Tripartite Motif-Containing Protein 22 Interacts with Class II Transactivator and Orchestrates Its Recruitment in Nuclear Bodies Containing TRIM19/PML and Cyclin T1.

Greta Forlani,Elisa Vicenzi,Roberto S Accolla,Giovanna Tosi,Guido Poli,Filippo Turrini

doi:10.3389/fimmu.2017.00564

Abstract

Among interferon (IFN) inducible antiviral factors both tripartite motif-containing protein 22 (TRIM22) and class II transactivator (CIITA) share the capacity of repressing human immunodeficiency virus type 1 (HIV-1) proviral transcription. TRIM22 is constitutively expressed in a subset of U937 cell clones poorly permissive to HIV-1 replication, whereas CIITA has been shown to inhibit virus multiplication in both T lymphocytic and myeloid cells, including poorly HIV-1 permissive U937 cells, by suppressing Tat-mediated transactivation of HIV-1 transcription. Therefore, we tested whether TRIM22 and CIITA could form a nuclear complex potentially endowed with HIV-1 repressive functions. Indeed, we observed that TRIM22, independent of its E3 ubiquitin ligase domain, interacts with CIITA and promotes its recruitment into nuclear bodies. Importantly, TRIM19/promyelocytic leukemia (PML) protein, another repressor of HIV-1 transcription also acting before proviral integration, colocalize in these nuclear bodies upon TRIM22 expression induced by IFN-γ. Finally, tTRIM22 nuclear bodies also contained CyclinT1, a crucial elongation factor of HIV-1 primary transcripts. These findings show that TRIM22 nuclear bodies are a site of recruitment of factors crucial for the regulation of HIV-1 transcription and highlight the potential existence of a concerted action between TRIM22, CIITA, and TRIM19/PML to maintain a state of proviral latency, at least in myeloid cells.

Highlights

Restriction factors (RF) are specialized host proteins sensing the presence of viral nucleic acids or proteins in order to protect cells from pathogen invasion; they are constitutively expressed prior to virus infection and are usually further inducible by interferons (IFNs) [1]
Cell lysates were IP with an anti-flag monoclonal antibody and tripartite motif-containing protein 22 (TRIM22)-bound proteins were assessed for the presence of class II transactivator (CIITA) by Western blotting with an anti-CIITA mAb
We here show that TRIM22 interacts with CIITA leading to the recruitment of CIITA into TRIM22-containing nuclear bodies

Summary

Introduction

Restriction factors (RF) are specialized host proteins sensing the presence of viral nucleic acids or proteins in order to protect cells from pathogen invasion; they are constitutively expressed prior to virus infection and are usually further inducible by interferons (IFNs) [1]. Tripartite motif-containing protein 22 (TRIM22) has been described to inhibit HIV-1 replication by either affecting virion production [13] if expressed in the cytoplasm, or by suppressing basal as well as phorbol ester-induced HIV-1 long terminal repeat (LTR)mediated transcription when present in the nucleus [14, 15]. In this regard, we have shown that TRIM22 inhibits HIV-1 transcription independent of Tat and NF-kB [15] by interfering with the binding of Specific protein 1 (Sp1) to the HIV-1 LTR promoter region [16]. We observed that TRIM22 inhibited HIV-1 replication in a subset of U937 promonocytic cell clones poorly permissive to HIV-1 replication [15]

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Results

Conclusion