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Mir IH, Thirunavukkarasu C. The relevance of acid sphingomyelinase as a potential target for therapeutic intervention in hepatic disorders: current scenario and anticipated trends. Arch Toxicol 2023; 97:2069-2087. [PMID: 37248308 PMCID: PMC10226719 DOI: 10.1007/s00204-023-03529-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 05/22/2023] [Indexed: 05/31/2023]
Abstract
Acid sphingomyelinase (ASMase) serves as one of the most remarkable enzymes in sphingolipid biology. ASMase facilitates the hydrolysis of sphingomyelin, yielding ceramide and phosphorylcholine via the phospholipase C signal transduction pathway. Owing to its prominent intervention in apoptosis, ASMase, and its product ceramide is now at the bleeding edge of lipid research due to the coalesced efforts of several research institutions over the past 40 years. ASMase-catalyzed ceramide synthesis profoundly alters the physiological properties of membrane structure in response to a broad range of stimulations, orchestrating signaling cascades for endoplasmic reticulum stress, autophagy, and lysosomal membrane permeabilization, which influences the development of hepatic disorders, such as steatohepatitis, hepatic fibrosis, drug-induced liver injury, and hepatocellular carcinoma. As a result, the potential to modulate the ASMase action with appropriate pharmaceutical antagonists has sparked a lot of curiosity. This article emphasizes the fundamental mechanisms of the systems that govern ASMase aberrations in various hepatic pathologies. Furthermore, we present an insight into the potential therapeutic agents used to mitigate ASMase irregularities and the paramountcy of such inhibitors in drug repurposing.
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Affiliation(s)
- Ishfaq Hassan Mir
- Department of Biochemistry and Molecular Biology, Pondicherry University, Puducherry, 605 014, India
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NOX as a Therapeutic Target in Liver Disease. Antioxidants (Basel) 2022; 11:antiox11102038. [PMID: 36290761 PMCID: PMC9598239 DOI: 10.3390/antiox11102038] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 10/12/2022] [Accepted: 10/13/2022] [Indexed: 11/17/2022] Open
Abstract
The nicotinamide adenine dinucleotide phosphate hydrogen oxidase (NADPH oxidase or NOX) plays a critical role in the inflammatory response and fibrosis in several organs such as the lungs, pancreas, kidney, liver, and heart. In the liver, NOXs contribute, through the generation of reactive oxygen species (ROS), to hepatic fibrosis by acting through multiple pathways, including hepatic stellate cell activation, proliferation, survival, and migration of hepatic stellate cells; hepatocyte apoptosis, enhancement of fibrogenic mediators, and mediation of an inflammatory cascade in both Kupffer cells and hepatic stellate cells. ROS are overwhelmingly produced during malignant transformation and hepatic carcinogenesis (HCC), creating an oxidative microenvironment that can cause different and various types of cellular stress, including DNA damage, ER stress, cell death of damaged hepatocytes, and oxidative stress. NOX1, NOX2, and NOX4, members of the NADPH oxidase family, have been linked to the production of ROS in the liver. This review will analyze some diseases related to an increase in oxidative stress and its relationship with the NOX family, as well as discuss some therapies proposed to slow down or control the disease's progression.
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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] [Track Full Text] [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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Murakami K, Tenge VR, Karandikar UC, Lin SC, Ramani S, Ettayebi K, Crawford SE, Zeng XL, Neill FH, Ayyar BV, Katayama K, Graham DY, Bieberich E, Atmar RL, Estes MK. Bile acids and ceramide overcome the entry restriction for GII.3 human norovirus replication in human intestinal enteroids. Proc Natl Acad Sci U S A 2020; 117:1700-1710. [PMID: 31896578 PMCID: PMC6983410 DOI: 10.1073/pnas.1910138117] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Human noroviruses (HuNoVs) cause sporadic and epidemic outbreaks of gastroenteritis in all age groups worldwide. We previously reported that stem cell-derived human intestinal enteroid (HIE) cultures support replication of multiple HuNoV strains and that some strains (e.g., GII.3) replicate only in the presence of bile. Heat- and trypsin-treatment of bile did not reduce GII.3 replication, indicating a nonproteinaceous component in bile functions as an active factor. Here we show that bile acids (BAs) are critical for GII.3 replication and replication correlates with BA hydrophobicity. Using the highly effective BA, glycochenodeoxycholic acid (GCDCA), we show BAs act during the early stage of infection, BA-dependent replication in HIEs is not mediated by detergent effects or classic farnesoid X receptor or Takeda G protein-coupled receptor 5 signaling but involves another G protein-coupled receptor, sphingosine-1-phosphate receptor 2, and BA treatment of HIEs increases particle uptake. We also demonstrate that GCDCA induces multiple cellular responses that promote GII.3 replication in HIEs, including enhancement of 1) endosomal uptake, 2) endosomal acidification and subsequent activity of endosomal/lysosomal enzyme acid sphingomyelinase (ASM), and 3) ceramide levels on the apical membrane. Inhibitors of endosomal acidification or ASM reduce GII.3 infection and exogenous addition of ceramide alone permits infection. Furthermore, inhibition of lysosomal exocytosis of ASM, which is required for ceramide production at the apical surface, decreases GII.3 infection. Together, our results support a model where GII.3 exploits rapid BA-mediated cellular endolysosomal dynamic changes and cellular ceramide to enter and replicate in jejunal HIEs.
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Affiliation(s)
- Kosuke Murakami
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
- Department of Virology II, National Institute of Infectious Diseases, Musashi-murayama, Tokyo 208-0011, Japan
| | - Victoria R Tenge
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Umesh C Karandikar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Shih-Ching Lin
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Sasirekha Ramani
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Khalil Ettayebi
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Sue E Crawford
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Xi-Lei Zeng
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Frederick H Neill
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - B Vijayalakshmi Ayyar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
| | - Kazuhiko Katayama
- Department of Virology II, National Institute of Infectious Diseases, Musashi-murayama, Tokyo 208-0011, Japan
- Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, Kitasato University, Tokyo 108-8641, Japan
| | - David Y Graham
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
- Department of Medicine, Michael E. DeBakey VA Medical Center, Houston, TX 77030
- Department of Medicine, Baylor College of Medicine, Houston, TX 77030
| | - Erhard Bieberich
- Department of Physiology, University of Kentucky, Lexington, KY 40506
| | - Robert L Atmar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030
- Department of Medicine, Baylor College of Medicine, Houston, TX 77030
| | - Mary K Estes
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030;
- Department of Medicine, Baylor College of Medicine, Houston, TX 77030
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Bile Acid-Activated Receptors: GPBAR1 (TGR5) and Other G Protein-Coupled Receptors. Handb Exp Pharmacol 2019; 256:19-49. [PMID: 31302759 DOI: 10.1007/164_2019_230] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The BA-responsive GPCRs S1PR2 and TGR5 are almost ubiquitously expressed in human and rodent tissues. In the liver, S1PR2 is expressed in all cell types, while TGR5 is predominately found in non-parenchymal cells. In contrast to S1PR2, which is mainly activated by conjugated bile acids (BAs), all BAs serve as ligands for TGR5 irrespective of their conjugation state and substitution pattern.Mice with targeted deletion of either S1PR2 or TGR5 are viable and develop no overt phenotype. In liver injury models, S1PR2 exerts pro-inflammatory and pro-fibrotic effects and thus aggravates liver damage, while TGR5 mediates anti-inflammatory, anti-cholestatic, and anti-fibrotic effects. Thus, inhibitors of S1PR2 signaling and agonists for TGR5 have been employed to attenuate liver injury in rodent models for cholestasis, nonalcoholic steatohepatitis, and fibrosis/cirrhosis.In biliary epithelial cells, both receptors activate a similar signaling cascade resulting in ERK1/2 phosphorylation and cell proliferation. Overexpression of both S1PR2 and TGR5 was found in human cholangiocarcinoma tissue as well as in CCA cell lines, where stimulation of both GPCRs resulted in transactivation of the epidermal growth factor receptor and triggered cell proliferation as well as increased cell migration and invasiveness.This chapter will focus on the function of S1PR2 and TGR5 in different liver cell types and summarizes current knowledge on the role of these receptors in liver disease models.
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Deutschmann K, Reich M, Klindt C, Dröge C, Spomer L, Häussinger D, Keitel V. Bile acid receptors in the biliary tree: TGR5 in physiology and disease. Biochim Biophys Acta Mol Basis Dis 2017; 1864:1319-1325. [PMID: 28844960 DOI: 10.1016/j.bbadis.2017.08.021] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 08/19/2017] [Accepted: 08/21/2017] [Indexed: 02/07/2023]
Abstract
Bile salts represent signalling molecules with a variety of endocrine functions. Bile salt effects are mediated by different receptor molecules, comprising ligand-activated nuclear transcription factors as well as G protein-coupled membrane-bound receptors. The farnesoid X receptor (FXR) and the plasma membrane-bound G protein-coupled receptor TGR5 (Gpbar-1) are prototypic bile salt receptors of both classes and are highly expressed in the liver including the biliary tree as well as in the intestine. In liver, TGR5 is localized in different non-parenchymal cells such as sinusoidal endothelial cells, Kupffer cells, hepatic stellate cells and small and large cholangiocytes. Through TGR5 bile salts can mediate choleretic, cell-protective as well as proliferative effects in cholangiocytes. A disturbance of these signalling mechanisms can contribute to the development of biliary diseases. In line with the important role of TGR5 for bile salt signalling, TGR5 knockout mice are more susceptible to cholestatic liver damage. Furthermore, in absence of TGR5 cholangiocyte proliferation in response to cholestasis is attenuated and intrahepatic and extrahepatic bile ducts show increased cell damage, underscoring the role of the receptor for biliary physiology. Decreased TGR5 expression may also contribute to the development or progression of cholangiopathies like primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) since reduced TGR5-dependent cell-protective mechanisms such as bicarbonate secretion renders cholangiocytes more vulnerable towards bile salt toxicity. Nevertheless, TGR5 overexpression or constant stimulation of the receptor can promote cholangiocyte proliferation leading to cyst growth in polycystic liver disease or even progression of cholangiocarcinoma. Not only the stimulation of TGR5-mediated pathways by suitable TGR5 agonists but also the inhibition of TGR5 signalling by the use of antagonists represent potential therapeutic approaches for different types of biliary diseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.
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Affiliation(s)
- Kathleen Deutschmann
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany
| | - Maria Reich
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany
| | - Caroline Klindt
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany
| | - Carola Dröge
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany
| | - Lina Spomer
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany
| | - Dieter Häussinger
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany
| | - Verena Keitel
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Medical Faculty at Heinrich-Heine-University, Moorenstrasse 5, 40225 Düsseldorf, Germany.
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7
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Webster CRL, Anwer MS. Hydrophobic bile acid apoptosis is regulated by sphingosine-1-phosphate receptor 2 in rat hepatocytes and human hepatocellular carcinoma cells. Am J Physiol Gastrointest Liver Physiol 2016; 310:G865-73. [PMID: 26999807 PMCID: PMC4895872 DOI: 10.1152/ajpgi.00253.2015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 03/14/2016] [Indexed: 01/31/2023]
Abstract
The hepatotoxic bile acid glycochenodeoxycholate (GCDC) modulates hepatocyte cell death through activation of JNK, Akt, and Erk. The nonhepatotoxic bile acid taurocholate activates Akt and Erk through the sphingosine-1-phosphate receptor 2 (S1PR2). The role of the S1PR2 in GCDC-mediated apoptosis and kinase activation is unknown. Studies were done in rat hepatocytes, HUH7 cells, and HUH7 cells stably transfected with rat Ntcp (HUH7-Ntcp). Cells were treated with GCDC and apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for the active cleaved fragment of caspase 3. Kinase activation was determined by immunoblotting with phospho-specific antibodies. JTE-013, an inhibitor of S1PR2, significantly attenuated morphological evidence of GCDC-induced apoptosis and prevented caspase 3 cleavage in rat hepatocytes and HUH7-Ntcp cells. In hepatocytes, JTE-013 mildly suppressed, augmented, and had no effect on GCDC-induced JNK, Akt, and Erk phosphorylation, respectively. Similar results were seen in HUH7-Ntcp cells except for mild suppression of JNK and Erk phosphorylation. Knockdown of S1PR2 in HUH7-Ntcp augmented Akt, inhibited JNK, and had no effect on Erk phosphorylation. GCDC failed to induce apoptosis or kinase activation in HUH7 cells. In conclusion, SIPR2 inhibition attenuates GCDC-induced apoptosis and inhibits and augments GCDC-induced JNK and Akt phosphorylation, respectively. In addition, GCDC must enter hepatocytes to mediate cell death or activate kinases. These results suggest that SIPR2 activation is proapoptotic in GCDC-induced cell death but that this effect is not due to direct ligation of the S1PR2 by the bile acid.
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Affiliation(s)
- Cynthia R L Webster
- Department of Clinical Science, Cummings School of Veterinary Medicine at Tufts University, Grafton, Massachusetts; and
| | - M Sawkat Anwer
- Department of Biomedical Science, Cummings School of Veterinary Medicine at Tufts University, Grafton, Massachusetts
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Reich M, Deutschmann K, Sommerfeld A, Klindt C, Kluge S, Kubitz R, Ullmer C, Knoefel WT, Herebian D, Mayatepek E, Häussinger D, Keitel V. TGR5 is essential for bile acid-dependent cholangiocyte proliferation in vivo and in vitro. Gut 2016; 65:487-501. [PMID: 26420419 DOI: 10.1136/gutjnl-2015-309458] [Citation(s) in RCA: 129] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 09/01/2015] [Indexed: 12/13/2022]
Abstract
OBJECTIVE Cholestatic liver diseases in humans as well as bile acid (BA)-feeding and common bile duct ligation (CBDL) in rodents trigger hyperplasia of cholangiocytes within the portal fields. Furthermore, elevation of BA levels enhances proliferation and invasiveness of cholangiocarcinoma (CCA) cells in animal models, thus promoting tumour progression. TGR5 is a G-protein coupled BA receptor, which is highly expressed in cholangiocytes and postulated to mediate the proliferative effects of BA. DESIGN BA-dependent cholangiocyte proliferation was examined in TGR5-knockout and wild type mice following cholic acid (CA)-feeding and CBDL. TGR5-dependent proliferation and protection from apoptosis was studied in isolated cholangiocytes and CCA cell lines following stimulation with TGR5 ligands and kinase inhibitors. TGR5 expression was analysed in human CCA tissue. RESULTS Cholangiocyte proliferation was significantly reduced in TGR5-knockout mice in response to CA-feeding and CBDL. Taurolithocholic acid and TGR5-selective agonists induced cholangiocyte proliferation through elevation of reactive oxygen species and cSrc mediated epidermal growth factor receptor transactivation and subsequent Erk1/2 phosphorylation only in wild type but not in TGR5-knockout-derived cells. In human CCA tissue TGR5 was overexpressed and the pathway of TGR5-dependent proliferation via epidermal growth factor receptor and extracellular signal-regulated kinase (ERK)1/2 activation also translated to CCA cell lines. Furthermore, apoptosis was inhibited by TGR5-dependent CD95 receptor serine phosphorylation. CONCLUSIONS TGR5 is an important mediator of BA-induced cholangiocyte proliferation in vivo and in vitro. Furthermore, TGR5 protects cholangiocytes from death receptor-mediated apoptosis. These mechanisms may protect cholangiocytes from BA toxicity under cholestatic conditions, however, they may trigger proliferation and apoptosis resistance in malignantly transformed cholangiocytes, thus promoting CCA progression.
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Affiliation(s)
- Maria Reich
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Kathleen Deutschmann
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Annika Sommerfeld
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Caroline Klindt
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Stefanie Kluge
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Ralf Kubitz
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Christoph Ullmer
- Roche Pharmaceutical Research and Early Development, Roche Innovation Center Basel, Basel, Switzerland
| | - Wolfram T Knoefel
- Department of General, Visceral, and Pediatric Surgery, Heinrich-Heine-University, Düsseldorf, Germany
| | - Diran Herebian
- Department of General Pediatrics, Neonatalogy and Pediatric Cardiology, Heinrich-Heine-University, Düsseldorf, Germany
| | - Ertan Mayatepek
- Department of General Pediatrics, Neonatalogy and Pediatric Cardiology, Heinrich-Heine-University, Düsseldorf, Germany
| | - Dieter Häussinger
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
| | - Verena Keitel
- Clinic for Gastroenterology, Hepatology and Infectious Diseases, Heinrich-Heine-University, Düsseldorf, Germany
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Paik YH, Kim J, Aoyama T, De Minicis S, Bataller R, Brenner DA. Role of NADPH oxidases in liver fibrosis. Antioxid Redox Signal 2014; 20:2854-72. [PMID: 24040957 PMCID: PMC4026397 DOI: 10.1089/ars.2013.5619] [Citation(s) in RCA: 158] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
SIGNIFICANCE Hepatic fibrosis is the common pathophysiologic process resulting from chronic liver injury, characterized by the accumulation of an excessive extracellular matrix. Multiple lines of evidence indicate that oxidative stress plays a pivotal role in the pathogenesis of liver fibrosis. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) is a multicomponent enzyme complex that generates reactive oxygen species (ROS) in response to a wide range of stimuli. In addition to phagocytic NOX2, there are six nonphagocytic NOX proteins. RECENT ADVANCES In the liver, NOX is functionally expressed both in the phagocytic form and in the nonphagocytic form. NOX-derived ROS contributes to various kinds of liver disease caused by alcohol, hepatitis C virus, and toxic bile acids. Recent evidence indicates that both phagocytic NOX2 and nonphagocytic NOX isoforms, including NOX1 and NOX4, mediate distinct profibrogenic actions in hepatic stellate cells, the main fibrogenic cell type in the liver. The critical role of NOX in hepatic fibrogenesis provides a rationale to assess pharmacological NOX inhibitors that treat hepatic fibrosis in patients with chronic liver disease. CRITICAL ISSUES Although there is compelling evidence indicating a crucial role for NOX-mediated ROS generation in hepatic fibrogenesis, little is known about the expression, subcellular localization, regulation, and redox signaling of NOX isoforms in specific cell types in the liver. Moreover, the exact mechanism of NOX-mediated fibrogenic signaling is still largely unknown. FUTURE DIRECTIONS A better understanding through further research about NOX-mediated fibrogenic signaling may enable the development of novel anti-fibrotic therapy using NOX inhibition strategy. Antio
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Affiliation(s)
- Yong-Han Paik
- 1 Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine , Seoul, Korea
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Abstract
PURPOSE OF REVIEW TGR5 (Gpbar-1) is an emerging drug target for metabolic, intestinal and liver diseases. In liver, the highest expression of TGR5 is found in biliary epithelial cells. This review focusses on the function of TGR5 in cholangiocytes and the potential role of the receptor in biliary diseases. RECENT FINDINGS TGR5 is localized in the primary cilium and the apical membrane domain of cholangiocytes, where the receptor exerts secretory, proliferative and antiapoptotic effects. Recent human and animal studies using bile acid analogues suggest a therapeutic potential for TGR5 in primary biliary cirrhosis but not in primary sclerosing cholangitis. SUMMARY TGR5 has protective functions in cholangiocytes. Further studies are needed to determine the therapeutic potential of TGR5 agonists and antagonists in biliary diseases.
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Perspective: TGR5 (Gpbar-1) in liver physiology and disease. Clin Res Hepatol Gastroenterol 2012; 36:412-9. [PMID: 22521118 DOI: 10.1016/j.clinre.2012.03.008] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2012] [Accepted: 03/02/2012] [Indexed: 02/06/2023]
Abstract
Bile acids are signaling molecules with diverse endocrine functions. Bile acid effects are mediated through the nuclear receptor farnesoid X receptor (FXR), the G-protein coupled receptor TGR5 (Gpbar-1) and various other bile acid sensing molecules. TGR5 is almost ubiquitously expressed and has been detected in different non-parenchymal cells of human and rodent liver. Here, TGR5 has anti-inflammatory, anti-apoptotic and choleretic functions. Mice with targeted deletion of TGR5 are protected from the development of cholesterol gallstones. Administration of specific TGR5 agonists lowers serum and liver triglyceride levels thereby reducing liver steatosis. Furthermore, activation of TGR5 promotes intestinal glucagon-like peptide-1 (GLP-1) release, thereby modulating glucose homeostasis and energy expenditure in brown adipose tissue and skeletal muscle. Additionally, TGR5 exerts anti-inflammatory actions resulting in decreased liver injury in animal models of sepsis. These beneficial effects make TGR5 an attractive therapeutic target for metabolic diseases, such as diabetes, obesity, atherosclerosis and steatohepatitis.
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12
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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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Keitel V, Cupisti K, Ullmer C, Knoefel WT, Kubitz R, Häussinger D. The membrane-bound bile acid receptor TGR5 is localized in the epithelium of human gallbladders. Hepatology 2009; 50:861-70. [PMID: 19582812 DOI: 10.1002/hep.23032] [Citation(s) in RCA: 194] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
UNLABELLED TGR5 (Gpbar-1) is a plasma membrane-bound, G protein-coupled receptor for bile acids. TGR5 messenger RNA (mRNA) has been detected in many tissues, including rat cholangiocytes and mouse gallbladder. A role for TGR5 in gallstone formation has been suggested, because TGR5 knockout mice did not develop gallstones when fed a lithogenic diet. In this study, expression and localization of TGR5 was studied in human gallbladders. TGR5 mRNA and protein were detected in all 19 gallbladders. Although TGR5 mRNA was significantly elevated in the presence of gallstones, no such relation was found for TGR5 protein levels. In order to study the localization of TGR5 in human gallbladders, a novel antibody was generated. The receptor was localized in the apical membrane and the rab11-positive recycling endosome of gallbladder epithelial cells. Furthermore, the TGR5 staining colocalized with the cyclic adenosine monophosphate-regulated chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) and the apical sodium-dependent bile salt uptake transporter, suggesting a functional coupling of TGR5 to bile acid uptake and chloride secretion. Stimulation with bile acids significantly increased cyclic adenosine monophosphate concentration in human gallbladder tissue. Incubation of gallbladder epithelial cells with a TGR5 agonist led to a rise of N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE)-fluorescence, suggestive of a decrease in intracellular chloride concentration. The TGR5 agonist-dependent increase in MQAE-fluorescence was absent in TGR5 knockout mice or in the presence of a CFTR inhibitor, indicating that TGR5 mediates chloride secretion via activation of CFTR. The presence of the receptor in both the plasma membrane and the recycling endosome indicate that TGR5 can be regulated by translocation. CONCLUSION The data suggest a role for TGR5 in bile acid-induced fluid secretion in biliary epithelial cells.
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Affiliation(s)
- Verena Keitel
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany
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14
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Deoxycholate, an endogenous cytotoxin/genotoxin, induces the autophagic stress-survival pathway: implications for colon carcinogenesis. J Toxicol 2009; 2009:785907. [PMID: 20130808 PMCID: PMC2814131 DOI: 10.1155/2009/785907] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 01/25/2009] [Accepted: 02/24/2009] [Indexed: 01/09/2023] Open
Abstract
We report that deoxycholate (DOC), a hydrophobic bile acid associated with a high-fat diet, activates the autophagic pathway in non-cancer colon epithelial cells (NCM-460), and that this activation contributes to cell survival. The DOC-induced increase in autophagy was documented by an increase in autophagic vacuoles (detected using transmission electron microscopy, increased levels of LC3-I and LC3-II (western blotting), an increase in acidic vesicles (fluorescence spectroscopy of monodansycadaverine and lysotracker red probes), and increased expression of the autophagic protein, beclin-1 (immunohistochemistry/western blotting). The DOC-induced increase in beclin-1 expression was ROS-dependent. Rapamycin (activator of autophagy) pre-treatment of NCM-460 cells significantly (P < .05) decreased, and 3-MA (inhibitor of autophagy) significantly (P < .05) increased the cell loss caused by DOC treatment, alone. Rapamycin pre-treatment of the apoptosis-resistant colon cancer cell line, HCT-116RC (developed in our laboratory), resulted in a significant decrease in DOC-induced cell death. Bafilomycin A(1) and hydroxychloroquine (inhibitors of the autophagic process) increased the DOC-induced percentage of apoptotic cells in HCT-116RC cells. It was concluded that the activation of autophagy by DOC has important implications for colon carcinogenesis and for the treatment of colon cancer in conjunction with commonly used chemotherapeutic agents.
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15
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Payne CM, Bernstein C, Dvorak K, Bernstein H. Hydrophobic bile acids, genomic instability, Darwinian selection, and colon carcinogenesis. Clin Exp Gastroenterol 2008; 1:19-47. [PMID: 21677822 PMCID: PMC3108627 DOI: 10.2147/ceg.s4343] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Sporadic colon cancer is caused predominantly by dietary factors. We have selected bile acids as a focus of this review since high levels of hydrophobic bile acids accompany a Western-style diet, and play a key role in colon carcinogenesis. We describe how bile acid-induced stresses cause cell death in susceptible cells, contribute to genomic instability in surviving cells, impose Darwinian selection on survivors and enhance initiation and progression to colon cancer. The most likely major mechanisms by which hydrophobic bile acids induce stresses on cells (DNA damage, endoplasmic reticulum stress, mitochondrial damage) are described. Persistent exposure of colon epithelial cells to hydrophobic bile acids can result in the activation of pro-survival stress-response pathways, and the modulation of numerous genes/proteins associated with chromosome maintenance and mitosis. The multiple mechanisms by which hydrophobic bile acids contribute to genomic instability are discussed, and include oxidative DNA damage, p53 and other mutations, micronuclei formation and aneuploidy. Since bile acids and oxidative stress decrease DNA repair proteins, an increase in DNA damage and increased genomic instability through this mechanism is also described. This review provides a mechanistic explanation for the important link between a Western-style diet and associated increased levels of colon cancer.
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Affiliation(s)
- Claire M Payne
- Department of Cell Biology and Anatomy, College of Medicine, University of Arizona, Tucson, Arizona, USA
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16
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Katona BW, Anant S, Covey DF, Stenson WF. Characterization of enantiomeric bile acid-induced apoptosis in colon cancer cell lines. J Biol Chem 2008; 284:3354-3364. [PMID: 19054763 DOI: 10.1074/jbc.m805804200] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bile acids are steroid detergents that are toxic to mammalian cells at high concentrations; increased exposure to these steroids is pertinent in the pathogenesis of cholestatic disease and colon cancer. Understanding the mechanisms of bile acid toxicity and apoptosis, which could include nonspecific detergent effects and/or specific receptor activation, has potential therapeutic significance. In this report we investigate the ability of synthetic enantiomers of lithocholic acid (ent-LCA), chenodeoxycholic acid (ent-CDCA), and deoxycholic acid (ent-DCA) to induce toxicity and apoptosis in HT-29 and HCT-116 cells. Natural bile acids were found to induce more apoptotic nuclear morphology, cause increased cellular detachment, and lead to greater capase-3 and -9 cleavage compared with enantiomeric bile acids in both cell lines. In contrast, natural and enantiomeric bile acids showed similar effects on cellular proliferation. These data show that bile acid-induced apoptosis in HT-29 and HCT-116 cells is enantiospecific, hence correlated with the absolute configuration of the bile steroid rather than its detergent properties. The mechanism of LCA- and ent-LCA-induced apoptosis was also investigated in HT-29 and HCT-116 cells. These bile acids differentially activate initiator caspases-2 and -8 and induce cleavage of full-length Bid. LCA and ent-LCA mediated apoptosis was inhibited by both pan-caspase and selective caspase-8 inhibitors, whereas a selective caspase-2 inhibitor provided no protection. LCA also induced increased CD95 localization to the plasma membrane and generated increased reactive oxygen species compared with ent-LCA. This suggests that LCA/ent-LCA induce apoptosis enantioselectively through CD95 activation, likely because of increased reactive oxygen species generation, with resulting procaspase-8 cleavage.
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Affiliation(s)
- Bryson W Katona
- Department of Developmental Biology, Division of Gastroenterology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Shrikant Anant
- Department of Medicine, University of Oklahoma Heath Sciences Center, Oklahoma City, Oklahoma 73104
| | - Douglas F Covey
- Department of Developmental Biology, Division of Gastroenterology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - William F Stenson
- Department of Medicine, Division of Gastroenterology, Washington University School of Medicine, St. Louis, Missouri 63110.
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17
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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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18
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Graf D, Haselow K, Münks I, Bode JG, Häussinger D. Caspase-mediated cleavage of the signal-transducing IL-6 receptor subunit gp130. Arch Biochem Biophys 2008; 477:330-8. [DOI: 10.1016/j.abb.2008.06.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2008] [Revised: 06/09/2008] [Accepted: 06/10/2008] [Indexed: 12/21/2022]
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19
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Abstract
Most of the previous work on the sphingolipid ceramide has been devoted to its function as an apoptosis inducer. Recent studies, however, have shown that in stem cells, ceramide has additional nonapoptotic functions. In this article, ceramide signaling will be reviewed in light of 'systems interface biology': as an interconnection of sphingolipid metabolism, membrane biophysics and cell signaling. The focus will be on the metabolic interconversion of ceramide and sphingomyelin or sphingosine-1-phosphate. Lipid rafts and sphingolipid-induced protein scaffolds will be discussed as a membrane interface for lipid-controlled cell signaling. Ceramide/sphingomyelin and ceramide/sphingosine-1-phosphate-interdependent cell-signaling pathways are significant for the regulation of cell polarity, apoptosis and/or proliferation, and as novel pharmacologic targets in cancer and stem cells.
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Affiliation(s)
- Erhard Bieberich
- Institute of Molecular Medicine & Genetics, School of Medicine, Medical College of Georgia, 1120 15th Street, Room CB-2803, Augusta, GA 30912, USA
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20
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Abstract
Mitochondria have multiple functions in eukaryotic cells and are organized into dynamic tubular networks that continuously undergo changes through coordinated fusion and fission and migration through the cytosol. Mitochondria integrate cell-signaling networks, especially those involving the intracellular messenger Ca(2+), into the regulation of metabolic pathways. Recently, it has become clear that mitochondria are central to the three main cell death pathways, namely necrosis, apoptosis, and autophagic cell death. This article discusses the role of mitochondria in drug-induced cholestatic injury to the liver. The role of mitochondria in the cellular adaptation against the toxic effects of bile acids is discussed also.
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Affiliation(s)
- George E N Kass
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, GU2 7XH, UK.
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21
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Abstract
Pharmacological interference with sphingolipid metabolizing enzymes promises to provide novel ways to modulate cellular pathways relevant in multiple diseases. In this review, we focus on two sphingolipid signaling molecules, sphingosine-1-phosphate (S1P) and ceramide, as they are involved in cell fate decisions (survival vs. apoptosis) and in a wide range of pathophysiological processes. For S1P, we will discuss sphingosine kinases and S1P lyase as the enzymes which are crucial for its production and degradation, respectively, emphasizing the potential therapeutic usefulness of inhibitors of these enzymes. For ceramide, we will concentrate on acid sphingomyelinase, and critically review the substantial literature which implicates this enzyme as a worthwhile target for pharmacological inhibitors. It will become clear that the task to validate these enzymes as drug targets is not finished and many questions regarding the therapeutic usefulness of their inhibitors remain unanswered. Still this approach holds promise for a number of totally new therapies, and, on the way, detailed insight into sphingolipid signaling pathways can be gained.
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Affiliation(s)
- Andreas Billich
- Novartis Institutes for BioMedical Research, Brunnerstrasse 59, A-1235 Vienna, Austria
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22
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Reinehr R, Sommerfeld A, Keitel V, Grether-Beck S, Häussinger D. Amplification of CD95 Activation by Caspase 8-induced Endosomal Acidification in Rat Hepatocytes. J Biol Chem 2008; 283:2211-22. [DOI: 10.1074/jbc.m706853200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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23
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Becker S, Reinehr R, Graf D, vom Dahl S, Häussinger D. Hydrophobic bile salts induce hepatocyte shrinkage via NADPH oxidase activation. Cell Physiol Biochem 2007; 19:89-98. [PMID: 17310103 DOI: 10.1159/000099197] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/06/2006] [Indexed: 01/25/2023] Open
Abstract
Hydrophobic bile salts activate NADPH oxidase through a ceramide and protein kinase Czeta-dependent pathway as an important upstream event of bile salt-induced hepatocyte apoptosis. As shown in the present study, hydrophobic bile salts such as glycochenodeoxycholate, taurochenodeoxycholate or taurolithocholylsulfate (TLCS) also induce within 30 min hepatocyte shrinkage in perfused rat liver. TLCS-induced hepatocyte shrinkage was strongly blunted in presence of desipramine, apocynin, bafilomycin and DIDS, i.e. maneuvres previously shown to inhibit TLCS-induced NADPH oxidase activation and the subsequent oxidative stress response. The antioxidant N-acetylcysteine inhibited TLCS-induced hepatocyte shrinkage. N-acetylcysteine by itself increased hepatocyte hydration, suggesting that a basal production of reactive oxygen intermediates is involved in the regulation of liver cell hydration. TLCS failed to induce shrinkage of hepatocytes from p47(phox) knock-out, but not control mice. Likewise, hepatocytes from p47(phox) knock-out mice were resistant towards TLCS-induced apoptosis and failed to activate the CD95 system. No cell shrinkage was observed in response to taurocholate and tauroursodesoxycholate, i.e. bile salts which do not induce an oxidative stress signal and apoptosis. NADPH oxidase activation also counteracts volume recovery in response to hyperosmotic hepatocyte shrinkage. The findings indicate that hydrophobic, proapoptotic bile salts induce hepatocyte shrinkage largely through NADPH oxidase-derived oxidative stress. Because cell shrinkage in turn activates NADPH oxidase, which blunts cell volume recovery, a vicious cycle ensues between oxidative stress and cell shrinkage, which propagates CD95 activation and may finally lead to apoptosis. In addition, cell shrinkage induced by proapoptotic bile salts may augment apoptosis by increasing protein breakdown and induction of cholestasis.
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Affiliation(s)
- Stephan Becker
- Clinic for Gastroenterology, Hepatology and Infectiology; Heinrich-Heine-University Düsseldorf
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24
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Reinehr R, Häussinger D. CD95 activation in the liver: ion fluxes and oxidative signaling. Arch Biochem Biophys 2007; 462:124-31. [PMID: 17258167 DOI: 10.1016/j.abb.2006.12.019] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2006] [Revised: 12/14/2006] [Accepted: 12/16/2006] [Indexed: 12/18/2022]
Abstract
Apoptosis is characterized by typical features as cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation. Whereas some signs of apoptosis are cell type-and death signal-dependent, apoptotic cell volume decrease is an early and ubiquitous event and little is known about the signalling events, which are localized upstream of the plasma membrane transport steps leading to apoptotic cell volume decrease and the proapoptotic events, which are induced by osmolyte loss and cell shrinkage. Ion fluxes and oxidative signaling were recently shown to play an important role in signal transduction with respect to apoptotic cell death within the liver, as a ceramide-dependent activation of the NADPH oxidase was identified as the source of reactive oxygen species generation in rat hepatocytes upon treatment with CD95 ligand, hydrophobic bile salts or hyperosmolarity. The NADPH oxidase-derived ROS signal then allows via Yes, JNK, and EGFR activation for CD95 tyrosine phosphorylation as a prerequisite for CD95 targeting to the plasma membrane and formation of the death inducing signalling complex. Other covalent modifications such as CD95-tyrosine-nitration or CD95-serine/threonine-phosphorylation can interfere with the CD95 activation process. The findings not only provide a mechanistic explanation for the high susceptibility of dehydrated cells for apoptosis, but also give insight into the role of ion fluxes and oxidative signaling with respect to apoptotic cell death within the liver.
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Affiliation(s)
- Roland Reinehr
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany
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25
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Abstract
Cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation are hallmarks of programmed apoptotic cell death. Herein, apoptotic volume decrease (AVD) is an early and ubiquitous event. Conversely, in hepatocytes, hyperosmotic cell shrinkage leads to an activation of the CD95 death receptor system, which involves CD95 tyrosine phosphorylation, CD95 oligomerization, and subsequent trafficking of the CD95 to the plasma membrane, and sensitizes hepatocytes toward CD95 ligand (CD95L)-induced apoptosis. Early signaling events leading to CD95 activation by hyperosmolarity have been identified. In hepatocytes, hyperosmotic exposure induces an almost instantaneous acidification of an acidic sphingomyelinase (ASM) containing endosomal compartment, which is followed by an increase in the intracellular ceramide concentration. Inhibition of anion channels or the vacuolar-type H(+)-ATPase abolishes not only endosomal acidification and subsequent ceramide generation, but also the otherwise observed hyperosmotically induced generation of reactive oxygen species (ROS) by NADPH oxidase isoforms. Hyperosmolarity-induced ROS formation then leads to a Src-family kinase Yes-mediated activation of the epidermal growth factor receptor (EGFR) and to an activation of the c-Jun-N-terminal kinase (JNK). JNK then provides a signal for CD95/EGFR association and subsequent CD95 tyrosine phosphorylation, which is mediated by the EGFR tyrosine kinase activity. CD95 tyrosine phosphorylation then allows for CD95 receptor oligomerization, translocation of the CD95/EGFR protein complex to the plasma membrane, and formation of the death inducing signaling complex (DISC). Mild hyperosmotic exposure, that is, 405 mosmol/liter, does not lead to a reduction of cell viability, even if DISC formation and subsequent caspase 8 and 3 activation occur, but sensitizes hepatocytes to CD95L-induced apoptosis. However, activation of the CD95 system by a more severe hyperosmotic challenge (>505 mosmol/liter) is followed by execution of the apoptotic cell death. Other covalent modifications of CD95, such as CD95 tyrosine nitration or CD95 serine/threonine phosphorylation, were shown to inhibit the CD95 activation process.
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Affiliation(s)
- Roland Reinehr
- Clinic for Gastroenterology, Hepatology, and Infectiology, Heinrich-Heine-University Düsseldorf, Germany
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