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Tang H, Wang R, Pang S, Han W, Zhang Q, Fang Q, Chen X, Huang Q, Qiu D, Zhou R, Li L. Native ApxIIA secreted by Actinobacillus pleuropneumoniae induces apoptosis in porcine alveolar macrophages dependent on concentration and acylation. Vet Microbiol 2023; 287:109908. [PMID: 37952264 DOI: 10.1016/j.vetmic.2023.109908] [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: 02/10/2023] [Revised: 10/27/2023] [Accepted: 10/30/2023] [Indexed: 11/14/2023]
Abstract
Actinobacillus pleuropneumoniae is an important swine respiratory pathogen causing substantial economic losses to the global pig industry. The Apx toxins of A. pleuropneumoniae belong to the RTX toxin family and are major virulence factors. In addition to hemolysis and/or cytotoxicity via pore-forming activity, RTX toxins, such as ApxIA of A. pleuropneumoniae, have been reported to cause other effects on target cells, e.g., apoptosis. A. pleuropneumoniae ApxIIA is expressed by most serotypes and has moderate hemolytic and cytotoxic activities. In this study, porcine alveolar macrophages (3D4/21) were stimulated with different concentrations of purified native ApxIIA from the serotype 7 strain AP76 which only secretes ApxIIA. By observation of nuclear condensation via fluorescent staining and detection of apoptosis and necrosis by flow cytometry, it was found that high and low concentrations of native ApxIIA mainly caused necrosis or apoptosis of 3D4/21 cells, respectively. ApxIIA purified from an AP76 mutant with a deleted acetyltransferase gene (apxIIC) did not induce necrosis nor apoptosis. Western blot analysis using specific antibodies showed that a cleaved caspase 3 and activated capase 9 was detected after treatment of cells with a low concentration of native ApxIIA, while general or specific inhibitors of caspase 3, 8, 9 blocked these effects. ApxIIA-induced apoptosis of macrophages may be a mechanism of A. pleuropneumoniae to escape host immune clearance.
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Affiliation(s)
- Hao Tang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Rong Wang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Siqi Pang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Weiyao Han
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Qiuhong Zhang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Qiong Fang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Xiabing Chen
- Institute of Animal Husbandry and Veterinary Science, Wuhan Academy of Agricultural Sciences, Wuhan, Hubei 430070, China
| | - Qi Huang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China; International Research Center for Animal Disease, Ministry of Science and Technology of the People's Republic of China, Wuhan, Hubei 430070, China
| | - Dexin Qiu
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China
| | - Rui Zhou
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China; International Research Center for Animal Disease, Ministry of Science and Technology of the People's Republic of China, Wuhan, Hubei 430070, China
| | - Lu Li
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China; International Research Center for Animal Disease, Ministry of Science and Technology of the People's Republic of China, Wuhan, Hubei 430070, China.
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Chacko FM, Schmitt L. Interaction of RTX toxins with the host cell plasma membrane. Biol Chem 2023:hsz-2022-0336. [PMID: 36907826 DOI: 10.1515/hsz-2022-0336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 02/27/2023] [Indexed: 03/14/2023]
Abstract
Repeats in ToXins (RTX) protein family is a group of exoproteins secreted by Type 1 secretion system (T1SS) of several Gram-negative bacteria. The term RTX is derived from the characteristic nonapeptide sequence (GGxGxDxUx) present at the C-terminus of the protein. This RTX domain binds to calcium ions in the extracellular medium after being secreted out of the bacterial cells, and this facilitates folding of the entire protein. The secreted protein then binds to the host cell membrane and forms pores via a complex pathway, which eventually leads to the cell lysis. In this review, we summarize two different pathways in which RTX toxins interact with host cell membrane and discuss the possible reasons for specific and unspecific activity of RTX toxins to different types of host cells.
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Affiliation(s)
- Feby M Chacko
- Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany
| | - Lutz Schmitt
- Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany
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Filipi K, Rahman WU, Osickova A, Osicka R. Kingella kingae RtxA Cytotoxin in the Context of Other RTX Toxins. Microorganisms 2022; 10:microorganisms10030518. [PMID: 35336094 PMCID: PMC8953716 DOI: 10.3390/microorganisms10030518] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 02/22/2022] [Accepted: 02/24/2022] [Indexed: 12/04/2022] Open
Abstract
The Gram-negative bacterium Kingella kingae is part of the commensal oropharyngeal flora of young children. As detection methods have improved, K. kingae has been increasingly recognized as an emerging invasive pathogen that frequently causes skeletal system infections, bacteremia, and severe forms of infective endocarditis. K. kingae secretes an RtxA cytotoxin, which is involved in the development of clinical infection and belongs to an ever-growing family of cytolytic RTX (Repeats in ToXin) toxins secreted by Gram-negative pathogens. All RTX cytolysins share several characteristic structural features: (i) a hydrophobic pore-forming domain in the N-terminal part of the molecule; (ii) an acylated segment where the activation of the inactive protoxin to the toxin occurs by a co-expressed toxin-activating acyltransferase; (iii) a typical calcium-binding RTX domain in the C-terminal portion of the molecule with the characteristic glycine- and aspartate-rich nonapeptide repeats; and (iv) a C-proximal secretion signal recognized by the type I secretion system. RTX toxins, including RtxA from K. kingae, have been shown to act as highly efficient ‘contact weapons’ that penetrate and permeabilize host cell membranes and thus contribute to the pathogenesis of bacterial infections. RtxA was discovered relatively recently and the knowledge of its biological role remains limited. This review describes the structure and function of RtxA in the context of the most studied RTX toxins, the knowledge of which may contribute to a better understanding of the action of RtxA in the pathogenesis of K. kingae infections.
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Sun H, Niu Q, Yang J, Zhao Y, Tian Z, Fan J, Zhang Z, Wang Y, Geng S, Zhang Y, Guan G, Williams DT, Luo J, Yin H, Liu Z. Transcriptome Profiling Reveals Features of Immune Response and Metabolism of Acutely Infected, Dead and Asymptomatic Infection of African Swine Fever Virus in Pigs. Front Immunol 2022; 12:808545. [PMID: 34975923 PMCID: PMC8714921 DOI: 10.3389/fimmu.2021.808545] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 11/29/2021] [Indexed: 12/16/2022] Open
Abstract
African swine fever virus (ASFV) infection can result in lethal disease in pigs. ASFV encodes 150-167 proteins, of which only approximately 50 encoded viral structure proteins are functionally known. ASFV also encodes some nonstructural proteins that are involved in the regulation of viral transcription, viral replication and evasion from host defense. However, the understanding of the molecular correlates of the severity of these infections is still limited. The purpose of this study was to compare host and viral gene expression differences and perform functional analysis in acutely infected, dead and cohabiting asymptomatic pigs infected with ASFV by using RNA-Seq technique; healthy pigs were used as controls. A total of 3,760 and 2,874 upregulated genes and 4,176 and 2,899 downregulated genes were found in healthy pigs vs. acutely infected, dead pigs or asymptomatic pigs, respectively. Additionally, 941 upregulated genes and 956 downregulated genes were identified in asymptomatic vs. acutely infected, dead pigs. Different alternative splicing (AS) events were also analyzed, as were gene chromosome locations, and protein-protein interaction (PPI) network prediction analysis was performed for significantly differentially expressed genes (DEGs). In addition, 30 DEGs were validated by RT-qPCR, and the results were consistent with the RNA-Seq results. We further analyzed the interaction between ASFV and its host at the molecular level and predicted the mechanisms responsible for asymptomatic pigs based on the selected DEGs. Interestingly, we found that some viral genes in cohabiting asymptomatic pigs might integrate into host genes (DP96R, I73R and L83L) or remain in the tissues of cohabiting asymptomatic pigs. In conclusion, the data obtained in the present study provide new evidence for further elucidating ASFV-host interactions and the ASFV infection mechanism and will facilitate the implementation of integrated strategies for controlling ASF spread.
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Affiliation(s)
- Hualin Sun
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Qingli Niu
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Jifei Yang
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Yaru Zhao
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Zhancheng Tian
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Jie Fan
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Zhonghui Zhang
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Yiwang Wang
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Shuxian Geng
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Yulong Zhang
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Guiquan Guan
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - David T Williams
- Commonwealth Scientific and Industrial Research Organization (CSIRO) Australian Centre for Disease Preparedness, Geelong, VIC, Australia
| | - Jianxun Luo
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
| | - Hong Yin
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Zhijie Liu
- African Swine Fever Regional Laboratory, China (Lanzhou) and State Key Laboratory of Veterinary Etiological Biology and Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China
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Li SC, Cheng YT, Wang CY, Wu JY, Chen ZW, Wang JP, Lin JH, Hsuan SL. Actinobacillus pleuropneumoniae exotoxin ApxI induces cell death via attenuation of FAK through LFA-1. Sci Rep 2021; 11:1753. [PMID: 33462305 PMCID: PMC7813829 DOI: 10.1038/s41598-021-81290-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 01/05/2021] [Indexed: 01/15/2023] Open
Abstract
ApxI exotoxin is an important virulence factor derived from Actinobacillus pleuropneumoniae that causes pleuropneumonia in swine. Here, we investigate the role of lymphocyte function-associated antigen 1 (LFA-1, CD11a/CD18), a member of the β2 integrin family, and the involvement of the integrin signaling molecules focal adhesion kinase (FAK) and Akt in ApxI cytotoxicity. Using Western blot analysis, we found that ApxI downregulated the activity of FAK and Akt in porcine alveolar macrophages (AMs). Preincubation of porcine AMs with an antibody specific for porcine CD18 reduced ApxI-induced cytotoxicity as measured by a lactate dehydrogenase release assay and decreased ApxI-induced FAK and Akt attenuation, as shown by Western blot analysis. Pretreatment with the chemical compounds PMA and SC79, which activate FAK and Akt, respectively, failed to overcome the ApxI-induced attenuation of FAK and Akt and death of porcine AMs. Notably, the transfection experiments revealed that ectopic expression of porcine LFA-1 (pLFA-1) conferred susceptibility to ApxI in ApxI-insensitive cell lines, including human embryonic kidney 293T cells and FAK-deficient mouse embryonic fibroblasts (MEFs). Furthermore, ectopic expression of FAK significantly reduced ApxI cytotoxicity in pLFA-1-cotransfected FAK-deficient MEFs. These findings show for the first time that pLFA-1 renders cells susceptible to ApxI and ApxI-mediated attenuation of FAK activity via CD18, thereby contributing to subsequent cell death.
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Affiliation(s)
- Siou-Cen Li
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, Taichung City, 402, Taiwan.,Animal Technology Laboratories, Agricultural Technology Research Institute, Hsinchu City, 300, Taiwan
| | - Yu-Tsen Cheng
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, Taichung City, 402, Taiwan
| | - Ching-Yang Wang
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, Taichung City, 402, Taiwan
| | - Jia-Ying Wu
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, Taichung City, 402, Taiwan
| | - Zeng-Weng Chen
- Animal Technology Laboratories, Agricultural Technology Research Institute, Hsinchu City, 300, Taiwan
| | - Jyh-Perng Wang
- Animal Technology Laboratories, Agricultural Technology Research Institute, Hsinchu City, 300, Taiwan
| | - Jiunn-Horng Lin
- Animal Technology Laboratories, Agricultural Technology Research Institute, Hsinchu City, 300, Taiwan
| | - Shih-Ling Hsuan
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, Taichung City, 402, Taiwan.
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Krueger E, Brown AC. Aggregatibacter actinomycetemcomitans leukotoxin: From mechanism to targeted anti-toxin therapeutics. Mol Oral Microbiol 2020; 35:85-105. [PMID: 32061022 DOI: 10.1111/omi.12284] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Revised: 02/12/2020] [Accepted: 02/13/2020] [Indexed: 12/13/2022]
Abstract
Aggregatibacter actinomycetemcomitans is a Gram-negative bacterium associated with localized aggressive periodontitis, as well as other systemic diseases. This organism produces a number of virulence factors, all of which provide some advantage to the bacterium. Several studies have demonstrated that clinical isolates from diseased patients, particularly those of African descent, frequently belong to specific clones of A. actinomycetemcomitans that produce significantly higher amounts of a protein exotoxin belonging to the repeats-in-toxin (RTX) family, leukotoxin (LtxA), whereas isolates from healthy patients harbor minimally leukotoxic strains. This finding suggests that LtxA might play a key role in A. actinomycetemcomitans pathogenicity. Because of this correlation, much work over the past 30 years has been focused on understanding the mechanisms by which LtxA interacts with and kills host cells. In this article, we review those findings, highlight the remaining open questions, and demonstrate how knowledge of these mechanisms, particularly the toxin's interactions with lymphocyte function-associated antigen-1 (LFA-1) and cholesterol, enables the design of targeted anti-LtxA strategies to prevent/treat disease.
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Affiliation(s)
- Eric Krueger
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA, USA
| | - Angela C Brown
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA, USA
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RTX Toxins Ambush Immunity's First Cellular Responders. Toxins (Basel) 2019; 11:toxins11120720. [PMID: 31835552 PMCID: PMC6950748 DOI: 10.3390/toxins11120720] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 12/05/2019] [Accepted: 12/07/2019] [Indexed: 01/17/2023] Open
Abstract
The repeats-in-toxin (RTX) family represents a unique class of bacterial exoproteins. The first family members described were toxins from Gram-negative bacterial pathogens; however, additional members included exoproteins with diverse functions. Our review focuses on well-characterized RTX family toxins from Aggregatibacteractinomycetemcomitans (LtxA), Mannheimiahaemolytica (LktA), Bordetella pertussis (CyaA), uropathogenic Escherichia coli (HlyA), and Actinobacillus pleuropneumoniae (ApxIIIA), as well as the studies that have honed in on a single host cell receptor for RTX toxin interactions, the β2 integrins. The β2 integrin family is composed of heterodimeric members with four unique alpha subunits and a single beta subunit. β2 integrins are only found on leukocytes, including neutrophils and monocytes, the first responders to inflammation following bacterial infection. The LtxA, LktA, HlyA, and ApxIIIA toxins target the shared beta subunit, thereby targeting all types of leukocytes. Specific β2 integrin family domains are required for the RTX toxin’s cytotoxic activity and are summarized here. Research examining the domains of the RTX toxins required for cytotoxic and hemolytic activity is also summarized. RTX toxins attack and kill phagocytic immune cells expressing a single integrin family, providing an obvious advantage to the pathogen. The critical question that remains, can the specificity of the RTX-β2 integrin interaction be therapeutically targeted?
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Frey J. RTX Toxins of Animal Pathogens and Their Role as Antigens in Vaccines and Diagnostics. Toxins (Basel) 2019; 11:toxins11120719. [PMID: 31835534 PMCID: PMC6950323 DOI: 10.3390/toxins11120719] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 12/03/2019] [Accepted: 12/04/2019] [Indexed: 01/19/2023] Open
Abstract
Exotoxins play a central role in the pathologies caused by most major bacterial animal pathogens. The large variety of vertebrate and invertebrate hosts in the animal kingdom is reflected by a large variety of bacterial pathogens and toxins. The group of repeats in the structural toxin (RTX) toxins is particularly abundant among bacterial pathogens of animals. Many of these toxins are described as hemolysins due to their capacity to lyse erythrocytes in vitro. Hemolysis by RTX toxins is due to the formation of cation-selective pores in the cell membrane and serves as an important marker for virulence in bacterial diagnostics. However, their physiologic relevant targets are leukocytes expressing β2 integrins, which act as specific receptors for RTX toxins. For various RTX toxins, the binding to the CD18 moiety of β2 integrins has been shown to be host specific, reflecting the molecular basis of the host range of RTX toxins expressed by bacterial pathogens. Due to the key role of RTX toxins in the pathogenesis of many bacteria, antibodies directed against specific RTX toxins protect against disease, hence, making RTX toxins valuable targets in vaccine research and development. Due to their specificity, several structural genes encoding for RTX toxins have proven to be essential in modern diagnostic applications in veterinary medicine.
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Affiliation(s)
- Joachim Frey
- Vetsuisse Facutly, University of Bern, 3012 Bern, Switzerland
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To H, Nagai S, Iwata A, Koyama T, Oshima A, Tsutsumi N. Genetic and antigenic characteristics of ApxIIA and ApxIIIA from Actinobacillus pleuropneumoniae serovars 2, 3, 4, 6, 8 and 15. Microbiol Immunol 2017; 60:447-58. [PMID: 27211905 DOI: 10.1111/1348-0421.12388] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 04/21/2016] [Accepted: 05/16/2016] [Indexed: 11/30/2022]
Abstract
Apx toxins produced by Actinobacillus pleuropneumoniae are essential components of new generation vaccines. In this study, apxIIA and apxIIIA genes of serovars 2, 3, 4, 6, 8 and 15 were cloned and sequenced. Amino acid sequences of ApxIIA proteins of serovars 2, 3, 4, 6, 8 and 15 were almost identical to those of serovars 1, 5, 7, 9 and 11-13. Immunoblot analysis showed that rApxIIA from serovars 2 and 15 reacts strongly with sera from animals infected with various serovars. Sequence analysis revealed that ApxIIIA proteins has two variants, one in strains of serovar 2 and the other in strains of serovars 3, 4, 6, 8 and 15. A mouse cross-protection study showed that mice actively immunized with rApxIIIA/2 or rApxIIIA/15 are protected against challenge with A. pleuropneumoniae strains of serovars 3, 4, 6, 8, 15, and 2 expressing ApxIII/15 and ApxIII/2, respectively. Similarly, mice passively immunized with rabbit anti-rApxIIIA/2 or anti-rApxIIIA/15 sera were found to be protected against challenge with strains of serovars 2 and 15. Our study revealed antigenic and sequence similarities within ApxIIA and ApxIIIA proteins, which may help in the development of effective vaccines against disease caused by A. pleuropneumoniae.
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Affiliation(s)
- Ho To
- Nippon Institute for Biological Science, 9-2221-1 Shinmachi, Ome, Tokyo 198-0024, Japan
| | - Shinya Nagai
- Nippon Institute for Biological Science, 9-2221-1 Shinmachi, Ome, Tokyo 198-0024, Japan
| | - Akira Iwata
- Nippon Institute for Biological Science, 9-2221-1 Shinmachi, Ome, Tokyo 198-0024, Japan
| | - Tomohiro Koyama
- Nippon Institute for Biological Science, 9-2221-1 Shinmachi, Ome, Tokyo 198-0024, Japan
| | - Atsushi Oshima
- Nippon Institute for Biological Science, 9-2221-1 Shinmachi, Ome, Tokyo 198-0024, Japan
| | - Nobuyuki Tsutsumi
- Nippon Institute for Biological Science, 9-2221-1 Shinmachi, Ome, Tokyo 198-0024, Japan
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Hsu CW, Li SC, Chang NY, Chen ZW, Liao JW, Chen TH, Wang JP, Lin JH, Hsuan SL. Involvement of NF-κB in regulation of Actinobacillus pleuropneumoniae exotoxin ApxI-induced proinflammatory cytokine production in porcine alveolar macrophages. Vet Microbiol 2016; 195:128-135. [PMID: 27771058 DOI: 10.1016/j.vetmic.2016.09.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 09/24/2016] [Accepted: 09/27/2016] [Indexed: 10/20/2022]
Abstract
Actinobacillus pleuropneumoniae is a crucial respiratory pathogen that causes fibrinous, hemorrhagic, necrotizing pleuropneumonia in pigs. A. pleuropneumoniae exotoxins (ApxI to IV) are the major virulence factors contributing to A. pleuropneumoniae pathogenesis. Previously, we demonstrated that ApxI induces the expression of proinflammatory cytokines in porcine alveolar macrophages (PAMs) via the mitogen-activated protein kinases (MAPKs) p38 and cJun NH2-terminal kinase (JNK). Nonetheless, the role of nuclear factor (NF)-κB-a transcription factor widely implicated in immune and inflammatory responses-in ApxI-elicited cytokine production has yet to be defined. In the present study, we examined the involvement of NF-κB in ApxI-elicited production of interleukin (IL)-1β, IL-8, and tumor necrosis factor (TNF)-α in PAMs and investigated the correlation between NF-κB and MAPK (p38 and JNK) pathways in this event. The results of Western blot analysis, confocal microscopy, and a DNA binding activity assay revealed that the classical NF-κB pathway was activated by ApxI, as evidenced by the decreased levels of IκB and subsequent NF-κB translocation and activation in ApxI-stimulated PAMs. Moreover, the blocking of ApxI-induced NF-κB activation significantly attenuated the levels of mRNA and protein secretion of IL-1β, IL-8, and TNF-α in PAMs. Notably, the attenuation of JNK activation by a specific inhibitor (SP600125) reduced ApxI-induced NF-κB activation, whereas a p38 blocker (SB203580) had no effect on the NF-κB pathway. Further examination revealed that the level of phosphorylation at serine 536 on the NF-κB p65 subunit was dependent on JNK activity. Collectively, this study, for the first time, demonstrates a pivotal role of NF-κB in ApxI-induced IL-1β, IL-8, and TNF-α production; JNK, but not p38, may positively affect the activation of the classical NF-κB pathway.
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Affiliation(s)
- Chiung-Wen Hsu
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 40227, Taiwan, ROC; Animal Technology Laboratories, Agricultural Technology Research Institute, No. 1, Ln. 51, Dahu Rd., Hsinchu City, 30093, Taiwan, ROC
| | - Siou-Cen Li
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 40227, Taiwan, ROC; Animal Technology Laboratories, Agricultural Technology Research Institute, No. 1, Ln. 51, Dahu Rd., Hsinchu City, 30093, Taiwan, ROC
| | - Nai-Yun Chang
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 40227, Taiwan, ROC
| | - Zeng-Weng Chen
- Animal Technology Laboratories, Agricultural Technology Research Institute, No. 1, Ln. 51, Dahu Rd., Hsinchu City, 30093, Taiwan, ROC
| | - Jiunn-Wang Liao
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 40227, Taiwan, ROC
| | - Ter-Hsin Chen
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 40227, Taiwan, ROC
| | - Jyh-Perng Wang
- Animal Technology Laboratories, Agricultural Technology Research Institute, No. 1, Ln. 51, Dahu Rd., Hsinchu City, 30093, Taiwan, ROC
| | - Jiunn-Horng Lin
- Animal Technology Laboratories, Agricultural Technology Research Institute, No. 1, Ln. 51, Dahu Rd., Hsinchu City, 30093, Taiwan, ROC
| | - Shih-Ling Hsuan
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, 40227, Taiwan, ROC.
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Expression of leucocyte function-associated antigen-1 and intercellular adhesion molecule-1 in the lungs of pigs infected with Actinobacillus pleuropneumoniae. J Comp Pathol 2012; 148:259-65. [PMID: 22819014 DOI: 10.1016/j.jcpa.2012.06.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 05/18/2012] [Accepted: 06/04/2012] [Indexed: 11/21/2022]
Abstract
The aim of this study was to determine the expression of leucocyte function-associated antigen (LFA)-1 (CD11a/CD18) by neutrophils and intercellular adhesion molecule (ICAM)-1 (CD54) by endothelial cells in the lungs of pigs that had been infected experimentally with Actinobacillus pleuropneumoniae. Sixty-four 7-week-old conventional pigs were allocated randomly into infected (n = 40) or control (n = 24) groups. Five infected and three uninfected pigs were killed at 3, 6, 9, 12, 24, 36, 48 and 60 h post inoculation (hpi). Strong immunohistochemical expression of LFA-1 and ICAM-1 was detected frequently in neutrophils in the alveolar space and in endothelial cells in the capillaries of the alveolar septa, respectively. LFA-1 and ICAM-1 expression appeared to correlate with the onset of neutrophil infiltration into the alveolar space. The interaction between ICAM-1 and LFA-1 may be associated with the adherence of neutrophils to vascular endothelium, thereby permitting transmigration of these cells into inflamed lung.
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Frey J. The role of RTX toxins in host specificity of animal pathogenic Pasteurellaceae. Vet Microbiol 2011; 153:51-8. [PMID: 21645978 DOI: 10.1016/j.vetmic.2011.05.018] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Revised: 04/29/2011] [Accepted: 05/10/2011] [Indexed: 10/18/2022]
Abstract
RTX toxins are bacterial pore-forming toxins that are particularly abundant among pathogenic species of Pasteurellaceae, in which they play a major role in virulence. RTX toxins of several primary pathogens of the family of Pasteurellaceae are directly involved in causing necrotic lesions in the target organs. Many RTX toxins are known as haemolysins because they lyse erythrocytes in vitro, an effect that is non-specific, but which serves as a useful marker in bacteriological identification and as an easily measurable signal in vitro in experimental studies. More recent studies have shown that the specific targets of most RTX toxins are leukocytes, with RTX toxins binding to the corresponding β-subunit (CD18) of β2 integrins and then exerting cytotoxic activity. After uptake by the target cell, at sub-lytic concentrations, some RTX toxins are transported to mitochondria and induce apoptosis. For several RTX toxins the binding to CD18 has been shown to be host specific and this seems to be the basis for the host range specificity of these RTX toxins. Observations on two very closely related species of the Pasteurellaceae family, Actinobacillus suis, a porcine pathogen particularly affecting suckling pigs, and Actinobacillus equuli subsp. haemolytica, which causes pyosepticaemia in new-born foals (sleepy foal disease), have revealed that they express different RTX toxins, named ApxI/II and Aqx, respectively. These RTX toxins are specifically cytotoxic for porcine and equine leukocytes, respectively. Furthermore, the ApxI and Aqx toxins of these species, when expressed in an isogenetic background in Escherichia coli, are specifically cytotoxic for leukocytes of their respective hosts. These data indicate the determinative role of RTX toxins in host specificity of pathogenic species of Pasteurellaceae.
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Affiliation(s)
- Joachim Frey
- Institute of Veterinary Bacteriology, University of Bern, Laenggasstrasse 122, CH-3012 Bern, Switzerland.
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Chen ZW, Chien MS, Chang NY, Chen TH, Wu CM, Huang C, Lee WC, Hsuan SL. Mechanisms underlying Actinobacillus pleuropneumoniae exotoxin ApxI induced expression of IL-1β, IL-8 and TNF-α in porcine alveolar macrophages. Vet Res 2011; 42:25. [PMID: 21314908 PMCID: PMC3041667 DOI: 10.1186/1297-9716-42-25] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Accepted: 01/13/2011] [Indexed: 11/12/2022] Open
Abstract
Actinobacillus pleuropneumoniae (A. pleuropneumoniae) causes fibrino-hemorrhagic necrotizing pleuropneumonia in pigs. Production of proinflammatory mediators in the lungs is an important feature of A. pleuropneumoniae infection. However, bacterial components other than lipopolysaccharide involved in this process remain unidentified. The goals of this study were to determine the role of A. pleuropneumoniae exotoxin ApxI in cytokine induction and to delineate the underlying mechanisms. Using real-time quantitative PCR analysis, we found native ApxI stimulated porcine alveolar macrophages (PAMs) to transcribe mRNAs of IL-1β, IL-8 and TNF-α in a concentration- and time-dependent manner. Heat-inactivation or pre-incubation of ApxI with a neutralizing antiserum attenuated ApxI bioactivity to induce cytokine gene expression. The secretion of IL-1β, IL-8 and TNF-α protein from PAMs stimulated with ApxI was also confirmed by quantitative ELISA. In delineating the underlying signaling pathways contributing to cytokine expression, we observed mitogen-activated protein kinases (MAPKs) p38 and cJun NH2-terminal kinase (JNK) were activated upon ApxI stimulation. Administration of an inhibitor specific to p38 or JNK resulted in varying degrees of attenuation on ApxI-induced cytokine expression, suggesting the differential regulatory roles of p38 and JNK in IL-1β, IL-8 and TNF-α production. Further, pre-incubation of PAMs with a CD18-blocking antibody prior to ApxI stimulation significantly reduced the activation of p38 and JNK, and subsequent expression of IL-1β, IL-8 or TNF-α gene, indicating a pivotal role of β2 integrins in the ApxI-mediated effect. Collectively, this study demonstrated ApxI induces gene expression of IL-1β, IL-8 and TNF-α in PAMs that involves β2 integrins and downstream MAPKs.
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Affiliation(s)
- Zeng-Weng Chen
- Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250, Kuo Kuang Road, Taichung, 402, Taiwan, ROC.
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