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      The Vibrio alginolyticus T3SS effectors, Val1686 and Val1680, induce cell rounding, apoptosis and lysis of fish epithelial cells

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          ABSTRACT

          Vibrio alginolyticus is a Gram-negative bacterium that is an opportunistic pathogen of both marine animals and people. Its pathogenesis likely involves type III secretion system (T3SS) mediated induction of rapid apoptosis, cell rounding and osmotic lysis of infected eukaryotic cells. Herein, we report that effector proteins, Val1686 and Val1680 from V. alginolyticus, were responsible for T3SS-mediated death of fish cells. Val1686 is a Fic-domain containing protein that not only contributed to cell rounding by inhibiting Rho guanosine triphosphatases (GTPases), but was requisite for the induction of apoptosis because the deletion mutant (Δ val1686) was severely weakened in its ability to induce cell rounding and apoptosis in fish cells. In addition, Val1686 alone was sufficient to induce cell rounding and apoptosis as evidenced by the transfection of Val1686 into fish cells. Importantly, the Fic-domain essential for cell rounding activity was equally important to activation of apoptosis of fish cells, indicating that apoptosis is a downstream event of Val1686-dependent GTPase inhibition. V. alginolyticus infection likely activates JNK and ERK pathways with sequential activation of caspases (caspase-8/-10, -9 and -3) and subsequent apoptosis. Val1680 contributed to T3SS-dependent lysis of fish cells in V. alginolyticus, but did not induce autophagy as has been reported for its homologue (VopQ) in V. parahaemolyticus. Together, Val1686 and Val1680 work together to induce apoptosis, cell rounding and cell lysis of V. alginolyticus-infected fish cells. These findings provide new insights into the mechanism of cell death caused by T3SS of V. alginolyticus.

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          Most cited references 43

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          Mitogen-activated protein kinases in apoptosis regulation.

          Cells are continuously exposed to a variety of environmental stresses and have to decide 'to be or not to be' depending on the types and strength of stress. Among the many signaling pathways that respond to stress, mitogen-activated protein kinase (MAPK) family members are crucial for the maintenance of cells. Three subfamilies of MAPKs have been identified: extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and p38-MAPKs. It has been originally shown that ERKs are important for cell survival, whereas JNKs and p38-MAPKs were deemed stress responsive and thus involved in apoptosis. However, the regulation of apoptosis by MAPKs is more complex than initially thought and often controversial. In this review, we discuss MAPKs in apoptosis regulation with attention to mouse genetic models and critically point out the multiple roles of MAPKs.
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            Type III protein secretion systems in bacterial pathogens of animals and plants.

             C Hueck (1998)
            Various gram-negative animal and plant pathogens use a novel, sec-independent protein secretion system as a basic virulence mechanism. It is becoming increasingly clear that these so-called type III secretion systems inject (translocate) proteins into the cytosol of eukaryotic cells, where the translocated proteins facilitate bacterial pathogenesis by specifically interfering with host cell signal transduction and other cellular processes. Accordingly, some type III secretion systems are activated by bacterial contact with host cell surfaces. Individual type III secretion systems direct the secretion and translocation of a variety of unrelated proteins, which account for species-specific pathogenesis phenotypes. In contrast to the secreted virulence factors, most of the 15 to 20 membrane-associated proteins which constitute the type III secretion apparatus are conserved among different pathogens. Most of the inner membrane components of the type III secretion apparatus show additional homologies to flagellar biosynthetic proteins, while a conserved outer membrane factor is similar to secretins from type II and other secretion pathways. Structurally conserved chaperones which specifically bind to individual secreted proteins play an important role in type III protein secretion, apparently by preventing premature interactions of the secreted factors with other proteins. The genes encoding type III secretion systems are clustered, and various pieces of evidence suggest that these systems have been acquired by horizontal genetic transfer during evolution. Expression of type III secretion systems is coordinately regulated in response to host environmental stimuli by networks of transcription factors. This review comprises a comparison of the structure, function, regulation, and impact on host cells of the type III secretion systems in the animal pathogens Yersinia spp., Pseudomonas aeruginosa, Shigella flexneri, Salmonella typhimurium, enteropathogenic Escherichia coli, and Chlamydia spp. and the plant pathogens Pseudomonas syringae, Erwinia spp., Ralstonia solanacearum, Xanthomonas campestris, and Rhizobium spp.
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              Protein delivery into eukaryotic cells by type III secretion machines.

              Bacteria that have sustained long-standing close associations with eukaryotic hosts have evolved specific adaptations to survive and replicate in this environment. Perhaps one of the most remarkable of those adaptations is the type III secretion system (T3SS)--a bacterial organelle that has specifically evolved to deliver bacterial proteins into eukaryotic cells. Although originally identified in a handful of pathogenic bacteria, T3SSs are encoded by a large number of bacterial species that are symbiotic or pathogenic for humans, other animals including insects or nematodes, and plants. The study of these systems is leading to unique insights into not only organelle assembly and protein secretion but also mechanisms of symbiosis and pathogenesis.
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                Author and article information

                Journal
                Virulence
                Virulence
                KVIR
                kvir20
                Virulence
                Taylor & Francis
                2150-5594
                2150-5608
                2018
                27 February 2018
                27 February 2018
                : 9
                : 1
                : 318-330
                Affiliations
                [a ]Institute of Marine Biology, College of Oceanography, Hohai University , Nanjing, Jiangsu, PR China
                [b ]Key Laboratory of Marine Bio-resources Sustainable Utilization, Key Laboratory of Applied Marine Biology of Guangdong Province, South China Sea Institute of Oceanology, Chinese Academy of Sciences , Guangzhou, Guangdong, PR China
                [c ]Paul G. Allen School for Global Animal Health, Washington State University , Pullman, WA, U.S
                [d ]Key Laboratory of South China Sea Fishery Resources Exploitation & Utilization, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences , Guangzhou, Guangdong, PR China
                Author notes
                CONTACT Zhe Zhao, Ph.D. zhezhao@ 123456hhu.edu.cn Institute of Marine Biology, College of Oceanography, Hohai University , No.1 Xikang Road, Nanjing 210098, P.R. China

                Supplemental data for this article can be accessed on the publisher's website.

                [†]

                The authors contributed equally to this work.

                Article
                1414134
                10.1080/21505594.2017.1414134
                5955196
                29252102
                © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 7, Tables: 0, Equations: 0, References: 58, Pages: 13
                Product
                Funding
                Funded by: National Natural Science Foundation of China (NSFC)
                Award ID: 41276163
                National Natural Science Foundation of China (NSFC), (41276163);
                Categories
                Research Paper

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