SUMO-Interacting Motifs of Human TRIM5α are Important for Antiviral Activity

Gloria Arriagada,Stephen P Goff,Lucia N Muntean,Michael Emerman

doi:10.1371/journal.ppat.1002019

Abstract

Human TRIM5α potently restricts particular strains of murine leukemia viruses (the so-called N-tropic strains) but not others (the B- or NB-tropic strains) during early stages of infection. We show that overexpression of SUMO-1 in human 293T cells, but not in mouse MDTF cells, profoundly blocks N-MLV infection. This block is dependent on the tropism of the incoming virus, as neither B-, NB-, nor the mutant R110E of N-MLV CA (a B-tropic switch) are affected by SUMO-1 overexpression. The block occurred prior to reverse transcription and could be abrogated by large amounts of restricted virus. Knockdown of TRIM5α in 293T SUMO-1-overexpressing cells resulted in ablation of the SUMO-1 antiviral effects, and this loss of restriction could be restored by expression of a human TRIM5α shRNA-resistant plasmid. Amino acid sequence analysis of human TRIM5α revealed a consensus SUMO conjugation site at the N-terminus and three putative SUMO interacting motifs (SIMs) in the B30.2 domain. Mutations of the TRIM5α consensus SUMO conjugation site did not affect the antiviral activity of TRIM5α in any of the cell types tested. Mutation of the SIM consensus sequences, however, abolished TRIM5α antiviral activity against N-MLV. Mutation of lysines at a potential site of SUMOylation in the CA region of the Gag gene reduced the SUMO-1 block and the TRIM5α restriction of N-MLV. Our data suggest a novel aspect of TRIM5α-mediated restriction, in which the presence of intact SIMs in TRIM5α, and also the SUMO conjugation of CA, are required for restriction. We propose that at least a portion of the antiviral activity of TRIM5α is mediated through the binding of its SIMs to SUMO-conjugated CA.

Highlights

Cells have developed many mechanisms to restrict viral infection
We have identified a new aspect of TRIM5a-mediated restriction of N-murine leukemia viruses (MLV): the involvement of the SUMO conjugation machinery
SUMO conjugation of MLV CA is an important step during viral infection, and our data suggest that innate immunity takes advantage of this process to restrict viral infection

Summary

Introduction

The adaptative immune response provides major protection against viral pathogens, but recently dominant-acting inhibitory gene products, called restriction factors, have been discovered that play an important role in limiting host susceptibility to viral infections. One class of such restriction factors blocks retroviral infection by targeting the incoming capsid protein (CA) (for review see [1]). Studies identified the Friend virus susceptibility factor 1 (Fv1) locus as a host gene determining the susceptibility of mice to infection by various strains of murine leukemia viruses (MLV) [2]. The mechanism by which Fv1 restricts MLV infection is unknown, but it is generally presumed that Fv1 somehow recognizes the incoming CA protein structure and prevents normal infection

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Discussion

Conclusion