title: Antiviral function of grouper MDA5 against iridovirus and nodavirus.
abstract: Melanoma differentiation-associated gene 5 (MDA5) is a critical member of retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) family which can recognize viral RNA and enhances antiviral response in host cells. In this study, a MDA5 homolog from orange spotted grouper (Epinephelus coioides) (EcMDA5) was cloned, and its roles on grouper virus infection were characterized. The full-length EcMDA5 cDNA encoded a polypeptide of 982 amino acids with 74% identity with MDA5 homolog from rock bream (Oplegnathus fasciatus). Amino acid alignment analysis indicated that EcMDA5 contained three functional domains: two caspase activation and recruitment domain (CARDs), a DEAD box helicase-like (DExDc) domain, a helicase superfamily C-terminal domain (HELICc), and a C-terminal regulatory domain (RD). Upon challenge with Singapore grouper iridovirus (SGIV) or polyinosin-polycytidylic acid (poly I:C), the transcript of EcMDA5 was significantly up-regulated especially at the early stage post-injection. Under fluorescence microscopy, we observed that EcMDA5 mostly localized in the cytoplasm of grouper spleen (GS) cells. Interestingly, during virus infection, the distribution pattern of EcMDA5 was significantly altered in SGIV infected cells, but not in red spotted grouper nervous necrosis virus (RGNNV) infected cells, suggested that EcMDA5 might interact with viral proteins during SGIV infection. The ectopic expression of EcMDA5 in vitro obviously delayed virus infection induced cytopathic effect (CPE) progression and significantly inhibited viral gene transcription of RGNNV and SGIV. Moreover, overexpression of EcMDA5 not only significantly increased interferon (IFN) and IFN-stimulated response element (ISRE) promoter activities in a dose dependent manner, but also enhanced the expression of IRF3, IRF7 and TRAF6. In addition, the transcription level of the proinflammatory factors, including TNF-α, IL-6 and IL-8 were differently altered by EcMDA5 overexpression during SGIV or RGNNV infection, suggesting that the regulation on proinflammatory cytokines by EcMDA5 were also important for RGNNV infection. Together, our results demonstrated for the first time that the inhibitory effect of fish MDA5 on iridovirus replication might be mainly through the regulation of proinflammatory cytokines.
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Youhua
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Yepin
authors.initials: Y
authors.lastname: Yu
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Min
authors.initials: M
authors.lastname: Yang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Linli
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China. Electronic address: huangxh@scsio.ac.cn.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Huang
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China; University of Chinese Academy of Sciences, Beijing, China. Electronic address: qinqw@scsio.ac.cn.
authors.forename: Qiwei
authors.initials: Q
authors.lastname: Qin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001492:Bass; D003001:Cloning, Molecular; D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004266:DNA Virus Infections / Q000235:genetics / Q000276:immunology / Q000662:veterinary* / Q000821:virology; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D005393:Fish Diseases / Q000235:genetics* / Q000276:immunology / Q000821:virology; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D030381:Nodaviridae / Q000502:physiology; D010802:Phylogeny; D012327:RNA Virus Infections / Q000235:genetics / Q000276:immunology / Q000662:veterinary* / Q000821:virology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017995:Ranavirus / Q000502:physiology; D016415:Sequence Alignment / Q000662:veterinary
chemical_list: D018076:DNA, Complementary; D029941:Fish Proteins; D012333:RNA, Messenger; D053487:DEAD-box RNA Helicases
keywords: Antiviral; Grouper; Iridovirus; MDA5; RGNNV