Role of Tax protein in human T-cell leukemia virus type-I leukemogenicity

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.

MicroRNAs and long non-coding RNAs during transcriptional regulation and latency of HIV and HTLV

Human immunodeficiency virus (HIV) and human T cell leukemia virus (HTLV) have replicative and latent stages of infection. The status of the viruses is dependent on the cells that harbour them and on different events that change the transcriptional and post-transcriptional events. Non-coding (nc)RNAs are key factors in the regulation of retrovirus replication cycles. Notably, micro (mi)RNAs and long non-coding (lnc)RNAs are important regulators that can induce switches between active transcription-replication and latency of retroviruses and have important impacts on their pathogenesis. Here, we review the functions of miRNAs and lncRNAs in the context of HIV and HTLV. We describe how specific miRNAs and lncRNAs are involved in the regulation of the viruses' transcription, post-transcriptional regulation and latency. We further discuss treatment strategies using ncRNAs for HIV and HTLV long remission, reactivation or possible cure.

Diversity of HLA-A2-Restricted and Immunodominant Epitope Repertoire of Human T-Lymphotropic Virus Type 1 (HTLV-1) Tax Protein: Novel Insights among N-Terminal, Central and C-Terminal Regions

The present study sought to search for the immunodominance related to the N-terminal, Central and C-terminal regions of HTLV-1 Tax using novel, cutting-edge peptide microarray analysis. In addition, in silico predictions were performed to verify the presence of nine amino acid peptides present along Tax restricted to the human leukocyte antigen (HLA)-A2.02*01 haplotype, as well as to verify the ability to induce pro-inflammatory and regulatory cytokines, such as IFN-γ and IL-4, respectively. Our results indicated abundant dose-dependent reactivity for HLA-A*02:01 in all regions (N-terminal, Central and C-terminal), but with specific hotspots. Furthermore, the results of fold-change over the Tax11–19 reactivity obtained at lower concentrations of HLA-A*02:01 reveal that peptides from the three regions contain sequences that react 100 times more than Tax11–19. On the other hand, Tax11–19 has similar or superior HLA-A*02:01 reactivity at higher concentrations of this haplotype. The in silico analysis showed a higher frequency of IFN-γ-inducing peptides in the N-terminal portion, while the C-terminal portion showed a higher frequency of IL-4 inducers. Taken together, these results shed light on the search for new Tax immunodominant epitopes, in addition to the canonic Tax11–19, for the rational design of immunomodulatory strategies for HTLV-1 chronic diseases.

Malignancy and viral infections in Sub-Saharan Africa: A review

The burden of malignancy related to viral infection is increasing in Sub-Saharan Africa (SSA). In 2018, approximately 2 million new cancer cases worldwide were attributable to infection. Prevention or treatment of these infections could reduce cancer cases by 23% in less developed regions and about 7% in developed regions. Contemporaneous increases in longevity and changes in lifestyle have contributed to the cancer burden in SSA. African hospitals are reporting more cases of cancer related to infection (e.g., cervical cancer in women and stomach and liver cancer in men). SSA populations also have elevated underlying prevalence of viral infections compared to other regions. Of 10 infectious agents identified as carcinogenic by the International Agency for Research on Cancer, six are viruses: hepatitis B and C viruses (HBV and HCV, respectively), Epstein-Barr virus (EBV), high-risk types of human papillomavirus (HPV), Human T-cell lymphotropic virus type 1 (HTLV-1), and Kaposi's sarcoma herpesvirus (KSHV, also known as human herpesvirus type 8, HHV-8). Human immunodeficiency virus type 1 (HIV) also facilitates oncogenesis. EBV is associated with lymphomas and nasopharyngeal carcinoma; HBV and HCV are associated with hepatocellular carcinoma; KSHV causes Kaposi's sarcoma; HTLV-1 causes T-cell leukemia and lymphoma; HPV causes carcinoma of the oropharynx and anogenital squamous cell cancer. HIV-1, for which SSA has the greatest global burden, has been linked to increasing risk of malignancy through immunologic dysregulation and clonal hematopoiesis. Public health approaches to prevent infection, such as vaccination, safer injection techniques, screening of blood products, antimicrobial treatments and safer sexual practices could reduce the burden of cancer in Africa. In SSA, inequalities in access to cancer screening and treatment are exacerbated by the perception of cancer as taboo. National level cancer registries, new screening strategies for detection of viral infection and public health messaging should be prioritized in SSA's battle against malignancy. In this review, we discuss the impact of carcinogenic viruses in SSA with a focus on regional epidemiology.

Tumor resident, TRA anti-viral CDR3 chemical sequence motifs are associated with a better breast cancer outcome

While for certain cancers, such as cervical cancer, the link to viral infections is very strong and very clear, other cancers represent a history of links to viral infections that are either co-morbidities or drive the cancer in ways that are not yet fully understood, for example the "hit and run" possibility. To further understand the connection of viral infections and the progress of breast cancer, we identified the chemical features of known anti-viral, T-cell receptor alpha chain (TRA) complementarity determining region-3 (CDR3) amino acid sequences among the CDR3s of breast cancer patient TRA recombinations and assessed the association of those features with patient outcomes. The application of this novel paradigm indicated consistent associations of tumor-derived, anti-CMV CDR3 chemical sequence motifs with better breast cancer patient outcomes but did not indicate an opportunity to establish risk stratifications for other cancer types. Interestingly, breast cancer samples with no detectable TRA recombinations represented a better outcome than samples with the non-anti-CMV CDR3s, further adding to a rapidly developing series of results allowing a distinction between positive and possibly harmful cancer immune responses.

Pathogenicity and virulence of human T lymphotropic virus type-1 (HTLV-1) in oncogenesis: adult T-cell leukemia/lymphoma (ATLL)

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive malignancy of CD4⁺ T lymphocytes caused by human T lymphotropic virus type-1 (HTLV-1) infection. HTLV-1 was brought to the World Health Organization (WHO) and researchers to address its impact on global public health, oncogenicity, and deterioration of the host immune system toward autoimmunity. In a minority of the infected population (3-5%), it can induce inflammatory networks toward HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), or hijacking the infected CD4⁺ T lymphocytes into T regulatory subpopulation, stimulating anti-inflammatory signaling networks, and prompting ATLL development. This review critically discusses the complex signaling networks in ATLL pathogenesis during virus-host interactions for better interpretation of oncogenicity and introduces the main candidates in the pathogenesis of ATLL. At least two viral factors, HTLV-1 trans-activator protein (TAX) and HTLV-1 basic leucine zipper factor (HBZ), are implicated in ATLL manifestation, interacting with host responses and deregulating cell signaling in favor of infected cell survival and virus dissemination. Such molecules can be used as potential novel biomarkers for ATLL prognosis or targets for therapy. Moreover, the challenging aspects of HTLV-1 oncogenesis introduced in this review could open new venues for further studies on acute leukemia pathogenesis. These features can aid in the discovery of effective immunotherapies when reversing the gene expression profile toward appropriate immune responses gradually becomes attainable.

Hijacking Host Immunity by the Human T-Cell Leukemia Virus Type-1: Implications for Therapeutic and Preventive Vaccines

Human T-cell Leukemia virus type-1 (HTLV-1) causes adult T-cell leukemia/lymphoma (ATLL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and other inflammatory diseases. High viral DNA burden (VL) in peripheral blood mononuclear cells is a documented risk factor for ATLL and HAM/TSP, and patients with HAM/TSP have a higher VL in cerebrospinal fluid than in peripheral blood. VL alone is not sufficient to differentiate symptomatic patients from healthy carriers, suggesting the importance of other factors, including host immune response. HTLV-1 infection is life-long; CD4+-infected cells are not eradicated by the immune response because HTLV-1 inhibits the function of dendritic cells, monocytes, Natural Killer cells, and adaptive cytotoxic CD8+ responses. Although the majority of infected CD4+ T-cells adopt a resting phenotype, antigen stimulation may result in bursts of viral expression. The antigen-dependent "on-off" viral expression creates "conditional latency" that when combined with ineffective host responses precludes virus eradication. Epidemiological and clinical data suggest that the continuous attempt of the host immunity to eliminate infected cells results in chronic immune activation that can be further exacerbated by co-morbidities, resulting in the development of severe disease. We review cell and animal model studies that uncovered mechanisms used by HTLV-1 to usurp and/or counteract host immunity.

Epigenetic perspectives of COVID-19: Virus infection to disease progression and therapeutic control

COVID-19 has caused numerous deaths as well as imposed social isolation and upheaval world-wide. Although, the genome and the composition of the virus, the entry process and replication mechanisms are well investigated from by several laboratories across the world, there are many unknown remaining questions. For example, what are the functions of membrane lipids during entry, packaging and exit of virus particles? Also, the metabolic aspects of the infected tissue cells are poorly understood. In the course of virus replication and formation of virus particles within the host cell, the enhanced metabolic activities of the host is directly proportional to viral loads. The epigenetic landscape of the host cells is also altered, particularly the expression/repression of genes associated with cellular metabolism as well as cellular processes that are antagonistic to the virus. Metabolic pathways are enzyme driven processes and the expression profile and mechanism of regulations of the respective genes encoding those enzymes during the course of pathogen invasion might be highly informative on the course of the disease. Recently, the metabolic profile of the patients' sera have been analysed from few patients. In view of this, and to gain further insights into the roles that epigenetic mechanisms might play in this scenario in regulation of metabolic pathways during the progression of COVID-19 are discussed and summarised in this contribution for ensuring best therapy.

Regulation of human T-cell leukemia virus type 1 antisense promoter by myocyte enhancer factor-2C in the context of adult T-cell leukemia and lymphoma

Adult T-cell leukemia and lymphoma (ATLL) is an intractable T-cell neoplasia caused by a retrovirus, namely human T-cell leukemia virus type 1 (HTLV-1). Patients suffering from ATLL present a poor prognosis and have a dearth of treatment options. In contrast to the sporadic expression of viral transactivator protein Tax present at the 5' promoter region long terminal repeats (LTR), HTLV-1 bZIP gene (HBZ) is encoded by 3'LTR (the antisense promoter) and maintains its constant expression in ATLL cells and patients. The antisense promoter is associated with selective retroviral gene expression and has been an understudied phenomenon. Herein, we delineate the activity of transcription factor MEF (myocyte enhancer factor)-2 family members, which were found to be enriched at the 3'LTR and play an important role in the pathogenesis of ATLL. Of the four MEF isoforms (A to D), MEF-2A and 2C were highly overexpressed in a wide array of ATLL cell lines and in acute ATLL patients. The activity of MEF-2 isoforms were determined by knockdown experiments that led to decreased cell proliferation and regulated cell cycle progression. High enrichment of MEF-2C was observed at the 3'LTR along with cofactors Menin and JunD resulting in binding of MEF-2C to HBZ at this region. Chemical inhibition of MEF-2 proteins resulted in the cytotoxicity of ATLL cells in vitro and reduction of proviral load in a humanized mouse model. Taken together, this study provides a novel mechanism of 3'LTR regulation and establishes MEF-2 signaling a potential target for therapeutic intervention for ATLL.

Rational design of chimeric Multiepitope Based Vaccine (MEBV) against human T-cell lymphotropic virus type 1: An integrated vaccine informatics and molecular docking based approach

Human T-cell lymphotropic virus type 1 (HTLV-1) is an infectious virus that has been linked to adult T cell leukemia /lymphoma, aggressive CD4-T cell malignancy and many other immune-related medical illnesses. So far, no effective vaccine is known to combat HTLV-1, hence, the current research work was performed to design a potential multi-epitope-based subunit vaccine (MEBV) by adopting the latest methodology of reverse vaccinology. Briefly, three highly antigenic proteins (Glycoprotein, Accessory protein, and Tax protein) with no or minimal (<37%) similarity with human proteome were sorted out and potential B- and T-cell epitopes were forecasted from them. Highly antigenic, immunogenic, non-toxic, non-allergenic and overlapping epitopes were short-listed for vaccine development. The chosen T-cell epitopes displayed a strong binding affinity with their corresponding Human Leukocyte Antigen alleles and demonstrated 95.8% coverage of the world's population. Finally, nine Cytotoxic T Lymphocytes, six Helper T Lymphocytes and five Linear B Lymphocytes epitopes, joint through linkers and adjuvant, were exploited to design the final MEBV construct, comprising of 382 amino acids. The developed MEBV structure showed highly antigenic properties while being non-toxic, soluble, non-allergenic, and stable in nature. Moreover, disulphide engineering further enhanced the stability of the final vaccine protein. Additionally, Molecular docking analysis and Molecular Dynamics (MD) simulations confirmed the strong association between MEBV construct and human pathogenic immune receptor TLR-3. Repeated-exposure simulations and Immune simulations ensured the rapid antigen clearance and higher levels of cell-mediated immunity, respectively. Furthermore, MEBV codon optimization and in-silico cloning was carried out to confirm its augmented expression. Results of our experiments suggested that the proposed MEBV could be a potential immunogenic against HTLV-1; nevertheless, additional wet lab experiments are needed to elucidate our conclusion.

The Effect of a Histone Deacetylase Inhibitor (AR-42) and Zoledronic Acid on Adult T-Cell Leukemia/Lymphoma Osteolytic Bone Tumors

Simple Summary

Adult T-cell leukemia (ATL) Leukemia is an aggressive, peripheral blood (T-cell) neoplasm associated with human T-cell leukemia virus type 1 (HTLV-1) infection. Recent studies have implicated dysregulated histone deacetylases in ATL pathogenesis. ATL modulates the bone microenvironment of patients and activates osteoclasts (bone resorbing cells) that cause severe bone loss. The objective of this study was to assess the individual and dual effects of AR-42 (HDACi) and zoledronic acid (Zol) on the growth of ATL cells in vitro and in vivo. AR-42 and Zol reduced the viability of ATL cells in vitro. Additionally, Zol and Zol/AR-42 decreased ATL tumor growth and halted osteolysis in bone tumor xenografts in immunodeficient mice in vivo. Our study suggests that dual targeting of ATL cells (using HDACi) and bone osteoclasts (using bisphosphonates) may be exploited as a valuable approach to reduce bone tumor burden and improve the life quality of ATL patients.

Abstract

Adult T-cell leukemia/lymphoma (ATL) is an intractable disease affecting nearly 4% of Human T-cell Leukemia Virus Type 1 (HTLV-1) carriers. Acute ATL has a unique interaction with bone characterized by aggressive bone invasion, osteolytic metastasis, and hypercalcemia. We hypothesized that dual tumor and bone-targeted therapies would decrease tumor burden in bone, the incidence of metastasis, and ATL-associated osteolysis. Our goal was to evaluate dual targeting of both ATL bone tumors and the bone microenvironment using an anti-tumor HDACi (AR-42) and an osteoclast inhibitor (zoledronic acid, Zol), alone and in combination. Our results showed that AR-42, Zol, and AR-42/Zol significantly decreased the viability of multiple ATL cancer cell lines in vitro. Zol and AR-42/Zol decreased tumor growth in vivo. Zol ± AR-42 significantly decreased ATL-associated bone resorption and promoted new bone formation. AR-42-treated ATL cells had increased mRNA levels of PTHrP, ENPP2 (autotaxin) and MIP-1α, and TAX viral gene expression. AR-42 alone had no significant effect on tumor growth or osteolysis in mice. These findings indicate that Zol adjuvant therapy has the potential to reduce growth of ATL in bone and its associated osteolysis.

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.

Polymorphisms in HTLV-1 Tax-responsive elements in HTLV-1-associated myelopathy/tropical spastic paraparesis patients are associated with reduced proviral load but not with disease progression

Human T-lymphotropic virus type 1 (HTLV-1) provirus expression is mainly directed by Tax-responsive elements (TRE) within the long terminal repeats (LTR). Mutations in TRE can reduce provirus expression and since a high proviral load (PVL) is a risk factor for the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), we evaluated polymorphisms in the 5' LTR and the association with PVL and disease progression. HTLV-1 LTR and tax sequences derived from asymptomatic carriers (AC) and HAM/TSP patients followed in a longitudinal study were analysed according to PVL and clinical severity. Individuals infected with HTLV-1 presenting the canonical TRE, considering strain ATK-1 as the consensus, displayed sustained higher PVL. By contrast, an LTR A125G mutation in TRE was associated with slightly reduced PVL only in HAM/TSP patients, although it did not influence the speed of disease progression. Moreover, this polymorphism was frequent in Latin American strains of the HTLV-1 Cosmopolitan Transcontinental subtype. Therefore, polymorphisms in the 5' TRE of HTLV-1 may represent one of the factors influencing PVL in HAM/TSP patients, especially in the Latin American population. Indeed, higher PVL in the peripheral blood has been associated with an increased inflammatory activity in the spinal cord and to a poorer prognosis in HAM/TSP. However, this event was not associated with TRE polymorphisms.

Real-World Data on Adult T-Cell Leukemia/Lymphoma in Latin America: A Study From the Grupo de Estudio Latinoamericano de Linfoproliferativos

PURPOSE

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive disease caused by the human T-cell leukemia virus type 1. Real-world data of ATLL in Latin America are lacking.

PATIENTS AND METHODS

We analyzed patients with ATLL (acute, lymphomatous, chronic, and smoldering) encountered in 11 Latin American countries between 1995 and 2019. Treatment response was assessed according to the 2009 consensus report. Survival curves were estimated using the Kaplan-Meier method and log-rank test.

RESULTS

We identified 253 patients; 226 (lymphomatous: n = 122, acute: n = 73, chronic: n = 26, and smoldering: n = 5) had sufficient data for analysis (median age 57 years). Most patients with ATLL were from Peru (63%), Chile (17%), Argentina (8%), and Colombia (7%). Hypercalcemia was positively associated with acute type (57% v lymphomatous 27%, P = .014). The median survival times (months) were 4.3, 7.9, 21.1, and not reached for acute, lymphomatous, chronic, and smoldering forms, with 4-year survival rates of 8%, 22%, 40%, and 80%, respectively. First-line zidovudine (AZT)-interferon alfa (IFN) resulted in an overall response rate of 63% (complete response [CR] 24%) for acute. First-line chemotherapy yielded an overall response rate of 41% (CR 29%) for lymphomatous. CR rate was 42% for etoposide, cyclophosphamide, vincristine, doxorubicin, and prednisone versus 12% for cyclophosphamide, vincristine, doxorubicin, and prednisone-like regimen (P < .001). Progression-free survival at 1 year for acute type patients treated with AZT-IFN was 67%, whereas 2-year progression-free survival in lymphomatous type patients who achieved CR after chemotherapy was 77%.

CONCLUSION

This study confirms Latin American ATLL presents at a younger age and has a high incidence of lymphomatous type, low incidence of indolent subtypes, and worse survival rates as compared with Japanese patients. In aggressive ATLL, chemotherapy remains the preferred choice for lymphomatous favoring etoposide-based regimen (etoposide, cyclophosphamide, vincristine, doxorubicin, and prednisone), whereas AZT-IFN remains a good first-line option for acute subtype.

Extracellular Vesicles from Infected Cells Are Released Prior to Virion Release

Here, we have attempted to address the timing of EV and virion release from virally infected cells. Uninfected (CEM), HIV-1-infected (J1.1), and human T cell leukemia virus-1 (HTLV-1)-infected (HUT102) cells were synchronized in G0. Viral latency was reversed by increasing gene expression with the addition of serum-rich media and inducers. Supernatants and cell pellets were collected post-induction at different timepoints and assayed for extracellular vesicle (EV) and autophagy markers; and for viral proteins and RNAs. Tetraspanins and autophagy-related proteins were found to be differentially secreted in HIV-1- and HTLV-1-infected cells when compared with uninfected controls. HIV-1 proteins were present at 6 h and their production increased up to 24 h. HTLV-1 proteins peaked at 6 h and plateaued. HIV-1 and HTLV-1 RNA production correlated with viral protein expression. Nanoparticle tracking analysis (NTA) showed increase of EV concentration over time in both uninfected and infected samples. Finally, the HIV-1 supernatant from the 6-h samples was found not to be infectious; however, the virus from the 24-h samples was successfully rescued and infectious. Overall, our data indicate that EV release may occur prior to viral release from infected cells, thereby implicating a potentially significant effect of EVs on uninfected recipient cells prior to subsequent viral infection and spread.

Spectrum of mutational signatures in T-cell lymphoma reveals a key role for UV radiation in cutaneous T-cell lymphoma

T-cell non-Hodgkin's lymphomas develop following transformation of tissue resident T-cells. We performed a meta-analysis of whole exome sequencing data from 403 patients with eight subtypes of T-cell non-Hodgkin's lymphoma to identify mutational signatures and associated recurrent gene mutations. Signature 1, indicative of age-related deamination, was prevalent across all T-cell lymphomas, reflecting the derivation of these malignancies from memory T-cells. Adult T-cell leukemia-lymphoma was specifically associated with signature 17, which was found to correlate with the IRF4 K59R mutation that is exclusive to Adult T-cell leukemia-lymphoma. Signature 7, implicating UV exposure was uniquely identified in cutaneous T-cell lymphoma (CTCL), contributing 52% of the mutational burden in mycosis fungoides and 23% in Sezary syndrome. Importantly this UV signature was observed in CD4 + T-cells isolated from the blood of Sezary syndrome patients suggesting extensive re-circulation of these T-cells through skin and blood. Analysis of non-Hodgkin's T-cell lymphoma cases submitted to the national 100,000 WGS project confirmed that signature 7 was only identified in CTCL strongly implicating UV radiation in the pathogenesis of cutaneous T-cell lymphoma.

The versatile role of exosomes in human retroviral infections: from immunopathogenesis to clinical application

Eukaryotic cells produce extracellular vesicles (EVs) mediating intercellular communication. These vesicles encompass many bio-molecules such as proteins, nucleic acids, and lipids that are transported between cells and regulate pathophysiological actions in the recipient cell. Exosomes originate from multivesicular bodies inside cells and microvesicles shed from the plasma membrane and participate in various pathological conditions. Retroviruses such as Human Immunodeficiency Virus -type 1 (HIV-1) and Human T-cell leukemia virus (HTLV)-1 engage exosomes for spreading and infection. Exosomes from virus-infected cells transfer viral components such as miRNAs and proteins that promote infection and inflammation. Additionally, these exosomes deliver virus receptors to target cells that make them susceptible to virus entry. HIV-1 infected cells release exosomes that contribute to the pathogenesis including neurological disorders and malignancy. Exosomes can also potentially carry out as a modern approach for the development of HIV-1 and HTLV-1 vaccines. Furthermore, as exosomes are present in most biological fluids, they hold the supreme capacity for clinical usage in the early diagnosis and prognosis of viral infection and associated diseases. Our current knowledge of exosomes' role from virus-infected cells may provide an avenue for efficient retroviruses associated with disease prevention. However, the exact mechanism involved in retroviruses infection/ inflammation remains elusive and related exosomes research will shed light on the mechanisms of pathogenesis.

Extracellular Vesicles in HTLV-1 Communication: The Story of an Invisible Messenger

Human T-cell lymphotropic virus type 1 (HTLV-1) infects 5-10 million people worldwide and is the causative agent of adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) as well as other inflammatory diseases. A major concern is that the most majority of individuals with HTLV-1 are asymptomatic carriers and that there is limited global attention by health care officials, setting up potential conditions for increased viral spread. HTLV-1 transmission occurs primarily through sexual intercourse, blood transfusion, intravenous drug usage, and breast feeding. Currently, there is no cure for HTLV-1 infection and only limited treatment options exist, such as class I interferons (IFN) and Zidovudine (AZT), with poor prognosis. Recently, small membrane-bound structures, known as extracellular vesicles (EVs), have received increased attention due to their potential to carry viral cargo (RNA and proteins) in multiple pathogenic infections (i.e., human immunodeficiency virus type I (HIV-1), Zika virus, and HTLV-1). In the case of HTLV-1, EVs isolated from the peripheral blood and cerebral spinal fluid (CSF) of HAM/TSP patients contained the viral transactivator protein Tax. Additionally, EVs derived from HTLV-1-infected cells (HTLV-1 EVs) promote functional effects such as cell aggregation which enhance viral spread. In this review, we present current knowledge surrounding EVs and their potential role as immune-modulating agents in cancer and other infectious diseases such as HTLV-1 and HIV-1. We discuss various features of EVs that make them prime targets for possible vehicles of future diagnostics and therapies.

Bovine leukemia virus relation to human breast cancer: Meta-analysis

Bovine leukemia virus (BLV) is a virus that infects cattle around the world and is very similar to the human T-cell leukemia virus (HTLV), which causes adult T-cell leukemia/lymphoma (ATL). Recently, presence of BLV DNA and protein was demonstrated in commercial bovine products and in humans. BLV DNA is generally found at higher rates in humans who have or will develop breast cancer, according to research done with subjects from several countries. These findings have led to a hypothesis that BLV transmission plays a role in breast cancer oncogenesis in humans. Here we summarize the current knowledge in the field.

Human T-cell lymphotropic virus type-1: a lifelong persistent infection, yet never truly silent

Human T-cell lymphotropic virus type-1 (HTLV-1) has a large global burden and in some key communities, such as Indigenous Australians living in remote areas, greater than 45% of people are infected. Despite HTLV-1 causing serious malignancy and myelopathic paraparesis, and a significant association with a range of inflammatory comorbidities and secondary infections that shorten lifespan, few biomedical interventions are available. HTLV-1 starkly contrasts with other blood-borne sexually transmitted viral infections, such as, HIV, hepatitis B virus, and hepatitis C virus, with no antiviral treatments that reduce virus-infected cells, no rapid diagnostics or biomarker assays suitable for use in remote settings, and no effective vaccine. We review how the replication strategies and molecular properties of HTLV-1 establish a long-term stealthy viral pathogenesis through a fine-tuned balance of persistence, immune cell dysfunction, and proliferation of proviral infected cells that collectively present robust barriers to treatment and prevention. An understanding of the nature of the HTLV-1 provirus and opposing actions of viral-coded negative-sense HBZ and positive-sense regulatory proteins Tax, p12 and its cleaved product p8, and p30, is needed to improve the biomedical tools for preventing transmission and improving the long-term health of people with this lifelong infection.

The Leukemic Fly: Promises and Challenges

Leukemia involves different types of blood cancers, which lead to significant mortality and morbidity. Murine models of leukemia have been instrumental in understanding the biology of the disease and identifying therapeutics. However, such models are time consuming and expensive in high throughput genetic and drug screening. Drosophilamelanogaster has emerged as an invaluable in vivo model for studying different diseases, including cancer. Fruit flies possess several hematopoietic processes and compartments that are in close resemblance to their mammalian counterparts. A number of studies succeeded in characterizing the fly's response upon the expression of human leukemogenic proteins in hematopoietic and non-hematopoietic tissues. Moreover, some of these studies showed that these models are amenable to genetic screening. However, none were reported to be tested for drug screening. In this review, we describe the Drosophila hematopoietic system, briefly focusing on leukemic diseases in which fruit flies have been used. We discuss myeloid and lymphoid leukemia fruit fly models and we further highlight their roles for future therapeutic screening. In conclusion, fruit fly leukemia models constitute an interesting area which could speed up the process of integrating new therapeutics when complemented with mammalian models.

The effect of alcoholic extract from Eucalyptus camaldulensis leaves on HTLV-1 Tax activities

HTLV-1 is a human retrovirus responsible for adult T-cell leukemia (ATL) and certain other clinical disorders. The viral Tax oncoprotein plays a central role in HTLV-1 pathogenicity, mainly due to its capacity of inducing the transcriptional activity of various transcriptional factors like NFқB. Eucalyptus camaldulensis (Ec) is considered as a traditional medicinal plant with valuable therapeutic effects. Here we evaluated the activity of its ethanolic leave extract on different Tax activities by testing its influence on Tax-induced activity of NFқB and HTLV-1 LTR in Jurkat cells. Our results showed that Ec inhibited Tax induced activation of NFқB -, SRF- dependent promoters and HTLV-1 LTR. Ec extract has no effect on the binding of Tax to NFқB while it strongly prevented the degradation of IҝBα induced by Tax probably as a result of preventing the link between Tax and IKKγ. In addition, increasing the cellular level of P-TEFb-cyclinT1 significantly reduced the inhibitory effect of Ec on Tax activities, probably by preventing the interaction between Tax and P-TEFb-cyclin T1. The 40%-MeOH fraction of this extract, which is rich with polyphenols, offered the highest inhibitory effect against Tax activities. Further studies are required for the isolation and identification of active component/s in this extract which may be developed in the future as preventive/curing drugs for HTLV-1 related diseases.

Reversal of CYLD phosphorylation as a novel therapeutic approach for adult T-cell leukemia/lymphoma (ATLL)

Adult T-cell leukemia/lymphoma (ATLL) is a malignancy of mature T cells associated with chronic infection by human T-cell lymphotropic virus type-1 (HTLV-1). ATLL patients with aggressive subtypes have dismal outcomes. We demonstrate that ATLL cells co-opt an early checkpoint within the tumor necrosis factor receptor 1 (TNFR1) pathway, resulting in survival advantage. This early checkpoint revolves around an interaction between the deubiquitinase CYLD and its target RIPK1. The status of RIPK1 K63-ubiquitination determines cell fate by creating either a prosurvival signal (ubiquitinated RIPK1) or a death signal (deubiquitinated RIPK1). In primary ATLL samples and in cell line models, an increased baseline level of CYLD phosphorylation was observed. We therefore tested the hypothesis that this modification of CYLD, which has been reported to inhibit its deubiquitinating function, leads to increased RIPK1 ubiquitination and thus provides a prosurvival signal to ATLL cells. CYLD phosphorylation can be pharmacologically reversed by IKK inhibitors, specifically by TBK1/IKKε and IKKβ inhibitors (MRT67307 and TPCA). Both of the IKK sub-families can phosphorylate CYLD, and the combination of MRT67307 and TPCA have a marked effect in reducing CYLD phosphorylation and triggering cell death. ATLL cells overexpressing a kinase-inactive TBK1 (TBK1-K38A) demonstrate lower CYLD phosphorylation and subsequently reduced proliferation. IKK blockade reactivates CYLD, as evidenced by the reduction in RIPK1 ubiquitination, which leads to the association of RIPK1 with the death-inducing signaling complex (DISC) to trigger cell death. In the absence of CYLD, RIPK1 ubiquitination remains elevated following IKK blockade and it does not associate with the DISC. SMAC mimetics can similarly disrupt CYLD phosphorylation and lead to ATLL cell death through reduction of RIPK1 ubiquitination, which is CYLD dependent. These results identify CYLD as a crucial regulator of ATLL survival and point to its role as a potential novel target for pharmacologic modification in this disease.

Targeting histone epigenetics to control viral infections

During the past decades, many studies have significantly broadened our understanding of complex virus-host interactions to control chromatin structure and dynamics.1, 2 However, the role and impact of such modifications during viral infections is not fully revealed. Indeed, this type of regulation is bidirectional between the virus and the host. While viral replication and gene expression are significantly impacted by histone modifications on the viral chromatin,³ studies have shown that some viral pathogens dynamically manipulate cellular epigenetic factors to enhance their own survival and pathogenesis, as well as escape the immune system defense lines.⁴ In this dynamic, histone posttranslational modifications (PTMs) appear to play fundamental roles in the regulation of chromatin structure and recruitment of other factors.⁵ Genuinely, those PTMs play a vital role in lytic infection, latency reinforcement, or, conversely, viral reactivation.⁶ In this chapter, we will examine and review the involvement of histone modifications as well as their potential manipulation to control infections during various viral life cycle stages, highlighting their prospective implications in the clinical management of human immunodeficiency virus (HIV), herpes simplex virus (HSV), human cytomegalovirus (HCMV), hepatitis B and C viruses (HBV and HCV, respectively), Epstein–Barr virus (EBV), and other viral diseases. Targeting histone modifications is critical in setting the treatment of chronic viral infections with both lytic and latent stages (HIV, HCMV, HSV, RSV), virus-induced cancers (HBV, HCV, EBV, KSHV, HPV), and epidemic/emerging viruses (e.g. influenza virus, arboviruses).

The rapidly changing landscape in mature T-cell lymphoma (MTCL) biology and management

Historical advances in the care of patients with non-Hodgkin lymphoma (NHL) have been restricted largely to patients with B-cell lymphoma. The peripheral T-cell lymphomas (PTCLs), which are rare and heterogeneous in nature, have yet to experience the same degree of improvement in outcome over the past 20 to 30 years. It is estimated that there are approximately 80,000 and 14,000 cases, respectively, of NHL and Hodgkin lymphoma per year in the United States. As a subgroup of NHL, the PTCLs account for 6% to 10% of all cases of NHL, making them exceedingly rare. In addition, the World Health Organization 2017 classification describes 29 distinct subtypes of PTCL. This intrinsic diversity, coupled with its rarity, has stymied progress in the disease. In addition, most subtypes carry an inferior prognosis compared with their B-cell counterparts, an outcome largely attributed to the fact that most treatment paradigms for patients with PTCL have been derived from B-cell neoplasms, a radically different disease. In fact, the first drug ever approved for patients with PTCL was approved only a decade ago. The plethora of recent drug approvals in PTCL, coupled with a deeper understanding of the molecular pathogenesis of the disease, has stimulated the field to pursue new avenues of research that are now largely predicated on the development of novel, targeted small molecules, which include a host of epigenetic modifiers and biologics. There is an expectation these advances may begin to favorably challenge the chemotherapy paradigms that have been used in the T-cell malignancies.

p30 protein: a critical regulator of HTLV-1 viral latency and host immunity

The extraordinarily high prevalence of HTLV-1 subtype C (HTLV-1C) in some isolated indigenous communities in Oceania and the severity of the health conditions associated with the virus impress the great need for basic and translational research to prevent and treat HTLV-1 infection. The genome of the virus’s most common subtype, HTLV-1A, encodes structural, enzymatic, and regulatory proteins that contribute to viral persistence and pathogenesis. Among these is the p30 protein encoded by the doubly spliced Tax-orf II mRNA, a nuclear/nucleolar protein with both transcriptional and post-transcriptional activity. The p30 protein inhibits the productive replication cycle via nuclear retention of the mRNA that encodes for both the viral transcriptional trans-activator Tax, and the Rex proteins that regulate the transport of incompletely spliced viral mRNA to the cytoplasm. In myeloid cells, p30 inhibits the PU-1 transcription factor that regulates interferon expression and is a critical mediator of innate and adaptive immunity. Furthermore, p30 alters gene expression, cell cycle progression, and DNA damage responses in T-cells, raising the hypothesis that p30 may directly contribute to T cell transformation. By fine-tuning viral expression while also inhibiting host innate responses, p30 is likely essential for viral infection and persistence. This concept is supported by the finding that macaques, a natural host for the closely genetically related simian T-cell leukemia virus 1 (STLV-1), exposed to an HTLV-1 knockout for p30 expression by a single point mutation do not became infected unless reversion and selection of the wild type HTLV-1 genotype occurs. All together, these data suggest that inhibition of p30 may help to curb and eventually eradicate viral infection by exposing infected cells to an effective host immune response.

HTLV-1 as a Model for Virus and Host Coordinated Immunoediting

Immunoediting is a process that occurs in cancer, whereby the immune system acts to initially repress, and subsequently promote the outgrowth of tumor cells through the stages of elimination, equilibrium, and escape. Here we present a model for a virus that causes cancer where immunoediting is coordinated through synergistic viral- and host-mediated events. We argue that the initial viral replication process of the Human T cell leukemia virus type I (HTLV-1), which causes adult T cell leukemia/lymphoma (ATL) in ~5% of individuals after decades of latency, harmonizes with the host immune system to create a population of cells destined for malignancy. Furthermore, we explore the possibility for HIV to fit into this model of immunoediting, and propose a non-malignant escape phase for HIV-infected cells that persist beyond equilibrium.

HTLV-1 Extracellular Vesicles Promote Cell-to-Cell Contact

Human T-cell leukemia virus-1 (HTLV-1) is a neglected and incurable retrovirus estimated to infect 5 to 10 million worldwide. Specific indigenous Australian populations report infection rates of more than 40%, suggesting a potential evolution of the virus with global implications. HTLV-1 causes adult T-cell leukemia/lymphoma (ATLL), and a neurological disease named HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). Even though HTLV-1 transmission primarily occurs from cell-to-cell, there is still a gap of knowledge regarding the mechanisms of viral spread and disease progression. We have recently shown that Extracellular Vesicles (EVs) ubiquitously produced by cells may be used by HTLV-1 to transport viral proteins and RNA, and elicit adverse effects on recipient uninfected cells. The viral proteins Tax and HBZ are involved in disease progression and impairment of autophagy in infected cells. Here, we show that activation of HTLV-1 via ionizing radiation (IR) causes a significant increase of intracellular Tax, but not EV-associated Tax. Also, lower density EVs from HTLV-1-infected cells, separated by an Iodixanol density gradient, are positive for gp61+++/Tax+++/HBZ+ proteins (HTLV-1 EVs). We found that HTLV-1 EVs are not infectious when tested in multiple cell lines. However, these EVs promote cell-to-cell contact of uninfected cells, a phenotype which was enhanced with IR, potentially promoting viral spread. We treated humanized NOG mice with HTLV-1 EVs prior to infection and observed an increase in viral RNA synthesis in mice compared to control (EVs from uninfected cells). Proviral DNA levels were also quantified in blood, lung, spleen, liver, and brain post-treatment with HTLV-1 EVs, and we observed a consistent increase in viral DNA levels across all tissues, especially the brain. Finally, we show direct implications of EVs in viral spread and disease progression and suggest a two-step model of infection including the release of EVs from donor cells and recruitment of recipient cells as well as an increase in recipient cell-to-cell contact promoting viral spread.

Inhibition of HTLV-1 Infection by HIV-1 First- and Second-Generation Integrase Strand Transfer Inhibitors

More than 10 million people worldwide are infected with the retrovirus human T-cell lymphotropic virus type 1 (HTLV-1). Infection phenotypes can range from asymptomatic to severe adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy. HTLV-1, like human immunodeficiency virus type 1 (HIV-1), is a blood-borne pathogen and viral infection happens in a similar fashion, with the major mode of transmission through breastfeeding. There is a strong correlation between time of infection and disease development, with a higher incidence of ATLL in patients infected during childhood. There is no successful therapeutic or preventative regimen for HTLV-1. It is therefore essential to develop therapies to inhibit transmission or block the onset/development of HTLV-1 associated diseases. Recently, we have seen the overwhelming success of integrase strand transfer inhibitors (INSTIs) in the treatment of HIV-1. Previously, raltegravir was shown to inhibit HTLV-1 infection. Here, we tested FDA-approved and two Phase II HIV-1 INSTIs in vitro and in a cell-to-cell infection model and show that they are highly active in blocking HTLV-1 infection, with bictegravir (EC₅₀ = 0.30 ± 0.17 nM) performing best overall. INSTIs, in particular bictegravir, are more potent in blocking HTLV-1 transmission than tenofovir disproxil fumarate (TDF), an RT inhibitor. Our data suggest that HIV-1 INSTIs could present a good clinical strategy in HTLV-1 management and justifies the inclusion of INSTIs in clinical trials.

Thymoquinone enhances the anticancer activity of doxorubicin against adult T-cell leukemia in vitro and in vivo through ROS-dependent mechanisms

AIMS

Adult T-cell leukemia (ATL) is a mature T-cell neoplasm associated with human T-cell lymphotropic virus (HTLV-1) infection. Major limitations in Doxorubicin (Dox) chemotherapy are tumor resistance and severe drug complications. Here, we combined Thymoquinone (TQ) with low concentrations of Dox and determined anticancer effects against ATL in cell culture and animal model.

MAIN METHODS

HTLV-1 positive (HuT-102) and HTLV-1 negative (Jurkat) CD4+ malignant T-cell lines were treated with TQ, Dox and combinations. Viability and cell cycle effects were determined by MTT assay and flow cytometry analysis, respectively. Combination effects on mitochondrial membrane potential and generation of reactive oxygen species (ROS) were assessed. Expression levels of key cell death proteins were investigated by western blotting. A mouse xenograft model of ATL in NOD/SCID was used for testing drug effects and tumor tissues were stained for Ki67 and TUNEL.

KEY FINDINGS

TQ and Dox caused greater inhibition of cell viability and increased sub-G1 cells in both cell lines compared to Dox or TQ alone. The combination induced apoptosis by increasing ROS and causing disruption of mitochondrial membrane potential. Pretreatment with N-acetyl cysteine (NAC) or pan caspase inhibitor significantly inhibited the apoptotic response suggesting that cell death is ROS- and caspase-dependent. TQ and Dox combination reduced tumor volume in NOD/SCID mice more significantly than single treatments through enhanced apoptosis without affecting the survival of mice.

SIGNIFICANCE

Our combination model offers the possibility to use up to twofold lower doses of Dox against ATL while exhibiting the same cancer inhibitory effects.

Portrait of the Intrinsically Disordered Side of the HTLV-1 Proteome

Intrinsically disordered proteins (IDPs) lack an ordered 3D structure. These proteins contain one or more intrinsically disordered protein regions (IDPRs). IDPRs interact promiscuously with other proteins, which leads to their structural transition from a disordered to an ordered state. Such interaction-prone regions of IDPs are known as molecular recognition features. Recent studies suggest that IDPs provide structural plasticity and functional diversity to viral proteins that are involved in rapid replication and immune evasion within the host cells. In the present study, we evaluated the prevalence of IDPs and IDPRs in human T lymphotropic virus type 1 (HTLV-1) proteome. We also investigated the presence of MoRF regions in the structural and nonstructural proteins of HTLV-1. We found abundant IDPRs in HTLV-1 bZIP factor, p30, Rex, and structural nucleocapsid p15 proteins, which are involved in diverse functions such as virus proliferation, mRNA export, and genomic RNA binding. Our study analyzed the HTLV-1 proteome with the perspective of intrinsic disorder identification. We propose that the intrinsic disorder analysis of HTLV-1 proteins may form the basis for the development of protein disorder-based drugs.

Non-Structural Proteins from Human T-cell Leukemia Virus Type 1 in Cellular Membranes-Mechanisms for Viral Survivability and Proliferation

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of illnesses, such as adult T-cell leukemia/lymphoma, myelopathy/tropical spastic paraparesis (a neurodegenerative disorder), and other diseases. Therefore, HTLV-1 infection is a serious public health concern. Currently, diseases caused by HTLV-1 cannot be prevented or cured. Hence, there is a pressing need to comprehensively understand the mechanisms of HTLV-1 infection and intervention in host cell physiology. HTLV-1-encoded non-structural proteins that reside and function in the cellular membranes are of particular interest, because they alter cellular components, signaling pathways, and transcriptional mechanisms. Summarized herein is the current knowledge about the functions of the membrane-associated p8^I, p12^I, and p13^II regulatory non-structural proteins. p12^I resides in endomembranes and interacts with host proteins on the pathways of signal transduction, thus preventing immune responses to the virus. p8^I is a proteolytic product of p12^I residing in the plasma membrane, where it contributes to T-cell deactivation and participates in cellular conduits, enhancing virus transmission. p13^II associates with the inner mitochondrial membrane, where it is proposed to function as a potassium channel. Potassium influx through p13^II in the matrix causes membrane depolarization and triggers processes that lead to either T-cell activation or cell death through apoptosis.

The Human T-Cell Leukemia Virus Type 1 Basic Leucine Zipper Factor Attenuates Repair of Double-Stranded DNA Breaks via Nonhomologous End Joining

Adult T-cell leukemia (ATL) is a fatal malignancy of CD4⁺ T cells infected with human T-cell leukemia virus type 1 (HTLV-1). ATL cells often exhibit random gross chromosomal rearrangements that are associated with the induction and improper repair of double-stranded DNA breaks (DSBs). The viral oncoprotein Tax has been reported to impair DSB repair but has not been shown to be consistently expressed throughout all phases of infection. The viral oncoprotein HTLV-1 basic leucine zipper (bZIP) factor (HBZ) is consistently expressed prior to and throughout disease progression, but it is unclear whether it also influences DSB repair. We report that HBZ attenuates DSB repair by nonhomologous end joining (NHEJ), in a manner dependent upon the bZIP domain. HBZ was found to interact with two vital members of the NHEJ core machinery, Ku70 and Ku80, and to be recruited to DSBs in a bZIP-dependent manner in vitro We observed that HBZ expression also resulted in a bZIP-dependent delay in DNA protein kinase (DNA-PK) activation following treatment with etoposide. Although Tax is reported to interact with Ku70, we did not find Tax expression to interfere with HBZ:Ku complex formation. However, as Tax was reported to saturate NHEJ, we found that this effect masked the attenuation of NHEJ by HBZ. Overall, these data suggest that DSB repair mechanisms are impaired not only by Tax but also by HBZ and show that HBZ expression may significantly contribute to the accumulation of chromosomal abnormalities during HTLV-1-mediated oncogenesis.IMPORTANCE Human T-cell leukemia virus type 1 (HTLV-1) infects 15 million to 20 million people worldwide. Approximately 90% of infected individuals are asymptomatic and may remain undiagnosed, increasing the risk that they will unknowingly transmit the virus. About 5% of the HTLV-1-positive population develop adult T-cell leukemia (ATL), a fatal disease that is not highly responsive to treatment. Although ATL development remains poorly understood, two viral proteins, Tax and HBZ, have been implicated in driving disease progression by manipulating host cell signaling and transcriptional pathways. Unlike Tax, HBZ expression is consistently observed in all infected individuals, making it important to elucidate the specific role of HBZ in disease progression. Here, we present evidence that HBZ could promote the accumulation of double-stranded DNA breaks (DSBs) through the attenuation of the nonhomologous end joining (NHEJ) repair pathway. This effect may lead to genome instability, ultimately contributing to the development of ATL.

Mouse Models That Enhanced Our Understanding of Adult T Cell Leukemia

Adult T cell Leukemia (ATL) is an aggressive lymphoproliferative malignancy secondary to infection by the human T-cell leukemia virus type I (HTLV-I) and is associated with a dismal prognosis. ATL leukemogenesis remains enigmatic. In the era of precision medicine in oncology, mouse models offer one of the most efficient in vivo tools for the understanding of the disease biology and developing novel targeted therapies. This review provides an up-to-date and comprehensive account of mouse models developed in the context of ATL and HTLV-I infection. Murine ATL models include transgenic animals for the viral proteins Tax and HBZ, knock-outs for key cellular regulators, xenografts and humanized immune-deficient mice. The first two groups provide a key understanding of the role of viral and host genes in the development of ATL, as well as their relationship with the immunopathogenic processes. The third group represents a valuable platform to test new targeted therapies against ATL.

NF-kappaB: Two Sides of the Same Coin

Nuclear Factor-kappa B (NF-κB) is a transcription factor family that regulates a large number of genes that are involved in important physiological processes, including survival, inflammation, and immune responses. More recently, constitutive expression of NF-κB has been associated with several types of cancer. In addition, microorganisms, such as viruses and bacteria, cooperate in the activation of NF-κB in tumors, confirming the multifactorial role of this transcription factor as a cancer driver. Recent reports have shown that the NF-κB signaling pathway should receive attention for the development of therapies. In addition to the direct effects of NF-κB in cancer cells, it might also impact immune cells that can both promote or prevent tumor development. Currently, with the rise of cancer immunotherapy, the link among immune cells, inflammation, and cancer is a major focus, and NF-κB could be an important regulator for the success of these therapies. This review discusses the contrasting roles of NF-κB as a regulator of pro- and antitumor processes and its potential as a therapeutic target.

Clonality of HTLV-1-infected T cells as a risk indicator for development and progression of adult T-cell leukemia

Adult T-cell leukemia (ATL) is an aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1) that develops along a carcinogenic process involving 5 or more genetic events in infected cells. The lifetime incidence of ATL among HTLV-1-infected individuals is approximately 5%. Although epidemiologic studies have revealed risk factors for ATL, the molecular mechanisms that determine the fates of carriers remain unclear. A better understanding of clonal composition and related longitudinal dynamics would clarify the process of ATL leukemogenesis and provide insights into the mechanisms underlying the proliferation of a malignant clone. Genomic DNA samples and clinical information were obtained from individuals enrolled in the Joint Study for Predisposing Factors for ATL Development, a Japanese prospective cohort study. Forty-seven longitudinal samples from 20 individuals (9 asymptomatic carriers and 11 patients with ATL at enrollment) were subjected to a clonality analysis. A method based on next-generation sequencing was used to characterize clones on the basis of integration sites. Relationships were analyzed among clonal patterns, clone sizes, and clinical status, including ATL onset and progression. Among carriers, those exhibiting an oligoclonal or monoclonal pattern with largely expanded clones subsequently progressed to ATL. All indolent patients who progressed to acute-type ATL exhibited monoclonal expansion. In both situations, the major expanded clone after progression was derived from the largest pre-existing clone. This study has provided the first detailed information regarding the dynamics of HTLV-1-infected T-cell clones and collectively suggests that the clonality of HTLV-1-infected cells could be a useful predictive marker of ATL onset and progression.

Effect of TPA and HTLV-1 Tax on BRCA1 and ERE controlled genes expression

Interference with the expression and/or functions of the multifunctional tumor suppressor BRCA1 leads to a high risk of breast and ovarian cancers. BRCA1 expression is usually activated by the estrogen (E2) liganded ERα receptor. Activated ERα is considered as a potent transcription factor which activates various genes expression by 2 pathways. A classical pathway, ERα binds directly to E2-responsive elements (EREs) in the promoters of the responsive genes and a non-classical pathway where ERα indirectly binds with the appropriate gene promoter. In our previous study, HTLV-1Tax was found to strongly inhibit ERα induced BRCA1 expression while stimulating ERα induced ERE dependent genes. TPA is a strong PKC activator which found to induce the expression of HTLV-1. Here we examined the effect of TPA on the expression of BRCA1 and genes controlled by ERE region in MCF-7 cells and on Tax activity on these genes. Our results showed strong stimulatory effect of TPA on both BRCA1 and ERE expression without treatment with E2. Tax did not show any significant effect on these TPA activities. It seems that TPA activation of BRCA1 and ERE expression is dependent on PKC activity but not through the NFκB pathway. However, 53BP1 may be involved in this TPA activity because its overexpression significantly reduced the TPA stimulatory effect on BRCA1 and ERE expression. Additionally, our Chip assay results probably exclude possible involvement of ERα pathway in this TPA activity because TPA did not interfere with the binding of ERα to both BRCA1 promoter and ERE region.

Adult T-cell leukemia: molecular basis for clonal expansion and transformation of HTLV-1-infected T cells

Adult T-cell leukemia (ATL) is an aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1) that develops through a multistep carcinogenesis process involving 5 or more genetic events. We provide a comprehensive overview of recently uncovered information on the molecular basis of leukemogenesis in ATL. Broadly, the landscape of genetic abnormalities in ATL that include alterations highly enriched in genes for T-cell receptor-NF-κB signaling such as PLCG1, PRKCB, and CARD11 and gain-of function mutations in CCR4 and CCR7 Conversely, the epigenetic landscape of ATL can be summarized as polycomb repressive complex 2 hyperactivation with genome-wide H3K27 me3 accumulation as the basis of the unique transcriptome of ATL cells. Expression of H3K27 methyltransferase enhancer of zeste 2 was shown to be induced by HTLV-1 Tax and NF-κB. Furthermore, provirus integration site analysis with high-throughput sequencing enabled the analysis of clonal composition and cell number of each clone in vivo, whereas multicolor flow cytometric analysis with CD7 and cell adhesion molecule 1 enabled the identification of HTLV-1-infected CD4+ T cells in vivo. Sorted immortalized but untransformed cells displayed epigenetic changes closely overlapping those observed in terminally transformed ATL cells, suggesting that epigenetic abnormalities are likely earlier events in leukemogenesis. These new findings broaden the scope of conceptualization of the molecular mechanisms of leukemogenesis, dissecting them into immortalization and clonal progression. These recent findings also open a new direction of drug development for ATL prevention and treatment because epigenetic marks can be reprogrammed. Mechanisms underlying initial immortalization and progressive accumulation of these abnormalities remain to be elucidated.

The Application of Humanized Mouse Models for the Study of Human Exclusive Viruses

The symbiosis between humans and viruses has allowed human tropic pathogens to evolve intricate means of modulating the human immune response to ensure its survival among the human population. In doing so, these viruses have developed profound mechanisms that mesh closely with our human biology. The establishment of this intimate relationship has created a species-specific barrier to infection, restricting the virus-associated pathologies to humans. This specificity diminishes the utility of traditional animal models. Humanized mice offer a model unique to all other means of study, providing an in vivo platform for the careful examination of human tropic viruses and their interaction with human cells and tissues. These types of animal models have provided a reliable medium for the study of human-virus interactions, a relationship that could otherwise not be investigated without questionable relevance to humans.

ATL-derived exosomes modulate mesenchymal stem cells: potential role in leukemia progression

Background

Exosomes are membrane nano-vesicles secreted by a multitude of cells that harbor biological constituents such as proteins, lipids, mRNA and microRNA. Exosomes can potentially transfer their cargo to other cells, implicating them in many patho-physiological processes. Mesenchymal stem cells (MSCs), residents of the bone marrow and metastatic niches, potentially interact with cancer cells and/or their derived exosomes. In this study, we investigated whether exosomes derived from adult T-cell leukemia/lymphoma (ATL) cells act as intercellular messengers delivering leukemia-related genes that modulate the properties of human MSCs in favor of leukemia. We hypothesized that the cargo of ATL-derived exosomes is transferred to MSCs and alter their functional behavior to support the establishment of the appropriate microenvironment for leukemia.

Results

We showed that both ATL cells (C81 and HuT-102) and patient-derived cells released Tax-containing exosomes. The cargo of HuT-102-derived exosomes consisted of miR-21, miR-155 and vascular endothelial growth factor. We demonstrated that HuT-102-derived exosomes not only deliver Tax to recipient MSCs, but also induce NF-κB activation leading to a change in cellular morphology, increase in proliferation and the induction of gene expression of migration and angiogenic markers.

Conclusions

This study demonstrates that ATL-derived exosomes deliver Tax and other leukemia-related genes to MSCs and alter their properties to presumably create a more conducive milieu for leukemia. These findings highlight the contribution of leukemia-derived exosomes in cellular transformation and their potential value as biomarkers and targets in therapeutic strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-016-0307-4) contains supplementary material, which is available to authorized users.

Differential effects of HTLV-1 Tax oncoprotein on the different estrogen-induced-ER α-mediated transcriptional activities

The activated estrogen (E2) receptor α (ERα) is a potent transcription factor that is involved in the activation of various genes by 2 different pathways; a classical and non-classical. In classical pathway, ERα binds directly to E2-responsive elements (EREs) located in the appropriate genes promoters and stimulates their transcription. However, in non-classical pathway, the ERα can indirectly bind with promoters and enhance their activity. For instance, ERα activates BRCA1 expression by interacting with jun/fos complex bound to the AP-1 site in BRCA1 promoter. Interference with the expression and/or functions of BRCA1, leads to high risk of breast or/and ovarian cancer. HTLV-1Tax was found to strongly inhibit BRCA1 expression by preventing the binding of E2-ERα complex to BRCA1 promoter. Here we examined Tax effect on ERα induced activation of genes by the classical pathway by testing its influence on E2-induced expression of ERE promoter-driven luciferase reporter (ERE-Luc). Our findings showed that E2 profoundly stimulated this reporter expression and that HTLV-1Tax significantly induced this stimulation. This result is highly interesting because in our previous study Tax was found to strongly block the E2-ERα-mediated activation of BRCA1 expression. ERα was found to produce a big complex by recruiting various cofactors in the nucleus before binding to the ERE region. We also found that only part of the reqruited cofactors are required for the transcriptional activity of ERα complex. Chip assay revealed that the binding of Tax to the ERα complex, did not interfere with its link to ERE region.

Cellular Immune Responses against Simian T-Lymphotropic Virus Type 1 Target Tax in Infected Baboons

There are currently 5 million to 10 million human T-lymphotropic virus type 1 (HTLV-1)-infected people, and many of them will develop severe complications resulting from this infection. A vaccine is urgently needed in areas where HTLV-1 is endemic. Many vaccines are best tested in nonhuman primate animal models. As a first step in designing an effective HTLV-1 vaccine, we defined the CD8(+) and CD4(+) T cell response against simian T-lymphotropic virus type 1 (STLV-1), a virus closely related to HTLV-1, in olive baboons (Papio anubis). Consistent with persistent antigenic exposure, we observed that STLV-1-specific CD8(+) T cells displayed an effector memory phenotype and usually expressed CD107a, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α). To assess the viral targets of the cellular immune response in STLV-1-infected animals, we used intracellular cytokine staining to detect responses against overlapping peptides covering the entire STLV-1 proteome. Our results show that, similarly to humans, the baboon CD8(+) T cell response narrowly targeted the Tax protein. Our findings suggest that the STLV-1-infected baboon model may recapitulate some of the important aspects of the human response against HTLV-1 and could be an important tool for the development of immune-based therapy and prophylaxis.

IMPORTANCE

HTLV-1 infection can lead to many different and often fatal conditions. A vaccine deployed in areas of high prevalence might reduce the incidence of HTLV-1-induced disease. Unfortunately, there are very few animal models of HTLV-1 infection useful for testing vaccine approaches. Here we describe cellular immune responses in baboons against a closely related virus, STLV-1. We show for the first time that the immune response against STLV-1 in naturally infected baboons is largely directed against the Tax protein. Similar findings in humans and the sequence similarity between the human and baboon viruses suggest that the STLV-1-infected baboon model might be useful for developing a vaccine against HTLV-1.

HTLV-1, Immune Response and Autoimmunity

Human T-lymphotropic virus type-1 (HTLV-1) infection is associated with adult T-cell leukemia/lymphoma (ATL). Tropical spastic paraparesis/HTLV-1-associated myelopathy (PET/HAM) is involved in the development of autoimmune diseases including Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), and Sjögren's Syndrome (SS). The development of HTLV-1-driven autoimmunity is hypothesized to rely on molecular mimicry, because virus-like particles can trigger an inflammatory response. However, HTLV-1 modifies the behavior of CD4⁺ T cells on infection and alters their cytokine production. A previous study showed that in patients infected with HTLV-1, the activity of regulatory CD4⁺ T cells and their consequent expression of inflammatory and anti-inflammatory cytokines are altered. In this review, we discuss the mechanisms underlying changes in cytokine release leading to the loss of tolerance and development of autoimmunity.

Activation of Tax protein by c-Jun-N-terminal kinase is not dependent on the presence or absence of the early growth response-1 gene product

The Tax protein of human T cell leukemia virus type 1 plays a major role in the pathogenesis of adult T cell leukemia (ATL), an aggressive neoplasia of CD4+ T cells. In the present study, we investigated whether the EGR-1 pathway is involved in the regulation of Tax-induced JNK expression in human Jurkat T cells transfected to express the Tax protein in the presence or absence of PMA or ionomycin. Overexpression of EGR-1 in Jurkat cells transfected to express Tax, promoted the activation of several genes, with the most potent being those that contained AP-1 (Jun/c-Fos), whereas knockdown of endogenous EGR-1 by small interfering RNA (siRNA) somewhat reduced Tax-mediated JNK-1 transcription. Additionally, luciferase-based AP-1 and NF-κB reporter gene assays demonstrated that inhibition of EGR-1 expression by an siRNA did not affect the transcriptional activity of a consensus sequence of either AP-1 or NF-κB. On the other hand, the apoptosis assay, using all-trans retinoic acid (ATRA) as an inducer of apoptosis, confirmed that siRNA against EGR-1 failed to suppress ATRA-induced apoptosis in Jurkat and Jurkat-Tax cells, as noted by the low levels of both DEVDase activity and DNA fragmentation, indicating that the induction of apoptosis by ATRA was Egr-1-independent. Finally, our data showed that activation of Tax by JNK-1 was not dependent on the EGR-1 cascade of events, suggesting that EGR-1 is important but not a determinant for the activity for Tax-induced proliferation of Jurkat cells.

High IFN-γ/IL-10 expression ratio and increased frequency of persistent human T-cell lymphotropic virus type 1-infected clones are associated with human T-cell lymphotropic virus type 1-associated myelopathy/tropical spastic paraparesis development

BACKGROUND/AIMS

Human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that causes a persistent infection, and only 0.5-5% of infected individuals will develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Therefore, we investigated parameters to discriminate HTLV-1 asymptomatic carriers (ACs) with an increased chance to develop HAM/TSP.

METHODS

We evaluated integration patterns of HTLV-1 provirus, the relative expression of HTLV-1 tax and HBZ mRNAs and of IFN-γ and IL-10 mRNAs, in addition to proviral load (PVL) levels.

RESULTS

HAM/TSP patients presented a higher number of large persistent HTLV-1-carrying clones compared to ACs, and the expression of the HTLV-1 tax and HBZ genes by infected cells was detected at low levels and correlated positively with PVL. In addition, HAM/TSP patients and ACs with high PVL expressed higher levels of IFN-γ mRNA in comparison to IL-10, while ACs with low PVL presented an equilibrate IFN-γ/IL-10 ratio.

CONCLUSIONS

The presence of large persistent HTLV-1-infected clones in association with viral gene expression, even at small levels, could stimulate the intense inflammatory response in HTLV-1-infected individuals. This was supported by a high ratio of IFN-γ/IL-10 relative expression in HAM/TSP patients and ACs with high PVL, indicating that these parameters could aid the identification of ACs with a high risk to develop HAM/TSP.

Disruption of Bcl-2 and Bcl-xL by viral proteins as a possible cause of cancer

The Bcl proteins play a critical role in apoptosis, as mutations in family members interfere with normal programmed cell death. Such events can cause cell transformation, potentially leading to cancer. Recent discoveries indicate that some viral proteins interfere with Bcl proteins either directly or indirectly; however, these data have not been systematically described. Some viruses encode proteins that reprogramme host cellular signalling pathways controlling cell differentiation, proliferation, genomic integrity, cell death, and immune system recognition. This review analyses and summarises the existing data and discusses how viral proteins interfere with normal pro- and anti-apoptotic functions of Bcl-2 and Bcl-xL. Particularly, this article focuses on how viral proteins, such as Herpesviruses, HTLV-1, HPV and HCV, block apoptosis and how accumulation of such interference predisposes cancer development. Finally, we discuss possible ways to prevent and treat cancers using a combination of traditional therapies and antiviral preparations that are effective against these viruses.

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.

Human viruses and cancer

The first human tumor virus was discovered in the middle of the last century by Anthony Epstein, Bert Achong and Yvonne Barr in African pediatric patients with Burkitt's lymphoma. To date, seven viruses -EBV, KSHV, high-risk HPV, MCPV, HBV, HCV and HTLV1- have been consistently linked to different types of human cancer, and infections are estimated to account for up to 20% of all cancer cases worldwide. Viral oncogenic mechanisms generally include: generation of genomic instability, increase in the rate of cell proliferation, resistance to apoptosis, alterations in DNA repair mechanisms and cell polarity changes, which often coexist with evasion mechanisms of the antiviral immune response. Viral agents also indirectly contribute to the development of cancer mainly through immunosuppression or chronic inflammation, but also through chronic antigenic stimulation. There is also evidence that viruses can modulate the malignant properties of an established tumor. In the present work, causation criteria for viruses and cancer will be described, as well as the viral agents that comply with these criteria in human tumors, their epidemiological and biological characteristics, the molecular mechanisms by which they induce cellular transformation and their associated cancers.

HTLV-1 Tax oncoprotein inhibits the estrogen-induced-ER α-Mediated BRCA1 expression by interaction with CBP/p300 cofactors

BRCA1 is a multifunctional tumor suppressor, whose expression is activated by the estrogen (E2)-liganded ERα receptor and regulated by certain recruited transcriptional co-activators. Interference with BRCA1 expression and/or functions leads to high risk of breast or/and ovarian cancer. Another multifunctional protein, HTLV-1Tax oncoprotein, is widely regarded as crucial for developing adult T-cell leukemia and other clinical disorders. Tax profile reveals that it can antagonize BRCA1 expression and/or functionality. Therefore, we hypothesize that Tax expression in breast cells can sensitize them to malignant transformation by environmental carcinogens. Here we examined Tax effect on BRCA1 expression by testing its influence on E2-induced expression of BRCA1 promoter-driven luciferase reporter (BRCA1-Luc). We found that E2 strongly stimulated this reporter expression by liganding to ERα, which consequently associated with BRCA1 promoter, while ERα concomitantly recruited CBP/p300 to this complex for co-operative enhancement of BRCA1 expression. Introducing Tax into these cells strongly blocked this E2-ERα-mediated activation of BRCA1 expression. We noted, also, that Tax exerted this inhibition by binding to CBP/p300 without releasing them from their complex with ERα. Chip assay revealed that the binding of Tax to the CBP/p300-ERα complex, prevented its link to AP1 site. Interestingly, we noted that elevating the intracellular pool of CBP or p300 to excessive levels dramatically reduced the Tax-mediated inhibition of BRCA1 expression. Exploring the mechanism of this reduction revealed that the excessive co-factors were sufficient to bind separately the free Tax molecules, thus lowering their amount in the CBP/p300-ERα complex and relieving, thereby, the inhibition of BRCA1 expression.