Rab20, a novel Rab small GTPase from orange-spotted grouper positively regulates host immune response against iridoviruses infection

Abstract

Rab20, a member of the Rab GTPase family, associates with membrane trafficking and immune response, which play important roles in bacteria control. However, little is known about the role of Rab20 during virus infection. Groupers (Epinephelus spp.) with high economic value are widely cultured in China and Southeast Asian countries. However, the cultured groupers have suffered from diseases caused by viruses such as Singapore grouper iridovirus (SGIV) resulting in huge economic losses. In this study, the roles of a novel Rab20 homolog (EcRab20), from orange-spotted grouper (Epinephelus coioides), on the infection of SGIV and host immune response were investigated. EcRab20 showed high sequence identity with other Rab20 from mammals to fishes. In healthy groupers, EcRab20 was predominantly expressed in immune organs, such as kidney, liver and spleen. After SGIV infection, the expression of EcRab20 in spleen was significantly up-regulated. Confocal imaging showed that EcRab20 distributed in the cytoplasm as punctate and vesicle-like structures, which was destructed by overexpression of the dominant negative EcRab20 (DN EcRab20). Moreover, EcRab20 notably colocalized with Golgi and early endosomes, partly colocalized with endoplasmic reticulum and late endosomes, but did not colocalize with mitochondria or lysosome. Ultimately, overexpression of EcRab20 significantly inhibited SGIV infection, whereas overexpression of DN EcRab20 promoted SGIV infection. Furthermore, using single particle imaging analysis, we found that EcRab20 or DN EcRab20 had no effect on the entry of SGIV. In addition, EcRab20 positively regulated the IFN immune and inflammatory responses. Taken together, these results demonstrated that EcRab20 affect SGIV infection by regulating the host immunity, providing a new idea of the anti-virus mechanisms of Rab20 against SGIV infection and contributing to design new antiviral strategies.