Trim28 acts as restriction factor of prototype foamy virus replication by modulating H3K9me3 marks and destabilizing the viral transactivator Tas

Peipei Yuan,Yang Guo,Shuang Wang,Jun Yin,Xueyan Xi,Xiaohua He,Jun Yan,Jochen Bodem,Biwen Peng,Song Han,Wanhong Liu

doi:10.1186/s12977-021-00584-y

Abstract

BackgroundPrototype foamy virus (PFV) is nonpathogenic complex retroviruses that express a transcriptional transactivator Tas, which is essential for the activity of viral long terminal repeat (LTR) promoter and internal promoter (IP). Tripartite motif-containing protein 28 (Trim28) is well known as a scaffold protein normally enriched in gene promoter region to repress transcription. We sought to determine if whether Trim28 could be enriched in PFV promoter region to participate the establishment of PFV latency infection.ResultsIn this study, we show that Trim28 restricts Tas-dependent transactivation activity of PFV promoter and negatively regulates PFV replication. Trim28 was found to be enriched in LTR instead of IP promoter regions of PFV genome and contribute to the maintenance of histone H3K9me3 marks on the LTR promoter. Furthermore, Trim28 interacts with Tas and colocalizes with Tas in the nucleus. Besides, we found that Trim28, an E3 ubiquitin ligase, binds directly to and promotes Tas for ubiquitination and degradation. And the RBCC domain of Trim28 is required for the ubiquitination and degradation of Tas.ConclusionsCollectively, our findings not only identify a host factor Trim28 negatively inhibits PFV replication by acting as transcriptional restriction factor enriched in viral LTR promoter through modulating H3K9me3 mark here, but also reveal that Trim28 mediated ubiquitin proteasome degradation of Tas as a mechanism underlying Trim28 restricts Tas-dependent transcription activity of PFV promoter and PFV replication. These findings provide new insights into the process of PFV latency establishment.Graphical

Highlights

Prototype foamy virus (PFV) is nonpathogenic complex retroviruses that express a transcriptional transactivator Tas, which is essential for the activity of viral long terminal repeat (LTR) promoter and internal promoter (IP)
Tripartite motif-containing protein 28 (Trim28) inhibits PFV replication and transcription To investigate the effect of Trim28 on PFV replication, we first used a PFV indicator cell line (PIC) in which a luciferase gene driven by the PFV LTR promoter was stably transfected into baby hamster kidney-21 (BHK21) cells
It can be used to measure virus titer of PFV and is more sensitive than TCID50 [29]. In this foamy virus activated luciferase (FAL) assay, Flag-Trim28 were transfected into HEK293T cells for 24 h, pCMV-Flag was transfected as a control, and the cells were challenged with PFV at a multiplicity of infection (MOI) of 0.1 for another 48 h, those infected HEK293T were incubated with PIC for 48 h, and RL-TK plasmid expressing Renilla luciferase was transfected into PIC as an internal control 12 h before incubation

Summary

Introduction

Prototype foamy virus (PFV) is nonpathogenic complex retroviruses that express a transcriptional transactivator Tas, which is essential for the activity of viral long terminal repeat (LTR) promoter and internal promoter (IP). Prototype foamy virus (PFV) belongs to the group of complex retroviruses, since it encodes the APOBEC3 antagonizing factor Bet and a transcriptional transactivator Tas [1,2,3]. These regulatory genes are expressed from an internal promoter (IP) localized in the env gene [4, 5], while the genomic RNA, the pol and env transcripts are expressed from the LTR promoter. The underlying mechanism of PFV latent infection remains elusive

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