Identification and characterization of scavenger receptor class B type 1 in orange-spotted grouper, Epinephelus coioides

Abstract

Scavenger receptor class B type 1 (SR-B1) is a cell surface transmembrane protein that plays a crucial role in the immune response against viral infections. To clarify the roles of fish SR-B1 in Singapore grouper iridovirus (SGIV) infection, we identified and characterized SR-B1 (Ec-SR-B1) in the orange-spotted grouper (Epinephelus coioides). The Ec-SR-B1 encoded a 487-amino acid protein with two transmembrane regions, CD36 domain and N-linked glycosylation sites, which shared high identities with reported SR-B1. The abundant transcriptional level of Ec-SR-B1 was found in intestine, liver, spleen and head kidney. And the Ec-SR-B1 expression was significantly up-regulated in grouper spleen (GS) cells after infection with SGIV in vitro. Subcellular localization analysis revealed that Ec-SR-B1 was distributed mainly in the cytoplasm and cell membrane. Overexpression of Ec-SR-B1 in vitro significantly inhibited SGIV infection in GS cells, as evidenced by reduced cytopathic effect (CPE), decreased SGIV major capsid protein (MCP) transcription and MCP protein expression. Further studies showed that overexpression of Ec-SR-B1 positively regulated proinflammatory cytokines, and enhanced IFN and NF-κB promoter activities. Moreover, overexpression of Ec-SR-B1 significantly inhibited SGIV entry into host cells. In summary, our results suggested that Ec-SR-B1 inhibited SGIV infection by regulating antiviral innate immune response and affecting viral entry.