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Modak B, Girkar S, Narayan R, Kapoor S. Mycobacterial Membranes as Actionable Targets for Lipid-Centric Therapy in Tuberculosis. J Med Chem 2022; 65:3046-3065. [PMID: 35133820 DOI: 10.1021/acs.jmedchem.1c01870] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Infectious diseases remain significant health concerns worldwide, and resistance is particularly common in patients with tuberculosis caused by Mycobacterium tuberculosis. The development of anti-infectives with novel modes of action may help overcome resistance. In this regard, membrane-active agents, which modulate membrane components essential for the survival of pathogens, present attractive antimicrobial agents. Key advantages of membrane-active compounds include their ability to target slow-growing or dormant bacteria and their favorable pharmacokinetics. Here, we comprehensively review recent advances in the development of membrane-active chemotypes that target mycobacterial membranes and discuss clinically relevant membrane-active antibacterial agents that have shown promise in counteracting bacterial infections. We discuss the relationship between the membrane properties and the synthetic requirements within the chemical scaffold, as well as the limitations of current membrane-active chemotypes. This review will lay the chemical groundwork for the development of membrane-active antituberculosis agents and will foster the discovery of more effective antitubercular agents.
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Affiliation(s)
- Biswabrata Modak
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Siddhali Girkar
- School of Chemical and Materials Sciences, Indian Institute of Technology Goa, Goa 403110, India
| | - Rishikesh Narayan
- School of Chemical and Materials Sciences, Indian Institute of Technology Goa, Goa 403110, India
| | - Shobhna Kapoor
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India.,Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima 739-8528, Japan
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2
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Flotillin-Dependent Membrane Microdomains Are Required for Functional Phagolysosomes against Fungal Infections. Cell Rep 2021; 32:108017. [PMID: 32814035 PMCID: PMC10054021 DOI: 10.1016/j.celrep.2020.108017] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 04/03/2020] [Accepted: 07/17/2020] [Indexed: 11/23/2022] Open
Abstract
Lipid rafts form signaling platforms on biological membranes with incompletely characterized role in immune response to infection. Here we report that lipid-raft microdomains are essential components of phagolysosomal membranes of macrophages and depend on flotillins. Genetic deletion of flotillins demonstrates that the assembly of both major defense complexes vATPase and NADPH oxidase requires membrane microdomains. Furthermore, we describe a virulence mechanism leading to dysregulation of membrane microdomains by melanized wild-type conidia of the important human-pathogenic fungus Aspergillus fumigatus resulting in reduced phagolysosomal acidification. We show that phagolysosomes with ingested melanized conidia contain a reduced amount of free Ca2+ ions and that inhibition of Ca2+-dependent calmodulin activity led to reduced lipid-raft formation. We identify a single-nucleotide polymorphism in the human FLOT1 gene resulting in heightened susceptibility for invasive aspergillosis in hematopoietic stem cell transplant recipients. Collectively, flotillin-dependent microdomains on the phagolysosomal membrane play an essential role in protective antifungal immunity.
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Fratini F, Raggi C, Sferra G, Birago C, Sansone A, Grasso F, Currà C, Olivieri A, Pace T, Mochi S, Picci L, Ferreri C, Di Biase A, Pizzi E, Ponzi M. An Integrated Approach to Explore Composition and Dynamics of Cholesterol-rich Membrane Microdomains in Sexual Stages of Malaria Parasite. Mol Cell Proteomics 2017; 16:1801-1814. [PMID: 28798222 DOI: 10.1074/mcp.m117.067041] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Revised: 08/04/2017] [Indexed: 12/26/2022] Open
Abstract
Membrane microdomains that include lipid rafts, are involved in key physiological and pathological processes and participate in the entry of endocellular pathogens. These assemblies, enriched in cholesterol and sphingolipids, form highly dynamic, liquid-ordered phases that can be separated from the bulk membranes thanks to their resistance to solubilization by nonionic detergents. To characterize complexity and dynamics of detergent-resistant membranes of sexual stages of the rodent malaria parasite Plasmodium berghei, here we propose an integrated study of raft components based on proteomics, lipid analysis and bioinformatics. This analysis revealed unexpected heterogeneity and unexplored pathways associated with these specialized assemblies. Protein-protein relationships and protein-lipid co-occurrence were described through multi-component networks. The proposed approach can be widely applied to virtually every cell type in different contexts and perturbations, under physiological and/or pathological conditions.
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Affiliation(s)
- Federica Fratini
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Carla Raggi
- §Istituto Superiore di Sanità, Dipartimento di Biologia Cellulare e Neuroscienze
| | - Gabriella Sferra
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Cecilia Birago
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Anna Sansone
- ¶Consiglio Nazionale delle Ricerche, I.S.O.F. - Bio Free Radicals
| | - Felicia Grasso
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Chiara Currà
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate.,From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Anna Olivieri
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Tomasino Pace
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Stefania Mochi
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Leonardo Picci
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Carla Ferreri
- ¶Consiglio Nazionale delle Ricerche, I.S.O.F. - Bio Free Radicals
| | - Antonella Di Biase
- ‖Istituto Superiore di Sanità, Dipartimento di Sanità Pubblica Veterinaria e Alimentare
| | - Elisabetta Pizzi
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate
| | - Marta Ponzi
- From the ‡Istituto Superiore di Sanità, Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate;
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Huang SH, Chi F, Peng L, Bo T, Zhang B, Liu LQ, Wu X, Mor-Vaknin N, Markovitz DM, Cao H, Zhou YH. Vimentin, a Novel NF-κB Regulator, Is Required for Meningitic Escherichia coli K1-Induced Pathogen Invasion and PMN Transmigration across the Blood-Brain Barrier. PLoS One 2016; 11:e0162641. [PMID: 27657497 PMCID: PMC5033352 DOI: 10.1371/journal.pone.0162641] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Accepted: 08/25/2016] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND NF-κB activation, pathogen invasion, polymorphonuclear leukocytes (PMN) transmigration (PMNT) across the blood-brain barrier (BBB) are the pathogenic triad hallmark features of bacterial meningitis, but the mechanisms underlying these events remain largely unknown. Vimentin, which is a novel NF-κB regulator, is the primary receptor for the major Escherichia coli K1 virulence factor IbeA that contributes to the pathogenesis of neonatal bacterial sepsis and meningitis (NSM). We have previously shown that IbeA-induced NF-κB signaling through its primary receptor vimentin as well as its co-receptor PTB-associated splicing factor (PSF) is required for pathogen penetration and leukocyte transmigration across the BBB. This is the first in vivo study to demonstrate how vimentin and related factors contributed to the pathogenic triad of bacterial meningitis. METHODOLOGY/PRINCIPAL FINDINGS The role of vimentin in IbeA+ E. coli K1-induced NF-κB activation, pathogen invasion, leukocyte transmigration across the BBB has now been demonstrated by using vimentin knockout (KO) mice. In the in vivo studies presented here, IbeA-induced NF-κB activation, E. coli K1 invasion and polymorphonuclear neutrophil (PMN) transmigration across the BBB were significantly reduced in Vim-/- mice. Decreased neuronal injury in the hippocampal dentate gyrus was observed in Vim-/- mice with meningitis. The major inflammatory regulator α7 nAChR and several signaling molecules contributing to NF-κB activation (p65 and p-CamKII) were significantly reduced in the brain tissues of the Vim-/- mice with E. coli meningitis. Furthermore, Vim KO resulted in significant reduction in neuronal injury and in α7 nAChR-mediated calcium signaling. CONCLUSION/SIGNIFICANCE Vimentin, a novel NF-κB regulator, plays a detrimental role in the host defense against meningitic infection by modulating the NF-κB signaling pathway to increase pathogen invasion, PMN recruitment, BBB permeability and neuronal inflammation. Our findings provide the first evidence for Vim-dependent mechanisms underlying the pathogenic triad of bacterial meningitis.
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Affiliation(s)
- Sheng-He Huang
- Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
- Saban Research Institute of Childrens Hospital Los Angeles, Department of Pediatrics, University of Southern California, Los Angeles, California, United States of America
- Department of Microbiology, School of Public Health and Tropocal Medicine, Southern Medical University, Guangzhou 510515, China
- * E-mail: (YHZ); (SHH)
| | - Feng Chi
- Saban Research Institute of Childrens Hospital Los Angeles, Department of Pediatrics, University of Southern California, Los Angeles, California, United States of America
- Department of Pathology, Southern California Research Center for ALPD and Cirrhosis, the Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
| | - Liang Peng
- Saban Research Institute of Childrens Hospital Los Angeles, Department of Pediatrics, University of Southern California, Los Angeles, California, United States of America
- Department of Clinic Laboratory, the Second Affiliated Hospital of Guangzhou Medical University, Guangzhou 510260, China
| | - Tao Bo
- Saban Research Institute of Childrens Hospital Los Angeles, Department of Pediatrics, University of Southern California, Los Angeles, California, United States of America
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, China
| | - Bao Zhang
- Saban Research Institute of Childrens Hospital Los Angeles, Department of Pediatrics, University of Southern California, Los Angeles, California, United States of America
- Department of Microbiology, School of Public Health and Tropocal Medicine, Southern Medical University, Guangzhou 510515, China
| | - Li-Qun Liu
- Saban Research Institute of Childrens Hospital Los Angeles, Department of Pediatrics, University of Southern California, Los Angeles, California, United States of America
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, China
| | - Xuedong Wu
- Department of Pediatrics, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China
| | - Nirit Mor-Vaknin
- Department of Internal Medicine, Division of Infectious Diseases, 5220 MSRB III, 1150 West Medical Center Drive, University of Michigan, Ann Arbor, MI, United States of America
| | - David M. Markovitz
- Department of Internal Medicine, Division of Infectious Diseases, 5220 MSRB III, 1150 West Medical Center Drive, University of Michigan, Ann Arbor, MI, United States of America
| | - Hong Cao
- Department of Microbiology, School of Public Health and Tropocal Medicine, Southern Medical University, Guangzhou 510515, China
| | - Yan-Hong Zhou
- Hubei Bioinformatics and Molecular Imaging Key Laboratory, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
- * E-mail: (YHZ); (SHH)
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Kumar GA, Jafurulla M, Chattopadhyay A. The membrane as the gatekeeper of infection: Cholesterol in host-pathogen interaction. Chem Phys Lipids 2016; 199:179-185. [PMID: 26902688 DOI: 10.1016/j.chemphyslip.2016.02.007] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2016] [Revised: 02/13/2016] [Accepted: 02/15/2016] [Indexed: 11/30/2022]
Abstract
The cellular plasma membrane serves as a portal for the entry of intracellular pathogens. An essential step for an intracellular pathogen to gain entry into a host cell therefore is to be able to cross the cell membrane. In this review, we highlight the role of host membrane cholesterol in regulating the entry of intracellular pathogens using insights obtained from work on the interaction of Leishmania and Mycobacterium with host cells. The entry of these pathogens is known to be dependent on host membrane cholesterol. Importantly, pathogen entry is inhibited either upon depletion (or complexation), or enrichment of membrane cholesterol. In other words, an optimum level of host membrane cholesterol is necessary for efficient infection by pathogens. In this overall context, we propose a general mechanism, based on cholesterol-induced conformational changes, involving cholesterol binding sites in host cell surface receptors that are implicated in this process. A therapeutic strategy targeting modulation of membrane cholesterol would have the advantage of avoiding the commonly encountered problem of drug resistance in tackling infection by intracellular pathogens. Insights into the role of host membrane cholesterol in pathogen entry would be instrumental in the development of novel therapeutic strategies to effectively tackle intracellular pathogenesis.
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Affiliation(s)
- G Aditya Kumar
- CSIR-Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
| | - Md Jafurulla
- CSIR-Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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6
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Hawkes D, Jones KL, Smyth RP, Pereira CF, Bittman R, Jaworowski A, Mak J. Properties of HIV-1 associated cholesterol in addition to raft formation are important for virus infection. Virus Res 2015; 210:18-21. [DOI: 10.1016/j.virusres.2015.06.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Revised: 06/25/2015] [Accepted: 06/25/2015] [Indexed: 11/28/2022]
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7
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Viswanathan G, Jafurulla M, Kumar GA, Raghunand TR, Chattopadhyay A. Dissecting the membrane cholesterol requirement for mycobacterial entry into host cells. Chem Phys Lipids 2015; 189:19-27. [DOI: 10.1016/j.chemphyslip.2015.05.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Revised: 05/19/2015] [Accepted: 05/21/2015] [Indexed: 12/28/2022]
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8
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Zheng SJ, Qu F, Li JF, Zhao J, Zhang JY, Liu M, Ren F, Chen Y, Zhang JL, Duan ZP. Serum sphingomyelin has potential to reflect hepatic injury in chronic hepatitis B virus infection. Int J Infect Dis 2015; 33:149-55. [PMID: 25625177 DOI: 10.1016/j.ijid.2015.01.020] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2014] [Revised: 01/18/2015] [Accepted: 01/19/2015] [Indexed: 02/07/2023] Open
Abstract
OBJECTIVE To explore the relation between serum sphingolipids and hepatic injury in chronic HBV infection. METHODS A cohort of participants including 48 healthy persons, 103 chronic HBV-infected patients containing chronic hepatitis B (CHB) and HBV-related cirrhosis were included. High performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) was performed to detect serum sphingolipids. The serological indicators were detected and quantified. The valid liver biopsy specimens were acquired from twenty five CHB. RESULTS Twenty four serum sphingolipids were detected. There were eighteen sphingolipids showing significant differences between the healthy control and chronic HBV infection groups. In patients with chronic HBV infection, fourteen sphingolipids differed significantly between CHB and HBV-related cirrhosis. Among sphingolipids with a significant difference in both HBV infection vs healthy control and CHB vs cirrhosis, seven sphingolipids were independently related to the presence of cirrhosis. SM(d18:1/24:0), a sphingomyelin (SM) compound, was found to have a negative correlation with model for end-stage liver disease (MELD) score. Additionally, SM(d18:1/24:0) was demonstrated to have a correlation with inflammation grades by liver biopsy in CHB patients. CONCLUSIONS Serum sphingolipids have close relation with hepatic injury in chronic HBV infection, especially that SM(d18:1/24:0) might be a potential serum biomarker.
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Affiliation(s)
- Su-Jun Zheng
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Feng Qu
- State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Jun-Feng Li
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China; Institute of Infectious Diseases, Department of Infectious Diseases, the First Hospital of Lanzhou University, Lanzhou, China
| | - Jing Zhao
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Jing-Yun Zhang
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Mei Liu
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Feng Ren
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Yu Chen
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Jin-Lan Zhang
- State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.
| | - Zhong-Ping Duan
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China.
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9
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Li JF, Qu F, Zheng SJ, Ren JY, Wu HL, Liu M, Liu H, Ren F, Chen Y, Zhang JL, Duan ZP. Plasma sphingolipids as potential indicators of hepatic necroinflammation in patients with chronic hepatitis C and normal alanine aminotransferase level. PLoS One 2014; 9:e95095. [PMID: 24736528 PMCID: PMC3988168 DOI: 10.1371/journal.pone.0095095] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 03/23/2014] [Indexed: 01/05/2023] Open
Abstract
Accurate estimation of hepatic necroinflammation caused by chronic hepatitis C (CHC) is crucial for prediction of prognosis and design of therapeutic strategy, which is particularly true for CHC patients with normal alanine aminotransferase (ALT) level. Recent studies have shown that sphingolipids have a close relationship with hepatitis C virus infection. The present study aimed to identify plasma sphingolipids related to hepatic necroinflammation. We included 120 treatment-naïve CHC patients and 64/120 had normal ALT levels (<40 U/L). CHC patients who underwent liver biopsies were subjected to Scheuer scoring analysis for scope of hepatic inflammation. Plasma sphingolipids were detected by high-performance liquid chromatography tandem mass spectrometry. Our results showed 44 plasma sphingolipids were detected altogether. Of all detected sphingolipids, hexosylceramide (HexCer) (d18∶1/22∶0) and HexCer (d18∶1/24∶0) showed a significant difference among G0/G1, G2, and G3/G4 (P<0.05). For identifying hepatic necroinflammation (G≥2), after adjusting other factors, the odds ratio (OR) of HexCer (d18∶1/22∶0) reached 1.01 (95% confidence interval [CI]: 1.00–1.02). Furthermore, the area under the curve (AUC) of HexCer (d18∶1/22∶0) was 0.7 (P = 0.01) and approached that of ALT (AUC = 0.78). However, in CHC patients with normal ALT, HexCer (d18∶1/22∶0) was an independent factor (OR: 1.02, 95% CI: 1.01–1.03) to identify the hepatic necroinflammation (G≥2). HexCer (d18∶1/22∶0) not only showed the largest AUC (0.78, P = 0.001), but also exhibited the highest specificity of all indicators. These results indicate that plasma HexCer (d18∶1/22∶0) is a potential indicator to distinguish hepatic necroinflammation in CHC patients. For CHC with normal ALT, the ability of HexCer (d18∶1/22∶0) to distinguish hepatic necroinflammation might be superior to conventional serum indicators.
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Affiliation(s)
- Jun-Feng Li
- The First Clinical Medical School, Lanzhou University, Lanzhou, China
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Feng Qu
- State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
| | - Su-Jun Zheng
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Jin-Yu Ren
- Evergreen Wellness Center, Kansas College of Chinese Medicine, Wichita, Kansas, United States of America
| | - Hui-Li Wu
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Mei Liu
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Hui Liu
- Department of Pathology, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Feng Ren
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Yu Chen
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
| | - Jin-Lan Zhang
- State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China
- * E-mail: (ZPD); (JLZ)
| | - Zhong-Ping Duan
- Artificial Liver Center, Beijing YouAn Hospital, Capital Medical University, Beijing, China
- * E-mail: (ZPD); (JLZ)
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Chattopadhyay A, Jafurulla M. Role of membrane cholesterol in leishmanial infection. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 749:201-13. [PMID: 22695847 DOI: 10.1007/978-1-4614-3381-1_14] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Chattopadhyay A, Jafurulla M. A novel mechanism for an old drug: amphotericin B in the treatment of visceral leishmaniasis. Biochem Biophys Res Commun 2011; 416:7-12. [PMID: 22100811 DOI: 10.1016/j.bbrc.2011.11.023] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Accepted: 11/04/2011] [Indexed: 11/28/2022]
Abstract
Visceral leishmaniasis (VL) is caused by various species of the genus Leishmania. Internalization of Leishmania into host cells is facilitated by a large number of receptors, and therefore no panacea is available for the treatment of leishmaniasis. We previously demonstrated the requirement of host membrane cholesterol in the entry of Leishmania into macrophages by cholesterol depletion using methyl-β-cyclodextrin (MβCD). We recently showed that leishmanial infection is inhibited upon sequestration of host membrane cholesterol using amphotericin B (AmB), considered as the best existing drug against VL. The reason for the antileishmanial activity of AmB is generally believed to be its ability to bind ergosterol in parasite membranes. Our recent results offer the opportunity to reexamine the mechanism behind the effectiveness of current AmB-based therapeutic strategies to treat leishmaniasis. We propose here a novel mechanism in which the effectiveness of AmB treatment could be partly based on its ability to sequester cholesterol in the host membrane, thereby abrogating macrophage-parasite interaction.
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Affiliation(s)
- Amitabha Chattopadhyay
- Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Hyderabad 500 007, India.
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12
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Phospholipase-D activity and inflammatory response induced by brown spider dermonecrotic toxin: Endothelial cell membrane phospholipids as targets for toxicity. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1811:84-96. [DOI: 10.1016/j.bbalip.2010.11.005] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 11/10/2010] [Accepted: 11/11/2010] [Indexed: 11/17/2022]
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13
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In vitro characterization of the microglial inflammatory response to Streptococcus suis, an important emerging zoonotic agent of meningitis. Infect Immun 2010; 78:5074-85. [PMID: 20876287 DOI: 10.1128/iai.00698-10] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Streptococcus suis is an important swine and human pathogen responsible for septicemia and meningitis. In vivo research in mice suggested that in the brain, microglia might be involved in activating the inflammatory response against S. suis. The aim of this study was to better understand the interactions between S. suis and microglia. Murine microglial cells were infected with a virulent wild-type strain of S. suis. Two isogenic mutants deficient at either capsular polysaccharide (CPS) or hemolysin production were also included. CPS contributed to S. suis resistance to phagocytosis and regulated the inflammatory response by hiding proinflammatory components from the bacterial cell wall, while the absence of hemolysin, a potential cytotoxic factor, did not have a major impact on S. suis interactions with microglia. Wild-type S. suis induced enhanced expression of Toll-like receptor 2 by microglial cells, as well as phosphotyrosine, protein kinase C, and different mitogen-activated protein kinase signaling events. However, cells infected with the CPS-deficient mutant showed overall stronger and more sustained phosphorylation profiles. CPS also modulated inducible nitric oxide synthase expression and further nitric oxide production from S. suis-infected microglia. Finally, S. suis-induced NF-κB translocation was faster for cells stimulated with the CPS-deficient mutant, suggesting that bacterial cell wall components are potent inducers of NF-κB. These results contribute to increase the knowledge of mechanisms underlying S. suis inflammation in the brain and will be useful in designing more efficient anti-inflammatory strategies for meningitis.
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Amano A, Furuta N, Tsuda K. Host membrane trafficking for conveyance of intracellular oral pathogens. Periodontol 2000 2010; 52:84-93. [PMID: 20017797 DOI: 10.1111/j.1600-0757.2009.00309.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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15
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Vieira FS, Corrêa G, Einicker-Lamas M, Coutinho-Silva R. Host-cell lipid rafts: a safe door for micro-organisms? Biol Cell 2010; 102:391-407. [PMID: 20377525 PMCID: PMC7161784 DOI: 10.1042/bc20090138] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Accepted: 02/10/2010] [Indexed: 12/20/2022]
Abstract
The lipid raft hypothesis proposed that these microdomains are small (10-200 nM), highly dynamic and enriched in cholesterol, glycosphingolipids and signalling phospholipids, which compartmentalize cellular processes. These membrane regions play crucial roles in signal transduction, phagocytosis and secretion, as well as pathogen adhesion/interaction. Throughout evolution, many pathogens have developed mechanisms to escape from the host immune system, some of which are based on the host membrane microdomain machinery. Thus lipid rafts might be exploited by pathogens as signalling and entry platforms. In this review, we summarize the role of lipid rafts as players in the overall invasion process used by different pathogens to escape from the host immune system.
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Affiliation(s)
- Flávia Sarmento Vieira
- Laboratório de Imunofisiologia, Universidade Federal do Rio de Janeiro, Instituto de Biofísica Carlos Chagas Filho, CCS, Rio de Janeiro, RJ, Brazil
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Vimentin-mediated signalling is required for IbeA+ E. coli K1 invasion of human brain microvascular endothelial cells. Biochem J 2010; 427:79-90. [PMID: 20088823 DOI: 10.1042/bj20091097] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
IbeA in meningitic Escherichia coli K1 strains has been described previously for its role in invasion of BMECs (brain microvascular endothelial cells). Vimentin was identified as an IbeA-binding protein on the surface of HBMECs (human BMECs). In the present study, we demonstrated that vimentin is a primary receptor required for IbeA+ E. coli K1-induced signalling and invasion of HBMECs, on the basis of the following observations. First, E44 (IbeA+ E. coli K1 strain) invasion was blocked by vimentin inhibitors (withaferin A and acrylamide), a recombinant protein containing the vimentin head domain and an antibody against the head domain respectively. Secondly, overexpression of GFP (green fluorescent protein)-vimentin and GFP-VDM (vimentin head domain deletion mutant) significantly increased and decreased bacterial invasion respectively. Thirdly, bacterial invasion was positively correlated with phosphorylation of vimentin at Ser82 by CaMKII (Ca2+/calmodulin-dependent protein kinase II) and IbeA+ E. coli-induced phosphorylation of ERK (extracellular-signal-regulated kinase). Blockage of CaMKII by KN93 and inhibition of ERK1/2 phosphorylation by PD098059 resulted in reduced IbeA+ E. coli invasion. Fourthly, IbeA+ E. coli and IbeA-coated beads induced the clustering of vimentin that was correlated with increased entry of bacteria and beads. Lastly, IbeA+ E. coli K1 invasion was inhibited by lipid-raft-disrupting agents (filipin and nystatin) and caveolin-1 siRNA (small interfering RNA), suggesting that caveolae/lipid rafts are signalling platforms for inducing IbeA-vimentin-mediated E. coli invasion of HBMECs. Taken together, the present studies suggest that a dynamic and function-related interaction between IbeA and its primary receptor vimentin at HBMEC membrane rafts leads to vimentin phosphorylation and ERK-mediated signalling, which modulate meningitic E. coli K1 invasion.
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Porphyromonas gingivalis outer membrane vesicles enter human epithelial cells via an endocytic pathway and are sorted to lysosomal compartments. Infect Immun 2009; 77:4187-96. [PMID: 19651865 DOI: 10.1128/iai.00009-09] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Porphyromonas gingivalis, a periodontal pathogen, secretes outer membrane vesicles (MVs) that contain major virulence factors, including major fimbriae and proteases termed gingipains, although it is not confirmed whether MVs enter host cells. In this study, we analyzed the mechanisms involved in the interactions of P. gingivalis MVs with human epithelial cells. Our results showed that MVs swiftly adhered to HeLa and immortalized human gingival epithelial cells in a fimbria-dependent manner and then entered via a lipid raft-dependent endocytic pathway. The intracellular MVs were subsequently routed to early endosome antigen 1-associated compartments and then were sorted to lysosomal compartments within 90 min, suggesting that intracellular MVs were ultimately degraded by the cellular digestive machinery. However, P. gingivalis MVs remained there for over 24 h and significantly induced acidified compartment formation after being taken up by the cellular digestive machinery. In addition, MV entry was shown to be mediated by a novel pathway for transmission of bacterial products into host cells, a Rac1-regulated pinocytic pathway that is independent of caveolin, dynamin, and clathrin. Our findings indicate that P. gingivalis MVs efficiently enter host cells via an endocytic pathway and survive within the endocyte organelles for an extended period, which provides better understanding of the role of MVs in the etiology of periodontitis.
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French CT, Panina EM, Yeh SH, Griffith N, Arambula DG, Miller JF. The Bordetella type III secretion system effector BteA contains a conserved N-terminal motif that guides bacterial virulence factors to lipid rafts. Cell Microbiol 2009; 11:1735-49. [PMID: 19650828 PMCID: PMC2788067 DOI: 10.1111/j.1462-5822.2009.01361.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Bordetella type III secretion system (T3SS) effector protein BteA is necessary and sufficient for rapid cytotoxicity in a wide range of mammalian cells. We show that BteA is highly conserved and functionally interchangeable between Bordetella bronchiseptica, Bordetella pertussis and Bordetella parapertussis. The identification of BteA sequences required for cytotoxicity allowed the construction of non-cytotoxic mutants for localization studies. BteA derivatives were targeted to lipid rafts and showed clear colocalization with cortical actin, ezrin and the lipid raft marker GM1. We hypothesized that BteA associates with the cytoplasmic face of lipid rafts to locally modulate host cell responses to Bordetella attachment. B. bronchiseptica adhered to host cells almost exclusively to GM1-enriched lipid raft microdomains and BteA colocalized to these same sites following T3SS-mediated translocation. Disruption of lipid rafts with methyl-beta-cyclodextrin protected cells from T3SS-induced cytotoxicity. Localization to lipid rafts was mediated by a 130-amino-acid lipid raft targeting domain at the N-terminus of BteA, and homologous domains were identified in virulence factors from other bacterial species. Lipid raft targeting sequences from a T3SS effector (Plu4750) and an RTX-type toxin (Plu3217) from Photorhabdus luminescens directed fusion proteins to lipid rafts in a manner identical to the N-terminus of BteA.
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Affiliation(s)
- Christopher T French
- Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
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Myelin, DIGs, and membrane rafts in the central nervous system. Prostaglandins Other Lipid Mediat 2009; 91:118-29. [PMID: 19379822 DOI: 10.1016/j.prostaglandins.2009.04.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Revised: 04/08/2009] [Accepted: 04/09/2009] [Indexed: 11/21/2022]
Abstract
Over the past 40 years our understanding of the organization of cell membranes has changed dramatically. Membranes are no longer viewed as a homogenous sea of phospholipids studded with randomly positioned islands of proteins. Our current view of the membrane involves the formation of small lipid clusters, comprised mainly of cholesterol and sphingolipids, known as membrane rafts. These lipid clusters apparently include and exclude specific proteins leading to the hypothesis that these domains (1) regulate cellular polarity and compartmentalization through trafficking and sorting, (2) provide platforms for cellular signaling and adhesion, and (3) function as cellular gate keepers. Tremendous controversy surrounds the concept of membrane rafts primarily because these small, highly dynamic entities are too small to be observed with traditional microscopic methods and the most utilized approach for raft analysis relies on poorly quantified, inconsistent biochemical extractions. New analytical approaches are being developed and applied to the study of membrane rafts and these techniques provide great promise for furthering our understanding of these enigmatic domains. In this review we will provide a brief summary of the current understanding of membrane rafts, utilizing the CNS myelin literature for illustrative purposes, and present caveats that should be considered when studying these domains.
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Yi F, Jin S, Li PL. Lipid raft-redox signaling platforms in plasma membrane. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2009; 580:93-107. [PMID: 19784595 DOI: 10.1007/978-1-60761-325-1_5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Membrane lipid rafts (LRs) have been demonstrated to be importantly involved in transmembrane signaling in a variety of mammalian cells. Many receptors can be aggregated within the LR clusters to form signaling platforms. Currently, LRs were reported to be clustered to aggregate, recruit, and assemble NADPH oxidase subunits and related proteins in various cells in response to various stimuli, forming redox signaling platforms. These LR signaling platforms may play important roles in the regulation of cellular activity and cell function, and also in the development of cell dysfunction or injury associated with various pathological stimuli. This LRs clustering-mediated mechanism is considered to take a center stage in redox signaling associated with death receptors. In this chapter, some basic methods and procedures for characterization of LR-redox signaling platforms formation and for determination of the function of these signaling platforms are described in detail, which include identification of LR-redox signaling platforms in cell membrane by using fluorescent or confocal microscopy of LR-redox signaling platforms and fluorescent resonance energy transfer analysis, isolation of LR-redox signaling platforms by flotation of detergent-resistant membranes, and function measurement of LR-redox signaling platforms by electron spin resonance spectroscopy. It is expected that information provided here will help readers to design necessary experiments in their studies on LR signaling platforms and redox regulation of cell function.
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Affiliation(s)
- Fan Yi
- Department of Pharmacology & Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA, USA
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Abstract
The current paradigm for managing infectious diseases has targeted unique processes or enzymes within pathogens. A serious disadvantage of this pathogen-directed drug targeting strategy has been the development of microbial drug resistance and consequent resurgence of once-contained infectious diseases. A new drug discovery paradigm has therefore emerged focusing on identifying and targeting host factors essential for pathogen entry, survival, and replication. Innovative strategies combining genome-wide computational biology, genomics, proteomics, and traditional forward and reverse genetics have identified host-pathogen interactions and host functions critical for the establishment of infection. Chemogenomics and chemical genetics have allowed rapid identification of new and existing licensed drugs with antimicrobial activity. Although most host-directed drug targeting studies have focused on viral infections, they have provided a proof of concept for similar approaches to bacterial and parasite infections. Future therapies may combine conventional targeting of microbial virulence factors, together with host-directed drug therapy and augmentation of protective host factors, to efficiently eliminate the invading pathogen.
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Affiliation(s)
- Anita Schwegmann
- Division of Immunology, Institute of Infectious Diseases and Molecular Medicine, Faculty of Health Sciences, University of Cape Town and The International Centre for Genetic Engineering and Biotechnology, Cape Town, South Africa.
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Zaidi T, Bajmoczi M, Zaidi T, Golan DE, Pier GB. Disruption of CFTR-dependent lipid rafts reduces bacterial levels and corneal disease in a murine model of Pseudomonas aeruginosa keratitis. Invest Ophthalmol Vis Sci 2008; 49:1000-9. [PMID: 18326723 DOI: 10.1167/iovs.07-0993] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
PURPOSE Pseudomonas aeruginosa enters corneal epithelial cells in vitro via membrane microdomains or lipid rafts. Bacterial entry, mediated by the cystic fibrosis transmembrane conductance regulator (CFTR), promotes infection and disease. This study was conducted to determine whether P. aeruginosa and CFTR are colocalized to rafts in isogenic corneal cells expressing wild-type (WT) or mutant DeltaF508-CFTR and whether disruption of the rafts both in vitro and in vivo affects the bacterial levels and the course of the disease. METHODS Transformed human corneal epithelial cells from a patient homozygous for DeltaF508-CFTR, and the same cells corrected with WT-CFTR, were exposed to six isolates of P. aeruginosa-three invasive and three cytotoxic strains-in the presence of beta-cyclodextrin (CD), which disrupts rafts. Association and cellular uptake of the invasive strains were measured, as was lactate dehydrogenase release induced by the cytotoxic strains. Scratch-injured mouse eyes were infected with the six P. aeruginosa strains, and the effect of prophylactic or therapeutic administration of CD on bacterial levels and disease was evaluated. RESULTS P. aeruginosa and CFTR were colocalized with lipid rafts in cells with WT-CFTR, and CD treatment of these cells disrupted bacterial association, internalization, and cytotoxic effects. Cells expressing DeltaF508-CFTR were marginally affected by CD. Prophylactic and therapeutic topical application of CD ameliorated corneal disease and reduced the bacterial count in the eye. CONCLUSIONS P. aeruginosa enters human corneal epithelial cells via lipid rafts containing CFTR, and disruption of raft-mediated uptake of this organism by CD protects against disease and reduces bacterial levels in the mouse model of keratitis.
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Affiliation(s)
- Tanweer Zaidi
- Channing Laboratory and Hematology Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
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Interactions between the products of the Herpes simplex genome and Alzheimer's disease susceptibility genes: relevance to pathological-signalling cascades. Neurochem Int 2007; 52:920-34. [PMID: 18164103 DOI: 10.1016/j.neuint.2007.11.003] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Revised: 11/08/2007] [Accepted: 11/19/2007] [Indexed: 01/07/2023]
Abstract
The products of the Herpes simplex (HSV-1) genome interact with many Alzheimer's disease susceptibility genes or proteins. These in turn affect those of the virus. For example, HSV-1 binds to heparan sulphate proteoglycans (HSPG2), or alpha-2-macroglobulin (A2M), and enters cells via nectin receptors, which are cleaved by gamma-secretase (APH1B, PSEN1, PSEN2, PEN2, NCSTN). The virus also binds to blood-borne lipoproteins and apolipoprotein E (APOE) is able to modify its infectivity. Viral uptake is cholesterol- and lipid raft-dependent (DHCR24, HMGCR, FDPS, RAFTLIN, SREBF1). The virus is transported to the nucleus via the dynein and kinesin (KNS2) motors associated with the microtubule network (MAPT). Amyloid precursor protein (APP) plays a role in this transport. Nuclear export is mediated via disruption of the nuclear lamina and binding to LMNA. Herpes simplex activates kinases (CDC2 and casein kinase 2) whose substrates include APOE, APP, MAPT, PSEN2, and SREBF1. A viral protein is also able to delete mitochondrial DNA, a situation prevalent in Alzheimer's disease. The virus binds to the host transcription factors transcription factor CP2 (TFCP2) and POU2F1 that control many other genes associated with Alzheimer's disease. Viral latency is controlled by IL6 and IL1B and at different stages of its life cycle the virus can either promote or attenuate apoptosis via Fas and tumor necrosis factor pathways (FAS, TNF, DAPK1, PARP1). Viral evasion strategies include inhibition of the antigen processor TAP2, the production of an Fc immunoglobulin receptor mimic (FCER1G) and inhibition of the viral-activated kinase EIF2AK2. These and other host/viral interactions, targeted to certain Alzheimer's disease susceptibility genes, support the idea that some form of synergy between the pathogen and genetic factors may play a role in the pathology of late-onset Alzheimer's disease.
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Teissier É, Pécheur EI. Lipids as modulators of membrane fusion mediated by viral fusion proteins. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:887-99. [PMID: 17882414 PMCID: PMC7080115 DOI: 10.1007/s00249-007-0201-z] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Revised: 05/17/2007] [Accepted: 06/11/2007] [Indexed: 11/24/2022]
Abstract
Enveloped viruses infect host cells by fusion of viral and target membranes. This fusion event is triggered by specific glycoproteins in the viral envelope. Fusion glycoproteins belong to either class I, class II or the newly described third class, depending upon their arrangement at the surface of the virion, their tri-dimensional structure and the location within the protein of a short stretch of hydrophobic amino acids called the fusion peptide, which is able to induce the initial lipid destabilization at the onset of fusion. Viral fusion occurs either with the plasma membrane for pH-independent viruses, or with the endosomal membranes for pH-dependent viruses. Although, viral fusion proteins are parted in three classes and the subcellular localization of fusion might vary, these proteins have to act, in common, on lipid assemblies. Lipids contribute to fusion through their physical, mechanical and/or chemical properties. Lipids can thus play a role as chemically defined entities, or through their preferential partitioning into membrane microdomains called “rafts”, or by modulating the curvature of the membranes involved in the fusion process. The purpose of this review is to make a state of the art on recent findings on the contribution of cholesterol, sphingolipids and glycolipids in cell entry and membrane fusion of a number of viral families, whose members bear either class I or class II fusion proteins, or fusion proteins of the recently discovered third class.
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Affiliation(s)
- Élodie Teissier
- Structural NMR and Bioinformatics, UMR CNRS 5086, Institut de Biologie et Chimie des Protéines, IFR 128 BioSciences Lyon-Gerland, 7 passage du Vercors, 69367 Lyon, France
| | - Eve-Isabelle Pécheur
- Structural NMR and Bioinformatics, UMR CNRS 5086, Institut de Biologie et Chimie des Protéines, IFR 128 BioSciences Lyon-Gerland, 7 passage du Vercors, 69367 Lyon, France
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Aguilar HC, Matreyek KA, Choi DY, Filone CM, Young S, Lee B. Polybasic KKR motif in the cytoplasmic tail of Nipah virus fusion protein modulates membrane fusion by inside-out signaling. J Virol 2007; 81:4520-32. [PMID: 17301148 PMCID: PMC1900187 DOI: 10.1128/jvi.02205-06] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The cytoplasmic tails of the envelope proteins from multiple viruses are known to contain determinants that affect their fusogenic capacities. Here we report that specific residues in the cytoplasmic tail of the Nipah virus fusion protein (NiV-F) modulate its fusogenic activity. Truncation of the cytoplasmic tail of NiV-F greatly inhibited cell-cell fusion. Deletion and alanine scan analysis identified a tribasic KKR motif in the membrane-adjacent region as important for modulating cell-cell fusion. The K1A mutation increased fusion 5.5-fold, while the K2A and R3A mutations decreased fusion 3- to 5-fold. These results were corroborated in a reverse-pseudotyped viral entry assay, where receptor-pseudotyped reporter virus was used to infect cells expressing wild-type or mutant NiV envelope glycoproteins. Differential monoclonal antibody binding data indicated that hyper- or hypofusogenic mutations in the KKR motif affected the ectodomain conformation of NiV-F, which in turn resulted in faster or slower six-helix bundle formation, respectively. However, we also present evidence that the hypofusogenic phenotypes of the K2A and R3A mutants were effected via distinct mechanisms. Interestingly, the K2A mutant was also markedly excluded from lipid rafts, where approximately 20% of wild-type F and the other mutants can be found. Finally, we found a strong negative correlation between the relative fusogenic capacities of these cytoplasmic-tail mutants and the avidities of NiV-F and NiV-G interactions (P = 0.007, r(2) = 0.82). In toto, our data suggest that inside-out signaling by specific residues in the cytoplasmic tail of NiV-F can modulate its fusogenicity by multiple distinct mechanisms.
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Affiliation(s)
- Hector C Aguilar
- Department of Microbiology, Immunology, and Molecular Genetics, David Geffen School of Medicine, University of California at Los Angeles, 609 Charles E. Young Drive East, Los Angeles, CA 90095, USA
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