Innate immune sensor LGP2 is cleaved by the Leader protease of foot-and-mouth disease virus.

Miguel Rodríguez Pulido,Francisco Sobrino,Adolfo García-Sastre,María Teresa Sánchez-Aparicio,Margarita Sáiz,Encarnación Martínez-Salas,Bert L Semler

doi:10.1371/journal.ppat.1007135

Abstract

The RNA helicase LGP2 (Laboratory of Genetics and Physiology 2) is a non-signaling member of the retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), whose pivotal role on innate immune responses against RNA viruses is being increasingly uncovered. LGP2 is known to work in synergy with melanoma differentiation-associated gene 5 (MDA5) to promote the antiviral response induced by picornavirus infection. Here, we describe the activity of the foot-and-mouth disease virus (FMDV) Leader protease (Lpro) targeting LGP2 for cleavage. When LGP2 and Lpro were co-expressed, cleavage products were observed in an Lpro dose-dependent manner while co-expression with a catalytically inactive Lpro mutant had no effect on LGP2 levels or pattern. We further show that Lpro localizes and immunoprecipitates with LGP2 in transfected cells supporting their interaction within the cytoplasm. Evidence of LGP2 proteolysis was also detected during FMDV infection. Moreover, the inhibitory effect of LGP2 overexpression on FMDV growth observed was reverted when Lpro was co-expressed, concomitant with lower levels of IFN-β mRNA and antiviral activity in those cells. The Lpro target site in LGP2 was identified as an RGRAR sequence in a conserved helicase motif whose replacement to EGEAE abrogated LGP2 cleavage by Lpro. Taken together, these data suggest that LGP2 cleavage by the Leader protease of aphthoviruses may represent a novel antagonistic mechanism for immune evasion.

Highlights

Antiviral response against RNA viruses greatly relies on detection of infection by cytoplasmic sensors
We further show that Leader protease (Lpro) localizes and immunoprecipitates with LGP2 in transfected cells supporting their interaction within the cytoplasm
LGP2 (Laboratory of Genetics and Physiology 2) is a cellular protein involved in sensing viral RNA during infection and plays a relevant role

Summary

Introduction

Antiviral response against RNA viruses greatly relies on detection of infection by cytoplasmic sensors. RIG-I and MDA5 contain N-terminal tandem caspase activation and recruitment domains (CARDs) which upon recognition of viral RNA, interact with the CARD of the mitochondrial activator of virus signaling (MAVS) protein, the essential adaptor molecule for RLR signaling. LGP2 is known to be widely involved in viral RNA recognition and regulation during innate immune responses, remaining the most enigmatic member of the RLR family [7] Both negative and positive regulatory roles have been reported for LGP2 in antiviral immunity. Single molecule RNA binding experiments and biochemical analysis revealed that ATP hydrolysis activity is required to enable LGP2 to efficiently engage diverse dsRNA species, and for enhancement of MDA5 signaling [8]. An RNA- and virus-independent inhibitory role for LGP2 in antiviral signaling has been reported, likely involving CARD-independent interaction with MAVS by competition with an essential kinase for binding and interfering with downstream signaling [10]

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