A tumour necrosis factor receptor-like protein encoded by Singapore grouper iridovirus modulates cell proliferation, apoptosis and viral replication

Abstract

It has been demonstrated that tumour necrosis factor receptor (TNFR) homologues encoded by viruses are usually involved in virus immune evasion by regulating the host immune response or mediating apoptotic cell death. Here, a novel TNFR-like protein encoded by Singapore grouper iridovirus (SGIV VP51) was cloned and characterized. Amino acid analysis showed that VP51 contained three cysteine-rich domains (CRDs) and a transmembrane domain at its C terminus. The expression of VP51 in vitro enhanced cell proliferation, and affected cell cycle progression via altering the G1/S transition. Furthermore, VP51 overexpression improved cell viability during SGIV infection via inhibiting virus-induced apoptosis, evidenced by the reduction of apoptotic bodies and the decrease of caspase-3 activation. In addition, overexpression of VP51 increased viral titre and the expression of viral structural protein gene MCP and cell proliferation promoting gene ICP-18. In contrast, the expression of the viral apoptosis inducing gene, LITAF, was significantly decreased. Although all three CRDs were essential for the action of VP51, CRD2 and CRD3 exerted more crucial roles on virus-induced apoptosis, viral gene transcription and virus production, while CRD1 was more crucial for cell proliferation. Together, SGIV TNFR-like products not only affected cell cycle progression and enhanced cell growth by increasing the expression of the virus encoded cell proliferation gene, but also inhibited virus-induced apoptotic cell death by decreasing the expression of the viral apoptosis inducing gene. Our results provided new insights into understanding the underlying mechanism by which iridovirus regulated the apoptotic pathway to complete its life cycle.

Mechanisms of Fish Macrophage Antimicrobial Immunity

“…By studying the TNF systems of teleost fish, we may garner greater insights into the evolutionary origins of these important and evolutionarily conserved cytokines and receptors. Indeed the importance of the teleost TNFα proteins to their immune defenses is underlined by the fact that a number of diverse viral fish pathogens encode decoy TNF receptors ( 207 – 210 ).…”

Palmitic Acid Promotes Virus Replication in Fish Cell by Modulating Autophagy Flux and TBK1-IRF3/7 Pathway

“…Among these pathogens, Singapore grouper iridovirus (SGIV) was identified for causing high fish mortality at different stages in grouper aquaculture (20,22). Efforts have been made in discovering the infection mechanisms of SGIV by characterizing the functions of host immune-related genes as well as crucial viral virulence genes (21,(24)(25)(26)(27)(28)(29)(30)(31). Additionally, findings of the role of lipids on modulating cell immunity have been advanced.…”

Antiviral activities of Glycyrrhiza uralensis components against Singapore grouper iridovirus

“…The expression levels of SGIV capsid protein MCP and envelope protein VP19 were detected by RT‐qPCR (Yu et al, 2019). The expression of target genes was normalized against β‐actin expression (Y. Yu, Huang, Wei, & Li, 2016). Table 1 lists the primers used for the assays.…”