Dynamic localization of tripartite motif-containing 22 in nuclear and nucleolar bodies

TRIM22. A Multitasking Antiviral Factor

Viral invasion of target cells triggers an immediate intracellular host defense system aimed at preventing further propagation of the virus. Viral genomes or early products of viral replication are sensed by a number of pattern recognition receptors, leading to the synthesis and production of type I interferons (IFNs) that, in turn, activate a cascade of IFN-stimulated genes (ISGs) with antiviral functions. Among these, several members of the tripartite motif (TRIM) family are antiviral executors. This article will focus, in particular, on TRIM22 as an example of a multitarget antiviral member of the TRIM family. The antiviral activities of TRIM22 against different DNA and RNA viruses, particularly human immunodeficiency virus type 1 (HIV-1) and influenza A virus (IAV), will be discussed. TRIM22 restriction of virus replication can involve either direct interaction of TRIM22 E3 ubiquitin ligase activity with viral proteins, or indirect protein–protein interactions resulting in control of viral gene transcription, but also epigenetic effects exerted at the chromatin level.

TRIMming Down Hormone-Driven Cancers: The Biological Impact of TRIM Proteins on Tumor Development, Progression and Prognostication

The tripartite motif (TRIM) protein family is attracting increasing interest in oncology. As a protein family based on structure rather than function, a plethora of biological activities are described for TRIM proteins, which are implicated in multiple diseases including cancer. With hormone-driven cancers being among the leading causes of cancer-related death, TRIM proteins have been described to portrait tumor suppressive or oncogenic activities in these tumor types. This review describes the biological impact of TRIM proteins in relation to hormone receptor biology, as well as hormone-independent mechanisms that contribute to tumor cell biology in prostate, breast, ovarian and endometrial cancer. Furthermore, we point out common functions of TRIM proteins throughout the group of hormone-driven cancers. An improved understanding of the biological impact of TRIM proteins in cancer may pave the way for improved prognostication and novel therapeutics, ultimately improving cancer care for patients with hormone-driven cancers.

Nuclear localization signal in TRIM22 is essential for inhibition of type 2 porcine reproductive and respiratory syndrome virus replication in MARC-145 cells

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes one of the most economically important swine diseases worldwide. Tripartite motif-containing 22 (TRIM22), a TRIM family protein, has been identified as a crucial restriction factor that inhibits a group of human viruses. Currently, the role of cellular TRIM22 in PRRSV infection remains unclear. In the present study, we analyzed the effect of TRIM22 on PRRSV replication in vitro and explored the underlying mechanism. Ectopic expression of TRIM22 impaired the viral replication, while TRIM22-RNAi favored the replication of PRRSV in MARC-145 cells. Additionally, we observed that TRIM22 deletion SPRY domain or Nuclear localization signal (NLS) losses the ability to inhibit PRRSV replication. Finally, Co-IP analysis identified that TRIM22 interacts with PRRSV nucleocapsid (N) protein through the SPRY domain, while the NLS2 motif of N protein is involved in interaction with TRIM22. Although the concentration of PRRSV N protein was not altered in the presence of TRIM22, the abundance of N proteins from simian hemorrhagic fever virus (SHFV), equine arteritis virus (EAV), and murine lactate dehydrogenase-elevating virus (LDV) diminished considerably with increasing TRIM22 expression. Together, our findings uncover a previously unrecognized role for TRIM22 and extend the antiviral effects of TRIM22 to arteriviruses.

Tripartite Motif 22 and Class II Transactivator Restriction Factors: Unveiling Their Concerted Action against Retroviruses

Coevolution of the three basic mechanisms of immunity, intrinsic, innate and adaptive, is a constant feature of the host defense against pathogens. Within this frame, a peculiar role is played by restriction factors (RFs), elements of intrinsic immunity that interfere with viral life cycle. Often considered as molecules whose specific functions are distinct and unrelated among themselves recent results indicate instead, at least for some of them, a concerted action against the pathogen. Here we review recent findings on the antiviral activity of tripartite motif 22 (TRIM22) and class II transactivator (CIITA), first discovered as human immunodeficiency virus 1 RFs, but endowed with general antiviral activity. TRIM22 and CIITA provide the first example of cellular proteins acting together to potentiate their intrinsic immunity.

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

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.

Identification of TRIM22 as a progesterone-responsive gene in Ishikawa endometrial cancer cells

Progesterone plays important roles in implantation and maintains pregnancy. It antagonizes estrogen-mediated cell proliferation and promotes differentiation in the uterus. The action of progesterone is mediated by specific receptors, namely, the progesterone receptors (PRs). We generated two Ishikawa cell clones stably expressing PR isoform A (PR-A) and identified progesterone-responsive genes using cDNA microarray analysis. Fifteen genes were identified as progesterone-responsive gene candidates by microarray analysis and their progesterone-responsiveness was shown by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis. Out of these 15 genes, we focused on TRIM22. A database search revealed a progesterone response element (PRE) located from the -25 to -11 bp region upstream of TRIM22 exon 1. This PRE had a 1-bp mismatch in the consensus PRE sequence. A chromatin immunoprecipitation assay revealed that the interaction of PR with the TRIM22 PRE region increased in a hormone-dependent manner. The progesterone-dependent enhancer activity of TRIM22 PRE was demonstrated using a luciferase assay. Based on these results, we propose that TRIM22 is a direct target gene of PR and that it can mediate progesterone actions in uterine cells.

TRIM22 can activate the noncanonical NF-κB pathway by affecting IKKα

Tripartite motif 22 (TRIM22) is involved in various cellular processes. It has been reported that TRIM22 can activate nuclear factor-κB (NF-κB) pathway, but the precise mechanism remains unclear. In this study, we explored the exact role of TRIM22 in activating the NF-κB pathway. Different to tumor necrosis factor-α (TNF-α) induction, we found that the overexpression of TRIM22 could induce the processing of p100 to p52 in HEK293T cells. Furthermore, based on the results of co-immunoprecipitation and co-localization experiments, we demonstrated that TRIM22 could interact with IκB kinase (IKK)α but not IKKβ and could increase the level and phosphorylation of IKKα through its really interesting new gene (RING) and spla-ryanodine receptor (SPRY) domains. These results suggest that TRIM22 is able to activate the noncanonical but not the canonical NF-κB pathway by activating IKKα. This finding will aid our understanding of the biological function of TRIM22.

Interferon alpha (IFNα)-induced TRIM22 interrupts HCV replication by ubiquitinating NS5A

TRIM22, a tripartite-motif (TRIM) protein, is upregulated upon interferon alpha (IFNα) administration to hepatitis C virus (HCV)-infected patients. However, the physiological role of TRIM22 upregulation remains unclear. Here, we describe a potential antiviral function of TRIM22's targeting of the HCV NS5A protein. NS5A is important for HCV replication and for resistance to IFNα therapy. During the first 24 h following the initiation of IFNα treatment, upregulation of TRIM22 in the peripheral blood mononuclear cells (PBMCs) of HCV patients correlated with a decrease in viral titer. This phenomenon was confirmed in the hepatocyte-derived cell line Huh-7, which is highly permissive for HCV infection. TRIM22 over-expression inhibited HCV replication, and Small interfering RNA (siRNA)-mediated knockdown of TRIM22 diminished IFNα-induced anti-HCV function. Furthermore, we determined that TRIM22 ubiquitinates NS5A in a concentration-dependent manner. In summary, our results suggest that TRIM22 upregulation is associated with HCV decline during IFNα treatment and plays an important role in controlling HCV replication in vitro.

Protein arginine methyltransferase 6 enhances ligand-dependent and -independent activity of estrogen receptor α via distinct mechanisms

Recent studies reported that protein arginine methyltransferase 6 (PRMT6) enhances estrogen-induced activity of estrogen receptor α (ERα) and dysfunction of PRMT6 is associated with overall better survival for ERα-positive breast cancer patients. However, it is unclear how PRMT6 promotes ERα activity. Here we report that PRMT6 specifically interacts with ERα at its ligand-binding domain. PRMT6 also methylates ERα both in vitro and in vivo. In addition to enhancing estrogen-induced ERα activity, PRMT6 over-expression up-regulates estrogen-independent activity of ERα and PRMT6 gene silencing in MCF7 cells inhibits ligand-independent ERα activation. More interestingly, the effect of PRMT6 on the ligand-independent ERα activity does not require its methyltransferase activity. Instead, PRMT6 competes with Hsp90 for ERα binding: PRMT6 and Hsp90 bindings to ERα are mutually exclusive and PRMT6 over-expression reduces ERα interaction with Hsp90. In conclusion, PRMT6 requires its methyltransferase activity to enhance ERα's ligand-induced activity, but its effect on ligand-independent activity is likely mediated through competing with Hsp90 for binding to the C-terminal domain of ERα. PRMT6-ERα interaction would prevent ERα-Hsp90 association. Since Hsp90 and associated chaperones serve to maintain ERα conformation for ligand-binding yet functionally inactive, inhibition of ERα-Hsp90 interaction would relieve ERα from the constraint of chaperone complex.

Down-regulation of tripartite-motif containing 22 expression in breast cancer is associated with a lack of p53-mediated induction

Tripartite-motif containing 22 (TRIM22) is a direct p53 target gene and inhibits the clonogenic growth of leukemic cells. Its expression in Wilms tumors is negatively associated with disease relapse. This study addresses if TRIM22 expression is de-regulated in breast carcinoma. Western blotting analysis of a panel of 10 breast cancer cell lines and 3 non-malignant mammary epithelial cell lines with a well-characterized TRIM22 monoclonal antibody showed that TRIM22 protein is greatly under-expressed in breast cancer cells as compared to non-malignant cell lines. Similarly, TRIM22 protein is significantly down-regulated in breast tumors as compared to matched normal breast tissues. Study of cell lines with methylation inhibitor and bisulfite sequencing indicates that TRIM22 promoter hypermethylation may not be the cause for TRIM22 under-expression in breast cancer. Instead, we found that TRIM22 protein level correlates strongly (R=0.79) with p53 protein level in normal breast tissue, but this correlation is markedly impaired (R=0.48) in breast cancer tissue, suggesting that there is some defects in p53 regulation of TRIM22 gene in breast cancer. This notion is supported by cell line studies, which showed that TRIM22 was no longer inducible by p53-activating genotoxic drugs in breast cancer cell lines and in a p53 null cell line H1299 transfected with wild type p53. In conclusion, this study shows that TRIM22 is greatly under-expressed in breast cancer. p53 dysfunction may be one of the mechanisms for TRIM22 down-regulation.

Characterization of TRIM62 as a RING finger E3 ubiquitin ligase and its subcellular localization

TRIM62, also named DEAR1, is a member of the TRIM/RBCC family, which includes proteins with conserved RING finger, B-box and coiled-coil domains. Several reports have identified a role for this family in cancer, retroviral infection and innate immunity. In this study, the E3 ubiquitin ligase activity and subcellular localization of TRIM62 were characterized. TRIM62, in association with the E2 enzyme UbcH5b, was found to catalyze self-ubiquitination in vitro, a process that required an intact RING finger domain. A ubiquitination assay performed in HEK293T cells further confirmed the E3 ubiquitin ligase activity and self-ubiquitination activity of TRIM62 and the requirement of the RING finger domain. Importantly, the treatment of HEK293T cells with a proteasome inhibitor stabilized poly-ubiquitinated TRIM62, indicating that self-ubiquitination promoted the proteasomal degradation of TRIM62. Additionally, TRIM62 and its two mutants were distinctly localized in the cytoplasm in both HEK293T and HeLa cells. Collectively, our data indicate that TRIM62, a cytoplasmic protein, is a RING finger domain-dependent E3 ubiquitin ligase that catalyzes self-ubiquitination both in vitro and in vivo.

Characterisation of human RING finger protein TRIM69, a novel testis E3 ubiquitin ligase and its subcellular localisation

The E3 ubiquitin ligase activity and subcellular localisation of human TRIM69 (hTRIM69) gene were studied. It was found that hTRIM69 mediated ubiquitination in an E2 conjugating enzyme selective fashion in vitro and an intact RING finger domain was indispensible for the process. Further evidences showed that hTRIM69 could mediate ubiquitination in vivo, which could be enhanced by a proteasome inhibitor. hTRIM69 was found to localise in both the cytoplasm and the nucleus in a speckled aggregating pattern, which also required an intact RING finger domain. Collectively, hTRIM69 is a novel E3 ubiquitin ligase identified from human testis and may function to ubiquitinate its particular substrates during spermatogenesis.

TRIM22: A Diverse and Dynamic Antiviral Protein

The tripartite motif (TRIM) family of proteins is an evolutionarily ancient group of proteins with homologues identified in both invertebrate and vertebrate species. Human TRIM22 is one such protein that has a dynamic evolutionary history that includes gene expansion, gene loss, and strong signatures of positive selection. To date, TRIM22 has been shown to restrict the replication of a number of viruses, including encephalomyocarditis virus (EMCV), hepatitis B virus (HBV), and human immunodeficiency virus type 1 (HIV-1). In addition, TRIM22 has also been implicated in cellular differentiation and proliferation and may play a role in certain cancers and autoimmune diseases. This comprehensive paper summarizes our current understanding of TRIM22 structure and function.

TRIM22 inhibits HIV-1 transcription independently of its E3 ubiquitin ligase activity, Tat, and NF-kappaB-responsive long terminal repeat elements

Previous studies identified clones of the U937 promonocytic cell line that were either permissive or nonpermissive for human immunodeficiency virus type 1 (HIV-1) replication. These clones were investigated further in the search for host restriction factors that could explain their differential capacity to support HIV-1 replication. Among known HIV-1 restriction factors screened, tripartite motif-containing protein 22 (TRIM22) was the only factor constitutively expressed in nonpermissive and absent in permissive U937 cells. Stable TRIM22 knockdown (KD) rescued HIV-1 long-terminal-repeat (LTR)-driven transcription in KD-nonpermissive cells to the levels observed in permissive cells. Conversely, transduction-mediated expression of TRIM22 in permissive cells reduced LTR-driven luciferase expression by ∼7-fold, supporting a negative role of TRIM22 in HIV-1 transcription. This finding was further confirmed in the human T cell line A3.01 expressing TRIM22. Moreover, overexpression of TRIM22 in 293T cells significantly impaired basal and phorbol myristate acetate-ionomycin-induced HIV-1 LTR-driven gene expression, whereas inhibition of tumor necrosis factor alpha-induced viral transcription was a consequence of lower basal expression. In agreement, TRIM22 equally inhibited an LTR construct lacking the tandem NF-κB binding sites. In addition, TRIM22 did not affect Tat-mediated LTR transactivation. Finally, these effects were independent of TRIM22 E3 ubiquitin-ligase activity. In the context of replication-competent virus, significantly higher levels of HIV-1 production were observed in KD-nonpermissive versus control nonpermissive U937 cells after infection. In contrast, lower peak levels of HIV-1 replication characterized U937 and A3.01 cells expressing TRIM22 versus their control transduced counterpart. Thus, nuclear TRIM22 significantly impairs HIV-1 replication, likely by interfering with Tat- and NF-κB-independent LTR-driven transcription.

Restriction factors of retroviral replication: the example of Tripartite Motif (TRIM) protein 5 alpha and 22

Viral tropism, replication, and pathogenesis are determined by multiple interactions between the pathogen and the host. In the case of retroviruses, and in particular, the human immunodeficiency virus, the specific interaction of the envelope protein with the host receptors and co-receptors is essential to gain entry in the cells. After entry, the success of retroviruses to complete their life cycle depends on a complex interplay between the virus and host proteins. Indeed, the cell environment is endowed with a number of factors that actively block distinct stage(s) in the microbial life cycle. Among these restriction factors, Tripartite Motif-5 alpha (TRIM5 alpha) has been extensively studied; however, other TRIM family members have been demonstrated to be anti-retroviral effector proteins. This article reviews, in particular, the current knowledge on the anti-retroviral effects of TRIM5 alpha and TRIM22.

B30.2/SPRY domain in tripartite motif-containing 22 is essential for the formation of distinct nuclear bodies

Tripartite motif-containing 22 (TRIM22) is an important antiviral protein that forms distinct nuclear bodies (NB) in many cell types. This study aims to identify functional domains/residues for TRIM22's nuclear localization and NB formation. Deletion of the really-interesting-new-gene (RING) domain, which is essential for its antiviral property, abolished TRIM22 NB formation. However, mutation of two critical residues Cys15 and Cys18 to alanine in the RING domain, did not affect NB formation notably. Although the deletion of the putative bipartite nuclear localization signal (NLS) abolished TRIM22 localization and NB formation, the B30.2/SplA and ryanodine receptor (SPRY) domain, and residues 491-494 specifically are also essential for nuclear localization and NB formation.