Tax contributes apoptosis resistance to HTLV-1-infected T cells via suppression of Bid and Bim expression

Dynamic Roles of RNA and RNA Epigenetics in HTLV-1 Biology

Since the discovery of RNA in the early 1900s, scientific understanding of RNA form and function has evolved beyond protein coding. Viruses, particularly retroviruses like human T-cell leukemia virus type 1 (HTLV-1), rely heavily on RNA and RNA post-transcriptional modifications to regulate the viral lifecycle, pathogenesis, and evasion of host immune responses. With the emergence of new sequencing technologies in the last decade, our ability to dissect the intricacies of RNA has flourished. The ability to study RNA epigenetic modifications and splice variants has become more feasible with the recent development of third-generation sequencing technologies, such as Oxford nanopore sequencing. This review will highlight the dynamic roles of known RNA and post-transcriptional RNA epigenetic modifications within HTLV-1 biology, including viral hbz, long noncoding RNAs, microRNAs (miRNAs), transfer RNAs (tRNAs), R-loops, N6-methyladenosine (m6A) modifications, and RNA-based therapeutics and vaccines.

The HTLV-I oncoprotein Tax inactivates the tumor suppressor FBXW7

Human T-cell leukemia virus type 1 (HTLV-I) is the etiological agent of adult T-cell leukemia (ATL). Mutational analysis has demonstrated that the tumor suppressor, F-box and WD repeat domain containing 7 (FBXW7/FBW7/CDC4), is mutated in primary ATL patients. However, even in the absence of genetic mutations, FBXW7 substrates are stabilized in ATL cells, suggesting additional mechanisms can prevent FBXW7 functions. Here, we report that the viral oncoprotein Tax represses FBXW7 activity, resulting in the stabilization of activated Notch intracellular domain, c-MYC, Cyclin E, and myeloid cell leukemia sequence 1 (BCL2-related) (Mcl-1). Mechanistically, we demonstrate that Tax directly binds to FBXW7 in the nucleus, effectively outcompeting other targets for binding to FBXW7, resulting in decreased ubiquitination and degradation of FBXW7 substrates. In support of the nuclear role of Tax, a non-degradable form of the nuclear factor kappa B subunit 2 (NFκB2/p100) was found to delocalize Tax to the cytoplasm, thereby preventing Tax interactions with FBXW7 and Tax-mediated inhibition of FBXW7. Finally, we characterize a Tax mutant that is unable to interact with FBXW7, unable to block FBXW7 tumor suppressor functions, and unable to effectively transform fibroblasts. These results demonstrate that HTLV-I Tax can inhibit FBXW7 functions without genetic mutations to promote an oncogenic state. These results suggest that Tax-mediated inhibition of FBXW7 is likely critical during the early stages of the cellular transformation process.

IMPORTANCE

F-box and WD repeat domain containing 7 (FBXW7), a critical tumor suppressor of human cancers, is frequently mutated or epigenetically suppressed. Loss of FBXW7 functions is associated with stabilization and increased expression of oncogenic factors such as Cyclin E, c-Myc, Mcl-1, mTOR, Jun, and Notch. In this study, we demonstrate that the human retrovirus human T-cell leukemia virus type 1 oncoprotein Tax directly interacts with FBXW7, effectively outcompeting other targets for binding to FBXW7, resulting in decreased ubiquitination and degradation of FBXW7 cellular substrates. We further demonstrate that a Tax mutant unable to interact with and inactivate FBXW7 loses its ability to transform primary fibroblasts. Collectively, our results describe a novel mechanism used by a human tumor virus to promote cellular transformation.

HTLV-1 Tax Tug-of-War: Cellular Senescence and Death or Cellular Transformation

Human T cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with a lymphoproliferative disease known as adult T cell leukemia/lymphoma (ATLL). HTLV-1 infection efficiently transforms human T cells in vivo and in vitro. The virus does not transduce a proto-oncogene, nor does it integrate into tumor-promoting genomic sites. Instead, HTLV-1 uses a random mutagenesis model, resulting in cellular transformation. Expression of the viral protein Tax is critical for the immortalization of infected cells by targeting specific cellular signaling pathways. However, Tax is highly immunogenic and represents the main target for the elimination of virally infected cells by host cytotoxic T cells (CTLs). In addition, Tax expression in naïve cells induces pro-apoptotic signals and has been associated with the induction of non-replicative cellular senescence. This review will explore these conundrums and discuss the mechanisms used by the Tax viral oncoprotein to influence life-and-death cellular decisions and affect HTLV-1 pathogenesis.

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.

Molecular insight into the study of adult T-cell leukemia/lymphoma (ATLL): Ten-year studies on HTLV-1 associated diseases in an endemic region

The outcome of successful infection, including human T-cell leukemia virus type 1 (HTLV-1), is determined by the interactions between the host and the infectious agent. Ten years of work on HTLV-1-associated diseases in an endemic region of Iran have been critically compared in the present study. The outstanding findings of RNA-seq, system biology analysis, and gene expression measurements on adult T-cell leukemia/lymphoma (ATLL) and enzootic bovine leukosis(EBL) in our lab encouraged us to investigate the significant role of oncogenes in the ATLL malignancy. Most studies assessed such interactions by the proviral load (PVL), Tax, and HBZ regulatory proteins in HTLV-1 and the host's immunological and cell cycle factors. The current study is a comprehensive comparing view of our previously published and unpublished results investigating the HTLV-1-host interactions leading to the transformation of the infected cell. The main focus has been on the essential proteins implicated in the virus dissemination, cell survival, and proliferation of infected cells toward leukemia development and progression. Similar to its homolog BLV-AS-1-2 in EBL, the HTLV-1-HBZ is a pivotal factor in the maintenance and progression of the ATLL. In addition, the inappropriate activities of the PI3K/Akt pathway, BRCAs, and RAD51 in the DNA repair system, which are orchestrating many other immortalization pathways, might be the central factors in the manifestation of ATLL. HTLV-1-HBZ and the host PI3K/Akt pathway, BCAs, and RAD51 could be suggested as influential targets for the prognosis and proper therapy of ATLL.

Inhibition of cell proliferation by Tas of foamy viruses through cell cycle arrest or apoptosis underlines the different mechanisms of virus-host interactions

Foamy viruses belong to the Spumaretrovirinae subfamily member of the Retroviridae family and produce nonpathogenic infection to hosts in the natural conditions. However, infections of foamy viruses can dramatically cause severe cytopathic effects in vitro. To date, the exact molecular mechanism has remained unclear which implied the tremendous importance of virus-host cell immune reactions. In this study, we found that the transactivator Tas in two foamy viruses isolated from Old World Monkey (OWM) induced obvious inhibition of cell proliferation via the upregulation of Foxo3a expression. It was mediated by the generation of ROS and the initiation of ER stress, and ultimately, the mitochondrial apoptosis pathway was triggered. Notably, PFV Tas contributed to the accumulation of G0/G1 phase cycle arrest induced by the activation of the p53 signaling pathway and the nuclear transportation of HDAC4 via upregulating PPM1E expression. Together, these results demonstrated the different survival strategies by which foamy virus can hijack host cell cytokines and regulate virus-host cell interactions.

HDAC inhibitors Panobinostat and Romidepsin enhance tax transcription in HTLV-1-infected cell lines and freshly isolated patients’ T-cells

The viral transactivator Tax plays a key role in HTLV-1 reactivation and de novo infection. Previous approaches focused on the histone deacetylase inhibitor (HDACi) Valproate as a latency-reversing agent to boost Tax expression and expose infected cells to the host’s immune response. However, following treatment with Valproate proviral load decreases in patients with HAM/TSP were only transient. Here, we hypothesize that other compounds, including more potent and selective HDACi, might prove superior to Valproate in manipulating Tax expression. Thus, a panel of HDACi (Vorinostat/SAHA/Zolinza, Panobinostat/LBH589/Farydak, Belinostat/PXD101/Beleodaq, Valproate, Entinostat/MS-275, Romidepsin/FK228/Istodax, and MC1568) was selected and tested for toxicity and potency in enhancing Tax expression. The impact of the compounds was evaluated in different model systems, including transiently transfected T-cells, chronically HTLV-1-infected T-cell lines, and freshly isolated PBMCs from HTLV-1 carriers ex vivo. We identified the pan-HDACi Panobinostat and class I HDACi Romidepsin as particularly potent agents at raising Tax expression. qRT-PCR analysis revealed that these inhibitors considerably boost tax and Tax-target gene transcription. However, despite this significant increase in tax transcription and histone acetylation, protein levels of Tax were only moderately enhanced. In conclusion, these data demonstrate the ability of Panobinostat and Romidepsin to manipulate Tax expression and provide a foundation for further research into eliminating latently infected cells. These findings also contribute to a better understanding of conditions limiting transcription and translation of viral gene products.

Time-course of host cell transcription during the HTLV-1 transcriptional burst

The human T-cell leukemia virus type 1 (HTLV-1) transactivator protein Tax has pleiotropic functions in the host cell affecting cell-cycle regulation, DNA damage response pathways and apoptosis. These actions of Tax have been implicated in the persistence and pathogenesis of HTLV-1-infected cells. It is now known that tax expression occurs in transcriptional bursts of the proviral plus-strand, but the effects of the burst on host transcription are not fully understood. We carried out RNA sequencing of two naturally-infected T-cell clones transduced with a Tax-responsive Timer protein, which undergoes a time-dependent shift in fluorescence emission, to study transcriptional changes during successive phases of the HTLV-1 plus-strand burst. We found that the transcriptional regulation of genes involved in the NF-κB pathway, cell-cycle regulation, DNA damage response and apoptosis inhibition were immediate effects accompanying the plus-strand burst, and are limited to the duration of the burst. The results distinguish between the immediate and delayed effects of HTLV-1 reactivation on host transcription, and between clone-specific effects and those observed in both clones. The major transcriptional changes in the infected host T-cells observed here, including NF-κB, are transient, suggesting that these pathways are not persistently activated at high levels in HTLV-1-infected cells. The two clones diverged strongly in their expression of genes regulating the cell cycle. Up-regulation of senescence markers was a delayed effect of the proviral plus-strand burst and the up-regulation of some pro-apoptotic genes outlasted the burst. We found that activation of the aryl hydrocarbon receptor (AhR) pathway enhanced and prolonged the proviral burst, but did not increase the rate of reactivation. Our results also suggest that sustained plus-strand expression is detrimental to the survival of infected cells.

A Motif-Based Network Analysis of Regulatory Patterns in Doxorubicin Effects on Treating Breast Cancer, a Systems Biology Study

Background

Breast cancer is the most common malignancy worldwide. Doxorubicin is an anthracycline used to treat breast cancer as the first treatment choice. Nevertheless, the molecular mechanisms underlying the response to Doxorubicin and its side effects are not comprehensively understood so far. We used systems biology and bioinformatics methods to identify essential genes and molecular mechanisms behind the body response to Doxorubicin and its side effects in breast cancer patients.

Methods

Omics data were extracted and analyzed to construct the protein-protein interaction and gene regulatory networks. Network analysis was performed to identify hubs, bottlenecks, clusters, and regulatory motifs to evaluate crucial genes and molecular mechanisms behind the body response to Doxorubicin and its side effects.

Results

Analyzing the constructed PPI and gene-TF-miRNA regulatory network showed that MCM3, MCM10, and TP53 are key hub-bottlenecks and seed proteins. Enrichment analysis also revealed cell cycle, TP53 signaling, Forkhead box O (FoxO) signaling, and viral carcinogenesis as essential pathways in response to this drug. Besides, SNARE interactions in vesicular transport and neurotrophin signaling were identified as pathways related to the side effects of Doxorubicin. The apoptosis induction, DNA repair, invasion inhibition, metastasis, and DNA replication are suggested as critical molecular mechanisms underlying Doxorubicin anti-cancer effect. SNARE interactions in vesicular transport and neurotrophin signaling and FoxO signaling pathways in glucose metabolism are probably the mechanisms responsible for side effects of Doxorubicin.

Conclusion

Following our model validation using the existing experimental data, we recommend our other newly predicted biomarkers and pathways as possible molecular mechanisms and side effects underlying the response to Doxorubicin in breast cancer requiring further investigations.

Nectin-2 Acts as a Viral Entry Mediated Molecule That Binds to Human Herpesvirus 6B Glycoprotein B

Human herpesvirus 6B (HHV-6B) is a T-lymphotropic virus and the etiological agent of exanthem subitum. HHV-6B is present in a latent or persistent form after primary infection and is produced in the salivary glands or transmitted to this organ. Infected individuals continue to secrete the virus in their saliva, which is thus considered a source for virus transmission. HHV-6B primarily propagates in T cells because its entry receptor, CD134, is mainly expressed by activated T cells. The virus then spreads to the host’s organs, including the salivary glands, nervous system, and liver. However, CD134 expression is not detected in these organs. Therefore, HHV-6B may be entering cells via a currently unidentified cell surface molecule, but the mechanisms for this have not yet been investigated. In this study, we investigated a CD134-independent virus entry mechanism in the parotid-derived cell line HSY. First, we confirmed viral infection in CD134-membrane unanchored HSY cells. We then determined that nectin cell adhesion molecule 2 (nectin-2) mediated virus entry and that HHV-6B-insensitive T-cells transduced with nectin-2 were transformed into virus-permissive cells. We also found that virus entry was significantly reduced in nectin-2 knockout parotid-derived cells. Furthermore, we showed that HHV-6B glycoprotein B (gB) interacted with the nectin-2 V-set domain. The results suggest that nectin-2 acts as an HHV-6B entry-mediated protein.

Oncogenic Viruses as Entropic Drivers of Cancer Evolution

Viral infection is an indisputable causal factor for nearly 17% of all human cancers. However, the diversity and complexity of oncogenic mechanisms raises new questions as to the mechanistic role of viruses in cancer. Classical viral oncogenes have been identified for all tumor-associated viruses. These oncogenes can have multiple oncogenic activities that may or may not be utilized in a particular tumor cell. In addition, stochastic events, like viral mutation and integration, as well as heritable host susceptibilities and immune deficiencies are also implicated in tumorigenesis. A more contemporary view of tumor biology highlights the importance of evolutionary forces that select for phenotypes better adapted to a complex and changing environment. Given the challenges of prioritizing singular mechanistic causes, it may be necessary to integrate concepts from evolutionary theory and systems biology to better understand viral cancer-driving forces. Here, we propose that viral infection provides a biological “entropy” that increases genetic variation and phenotypic plasticity, accelerating the main driving forces of cancer cell evolution. Viruses can also influence the evolutionary selection criteria by altering the tumor microenvironment and immune signaling. Utilizing concepts from cancer cell evolution, population genetics, thermodynamics, and systems biology may provide new perspectives on viral oncogenesis and identify novel therapeutic strategies for treating viruses and cancer.

Non-cytotoxic 1,2,3-triazole tethered fused heterocyclic ring derivatives display Tax protein inhibition and impair HTLV-1 infected cells

Human T cell lymphotropic virus type 1 (HTLV-1) is a human retrovirus that infects approximately 10-20 million people worldwide and causes an aggressive neoplasia (adult T-cell leukemia/lymphoma - ATL). Therapeutic approaches for the treatment of ATL have variable effectiveness and poor prognosis, thus requiring strategies to identify novel compounds with activity on infected cells. In this sense, we initially screened a small series of 25 1,2,3-triazole derivatives to discover cell proliferation inhibitors and apoptosis inducers in HTLV-1-infected T-cell line (MT-2) for further assessment of their effect on viral tax activity through inducible-tax reporter cell line (Jurkat LTR-GFP). Eight promising compounds (02, 05, 06, 13, 15, 21, 22 and 25) with activity ≥70% were initially selected, based on a suitable cell-based assay using resazurin reduction method, and evaluated towards cell cycle, apoptosis and Tax/GFP expression analyses through flow cytometry. Compound 02 induced S phase cell cycle arrest and compounds 05, 06, 22 and 25 promoted apoptosis. Remarkably, compounds 22 and 25 also reduced GFP expression in an inducible-tax reporter cell, which suggests an effect on Tax viral protein. More importantly, compounds 02, 22 and 25 were not cytotoxic in human hepatoma cell line (Huh-7). Therefore, the discovery of 3 active and non-cytotoxic compounds against HTLV-1-infected cells can potentially contribute, as an initial promising strategy, to the development process of new drugs against ATL.

Oxygen Sensing and Viral Replication: Implications for Tropism and Pathogenesis

The ability to detect and respond to varying oxygen tension is an essential prerequisite to life. Several mechanisms regulate the cellular response to oxygen including the prolyl hydroxylase domain (PHD)/factor inhibiting HIF (FIH)-hypoxia inducible factor (HIF) pathway, cysteamine (2-aminoethanethiol) dioxygenase (ADO) system, and the lysine-specific demethylases (KDM) 5A and KDM6A. Using a systems-based approach we discuss the literature on oxygen sensing pathways in the context of virus replication in different tissues that experience variable oxygen tension. Current information supports a model where the PHD-HIF pathway enhances the replication of viruses infecting tissues under low oxygen, however, the reverse is true for viruses with a selective tropism for higher oxygen environments. Differences in oxygen tension and associated HIF signaling may play an important role in viral tropism and pathogenesis. Thus, pharmaceutical agents that modulate HIF activity could provide novel treatment options for viral infections and associated pathological conditions.

Polyploid Giant Cancer Cells, a Hallmark of Oncoviruses and a New Therapeutic Challenge

Tumors are renowned as intricate systems that harbor heterogeneous cancer cells with distinctly diverse molecular signatures, sizes and genomic contents. Among those various genomic clonal populations within the complex tumoral architecture are the polyploid giant cancer cells (PGCC). Although described for over a century, PGCC are increasingly being recognized for their prominent role in tumorigenesis, metastasis, therapy resistance and tumor repopulation after therapy. A shared characteristic among all tumors triggered by oncoviruses is the presence of polyploidy. Those include Human Papillomaviruses (HPV), Epstein Barr Virus (EBV), Hepatitis B and C viruses (HBV and HCV, respectively), Human T-cell lymphotropic virus-1 (HTLV-1), Kaposi's sarcoma herpesvirus (KSHV) and Merkel polyomavirus (MCPyV). Distinct viral proteins, for instance Tax for HTLV-1 or HBx for HBV have demonstrated their etiologic role in favoring the appearance of PGCC. Different intriguing biological mechanisms employed by oncogenic viruses, in addition to viruses with high oncogenic potential such as human cytomegalovirus, could support the generation of PGCC, including induction of endoreplication, inactivation of tumor suppressors, development of hypoxia, activation of cellular senescence and others. Interestingly, chemoresistance and radioresistance have been reported in the context of oncovirus-induced cancers, for example KSHV and EBV-associated lymphomas and high-risk HPV-related cervical cancer. This points toward a potential linkage between the previously mentioned players and highlights PGCC as keystone cancer cells in virally-induced tumors. Subsequently, although new therapeutic approaches are actively needed to fight PGCC, attention should also be drawn to reveal the relationship between PGCC and oncoviruses, with the ultimate goal of establishing effective therapeutic platforms for treatment of virus-associated cancers. This review discusses the presence of PGCCs in tumors induced by oncoviruses, biological mechanisms potentially favoring their appearance, as well as their consequent implication at the clinical and therapeutic level.

Interaction of perforin and granzyme B and HTLV-1 viral factors is associated with Adult T cell Leukemia development

Objective(s):

Human T cell leukaemia virus type 1 (HTLV-1) is associated with adult T cell leukaemia (ATL), a malignant lymphoproliferative disease that infects CD4 T cells. It is not clear why the majority of HTLV-1-infected individuals remain asymptomatic carries (ACs) and a minority develop ATL. Cellular immune response has a critical role in ATL and destroys malignant and HTLV-1-infected cells. Perforin and granzyme have important functional roles in apoptosis and destruction of infected cells. In the present study we examined the role of perforin and granzyme in ATL patients and ACs.

Materials and Methods:

Peripheral blood mononuclear cells (PBMCs) were isolated from ATL patients and ACs by using Ficoll-hypaque density centrifugation. RNA was extracted and cDNA was synthesized. A real-time PCR TaqMan method was designed and optimized for evaluation of perforin, granzyme, tax, and HBZ gene expression. HTLV-1 proviral load (PVL) was quantified in patients with ATL and ACs.

Results:

The mRNA expression of tax and HBZ was significantly higher in ATL patients than ACs (P=0.011 and P=0.0001,respectively). The HTLV-1 PVL was higher in ATL patients compared to with AC group (P=0.015). There was a significant increase in perforin gene expression in ACs compared with ATL patients (P=0.002). Furthermore, the expression of granzyme was also higher in ACs compared with ATL patients, and significant differences were observed between the two groups (P=0.036).

Conclusion:

Low expression of perforin and granzyme in ATL patients seems to influence the efficiency of CTL function and destruction of HTLV-1-infected cells, which might contribute to the disease pathogenesis.

Development of anti-human CADM1 monoclonal antibodies as a potential therapy for adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a highly invasive and refractory T-cell malignancy, with poor prognosis. We previously identified that cell adhesion molecule 1 (CADM1) is overexpressed consistently in ATLL cells, and that CADM1 expression increases the adhesion capacity of ATLL cells to endothelial cells and promotes the organ invasion of ATLL cells in a xenograft mouse model. In this study, we first show that newly developed several anti-human CADM1 antibodies, which were complete human IgG antibodies generated by phage display method, specifically recognize CADM1 on ATLL cells. Although most of the CADM1 antibodies did not have a direct cytotoxic effect against CADM1-positive ATLL cells, clone 089-084 exhibited weak but significant antibody-dependent cell-mediated cytotoxic activity. Moreover, clone 103-189 effectively inhibits the interaction between endothelial cells and CADM1-positive ATLL cells. Furthermore, in mice bearing intra-splenic transplantation of EL4 mouse lymphoma cells expressing CADM1, the treatment of 103-189 significantly suppressed the organ invasion of CADM1-positive EL4 cells, resulting in improved survival time of mice. Therefore, since the anti-CADM1 antibody may be useful for the suppression of organ invasion in ATLL patients, combination use of the anti-CADM1 antibody with chemotherapy drugs could be beneficial for the efficient elimination of ATLL cells.

The Role of Chemokines in the Pathogenesis of HTLV-1

Human T cell leukemia virus type 1 (HTLV-1) is a human retrovirus that is associated with two main diseases: HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma (ATL). Chemokines are highly specialized groups of cytokines that play important roles in organizing, trafficking, homing, and in the migration of immune cells to the bone marrow, lymphoid organs and sites of infection and inflammation. Aberrant expression or function of chemokines, or their receptors, has been linked to the protection against or susceptibility to specific infectious diseases, as well as increased the risk of autoimmune diseases and malignancy. Chemokines and their receptors participate in pathogenesis of HTLV-1 associated diseases from inflammation in the central nervous system (CNS) which occurs in cases of HAM/TSP to T cell immortalization and tissue infiltration observed in ATL patients. Chemokines represent viable effective prognostic biomarkers for HTLV-1-associated diseases which provide the early identification of high-risk, treatment possibilities and high-yielding clinical trials. This review focuses on the emerging roles of these molecules in the outcome of HTLV-1-associated diseases.

Expression changes of cytotoxicity and apoptosis genes in HTLV-1-associated myelopathy/tropical spastic paraparesis patients from the perspective of system virology

Although human T-cell lymphotropic virus type-1 (HTLV-1) was the first retrovirus among human pathogens to be identified, insufficient information on the pathogenesis of HTLV-1 infection means that no precise mechanism has yet been provided for HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Based on previous studies, it was found that apoptosis and inflammation stimulation were among the most important mechanisms underlying HAM/TSP. The present study provides an in-silico analysis of the microarray data related to HAM/TSP patients. Expression changes of the genes responsible for cytotoxicity and apoptosis processes of HAM/TSP patients and asymptomatic carriers were investigated. Expression of the genes involved in cytotoxicity and apoptosis in HAM/TSP patients was decreased; hence, a model was proposed indicating that the spread of immune responses in HAM/TSP may be due to expression of HTLV-1 virulence factors and the resistance of HTLV-1-infected cells to apoptosis.

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.

HTLV-1 basic leucine zipper factor protects cells from oxidative stress by upregulating expression of Heme Oxygenase I

Adult T-cell Leukemia (ATL) is a lymphoproliferative disease of CD4+ T-cells infected with Human T-cell Leukemia Virus type I (HTLV-1). With the exception of allogeneic hematopoietic stem cell transplantation, there are no effective treatments to cure ATL, and ATL cells often acquire resistance to conventional chemotherapeutic agents. Accumulating evidence shows that development and maintenance of ATL requires key contributions from the viral protein, HTLV-1 basic leucine zipper factor (HBZ). In this study we found that HBZ activates expression of Heme Oxygenase 1 (HMOX-1), a component of the oxidative stress response that functions to detoxify free heme. Transcription of HMOX1 and other antioxidant genes is regulated by the small Mafs. These cellular basic leucine zipper (bZIP) factors control transcription by forming homo- or heterodimers among themselves or with other cellular bZIP factors that then bind Maf responsive elements (MAREs) in promoters or enhancers of antioxidant genes. Our data support a model in which HBZ activates HMOX1 transcription by forming heterodimers with the small Mafs that bind MAREs located in an upstream enhancer region. Consistent with this model, we found that HMOX-1 is upregulated in HTLV-1-transformed T-cell lines and confers these cells with resistance to heme-induced cytotoxicity. In this context, HBZ-mediated activation of HMOX-1 expression may contribute to resistance of ATL cells to certain chemotherapeutic agents. We also provide evidence that HBZ counteracts oxidative stress caused by two other HTLV-1-encoded proteins, Tax and p13. Tax induces oxidative stress as a byproduct of driving mitotic expansion of infected cells, and p13 is believed to induce oxidative stress to eliminate infected cells that have become transformed. Therefore, in this context, HBZ-mediated activation of HMOX-1 expression may facilitate transformation. Overall, this study characterizes a novel function of HBZ that may support the development and maintenance of ATL.

Antitumor Effect of Periplocin in TRAIL-Resistant gastric cancer cells via upregulation of death receptor through activating ERK1/2-EGR1 pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor family, induces apoptosis in a variety of cancer cells. However, gastric cancer (GC) cells are insensitive to TRAIL usually. In the previous study, we showed that Periplocin could induce apoptosis in GC cells via the activation of ERK1/2-EGR1 pathway. In the present study, we have shown that the combination of Periplocin and TRAIL had a greater inhibitory effect on gastric cancer cell viability in vitro and in vivo than Periplocin or TRAIL alone. Through upregulating the expression of DR4 and DR5 at transcriptional and protein levels, Periplocin enhanced the sensitivity of gastric cancer cells to TRAIL. Furthermore, enhanced activity of ERK1/2-EGR1 pathway was responsible for upregulating of DR4 and DR5 uponPeriplocin treatment, subsequently reducing the expression of Mcl-1 and Bcl2 and activating Bid and caspase-3/8. Collectively, these data implied that Periplocin might act as a sensitizer of TRAIL and could be a potential strategy for the treatment of GC.

Transcription factor E3 protects against cadmium-induced apoptosis by maintaining the lysosomal-mitochondrial axis but not autophagic flux in Neuro-2a cells

Cadmium (Cd), is a well-known environmental and occupational hazard with a potent neurotoxic action. However, the mechanism underlying cadmium-induced neurotoxicity remains unclear. Herein, we exposed Neuro-2a cells to different concentrations of cadmium chloride (CdCl₂) (12.5, 25 and 50 μM) for 24 h and found that Cd significantly induced lysosomal membrane permeabilization (LMP) with the release of cathepsin B (CTSB) to the cytosol, which in turn caused the release of mitochondrial cytochrome c (Cyt c) and eventually triggered caspase-dependent apoptosis. Interestingly, Cd decreased TFE3 expression but induced the nuclear translocation of TFE3 and TFE3 target-gene expression, which might be associated with lysosomal stress mediated by Cd. Notably, Tfe3 overexpression protected against Cd-induced neurotoxicity by maintaining the lysosomal-mitochondrial axis, and the protective effect of TFE3 is not dependent on the restoration of autophagic flux. In conclusion, our study demonstrated for the first time that lysosomal-mitochondrial axis dependent apoptosis, a neglected mechanism, may be the most important reason for Cd-induced neurotoxicity and that manipulation of TFE3 signaling may be a potential therapeutic approach for treatment of Cd-induced neurotoxicity.

BH3-only protein BIM: An emerging target in chemotherapy

BH3-only proteins constitute major proportion of pro-apoptotic members of B-cell lymphoma 2 (Bcl-2) family of apoptotic regulatory proteins and participate in embryonic development, tissue homeostasis and immunity. Absence of BH3-only proteins contributes to autoimmune disorders and tumorigenesis. Bim (Bcl-2 Interacting Mediator of cell death), most important member of BH3-only proteins, shares a BH3-only domain (9-16 aa) among 4 domains (BH1-BH4) of Bcl-2 family proteins and highly pro-apoptotic in nature. Bim initiates the intrinsic apoptotic pathway under both physiological and patho-physiological conditions. Reduction in Bim expression was found to be associated with tumor promotion and autoimmunity, while overexpression inhibited tumor growth and drug resistance as cancer cells suppress Bim expression and stability. Apart from its role in normal homeostasis, Bim has emerged as a central player in regulation of tumorigenesis, therefore gaining attention as a plausible target for chemotherapy. Regulation of Bim expression and stability is complicated and regulated at multiple levels viz. transcriptional, post-transcriptional, post-translational (preferably by phosphorylation and ubiquitination), epigenetic (by promoter acetylation or methylation) including miRNAs. Furthermore, control over Bim expression and stability may be exploited to enhance chemotherapeutic efficacy, overcome drug resistance and select anticancer drug regimen as various chemotherapeutic agents exploit Bim as an executioner of cell death. Owing to its potent anti-tumorigenic activity many BH3 mimetics e.g. ABT-737, ABT-263, obatoclax, AT-101and A-1210477 have been developed and entered in clinical trials. It is more likely that in near future strategies commanding Bim expression and stability ultimately lead to Bim based therapeutic regimen for cancer treatment.

Evaluation of INOS, ICAM-1, and VCAM-1 gene expression: A study of adult T cell leukemia malignancy associated with HTLV-1

The main aim of this study was to evaluate the expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and inducible nitric oxide synthase (iNOS) as host factors, and proviral load as the viral parameter, in adult T-cell leukemia/lymphoma (ATLL) individuals and healthy carrier (HC(s)) groups. Peripheral blood mononuclear cells (PBMC) from ATLL patients (n = 17) and HC subjects (as the control group, n = 17) were evaluated using real-time PCR to determine the levels of HTLV-1 proviral load and mRNA expression of ICAM, VCAM-1, and iNOS. ICAM-1 was significantly lower in ATLL patients than in control subjects. Although the expression of VCAM-1 was higher in ATLL individuals, there was no significant difference between the studied groups. In addition, no iNOS expression was found in ATLL patients, when compared to the HCs subjects, while ATLL patients demonstrated a higher level of proviral load when compared to the control group. Considering the importance of ICAM-1 in facilitating immune recognition of infected cells, it is posited that reduction of ICAM-1 expression is a unique strategy for circumventing appropriate immune responses that are mediated by different accessory proteins. Additionally, as the viral regulatory protein Tax and the NF-κB pathway play pivotal roles in expression of iNOS, lack of the latter in ATLL patients may be related to the level of Tax expression, disruption of the NF-κB pathway, or the occurrence of epigenetical mechanisms in the human iNOS promoter. Further studies are recommended to gain a better understanding of the interaction between host and viral factors in HTLV-1 pathogenesis and to identify a possible therapeutic target for ATLL.

Induction of apoptosis by HBI-8000 in adult T-cell leukemia/lymphoma is associated with activation of Bim and NLRP3

Adult T‐cell leukemia/lymphoma (ATL) is an aggressive T‐cell malignancy caused by human T‐cell lymphotropic virus 1. Treatment options for acute ATL patients include chemotherapy, stem cell transplantation, and recently the anti‐chemokine (C‐C motif) receptor 4 antibody, although most patients still have a poor prognosis and there is a clear need for additional options. HBI‐8000 is a novel oral histone deacetylase inhibitor with proven efficacy for treatment of T‐cell lymphomas that recently received approval in China. In the present study, we evaluated the effects of HBI‐8000 on ATL‐derived cell lines and primary cells obtained from Japanese ATL patients. In most cases HBI‐8000 induced apoptosis in both primary ATL cells and cell lines. In addition, findings obtained with DNA microarray suggested Bim activation and, interestingly, the contribution of the NLR family, pyrin domain containing 3 (NLRP3) inflammasome pathway in HBI‐8000‐induced ATL cell death. Further investigations using siRNAs confirmed that Bim contributes to HBI‐8000‐induced apoptosis. Our results provide a rationale for a clinical investigation of the efficacy of HBI‐8000 in patients with ATL. Although the role of NLRP3 inflammasome activation in ATL cell death remains to be verified, HBI‐8000 may be part of a novel therapeutic strategy for cancer based on the NLRP3 pathway.

Polycomb-dependent epigenetic landscape in adult T-cell leukemia

Adult T-cell leukemia-lymphoma (ATL) shows global gene expression alterations that confer cellular characteristics and unfavorable prognosis. However, molecular mechanisms of the sustained expression changes are largely unknown, because there is no study addressing the relationship between landscapes of the gene expression and epigenetic modifications. Here, we analyzed ATL epigenome and integrated it with transcriptome from primary ATL cells and those from corresponding normal CD4(+)T cells to decipher ATL-specific "epigenetic code" that was critical for cell identity. We found that polycomb-repressive complex 2 (PRC2)-mediated trimethylation at histone H3Lys27 (H3K27me3) was significantly and frequently reprogrammed at half of genes in ATL cells. A large proportion of the abnormal gene downregulation was detected at the early stage of disease progression and was explained by H3K27me3 accumulation. The global H3K27me3 alterations involved ATL-specific gene expression changes that included several tumor suppressors, transcription factors, epigenetic modifiers, miRNAs, and developmental genes, suggesting diverse outcomes by the PRC2-dependent hierarchical regulation. Interestingly, a key enzyme, EZH2, was sensitive to promiscuous signaling network including the NF-κB pathway and was functionally affected by human T-cell leukemia virus type I (HTLV-1) Tax. The Tax-dependent immortalized cells showed H3K27me3 reprogramming that was significantly similar to that of ATL cells. Of note, a majority of the epigenetic silencing has occurred in leukemic cells from indolent ATL and also in HTLV-1-infected T cells from asymptomatic HTLV-1 carriers. Because pharmacologic inhibition of EZH2 reversed epigenetic disruption and selectively eliminated leukemic and HTLV-1-infected cells, targeting the epigenetic elements will hold great promise in treatment and prevention of the onset of ATL and HTLV-1-related diseases.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.