cultured hepatocytes. Ras activation was dependent on PI 3-kinase activity, without the involvement of protein kinase C- and genistein-sensitive tyrosine kinases. Ras activation by TUDC was followed by an activation of the mitogen-activated protein kinases extracellular-signal-regulated kinase-1 (Erk-1) and Erk-2. In perfused rat liver, PI 3-kinase inhibitors largely abolished the stimulatory effect of TUDC on taurocholate excretion, suggesting an important role for a PI 3-kinase/Ras/Erk pathway in the choleretic effect of TUDC.
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Webster CR, Blanch CJ, Phillips J, Anwer MS. Cell swelling-induced translocation of rat liver Na(+)/taurocholate cotransport polypeptide is mediated via the phosphoinositide 3-kinase signaling pathway. J Biol Chem 2000; 275:29754-60. [PMID: 10889198 DOI: 10.1074/jbc.m002831200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cell swelling stimulates phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) in hepatocytes, and the PI3K signaling pathway is involved in cAMP-mediated translocation of sinusoidal Na(+)/taurocholate (TC) cotransporter (Ntcp) to the plasma membrane. We determined whether cell swelling also stimulates TC uptake and Ntcp translocation via the PI3K and/or MAPK signaling pathway. All studies were conducted in isolated rat hepatocytes. Hepatocyte swelling induced by hypotonic media resulted in: 1) time- and medium osmolarity-dependent increases in TC uptake, 2) an increase in the V(max) of Na(+)/TC cotransport, and 3) wortmannin-sensitive increases in TC uptake and plasma membrane Ntcp mass. Hepatocyte swelling also induced wortmannin-sensitive activation of PI3K, protein kinase B, and p70(S6K). Rapamycin, an inhibitor of p70(S6K), inhibited cell swelling-induced activation of p70(S6K) but failed to inhibit cell swelling-induced stimulation of TC uptake. Because PD98095, an inhibitor of MAPK, did not inhibit cell swelling-induced increases in TC uptake, it is unlikely that the effect of cell swelling on TC uptake is mediated via the MAPK signaling pathway. Taken together, these results indicate that 1) cell swelling stimulates TC uptake by translocating Ntcp to the plasma membrane, 2) this effect is mediated via the PI3K, but not MAPK, signaling pathway, and 3) protein kinase B, but not p70(S6K), is a likely downstream effector of PI3K.
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Affiliation(s)
- C R Webster
- Department of Biomedical Sciences, Tufts University School of Veterinary Medicine, North Grafton, Massachusetts 01536, USA
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47
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Han B, Klonowski-Stumpe H, Lüthen R, Schreiber R, Häussinger D, Niederau C. Menadione-induced oxidative stress inhibits cholecystokinin-stimulated secretion of pancreatic acini by cell dehydration. Pancreas 2000; 21:191-202. [PMID: 10975714 DOI: 10.1097/00006676-200008000-00013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
The present study evaluated the effects of free radicals generated by menadione on morphology and function of pancreatic acinar cells focusing on enzyme secretion, stimulus-secretion coupling, and cell hydration. Various experiments evaluated morphology and function of isolated rat pancreatic acinar cells exposed to menadione. Menadione instantaneously generated free radicals (luminol and deoxyribose assays) followed by a time-dependent cell injury (uptake of trypan blue). Early ultrastructural changes included vacuolization and alterations of mitochondria, endoplasmic reticulum, and nucleus. Menadione caused a rapid glutathione oxidation followed by a depletion in reduced glutathione. An increase in lipid peroxides and a depletion of adenosine triphosphate were seen only after 30-60 minutes. Menadione markedly inhibited amylase release stimulated by cholecystokinin (CCK) and carbachol and simultaneously caused cell shrinkage after a few minutes. Similar degrees of cell shrinkage induced by hyperosmolar incubation and by menadione inhibited amylase secretion to a similar extent. CCK binding and its effect on calcium and inositol 1,4,5-trisphosphate (IP3) were not affected by menadione. Menadione (without CCK) induced an instantaneous increase of intracellular calcium followed by a slow constant increase. In single cells, menadione induced calcium oscillations with a frequency lower than that seen after CCK stimulation. Some morphologic and functional alterations owing to menadione-induced oxidative stress may be caused by adenosine triphosphate and glutathione depletion, lipid peroxidation, and changes in cytosolic calcium. The marked inhibition of secretagogue-stimulated enzyme secretion owing to menadione may be mediated to a large part by cell dehydration, whereas classical steps of stimulus-secretion coupling like receptor binding, calcium release, and IP3 generation remained unchanged.
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Affiliation(s)
- B Han
- Department of Medicine, Hepatology and Infectious Diseases, Heinrich-Heine-University of Düsseldorf Germany
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Schmitt M, Kubitz R, Wettstein M, vom Dahl S, Häussinger D. Retrieval of the mrp2 gene encoded conjugate export pump from the canalicular membrane contributes to cholestasis induced by tert-butyl hydroperoxide and chloro-dinitrobenzene. Biol Chem 2000; 381:487-95. [PMID: 10937881 DOI: 10.1515/bc.2000.063] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Oxidative stress is known to induce cholestasis, but the underlying mechanisms are poorly understood. In this study we have characterized the short-term effects of tert-butyl hydroperoxide (t-BOOH)- and 1-chloro-2,4-dinitrobenzene (CDNB) on the mrp2 gene encoded canalicular export pump (Mrp2). The effects of t-BOOH and CDNB on bile formation, tissue GSH levels and subcellular Mrp2 localization were studied in perfused rat liver. Both, t-BOOH (0.5 mM) and CDNB (0.1 mM) induced within 60 min a decrease of hepatic GSH levels by more than 90% and an almost complete cessation of bile flow. As revealed by confocal laser scanning microscopy, this cholestasis was accompanied by a loss of immunoreactive MRP2 from the canalicular membrane and its appearance inside the hepatocytes in putative intracellular vesicles. On the other hand, the intracellular distribution of dipeptidyl peptidase IV (DPPIV), another canalicular protein, and of zonula occludens associated polypeptide (ZO-1) remained unaffected, indicating selectivity of the Mrp2 retrieval pattern. Both, t-BOOH and CDNB induced a rapid net K+ efflux from the liver and a significant decrease of liver cell hydration. We conclude that severe glutathione depletion induces cholestasis by a retrieval of Mrp2, but not of DPPIV from the canalicular membrane. The underlying mechanism is unclear; however, a decrease in liver cell hydration, which occurs under these conditions, may contribute to this effect.
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Affiliation(s)
- M Schmitt
- Medizinische Universitätsklinik, Heinrich-Heine-Universität, Düsseldorf, Germany
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Kim RD, Darling CE, Cerwenka H, Chari RS. Hypoosmotic stress activates p38, ERK 1 and 2, and SAPK/JNK in rat hepatocytes. J Surg Res 2000; 90:58-66. [PMID: 10781376 DOI: 10.1006/jsre.2000.5866] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND Following hepatocyte injury, changes in the perihepatocyte milieu modulate cell volume and influence growth. Hypoosmotic stress activates nuclear factor-kappa B (NF-kappaB), a transcription factor believed to prime cell cycle progression in hepatocytes. In this study, we investigate the role of mitogen-activated protein kinases (MAPKs) in the activation of NF-kappaB. MATERIALS AND METHODS Quiescent primary hepatocytes were exposed to hypoosmotic serum-free William's E (WE) medium (200 mOsm/liter), with or without a 1-h pretreatment with either PD 98059 (15 microM) or SB 202190 (3 microM). Parallel experiments were conducted using hepatocyte growth factor (HGF) at 0.1 mg/ml and normoosmotic WE medium as positive and negative controls, respectively (n = 3). Relative densitometries of Western blots measured phosphorylated cytoplasmic p38, ERK 1 and 2, and SAPK/JNK. Electromobility shift assays examined nuclear NF-kappaB activation. RESULTS (i) Hypoosmolar WE medium phosphorylated p38, ERK 1 and 2, and SAPK/JNK by 5 min. (ii) Hypoosmolar WE medium activated NF-kappaB at 60 min. (iii) HGF phosphorylated all three MAPKs and activated NF-kappaB with profiles similar to those of hypoosmotic stress. (iv) Both PD 98059 and SB 202190 abrogated the activation of NF-kappaB in HGF-stimulated cells but not in hypoosmotically stressed cells. CONCLUSION (i) Both hypoosmotic cell swelling and HGF phosphorylate p38, ERK 1 and 2, and SAPK/JNK, and (ii) HGF, but not hypoosmotic stress, activates NF-kappaB via p38 and ERK 1 and 2 phosphorylation. These data suggest that cell swelling activates NF-kappaB through a pathway separate from that of growth factors.
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Affiliation(s)
- R D Kim
- Department of Surgery, University of Massachusetts Medical School, Worcester, MA 01655, USA
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Abstract
The alterations of hepatobiliary transport that occur in cholestasis can be divided into primary defects, such as mutations of transporter genes or acquired dysfunctions of transport systems that cause defective canalicular or cholangiocellular secretion, and secondary defects, which result from biliary obstruction. The dysfunction of distinct biliary transport systems as a primary cause of cholestasis is exemplified by the genetic defects in progressive familial intrahepatic cholestasis or by the direct inhibition of transporter gene expression by cytokines. In both, the hepatocellular accumulation of toxic cholephilic compounds causes multiple alterations of hepatocellular transporter expression. In addition, lack of specific components of bile caused by a defective transporter, as in the case of mdr2/MDR3 deficiency, unmasks the toxic potential of other components. The production of bile is critically dependent upon the coordinated regulation and function of sinusoidal and canalicular transporters, for instance of Na+-taurocholate cotransporting polypeptide (NTCP) and bile salt export pump (BSEP). Whereas the downregulation of the unidirectional sinusoidal uptake system NTCP protects the hepatocyte from further intracellular accumulation of bile salts, the relative preservation of canalicular BSEP expression serves to uphold bile salt secretion, even in complete biliary obstruction. Conversely, the strong downregulation of canalicular MRP2 (MRP, multidrug resistance protein) in cholestasis forces the hepatocyte to upregulate basolateral efflux systems such as MRP3 and MRP1, indicating an inverse regulation of basolateral and apical transporters The regulation of hepatocellular transporters in cholestasis adheres to the law of parsimony, since many of the cellular mechanisms are pivotally governed by the effect of bile salts. The discovery that bile salts are the natural ligand of the farnesoid X receptor has shown us how the major bile component is able to regulate its own enterohepatic circulation by affecting transcription of the genes critically involved in transport and metabolism.
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