Fish RIP1 Mediates Innate Antiviral Immune Responses Induced by SGIV and RGNNV Infection.

Xin Zhang,Jingguang Wei,Zetian Liu,Siting Wu,Qiwei Qin,Mengshi Sun

doi:10.3389/fimmu.2020.01718

Abstract

Receptor interacting protein 1 (RIP1) is an essential sensor of cellular stress, which may respond to apoptosis or cell survival and participate in antiviral pathways. To investigate the roles of fish RIP1 in Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) infection, a RIP1 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP1) was cloned and characterized. EcRIP1 encoded a 679 amino acid protein that shares 83.28% identity with that of Perca flavescens and contained a homologous N-terminal kinase (S-TKc) domain, a RIP isotype interaction motif (RHIM), and a C-terminal domain (DD). EcRIP1 was predominantly detected in immune tissues, and its expression was induced by RGNNV or SGIV infection in vitro. Subcellular localization showed that EcRIP1 was distributed in the cytoplasm with point-like uniform and dot-like aggregation forms. Overexpression of EcRIP1 inhibited SGIV and RGNNV replication and positively regulated the expression levels of interferon (IFN) and IFN-stimulated genes and pro-inflammatory factors. EcRIP1 may interact with grouper tumor necrosis factor receptor type 1-associated DEATH domain protein (EcTRADD) to promote SGIV-induced apoptosis, and interact with grouper Toll/interleukin-1 receptor (TIR) domain containing adapter inducing interferon-β (EcTRIF) and participate in Myeloid Differentiation Factor 88 (MyD88)-independent toll-like receptor (TLR) signaling. EcRIP1 may also interact with grouper tumor necrosis factor receptor-associated factors (TRAFs) as intracellular linker proteins and mediate the signaling of various downstream signaling pathways, including NF-κB and IFN. These results suggest that EcRIP1 may inhibit SGIV and RGNNV infection by regulating apoptosis and various signaling molecules. Our study offers new insights into the regulatory mechanism of RIP1-related signaling, and provides a novel perspective on fish diseases mediated by RIP1.

Highlights

Cells can respond to the stress of distinct pathogens by regulating cell signaling pathways mediated by nuclear factor-κB (NF-κB), interferon (IFN), or p53 transcription factors [1, 2]
EcRIP1 is clustered in the Osteichthyes branch, and the Receptor interacting protein 1 (RIP1) subfamily is conservative among Osteichthyes (Figures 1B,C)
The truncated mutants containing only the kinase domain of EcRIP1 did not activate the NF-κB response, whereas the truncated mutants containing the death domain (DD) alone or together with the intermediate domain (ID) were more effective than the full-length EcRIP1 (Figure 3D)

Summary

Introduction

Cells can respond to the stress of distinct pathogens (e.g., viruses and bacteria) by regulating cell signaling pathways mediated by nuclear factor-κB (NF-κB), interferon (IFN), or p53 transcription factors [1, 2]. These cellular signaling pathways can be induced by target genes to regulate a variety of vital biological processes, including immune responses, inflammatory reactions, and apoptosis [3]. In an attempt to understand how cells balance and regulate survival and death decisions under external stimuli, we began to focus on receptorinteracting protein (RIP) family kinases, which are thought to be essential sensors of cellular stress [4, 5]. The kinase domain of RPI1 may play an important role in cell necrosis [1]

Methods

Results

Conclusion