TRIM25 Is Required for the Antiviral Activity of Zinc Finger Antiviral Protein

Abstract

Zinc finger antiviral protein (ZAP) is a host factor that specifically inhibits the replication of certain viruses by binding to viral mRNAs and repressing the translation and/or promoting the degradation of target mRNA. In addition, ZAP regulates the expression of certain cellular genes. Here, we report that tripartite motif-containing protein 25 (TRIM25), a ubiquitin E3 ligase, is required for the antiviral activity of ZAP. Downregulation of endogenous TRIM25 abolished ZAP's antiviral activity. The E3 ligase activity of TRIM25 is required for this regulation. TRIM25 mediated ZAP ubiquitination, but the ubiquitination of ZAP itself did not seem to be required for its antiviral activity. Downregulation of endogenous ubiquitin or overexpression of the deubiquitinase OTUB1 impaired ZAP's activity. We provide evidence indicating that TRIM25 modulates the target RNA binding activity of ZAP. These results uncover a mechanism by which the antiviral activity of ZAP is regulated.IMPORTANCE ZAP is a host antiviral factor that specifically inhibits the replication of certain viruses, including HIV-1, Sindbis virus, and Ebola virus. ZAP binds directly to target mRNA, and it represses the translation and promotes the degradation of target mRNA. While the mechanisms by which ZAP posttranscriptionally inhibits target RNA expression have been extensively studied, how its antiviral activity is regulated is not very clear. Here, we report that TRIM25, a ubiquitin E3 ligase, is required for the antiviral activity of ZAP. Downregulation of endogenous TRIM25 remarkably abolished ZAP's activity. TRIM25 is required for ZAP optimal binding to target mRNA. These results help us to better understand how the antiviral activity of ZAP is regulated.

Ubiquitin-dependent and -independent roles of E3 ligase RIPLET in innate immunity

“…The lack of impact of TRIM25 on RIG-I function was surprising given the widely held view of its essential role in RIG-I signaling. Considering the growing list of RIG-I-independent functions of TRIM25 in antiviral immunity-in part mediated by its RNA binding activity (Choudhury et al, 2014;Manokaran et al, 2015;Meyerson et al, 2017) and its interaction with ZAP Zheng et al, 2017)-the precise nature of the observed effect of TRIM25 on RIG-I 2CARD requires more detailed investigation.…”

“…However, given the previous finding that RNA binding is sufficient to release 2CARD (Kowalinski et al, 2011), it was unclear whether RIPLET indeed acts to release 2CARD and if so, how. At the same time, accumulating evidence suggested that TRIM25 has multiple, RIG-I-independent antiviral functions (Choudhury et al, 2014;Li et al, 2017;Manokaran et al, 2015;Meyerson et al, 2017;Zheng et al, 2017), raising the question whether the observed effect of TRIM25 on RIG-I represents a direct or an indirect effect.We here report a combination of cellular and biochemical data showing that RIG-I activation is dependent on RIPLET, not TRIM25, and that RIPLET suffices to ubiquitinate and activate RIG-I. In addition, RIPLET recognizes the filamentous form of RIG-I using two distinct binding modes, the interplays of which offer previously unrecognized mechanisms for ligand discrimination and receptor clustering.…”

“…However, given the previous finding that RNA binding is sufficient to release 2CARD (Kowalinski et al, 2011), it was unclear whether RIPLET indeed acts to release 2CARD and if so, how. At the same time, accumulating evidence suggested that TRIM25 has multiple, RIG-I-independent antiviral functions (Choudhury et al, 2014;Li et al, 2017;Manokaran et al, 2015;Meyerson et al, 2017;Zheng et al, 2017), raising the question whether the observed effect of TRIM25 on RIG-I represents a direct or an indirect effect.…”

The impact of PARPs and ADP-ribosylation on inflammation and host–pathogen interactions

“…In addition, ZAP antiviral activity is enhanced by the ubiquitin ligase activity of TRIM25. TRIM25 binds to ZAP and ubiquitinates unknown proteins to enhance the antiviral activity of ZAP (Li et al 2017;Zheng et al 2017).…”

TRIM25 in the Regulation of the Antiviral Innate Immunity

“…In addition to RIG-I, TRIM25 also positively regulates the melanoma differentiation-associated protein 5 (MDA5)-MAVS-TRAF6 antiviral axis leading to activation of NF-κB (90). Also, it has been recently reported that the antiviral action of zing-finger antiviral protein (ZAP), a cellular protein that inhibits viral mRNAs translation, is enhanced by interaction with the SPRY domain of TRIM25 (91,92).…”