Highlights on distinctive structural and functional properties of HTLV Tax proteins

Phylogenetic and Mutational Analysis of the Tax Gene in the Human T-Lymphotropic Virus 1-Associated HAM/TSP in Comparison with Asymptomatic Careers

Background

Human T-lymphotropic virus 1 (HTLV-1) is a member of the Retroviridae family that can cause two groups of diseases: HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T-cell leukemia/lymphoma (ATLL). Despite HTLV having seven different subtypes, cosmopolitan subtype A is responsible for most HTLV-1-related disorders and is the most widely dispersed type globally, including in the Middle East, known to be an endemic area for the virus. Therefore, due to the importance of determining the subtypes of this virus, we aimed to explore the subtypes of HTLV-1 in Iran.

Methods

In this cross-sectional study, we screened 140 Blood samples for HAM/TSP infection and approximately 4,500 samples for asymptomatic carriers (ACs) from Sina Hospital, Iran between 2020 and 2021. Positive samples were used for phylogenetic and mutational analysis to compare ACs and HAM/TSP cases via the Tax segment of HTLV. To identify the genotype of positive samples, the Maximum Likelihood method was used to construct the phylogenetic tree based on the positive samples.

Results

All Iranian isolates were clustered as HTLV-1a subgroups. Moreover, all of our samples have undergone positive selection pressure. Furthermore, we detected unique mutations in Iranian HAM/TSP and ACs sequences.

Conclusion

All of the Iranian Tax proteins are under positive selection pressure with respect to Japanese isolates. Interestingly, we detect specific mutation patterns in the sequences. Positions 51, 82, 109, 172, 232, and 339 in the aa sequence have undergone mutations specific to Iranian HTLV-1; and in positions 22 and 146 aa we detected mutations unique to ACs and HAM/TSP, respectively.

A Panel of Eight miRNAs Is Deregulated in HTLV-2 Infected PBMCs and BJABGu Cell Line

Despite human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 being retroviruses closely related at a genomic level, HTLV-2 differs from HTLV-1 in terms of pathogenicity in both single infection and coinfection contexts. Moreover, the HTLV-2 association with clinical outcomes is still debated and several mechanisms underlying HTLV-2 infection remain unexplored as well. Cellular miRNAs are key factors in the post-transcriptional regulation of gene expression and they are known to be potential targets for several pathogens to control the host microenvironment and, in particular, escape immune responses. Here, we identified a HTLV-2-related signature of eight miRNAs (miR-125a-3p, miR-381-3p, miR-502-5p, miR-708-5p, miR-548d-5p, miR-548c-5p, miR-1-3p, and miR-511-5p) in both HTLV-2 infected PBMC and BJABGu cell lines. Altered miRNA expression patterns were correlated with the impairment of Th cell differentiation and signaling pathways driven by cytokines and transcriptional factors such as the Runt-related transcription factor (RUNX) family members. Specifically, we demonstrated that the RUNX2 protein was significantly more expressed in the presence of Tax-2 compared with Tax-1 in an in vitro cell model. To the best of our knowledge, these data represent the first contribution to elucidating the HTLV-2 mediated alteration of host cell miRNA profiles that may impact on HTLV-2 replication and persistent infection.

Alternative NF-κB Signaling Discriminates Induction of the Tumor Marker Fascin by the Viral Oncoproteins Tax-1 and Tax-2 of Human T-Cell Leukemia Viruses

Transcriptional regulation of the actin-bundling protein and tumor marker Fascin is highly diverse depending on cell and tumor type. Previously, we discovered that the viral oncoprotein Tax-1 of human T-cell leukemia virus type 1 (HTLV-1) considerably enhances Fascin expression in T-cells, depending on classical NF-κB signaling. In this study, we asked if the non-oncogenic Tax-2 of the related HTLV-2 is still able to induce Fascin by using luciferase assays, immunoblot, and qPCR. We found that Tax-2 only slightly induces Fascin expression compared to Tax-1; however, both Tax-1 and Tax-2 comparably activated a 1.6 kb fragment in the human Fascin promoter including Tax-responsive elements. Furthermore, we identified a link between Tax-induced activity of the alternative NF-κB pathway and Fascin induction. While treatment with the second mitochondria-derived activator of caspases (SMAC)-mimetic AZD5582, a compound known to robustly activate alternative NF-κB signaling, did not induce Fascin, combination of AZD5582 with activation of classical NF-κB signaling by Tax-2 significantly induced Fascin expression. In conclusion, our data demonstrate that both classical and alternative NF-κB activity are necessary for strong Fascin induction by the viral Tax oncoproteins, thus, shedding new light on the regulation of Fascin in T-cells and during viral transformation.

Exosomes: Emerging implementation of nanotechnology for detecting and managing novel corona virus- SARS-CoV-2

The spread of SARS-CoV-2 as an emerging novel coronavirus disease (COVID-19) had progressed as a worldwide pandemic since the end of 2019. COVID-19 affects firstly lungs tissues which are known for their very slow regeneration. Afterwards, enormous cytokine stimulation occurs in the infected cells immediately after a lung infection which necessitates good management to save patients. Exosomes are extracellular vesicles of nanometric size released by reticulocytes on maturation and are known to mediate intercellular communications. The exosomal cargo serves as biomarkers in diagnosing various diseases; moreover, exosomes could be employed as nanocarriers in drug delivery systems. Exosomes look promising to combat the current pandemic since they contribute to the immune response against several viral pathogens. Many studies have proved the potential of using exosomes either as viral elements or host systems that acquire immune-stimulatory effects and could be used as a vaccine or drug delivery tool. It is essential to stop viral replication, prevent and reverse the massive storm of cytokine that worsens the infected patients' situations for the management of COVID-19. The main benefits of exosomes could be; no cells will be introduced, no chance of mutation, lack of immunogenicity and the damaged genetic material that could negatively affect the recipient is avoided. Additionally, it was found that exosomes are static with no ability for in vivo reproduction. The current review article discusses the possibilities of using exosomes for detecting novel coronavirus and summarizes state of the art concerning the clinical trials initiated for examining the use of COVID-19 specific T cells derived exosomes and mesenchymal stem cells derived exosomes in managing COVID-19.

Characterizing the Interaction between the HTLV-1 Transactivator Tax-1 with Transcription Elongation Factor ELL2 and Its Impact on Viral Transactivation

The human T-cell leukemia virus type 1 (HTLV-1)-encoded transactivator and oncoprotein Tax-1 is essential for HTLV-1 replication. We recently found that Tax-1 interacts with transcription elongation factor for RNA polymerase II 2, ELL2, which enhances Tax-1-mediated transactivation of the HTLV-1 promotor. Here, we characterize the Tax-1:ELL2 interaction and its impact on viral transactivation by confocal imaging, co-immunoprecipitation, and luciferase assays. We found that Tax-1 and ELL2 not only co-precipitate, but also co-localize in dot-like structures in the nucleus. Tax-1:ELL2 complex formation occurred independently of Tax-1 point mutations, which are crucial for post translational modifications (PTMs) of Tax-1, suggesting that these PTMs are irrelevant for Tax-1:ELL2 interaction. In contrast, Tax-1 deletion mutants lacking either N-terminal (aa 1-37) or C-terminal regions (aa 150-353) of Tax-1 were impaired in interacting with ELL2. Contrary to Tax-1, the related, non-oncogenic Tax-2B from HTLV-2B did not interact with ELL2. Finally, we found that ELL2-R1 (aa 1-353), which carries an RNA polymerase II binding domain, and ELL2-R3 (aa 515-640) are sufficient to interact with Tax-1; however, only ELL2-truncations expressing R1 could enhance Tax-1-mediated transactivation of the HTLV-1 promoter. Together, this study identifies domains in Tax-1 and ELL2 being required for Tax-1:ELL2 complex formation and for viral transactivation.

Retroviral Antisense Transcripts and Genes: 33 Years after First Predicted, a Silent Retroviral Revolution?

Paradigm shifts throughout the history of microbiology have typically been ignored, or met with skepticism and resistance, by the scientific community. This has been especially true in the field of virology, where the discovery of a "contagium vivum fluidum", or infectious fluid remaining after excluding bacteria by filtration, was initially ignored because it did not coincide with the established view of microorganisms. Subsequent studies on such infectious agents, eventually termed "viruses", were met with skepticism. However, after an abundance of proof accumulated, viruses were eventually acknowledged as defined microbiological entities. Next, the proposed role of viruses in oncogenesis in animals was disputed, as was the unique mechanism of genome replication by reverse transcription of RNA by the retroviruses. This same pattern of skepticism holds true for the prediction of the existence of retroviral "antisense" transcripts and genes. From the time of their discovery, it was thought that retroviruses encoded proteins on only one strand of proviral DNA. However, in 1988, it was predicted that human immunodeficiency virus type 1 (HIV-1), and other retroviruses, express an antisense protein encoded on the DNA strand opposite that encoding the known viral proteins. Confirmation came quickly with the characterization of the antisense protein, HBZ, of the human T-cell leukemia virus type 1 (HTLV-1), and the finding that both the protein and its antisense mRNA transcript play key roles in viral replication and pathogenesis. However, acceptance of the existence, and potential importance, of a corresponding antisense transcript and protein (ASP) in HIV-1 infection and pathogenesis has lagged, despite gradually accumulating theoretical and experimental evidence. The most striking theoretical evidence is the finding that asp is highly conserved in group M viruses and correlates exclusively with subtypes, or clades, responsible for the AIDS pandemic. This review outlines the history of the major shifts in thought pertaining to the nature and characteristics of viruses, and in particular retroviruses, and details the development of the hypothesis that retroviral antisense transcripts and genes exist. We conclude that there is a need to accelerate studies on ASP, and its transcript(s), with the view that both may be important, and overlooked, targets in anti-HIV therapeutic and vaccine strategies.

Molecular epidemiology and phylogenetic analysis of human T-lymphotropic virus type 1 in the tax gene and it association with adult t-cell leukemia/lymphoma disorders

Background and Objectives:

Human T-lymphotropic virus type-1 (HTLV-1) belongs to retrovirus family that causes the neurological disorder HTLV-1 adult T-cell leukemia/lymphoma (ATLL). Since 1980, seven subtypes of the virus have been recognized. HTLV-1 is prevalent and endemic in some regions, such as Africa, Japan, South America and Iran as the endemic regions of the HTLV-1 in the Middle East. To study HTLV-1 subtypes and routes of virus spread in Iran, phylogenetic and phylodynamic analyses were performed and for as much as no previous phylogenetic studies were conducted in Tehran, we do this survey. To this purpose, the Tax region of HTLV-1 was used.

Materials and Methods:

In this study 100 samples were collected from blood donors in Tehran. All samples were screened for anti-HTLV-I antibodies by ELISA. Then, genomic DNA was extracted from all positive samples (10 people), and for confirmation of infection, ordinary PCR was performed for both the HBZ and LTR regions. Moreover, the Tax region was amplified and purified PCR products were sequenced and analyzed, and finally, a phylogenetic tree was constructed using Mega X software.

Results:

Phylogenetic analysis confirmed that isolates from Iran, Japan, Brazil, and Africa are located within the extensive “transcontinental” subgroup A clade of HTLV-1 Cosmopolitan subtype a. The Japanese sequences are the closest to the Iranian sequences and have the most genetic similarity with them.

Conclusion:

Through phylogenetic and phylodynamic analyses HTLV-1 strain in Tehran were characterized in Iran. The appearance of HTLV-1 in Iran was probably happened by the ancient Silk Road which linked China to Antioch.

HTLV-1 Infection and Pathogenesis: New Insights from Cellular and Animal Models

Since the discovery of the human T-cell leukemia virus-1 (HTLV-1), cellular and animal models have provided invaluable contributions in the knowledge of viral infection, transmission and progression of HTLV-associated diseases. HTLV-1 is the causative agent of the aggressive adult T-cell leukemia/lymphoma and inflammatory diseases such as the HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). Cell models contribute to defining the role of HTLV proteins, as well as the mechanisms of cell-to-cell transmission of the virus. Otherwise, selected and engineered animal models are currently applied to recapitulate in vivo the HTLV-1 associated pathogenesis and to verify the effectiveness of viral therapy and host immune response. Here we review the current cell models for studying virus–host interaction, cellular restriction factors and cell pathway deregulation mediated by HTLV products. We recapitulate the most effective animal models applied to investigate the pathogenesis of HTLV-1-associated diseases such as transgenic and humanized mice, rabbit and monkey models. Finally, we summarize the studies on STLV and BLV, two closely related HTLV-1 viruses in animals. The most recent anticancer and HAM/TSP therapies are also discussed in view of the most reliable experimental models that may accelerate the translation from the experimental findings to effective therapies in infected patients.

A novel positive feedback-loop between the HTLV-1 oncoprotein Tax and NF-κB activity in T-cells

Background

Human T-cell leukemia virus type 1 (HTLV-1) infects primarily CD4⁺ T-lymphocytes and evoques severe diseases, predominantly Adult T-Cell Leukemia/ Lymphoma (ATL/L) and HTLV-1-associated Myelopathy/ Tropical Spastic Paraparesis (HAM/TSP). The viral transactivator of the pX region (Tax) is important for initiating malignant transformation, and deregulation of the major signaling pathway nuclear factor of kappa B (NF-κB) by Tax represents a hallmark of HTLV-1 driven cancer.

Results

Here we found that Tax mutants which are defective in NF-κB signaling showed diminished protein expression levels compared to Tax wildtype in T-cells, whereas Tax transcript levels were comparable. Strikingly, constant activation of NF-κB signaling by the constitutive active mutant of inhibitor of kappa B kinase (IKK2, IKK-β), IKK2-EE, rescued protein expression of the NF-κB defective Tax mutants M22 and K1-10R and even increased protein levels of Tax wildtype in various T-cell lines while Tax transcript levels were only slightly affected. Using several Tax expression constructs, an increase of Tax protein occurred independent of Tax transcripts and independent of the promoter used. Further, Tax and M22 protein expression were strongly enhanced by 12-O-Tetradecanoylphorbol-13-Acetate [TPA; Phorbol 12-myristate 13-acetate (PMA)]/ ionomycin, inducers of NF-κB and cytokine signaling, but not by tumor necrosis factor alpha (TNF-α). On the other hand, co-expression of Tax with a dominant negative inhibitor of κB, IκBα-DN, or specific inhibition of IKK2 by the compound ACHP, led to a vast decrease in Tax protein levels to some extent independent of Tax transcripts in transiently transfected and Tax-transformed T-cells. Cycloheximide chase experiments revealed that co-expression of IKK2-EE prolongs the half-life of M22, and constant repression of NF-κB signaling by IκBα-DN strongly reduces protein stability of Tax wildtype suggesting that NF-κB activity is required for Tax protein stability. Finally, protein expression of Tax and M22 could be recovered by NH₄Cl and PYR-41, inhibitors of the lysosome and the ubiquitin-activating enzyme E1, respectively.

Conclusions

Together, these findings suggest that Tax’s capability to induce NF-κB is critical for protein expression and stabilization of Tax itself. Overall, identification of this novel positive feedback loop between Tax and NF-κB in T-cells improves our understanding of Tax-driven transformation.

The ESCRT-0 Protein HRS Interacts with the Human T Cell Leukemia Virus Type 2 Antisense Protein APH-2 and Suppresses Viral Replication

The divergent clinical outcomes of human T cell leukemia virus type 1 (HTLV-1) and HTLV-2 infections have been attributed to functional differences in their antisense proteins. In contrast to HTLV-1 bZIP factor (HBZ), the role of the antisense protein of HTLV-2 (APH-2) in HTLV-2 infection is poorly understood. In previous studies, we identified the endosomal sorting complex required for transport 0 (ESCRT-0) subunit HRS as a novel interaction partner of APH-2 but not HBZ. HRS is a master regulator of endosomal protein sorting for lysosomal degradation and is hijacked by many viruses to promote replication. However, no studies to date have shown a link between HTLVs and HRS. In this study, we sought to characterize the interaction between HRS and APH-2 and to investigate the impact of HRS on the life cycle of HTLV-2. We confirmed a direct specific interaction between APH-2 and HRS and showed that the CC2 domain of HRS and the N-terminal domain of APH-2 mediate their interaction. We demonstrated that HRS recruits APH-2 to early endosomes, possibly furnishing an entry route into the endosomal/lysosomal pathway. We demonstrated that inhibition of this pathway using either bafilomycin or HRS overexpression substantially extends the half-life of APH-2 and stabilizes Tax2B expression levels. We found that HRS enhances Tax2B-mediated long terminal repeat (LTR) activation, while depletion of HRS enhances HTLV-2 production and release, indicating that HRS may have a negative impact on HTLV-2 replication. Overall, our study provides important new insights into the role of the ESCRT-0 HRS protein, and by extension the ESCRT machinery and the endosomal/lysosomal pathway, in HTLV-2 infection.IMPORTANCE While APH-2 is the only viral protein consistently expressed in infected carriers, its role in HTLV-2 infection is poorly understood. In this study, we characterized the interaction between the ESCRT-0 component HRS and APH-2 and explored the role of HRS in HTLV-2 replication. HRS is a master regulator of protein sorting for lysosomal degradation, a feature that is manipulated by several viruses to promote replication. Unexpectedly, we found that HRS targets APH-2 and possibly Tax2B for lysosomal degradation and has an overall negative impact on HTLV-2 replication and release. The negative impact of interactions between HTLV-2 regulatory proteins and HRS, and by extension the ESCRT machinery, may represent an important strategy used by HTLV-2 to limit virus production and to promote persistence, features that may contribute to the limited pathogenic potential of this infection.

NF-κB and MicroRNA Deregulation Mediated by HTLV-1 Tax and HBZ

The risk of developing adult T-cell leukemia/lymphoma (ATLL) in individuals infected with human T-cell lymphotropic virus 1 (HTLV-1) is about 3-5%. The mechanisms by which the virus triggers this aggressive cancer are still an area of intensive investigation. The viral protein Tax-1, together with additional regulatory proteins, in particular HTLV-1 basic leucine zipper factor (HBZ), are recognized as relevant viral factors required for both viral replication and transformation of infected cells. Tax-1 deregulates several cellular pathways affecting the cell cycle, survival, and proliferation. The effects of Tax-1 on the NF-κB pathway have been thoroughly studied. Recent studies also revealed the impact of Tax-1 and HBZ on microRNA expression. In this review, we summarize the recent progress in understanding the contribution of HTLV-1 Tax- and HBZ-mediated deregulation of NF-κB and the microRNA regulatory network to HTLV-1 pathogenesis.

Nanomedicinal strategies as efficient therapeutic interventions for delivery of cancer vaccines

The applications of gene therapy-based treatment of cancers were started almost two decades back as a boon over the chemotherapeutic treatment strategies. Gene therapy helps in correcting the genetic sequences for treatment of cancers, thus also acts like a vaccine to induce the cellular and humoral immunity. However, the cancer vaccines typically suffer from a series of biopharmaceutical challenges due to poor solubility, low systemic availability and lack of targeting ability. Owing to these challenges, the physicians and pharmaceutical scientists have explored the applications of nanocarriers as quite promising systems for effective treatment against the tumors. A series of nanotherapeutic systems are available to date for diverse drug therapy applications. Systematic understanding on the preparation, evaluation and application of nanomedicines as a carrier system for delivering the cancer vaccines is highly important. The present review article provides an in-depth understanding on the challenges associated with cancer vaccine delivery and current opportunities with diverse nanomedicinal carriers being available for treatment of cancers.

Post-transcriptional Regulation of HTLV Gene Expression: Rex to the Rescue

Human T-lymphotropic virus type 1 (HTLV-1) and other members of the Deltaretrovirus genus code for a regulatory protein named Rex that binds to the Rex-responsive element present on viral mRNAs. Rex rescues viral mRNAs from complete splicing or degradation and guides them to the cytoplasm for translation. The activity of Rex is essential for expression of viral transcripts coding for the virion components and thus represents a potential target for virus eradication. We present an overview of the functional properties of the HTLV-1 and HTLV-2 Rex proteins (Rex-1 and Rex-2), outline mechanisms controlling Rex function, and discuss similarities and differences in the sequences of Rex coded by HTLV-1, -2, -3, and -4 that may influence their molecular anatomy and functional properties.

TRAF3 Is Required for NF-κB Pathway Activation Mediated by HTLV Tax Proteins

Human T-cell leukemia viruses type 1 (HTLV-1) and type 2 (HTLV-2) share a common genome organization and expression strategy but have distinct pathological properties. HTLV-1 is the etiological agent of Adult T-cell Leukemia (ATL) and of HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP), whereas HTLV-2 does not cause hematological disorders and is only sporadically associated with cases of subacute myelopathy. Both HTLV genomes encode two regulatory proteins that play a pivotal role in pathogenesis: the transactivating Tax-1 and Tax-2 proteins and the antisense proteins HBZ and APH-2, respectively. We recently reported that Tax-1 and Tax-2 form complexes with the TNF-receptor associated factor 3, TRAF3, a negative regulator of the non-canonical NF-κB pathway. The NF-κB pathway is constitutively activated by the Tax proteins, whereas it is inhibited by HBZ and APH-2. The antagonistic effects of Tax and antisense proteins on NF-κB activation have not yet been fully clarified. Here, we investigated the effect of TRAF3 interaction with HTLV regulatory proteins and in particular its consequence on the subcellular distribution of the effector p65/RelA protein. We demonstrated that Tax-1 and Tax-2 efficiency on NF-κB activation is impaired in TRAF3 deficient cells obtained by CRISPR/Cas9 editing. We also found that APH-2 is more effective than HBZ in preventing Tax-dependent NF-κB activation. We further observed that TRAF3 co-localizes with Tax-2 and APH-2 in cytoplasmic complexes together with NF-κB essential modulator NEMO and TAB2, differently from HBZ and TRAF3. These results contribute to untangle the mechanism of NF-κB inhibition by HBZ and APH-2, highlighting the different role of the HTLV-1 and HTLV-2 regulatory proteins in the NF-κB activation.

Hypericin-photodynamic therapy inhibits the growth of adult T-cell leukemia cells through induction of apoptosis and suppression of viral transcription

BACKGROUND

Adult T-cell leukemia (ATL) is an aggressive neoplasm caused by human T-cell leukemia virus type 1 (HTLV-1). ATL carries a poor prognosis due to chemotherapy resistance. Thus, it is urgent to develop new treatment strategies. Hypericin (HY) is a new-type of photosensitizer in the context of photodynamic therapy (PDT) due to its excellent photosensitizing properties and anti-tumor activities.

RESULTS

In the present study, we investigated the efficacy of hypericin in ATL cells. Clinically achievable concentrations of hypericin in association with PDT induced the inhibition of cell proliferation in ATL cell lines with minimal effect on peripheral blood CD4⁺ T lymphocytes. Moreover, hypericin-PDT treatment caused apoptosis and G2/M phase cell cycle arrest in leukemic cells. Western blot analyses revealed that hypericin-PDT treatment resulted in downregulation of Bcl-2 and enhanced the expression of Bad, cytochrome C, and AIF. Cleavage of caspases-3/-7/-9/-8, Bid, and PARP was increased in hypericin-PDT-treated ATL cells. In a luciferase assay, hypericin-PDT treatment was able to activate the promoter activity of Bax and p53, resulting in enhanced expression of Bax and p53 proteins. Finally, hypericin-PDT treatment suppressed the expression of viral protein HBZ and Tax by blocking the promoter activity via HTLV-1 5'LTR and 3'LTR.

CONCLUSIONS

Our results revealed that hypericin-PDT is highly effective against ATL cells by induction of apoptosis and suppression of viral transcription. These studies highlight the promising use of hypericin-PDT as a targeted therapy for ATL.

High CD8 T cell percentage and HCV replication control are common features in HIV-1 controllers and HTLV-2-co-infected patients with a history of injection drug use

HTLV-2/HIV-1-coinfected patients and HIV-infected patients with natural HIV-1 control show an immune capacity that allows some control of viral infections. These two groups of patients have showed an immune capacity that allows them to have some control over viral infections, very strong control of HIV-1 replication in the case of HIV-1 controllers. The purpose of this retrospective cross-sectional study was to compare viral and immunologic parameters between three cohorts of Caucasian adult HIV-1-infected patients, including HIV-1 controllers (29 patients), HTLV-2/HIV-1 chronic progressors (56 patients), and HIV-1 chronic progressors (101 patients), followed in two different tertiary University Hospitals in Spain. Demographic parameters, nadir CD4 T cell count, CD4 and CD8 T cell counts and percentage, anti-HCV antibodies, HCV RNA load, HCV genotype, HIV-1 RNA loads, and anti-HTLV-2 antibodies were analyzed. HIV-1 controllers and HTLV-2/HIV-1 chronic progressors were younger and with shorter time since HIV-1 diagnosis compared to HIV-1 chronic progressors. HIV-1 controllers and HTLV-2/HIV-1 chronic progressors had significantly higher CD8 T cell percentage (p = 0.002 and p = 0.016, respectively) and lower levels of HCV RNA loads (0.015 and 0.007, respectively) compared to that of HIV-1 chronic progressors. Multivariate analyses showed that gender and HTLV-2 infection were independently associated to HCV RNA load, while only HTLV-2 infection was independently associated to CD8 T cell percentage. The implication of HTLV-2 infection in the control of HIV-1 and HCV infections is worth being further analyze.

Deregulation of the Notch pathway as a common road in viral carcinogenesis

The Notch pathway is a conserved signaling pathway and a form of direct cell-cell communication related to many biological processes during development and adulthood. Deregulation of the Notch pathway is involved in many diseases, including cancer. Almost 20% of all cancer cases have an infectious etiology, with viruses responsible for at least 1.5 million new cancer cases per year. Seven groups of viruses have been classified as oncogenic: hepatitis B and C viruses (HBV and HCV respectively), Epstein-Barr virus (EBV), Kaposi sarcoma-associated herpesvirus (KSHV), human T lymphotropic virus (HTLV-1), human papillomavirus (HPV), and Merkel cell polyomavirus (MCPyV). These viruses share the ability to manipulate a variety of cell pathways that are critical in proliferation and differentiation, leading to malignant transformation. Viral proteins interact directly or indirectly with different members of the Notch pathway, altering their normal function. This review focuses exclusively on the direct interactions of viral oncoproteins with Notch elements, providing a deeper understanding of the dual behavior of the Notch pathway as activator or suppressor of neoplasia in virus-related cancers.

A Preclinical Model for the ATLL Lymphoma Subtype With Insights Into the Role of Microenvironment in HTLV-1-Mediated Lymphomagenesis

Adult T cell Leukemia/Lymphoma (ATLL) is a mature T cell malignancy associated with Human T cell Leukemia Virus type 1 (HTLV-1) infection. Among its four main clinical subtypes, the prognosis of acute and lymphoma variants remains poor. The long latency (3–6 decades) and low incidence (3–5%) of ATLL imply the involvement of viral and host factors in full-blown malignancy. Despite multiple preclinical and clinical studies, the contribution of the stromal microenvironment in ATLL development is not yet completely unraveled. The aims of this study were to investigate the role of the host microenvironment, and specifically fibroblasts, in ATLL pathogenesis and to propose a murine model for the lymphoma subtype. Here we present evidence that the oncogenic capacity of HTLV-1-immortalized C91/PL cells is enhanced when they are xenotransplanted together with human foreskin fibroblasts (HFF) in immunocompromised BALB/c Rag2^-/-γ_c^-/- mice. Moreover, cell lines derived from a developed lymphoma and their subsequent in vivo passages acquired the stable property to induce aggressive T cell lymphomas. In particular, one of these cell lines, C91/III cells, consistently induced aggressive lymphomas also in NOD/SCID/IL2Rγ_c KO (NSG) mice. To dissect the mechanisms linked to this enhanced tumorigenic ability, we quantified 45 soluble factors released by these cell lines and found that 21 of them, mainly pro-inflammatory cytokines and chemokines, were significantly increased in C91/III cells compared to the parental C91/PL cells. Moreover, many of the increased factors were also released by human fibroblasts and belonged to the known secretory pattern of ATLL cells. C91/PL cells co-cultured with HFF showed features reminiscent of those observed in C91/III cells, including a similar secretory pattern and a more aggressive behavior in vivo. On the whole, our data provide evidence that fibroblasts, one of the major stromal components, might enhance tumorigenesis of HTLV-1-infected and immortalized T cells, thus throwing light on the role of microenvironment contribution in ATLL pathogenesis. We also propose that the lymphoma induced in NSG mice by injection with C91/III cells represents a new murine preclinical ATLL model that could be adopted to test novel therapeutic interventions for the aggressive lymphoma subtype.

Role of Exosomes in Human Retroviral Mediated Disorders

Retroviruses comprise an ancient and varied group of viruses with the unique ability to integrate DNA from an RNA transcript into the genome, a subset of which are able to integrate in humans. The timing of these integrations during human history has dictated whether these viruses have remained exogenous and given rise to various human diseases or have become inseparable from the host genome (endogenous retroviruses). Given the ability of retroviruses to integrate into the host and subsequently co-opt host cellular process for viral propagation, retroviruses have been shown to be closely associated with several cellular processes including exosome formation. Exosomes are 30-150 nm unilamellar extracellular vesicles that originate from intraluminal vesicles (ILVs) that form in the endosomal compartment. Exosomes have been shown to be important in intercellular communication and immune cell function. Almost every cell type studied has been shown to produce these types of vesicles, with the cell type dictating the contents, which include proteins, mRNA, and miRNAs. Importantly, recent evidence has shown that infection by viruses, including retroviruses, alter the contents and subsequent function of produced exosomes. In this review, we will discuss the important retroviruses associated with human health and disease. Furthermore, we will delve into the impact of exosome formation and manipulation by integrated retroviruses on human health, survival, and human retroviral disease pathogenesis.

HTLV Deregulation of the NF-κB Pathway: An Update on Tax and Antisense Proteins Role

Human T-cell lymphotropic virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia (ATL), an aggressive CD4+/CD25+ T-cell malignancy and of a severe neurodegenerative disease, HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). The chronic activation or deregulation of the canonical and non-canonical nuclear factor kappa B (NF-κB) pathways play a crucial role in tumorigenesis. The HTLV-1 Tax-1 oncoprotein is a potent activator of the NF-κB transcription factors and the NF-κB response is required for promoting the development of HTLV-1 transformed cell lines. The homologous retrovirus HTLV-2, which also expresses a Tax-2 transforming protein, is not associated with ATL. In this review, we provide an updated synopsis of the role of Tax-1 in the deregulation of the NF-κB pathway, highlighting the differences with the homologous Tax-2. Special emphasis is directed toward the understanding of the molecular mechanisms involved in NF-κB activation resulting from Tax interaction with host factors affecting several cellular processes, such as cell cycle, apoptosis, senescence, cell proliferation, autophagy, and post-translational modifications. We also discuss the current knowledge on the role of the antisense viral protein HBZ in down-regulating the NF-κB activation induced by Tax, and its implication in cellular senescence. In addition, we review the recent studies on the mechanism of HBZ-mediated inhibition of NF-κB activity as compared to that exerted by the HTLV-2 antisense protein, APH-2. Finally, we discuss recent advances aimed at understanding the role exerted in the development of ATL by the perturbation of NF-κB pathway by viral regulatory proteins.

EGF Uptake and Degradation Assay to Determine the Effect of HTLV Regulatory Proteins on the ESCRT-Dependent MVB Pathway

The endosomal sorting complex required for transport (ESCRT) pathway plays key roles in multivesicular bodies (MVBs) formation and lysosomal degradation of membrane receptors, viral budding, and midbody abscission during cytokinesis. The epidermal growth factor receptor (EGFR) is regarded as a prototypical cargo of the MVB/ESCRT pathway and following stimulation by epidermal growth factor (EGF) EGFR/EGF complexes are internalized, sorted into MVBs, and degraded by lysosomes or recycled back to the cell membrane. Here, we describe an assay to analyze the effect of human T-cell leukemia (HTLV) regulatory proteins on the functionality of ESCRT-dependent MVB/lysosomal trafficking of EGFR/EGF complexes. This is performed by direct visualization and quantification of the rate of EGF-Alexa595/EGFR internalization and degradation in HeLa cells expressing HTLV regulatory proteins by immunofluorescence and western blot.

Stability of the HTLV-1 Antisense-Derived Protein, HBZ, Is Regulated by the E3 Ubiquitin-Protein Ligase, UBR5

Human T-cell leukemia virus type 1 (HTLV-1) encodes a protein derived from the antisense strand of the proviral genome designated HBZ (HTLV-1 basic leucine zipper factor). HBZ is the only viral gene consistently expressed in infected patients and adult T-cell leukemia/lymphoma (ATL) tumor cell lines. It functions to antagonize many activities of the Tax viral transcriptional activator, suppresses apoptosis, and supports proliferation of ATL cells. Factors that regulate the stability of HBZ are thus important to the pathophysiology of ATL development. Using affinity-tagged protein and shotgun proteomics, we identified UBR5 as a novel HBZ-binding partner. UBR5 is an E3 ubiquitin-protein ligase that functions as a key regulator of the ubiquitin proteasome system in both cancer and developmental biology. Herein, we investigated the role of UBR5 in HTLV-1-mediated T-cell transformation and leukemia/lymphoma development. The UBR5/HBZ interaction was verified in vivo using over-expression constructs, as well as endogenously in T-cells. shRNA-mediated knockdown of UBR5 enhanced HBZ steady-state levels by stabilizing the HBZ protein. Interestingly, the related HTLV-2 antisense-derived protein, APH-2, also interacted with UBR5 in vivo. However, knockdown of UBR5 did not affect APH-2 protein stability. Co-immunoprecipitation assays identified ubiquitination of HBZ and knockdown of UBR5 resulted in a decrease in HBZ ubiquitination. MS/MS analysis identified seven ubiquitinated lysines in HBZ. Interestingly, UBR5 expression was upregulated in established T lymphocytic leukemia/lymphoma cell lines and the later stage of T-cell transformation in vitro. Finally, we demonstrated loss of UBR5 decreased cellular proliferation in transformed T-cell lines. Overall, our study provides evidence for UBR5 as a host cell E3 ubiquitin-protein ligase responsible for regulating HBZ protein stability. Additionally, our data suggests UBR5 plays an important role in maintaining the proliferative phenotype of transformed T-cell lines.

Positive and Negative Regulation of Type I Interferons by the Human T Cell Leukemia Virus Antisense Protein HBZ

The pathogenesis of human T cell leukemia virus type 1 (HTLV-1) is strongly linked to the viral regulatory proteins Tax1 and HBZ, whose opposing functions contribute to the clinical outcome of infection. Type I interferons alpha and beta (IFN-α and IFN-β) are key cytokines involved in innate immunity, and IFN-α, in combination with other antivirals, is extensively used in the treatment of HTLV-1 infection. The relationship between HTLV-1 and IFN signaling is unclear, and to date the effect of HBZ on this pathway has not been examined. Here we report that HBZ significantly enhances interferon regulatory factor 7 (IRF7)-induced IFN-α- and IFN-stimulated response element (ISRE) promoter activities and IFN-α production and can counteract the inhibitory effect of Tax1. In contrast to this, we show that HBZ and Tax1 cooperate to inhibit the induction of IFN-β and ISRE promoters by IRF3 and IFN-β production. In addition, we reveal that HBZ enhances ISRE activation by IFN-α. We further show that HBZ enhances IRF7 and suppresses IRF3 activation by TBK1 and IKKε. We demonstrate that HBZ has no effect on virus-induced nuclear accumulation of IRF3, suggesting that it may inhibit IRF3 activity at a transcriptional level. We show that HBZ physically interacts with IRF7 and IKKε but not with IRF3 or TBK1. Overall, our findings suggest that both HBZ and Tax1 are negative regulators of immediate early IFN-β innate immune responses, while HBZ but not Tax1 positively regulates the induction of IFN-α and downstream IFN-α signaling.IMPORTANCE Type I interferons are powerful antiviral cytokines and are used extensively in the treatment of HTLV-1-induced adult T cell leukemia (ATL). To date, the relationship between HTLV-1 and the IFN pathway is poorly understood, and studies so far have focused on Tax1. Our study is unique in that it examined the effect of HBZ, alone or in combination with Tax1, on type I IFN signaling. This is important because HBZ is frequently the only viral protein expressed in infected cells, particularly at later stages of infection. A better understanding of the how HBZ regulates IFN signaling may lead to the development of therapeutics that can modify such responses and improve the clinical outcome for infected individuals.

Human T-cell lymphotropic virus type 1 and its oncogenesis

Human T-cell lymphotropic virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia/lymphoma (ATL), a rapidly progressing clonal malignancy of CD4+ T lymphocytes. Exploring the host-HTLV-1 interactions and the molecular mechanisms underlying HTLV-1-mediated tumorigenesis is critical for developing efficient therapies against the viral infection and associated leukemia/lymphoma. It has been demonstrated to date that several HTLV-1 proteins play key roles in the cellular transformation and immortalization of infected T lymphocytes. Of note, the HTLV-1 oncoprotein Tax inhibits the innate IFN response through interaction with MAVS, STING and RIP1, causing the suppression of TBK1-mediated phosphorylation of IRF3/IRF7. The HTLV-1 protein HBZ disrupts genomic integrity and inhibits apoptosis and autophagy of the target cells. Furthermore, it is revealed that HBZ enhances the proliferation of ATL cells and facilitates evasion of the infected cells from immunosurveillance. These studies provide insights into the molecular mechanisms by which HTLV-1 mediates the formation of cancer as well as useful strategies for the development of new therapeutic interventions against ATL. In this article, we review the recent advances in the understanding of the pathogenesis, the underlying mechanisms, clinical diagnosis and treatment of the disease caused by HTLV-1 infection. In addition, we discuss the future direction for targeting HTLV-1-associated cancers and strategies against HTLV-1.

A Luciferase Functional Quantitative Assay for Measuring NF-ĸB Promoter Transactivation Mediated by HTLV-1 and HTLV-2 Tax Proteins

HTLV-1 and HTLV-2 viruses express Tax transactivator proteins required for viral genome transcription and capable of transforming cells in vivo and in vitro. Although Tax oncogenic potential needs to be further elucidated, it is well established that Tax proteins activate, among others, transcription factors of the NF-ĸB family, which are involved in immune and inflammatory responses, cell growth, apoptosis, stress responses and oncogenesis. Here, we describe a reporter gene assay applied for quantitative analysis of Tax-dependent NF-ĸB activation. The procedure is based on co-transfection of two individual vectors containing the cDNA for firefly and Renilla luciferase enzymes and vectors expressing Tax proteins. The luciferase expression is driven by cis-NF-ĸB promoter regulatory elements responsive to Tax transactivating factor. This assay is particularly useful to investigate Tax influence on NF-ĸB activation mediated by viral or host factors.

Enhanced Stabilization of MCL1 by the Human T-Cell Leukemia Virus Type 1 bZIP Factor Is Modulated by Blocking the Recruitment of Cullin 1 to the SCF Complex

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus that is the etiological agent of adult T-cell leukemia (ATL). The HTLV-1 basic leucine zipper factor (HBZ), which is encoded by the minus strand of the provirus, is constitutively expressed in all ATL patient cells and likely contributes to the development and maintenance of ATL. Furthermore, the overexpression of the myeloid cell leukemia 1 (MCL1) protein is frequently observed in hematological cancers as well as several other types of cancers. Here, we found that the expression of HBZ in cells stabilized MCL1 protein expression and suppressed the MCL1-mediated release of cytochrome c from the mitochondria. This effect was mediated by inhibition of the ubiquitin-dependent degradation of MCL1. In a serial binding assay, HBZ interacted with cullin 1 (CUL1) through a head-to-tail interaction. The association between CUL1 and Skp1, which serves as the molecular scaffold for the components of SCF ubiquitin ligase complexes, was markedly repressed in the presence of HBZ. Mechanistic analysis indicated that HBZ abrogated the CUL1 association with Skp1, which in turn promoted the cellular expression of MCL1. This novel function of HBZ likely plays a role in the viral pathogenesis of HTLV-1 and provides important insights into our understanding of the development of ATL.

Exosomes in Viral Disease

Viruses have evolved many mechanisms by which to evade and subvert the immune system to ensure survival and persistence. However, for each method undertaken by the immune system for pathogen removal, there is a counteracting mechanism utilized by pathogens. The new and emerging role of microvesicles in immune intercellular communication and function is no different. Viruses across many different families have evolved to insert viral components in exosomes, a subtype of microvesicle, with many varying downstream effects. When assessed cumulatively, viral antigens in exosomes increase persistence through cloaking viral genomes, decoying the immune system, and even by increasing viral infection in uninfected cells. Exosomes therefore represent a source of viral antigen that can be used as a biomarker for disease and targeted for therapy in the control and eradication of these disorders. With the rise in the persistence of new and reemerging viruses like Ebola and Zika, exploring the role of exosomes become more important than ever.

Historical review of the causes of cancer

In the early 1900s, numerous seminal publications reported that high rates of cancer occurred in certain occupations. During this period, work with infectious agents produced only meager results which seemed irrelevant to humans. Then in the 1980s ground breaking evidence began to emerge that a variety of viruses also cause cancer in humans. There is now sufficient evidence of carcinogenicity in humans for human T-cell lymphotrophic virus, human immunodeficiency virus, hepatitis B virus, hepatitis C virus, human papillomavirus, Epstein-Barr virus, and human herpes virus 8 according to the International Agency for Research on Cancer (IARC). Many other causes of cancer have also been identified by the IARC, which include: Sunlight, tobacco, pharmaceuticals, hormones, alcohol, parasites, fungi, bacteria, salted fish, wood dust, and herbs. The World Cancer Research Fund and the American Institute for Cancer Research have determined additional causes of cancer, which include beta carotene, red meat, processed meats, low fibre diets, not breast feeding, obesity, increased adult height and sedentary lifestyles. In brief, a historical review of the discoveries of the causes of human cancer is presented with extended discussions of the difficulties encountered in identifying viral causes of cancer.

Functional Comparison of HBZ and the Related APH-2 Protein Provides Insight into Human T-Cell Leukemia Virus Type 1 Pathogenesis

Human T-cell leukemia virus type 1 (HTLV-1) and type 2 (HTLV-2) are highly related retroviruses that transform T cells in vitro but have distinct pathological outcomes in vivo. HTLV-1 encodes a protein from the antisense strand of its proviral genome, the HTLV-1 basic leucine zipper factor (HBZ), which inhibits Tax-1-mediated viral transcription and promotes cell proliferation, a high proviral load, and persistence in vivo. In adult T-cell leukemia/lymphoma (ATL) cell lines and patient T cells, hbz is often the only viral gene expressed. The antisense strand of the HTLV-2 proviral genome also encodes a protein termed APH-2. Like HBZ, APH-2 is able to inhibit Tax-2-mediated viral transcription and is detectable in most primary lymphocytes from HTLV-2-infected patients. However, unlike HBZ, the loss of APH-2 in vivo results in increased viral replication and proviral loads, suggesting that HBZ and APH-2 modulate the virus and cellular pathways differently. Herein, we examined the effect of APH-2 on several known HBZ-modulated pathways: NF-κB (p65) transactivation, transforming growth factor β (TGF-β) signaling, and interferon regulatory factor 1 (IRF-1) transactivation. Like HBZ, APH-2 has the ability to inhibit p65 transactivation. Conversely, HBZ and APH-2 have divergent effects on TGF-β signaling and IRF-1 transactivation. Quantitative PCR and protein half-life experiments revealed a substantial disparity between HBZ and APH-2 transcript levels and protein stability, respectively. Taken together, our data further elucidate the functional differences between HBZ and APH-2 and how these differences can have profound effects on the survival of infected cells and, ultimately, pathogenesis.

IMPORTANCE

Human T-cell leukemia virus type 1 (HTLV-1) and type 2 (HTLV-2) are highly related retroviruses that have distinct pathological outcomes in infected hosts. Functional comparisons of HTLV-1 and HTLV-2 proteins provide a better understanding about how HTLV-1 infection is associated with disease and HTLV-2 infection is not. The HTLV genome antisense-strand genes hbz and aph-2 are often the only viral genes expressed in HTLV-infected T cells. Previously, our group found that HTLV-1 HBZ and HTLV-2 APH-2 had distinct effects in vivo and hypothesized that the differences in the interactions of HBZ and APH-2 with important cell signaling pathways dictate whether cells undergo proliferation, apoptosis, or senescence. Ultimately, these functional differences may affect how HTLV-1 causes disease but HTLV-2 generally does not. In the current study, we compared the effects of HBZ and APH-2 on several HTLV-relevant cellular pathways, including the TGF-β signaling, NF-κB activation, and IRF-1 transactivation pathways.

Tax secretion from peripheral blood mononuclear cells and Tax detection in plasma of patients with human T-lymphotropic virus-type 1-associated myelopathy/tropical spastic paraparesis and asymptomatic carriers

Human T-lymphotropic virus-type 1 (HTLV-1) is the etiologic agent of the neurologic disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Tax viral protein plays a critical role in viral pathogenesis. Previous studies suggested that extracellular Tax might involve cytokine-like extracellular effects. We evaluated Tax secretion in 18 h-ex vivo peripheral blood mononuclear cells (PBMCs) cultures from 15 HAM/TSP patients and 15 asymptomatic carriers. Futhermore, Tax plasma level was evaluated from other 12 HAM/TSP patients and 10 asymptomatic carriers. Proviral load and mRNA encoding Tax were quantified by PCR and real-time RT-PCR, respectively. Intracellular Tax in CD4(+)CD25(+) cells occurred in 100% and 86.7% of HAM/TSP patients and asymptomatic carriers, respectively. Percentage of CD4(+)CD25(+) Tax+, proviral load and mRNA encoding Tax were significantly higher in HAM/TSP patients. Western blot analyses showed higher secretion levels of ubiquitinated Tax in HAM/TSP patients than in asymptomatic carriers. In HTLV-1-infected subjects, Western blot of plasma Tax showed higher levels in HAM/TSP patients than in asymptomatic carriers, whereas no Tax was found in non-infected subjects. Immunoprecipitated plasma Tax resolved on SDS-PAGE gave two major bands of 57 and 48 kDa allowing identification of Tax and Ubiquitin peptides by mass spectrometry. Relative percentage of either CD4(+)CD25(+) Tax+ cells, or Tax protein released from PBMCs, or plasma Tax, correlates neither with tax mRNA nor with proviral load. This fact could be explained by a complex regulation of Tax expression. Tax secreted from PBMCs or present in plasma could potentially become a biomarker to distinguish between HAM/TSP patients and asymptomatic carriers.

Akt Pathway Activation by Human T-cell Leukemia Virus Type 1 Tax Oncoprotein

Human T-cell leukemia virus (HTLV) type 1, the etiological agent of adult T-cell leukemia, expresses the viral oncoprotein Tax1. In contrast, HTLV-2, which expresses Tax2, is non-leukemogenic. One difference between these homologous proteins is the presence of a C-terminal PDZ domain-binding motif (PBM) in Tax1, previously reported to be important for non-canonical NFκB activation. In contrast, this study finds no defect in non-canonical NFκB activity by deletion of the Tax1 PBM. Instead, Tax1 PBM was found to be important for Akt activation. Tax1 attenuates the effects of negative regulators of the PI3K-Akt-mammalian target of rapamycin pathway, phosphatase and tensin homologue (PTEN), and PHLPP. Tax1 competes with PTEN for binding to DLG-1, unlike a PBM deletion mutant of Tax1. Forced membrane expression of PTEN or PHLPP overcame the effects of Tax1, as measured by levels of Akt phosphorylation, and rates of Akt dephosphorylation. The current findings suggest that Akt activation may explain the differences in transforming activity of HTLV-1 and -2.

Human T-cell leukemia virus type-I Tax induces the expression of CD83 on T cells

BACKGROUND

CD83, a cell surface glycoprotein that is stably expressed on mature dendritic cells, can be transiently induced on other hematopoietic cell lineages upon cell activation. In contrast to the membrane form of CD83, soluble CD83 appears to be immunosuppressive. In an analysis of the phenotype of leukemic CD4(+) T cells from patients with adult T-cell leukemia (ATL), we found that a number of primary CD4(+) T cells became positive for cell surface CD83 after short-term culture, and that most of these CD83(+) CD4(+) T cells were positive for human T-cell leukemia virus type-I (HTLV-I) Tax (Tax1). We hypothesized that Tax1 is involved in the induction of CD83.

RESULT

We found that CD83 was expressed selectively on Tax1-expressing human CD4(+) T cells in short-term cultured peripheral blood mononuclear cells (PBMCs) isolated from HTLV-I(+) donors, including ATL patients and HTLV-I carriers. HTLV-I-infected T cell lines expressing Tax1 also expressed cell surface CD83 and released soluble CD83. CD83 can be expressed in the JPX-9 cell line by cadmium-mediated Tax1 induction and in Jurkat cells or PBMCs by Tax1 introduction via infection with a recombinant adenovirus carrying the Tax1 gene. The CD83 promoter was activated by Tax1 in an NF-κB-dependent manner. Based on a previous report showing soluble CD83-mediated prostaglandin E2 (PGE2) production from human monocytes in vitro, we tested if PGE2 affected HTLV-I propagation, and found that PGE2 strongly stimulated expression of Tax1 and viral structural molecules.

CONCLUSIONS

Our results suggest that HTLV-I induces CD83 expression on T cells via Tax1 -mediated NF-κB activation, which may promote HTLV-I infection in vivo.

ATL response to arsenic/interferon therapy is triggered by SUMO/PML/RNF4-dependent Tax degradation

Survival of ATL cells depends on continuous Tax expression. Arsenic/interferon combination induces SUMO/PML/RNF4-mediated Tax degradation.

HTLV-1 Tax protein recruitment into IKKε and TBK1 kinase complexes enhances IFN-I expression

The Tax protein expressed by human T-cell leukemia virus type 1 (HTLV-1) plays a pivotal role in the deregulation of cellular pathways involved in the immune response, inflammation, cell survival, and cancer. Many of these effects derive from Tax multiple interactions with host factors, including the subunits of the IKK-complex that are required for NF-κB activation. IKKɛ and TBK1 are two IKK-related kinases that allow the phosphorylation of interferon regulatory factors that trigger IFN type I gene expression. We observed that IKKɛ and TBK1 recruit Tax into cellular immunocomplexes. We also found that TRAF3, which regulates cell receptor signaling effectors, forms complexes with Tax. Transactivation analyses revealed that expression of Tax, in presence of IKKɛ and TBK1, enhances IFN-β promoter activity, whereas the activation of NF-κB promoter is not modified. We propose that Tax may be recruited into the TBK1/IKKɛ complexes as a scaffolding-adaptor protein that enhances IFN-I gene expression.

HTLV-1 Tax-mediated inhibition of FOXO3a activity is critical for the persistence of terminally differentiated CD4+ T cells

The mechanisms involved in the persistence of activated CD4+ T lymphocytes following primary human T leukemia/lymphoma virus type 1 (HTLV-1) infection remain unclear. Here, we demonstrate that the HTLV-1 Tax oncoprotein modulates phosphorylation and transcriptional activity of the FOXO3a transcription factor, via upstream activation of the AKT pathway. De novo HTLV-1 infection of CD4+ T cells or direct lentiviral-mediated introduction of Tax led to AKT activation and AKT-dependent inactivation of FOXO3a, via phosphorylation of residues Ser253 and Thr32. Inhibition of FOXO3a signalling led to the long-term survival of a population of highly activated, terminally differentiated CD4+Tax+CD27negCCR7neg T cells that maintained the capacity to disseminate infectious HTLV-1. CD4+ T cell persistence was reversed by chemical inhibition of AKT activity, lentiviral-mediated expression of a dominant-negative form of FOXO3a or by specific small interfering RNA (siRNA)-mediated silencing of FOXO3a. Overall this study provides new mechanistic insight into the strategies used by HTLV-1 to increase long-term maintenance of Tax+CD4+ T lymphocytes during the early stages of HTLV-1 pathogenesis.

ADAR1 enhances HTLV-1 and HTLV-2 replication through inhibition of PKR activity

Background

The role of innate immunity in general and of type I interferon (IFN-I) in particular in HTLV-1 pathogenesis is still a matter of debate. ADAR1-p150 is an Interferon Stimulated Gene (ISG) induced by IFN-I that can edit viral RNAs. We therefore investigated whether it could play the role of an anti-HTLV factor.

Results

We demonstrate here that ADAR1 is also expressed in the absence of IFN stimulation in activated primary T-lymphocytes that are the natural target of this virus and in HTLV-1 or HTLV-2 chronically infected T-cells. ADAR1 expression is also increased in primary lymphocytes obtained from HTLV-1 infected individuals. We show that ADAR1 enhances HTLV-1 and HTLV-2 infection in T-lymphocytes and that this proviral effect is independent from its editing activity. ADAR1 expression suppresses IFN-α inhibitory effect on HTLV-1 and HTLV-2 and acts through the repression of PKR phosphorylation.

Discussion

This study demonstrates that two interferon stimulated genes, i.e. PKR and ADAR1 have opposite effects on HTLV replication in vivo. The balanced expression of those proteins could determine the fate of the viral cycle in the course of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0093-9) contains supplementary material, which is available to authorized users.

Regulation of HTLV-1 tax stability, cellular trafficking and NF-κB activation by the ubiquitin-proteasome pathway

Human T-cell leukemia virus type 1 (HTLV-1) is a complex retrovirus that infects CD4+ T cells and causes adult T-cell leukemia/lymphoma (ATLL) in 3%–5% of infected individuals after a long latent period. HTLV-1 Tax is a trans-activating protein that regulates viral gene expression and also modulates cellular signaling pathways to enhance T-cell proliferation and cell survival. The Tax oncoprotein promotes T-cell transformation, in part via constitutive activation of the NF-κB transcription factor; however, the underlying mechanisms remain unknown. Ubiquitination is a type of post-translational modification that occurs in a three-step enzymatic cascade mediated by E1, E2 and E3 enzymes and regulates protein stability as well as signal transduction, protein trafficking and the DNA damage response. Emerging studies indicate that Tax hijacks the ubiquitin machinery to activate ubiquitin-dependent kinases and downstream NF-κB signaling. Tax interacts with the E2 conjugating enzyme Ubc13 and is conjugated on C-terminal lysine residues with lysine 63-linked polyubiquitin chains. Tax K63-linked polyubiquitination may serve as a platform for signaling complexes since this modification is critical for interactions with NEMO and IKK. In addition to NF-κB signaling, mono- and polyubiquitination of Tax also regulate its subcellular trafficking and stability. Here, we review recent advances in the diverse roles of ubiquitin in Tax function and how Tax usurps the ubiquitin-proteasome pathway to promote oncogenesis.

The intricate interplay between RNA viruses and NF-κB

RNA viruses have rapidly evolving genomes which often allow cross-species transmission and frequently generate new virus variants with altered pathogenic properties. Therefore infections by RNA viruses are a major threat to human health. The infected host cell detects trace amounts of viral RNA and the last years have revealed common principles in the biochemical mechanisms leading to signal amplification that is required for mounting of a powerful antiviral response. Components of the RNA sensing and signaling machinery such as RIG-I-like proteins, MAVS and the inflammasome inducibly form large oligomers or even fibers that exhibit hallmarks of prions. Following a nucleation event triggered by detection of viral RNA, these energetically favorable and irreversible polymerization events trigger signaling cascades leading to the induction of antiviral and inflammatory responses, mediated by interferon and NF-κB pathways. Viruses have evolved sophisticated strategies to manipulate these host cell signaling pathways in order to ensure their replication. We will discuss at the examples of influenza and HTLV-1 viruses how a fascinating diversity of biochemical mechanisms is employed by viral proteins to control the NF-κB pathway at all levels.

HTLV-1 and HTLV-2: highly similar viruses with distinct oncogenic properties

HTLV-1 and HTLV-2 share broad similarities in their overall genetic organization and expression pattern, but they differ substantially in their pathogenic properties. This review outlines distinctive features of HTLV-1 and HTLV-2 that might provide clues to explain their distinct clinical outcomes. Differences in the kinetics of viral mRNA expression, functional properties of the regulatory and accessory proteins, and interactions with cellular factors and signal transduction pathways are discussed.