Hua Cheng

Reducing the global burden of HTLV-1 infection: An agenda for research and action

&NA; Even though an estimated 10–20 million people worldwide are infected with the oncogenic retrovirus, human T‐lymphotropic virus type 1 (HTLV‐1), its epidemiology is poorly understood, and little effort has been made to reduce its prevalence. In response to this situation, the Global Virus Network launched a taskforce in 2014 to develop new methods of prevention and treatment of HTLV‐1 infection and promote basic research. HTLV‐1 is the etiological agent of two life‐threatening diseases, adult T‐cell leukemia and HTLV‐associated myelopathy/tropical spastic paraparesis, for which no effective therapy is currently available. Although the modes of transmission of HTLV‐1 resemble those of the more familiar HIV‐1, routine diagnostic methods are generally unavailable to support the prevention of new infections. In the present article, the Taskforce proposes a series of actions to expand epidemiological studies; increase research on mechanisms of HTLV‐1 persistence, replication and pathogenesis; discover effective treatments; and develop prophylactic and therapeutic vaccines. HighlightsThis review outlines priorities and open questions in HTLV research:Review the global prevalence of HTLV‐1 infection and identify opportunities and means to expand epidemiological studies.Identify biomarkers to predict disease progression.Develop prophylactic and therapeutic vaccines.Screen for existing and novel drugs to improve therapy.Perform basic research to unravel mechanisms of pathogenesis and open insights into novel treatments.

HTLV-1 Tax deregulates autophagy by recruiting autophagic molecules into lipid raft microdomains

The retroviral oncoprotein Tax from human T-cell leukemia virus type 1 (HTLV-1), an etiological factor that causes adult T-cell leukemia and lymphoma, has a crucial role in initiating T-lymphocyte transformation by inducing oncogenic signaling activation. We here report that Tax is a determining factor for dysregulation of autophagy in HTLV-1-transformed T cells and Tax-immortalized CD4 memory T cells. Tax facilitated autophagic process by activating inhibitor of κB (IκB) kinase (IKK) complex, which subsequently recruited an autophagy molecular complex containing Beclin1 and Bif-1 to the lipid raft microdomains. Tax engaged a crosstalk between IKK complex and autophagic molecule complex by directly interacting with both complexes, promoting assembly of LC3+ autophagosomes. Moreover, expression of lipid raft-targeted Bif-1 or Beclin1 was sufficient to induce formation of LC3+ autophagosomes, suggesting that Tax recruitment of autophagic molecules to lipid rafts is a dominant strategy to deregulate autophagy in the context of HTLV-1 transformation of T cells. Furthermore, depletion of autophagy molecules such as Beclin1 and PI3 kinase class III resulted in impaired growth of HTLV-1-transformed T cells, indicating a critical role of Tax-deregulated autophagy in promoting survival and transformation of virally infected T cells.

HTLV-2 Tax Immortalizes Human CD4+ Memory T Lymphocytes by Oncogenic Activation and Dysregulation of Autophagy

Background: Human T cell leukemia virus type 2 (HTLV-2) encodes a viral transactivator Tax. Results: HTLV-2 Tax efficiently immortalizes human memory T lymphocytes with distinct T cell subtypes. Conclusion: HTLV-2 Tax connects IκB kinase complex to autophagy pathways for promoting T cell survival and proliferation. Significance: Learning the oncogenic potential of HTLV-2 Tax is critical for understanding HTLV-2 pathogenesis. Human T cell leukemia virus type 1 and type 2 (HTLV-1 and -2) are two closely related retroviruses with the former causing adult T cell leukemia. HTLV-2 infection is prevalent among intravenous drug users, and the viral genome encodes the viral transactivator Tax, which is highly homologous to the transforming protein Tax from HTLV-1. However, the link between HTLV-2 infection and leukemia has not been established. In the present study, we evaluated the activity of HTLV-2 Tax in promoting aberrant proliferation of human CD4 T lymphocytes. Tax2 efficiently immortalized CD4+ memory T lymphocytes with a CD3/TCRαβ/CD4/CD25/CD45RO/CD69 immunophenotype, promoted constitutive activation of PI3K/Akt, IκB kinase/NF-κB, mitogen-activated protein kinase, and STAT3, and it also increased the level of Mcl-1. Disruption of these oncogenic pathways led to growth retardation and apoptotic cell death of the Tax2-established T cell lines. We further found that Tax2 induced autophagy by interacting with the autophagy molecule complex containing Beclin1 and PI3K class III to form the LC3+ autophagosome. Tax2-mediated autophagy promoted survival and proliferation of the immortalized T cells. The present study demonstrated the oncogenic properties of Tax2 in human T cells and also implicated Tax2 in serving as a molecular tool to generate distinct T cell subtype lines.

Niclosamide, an anti-helminthic molecule, downregulates the retroviral oncoprotein Tax and pro-survival Bcl-2 proteins in HTLV-1-transformed T lymphocytes.

Adult T cell leukemia and lymphoma (ATL) is a highly aggressive form of hematological malignancy and is caused by chronic infection of human T cell leukemia virus type 1 (HTLV-1). The viral genome encodes an oncogenic protein, Tax, which plays a key role in transactivating viral gene transcription and in deregulating cellular oncogenic signaling to promote survival, proliferation and transformation of virally infected T cells. Hence, Tax is a desirable therapeutic target, particularly at early stage of HTLV-1-mediated oncogenesis. We here show that niclosamide, an anti-helminthic molecule, induced apoptosis of HTLV-1-transformed T cells. Niclosamide facilitated degradation of the Tax protein in proteasome. Consistent with niclosamide-mediated Tax degradation, this compound inhibited activities of MAPK/ERK1/2 and IκB kinases. In addition, niclosamide downregulated Stat3 and pro-survival Bcl-2 family members such as Mcl-1 and repressed the viral gene transcription of HTLV-1 through induction of Tax degradation. Since Tax, Stat3 and Mcl-1 are crucial molecules for promoting survival and growth of HTLV-1-transformed T cells, our findings demonstrate a novel mechanism of niclosamide in inducing Tax degradation and downregulating various cellular pro-survival molecules, thereby promoting apoptosis of HTLV-1-associated leukemia cells.

The autophagy molecule Beclin 1 maintains persistent activity of NF-κB and Stat3 in HTLV-1-transformed T lymphocytes

The retroviral oncoprotein Tax from human T cell leukemia virus type 1 (HTLV-1) induces persistent activation of IκB kinase (IKK)/NF-κB signaling, an essential step for initiating HTLV-1 oncogenesis. The regulation of the IKK/NF-κB signaling in HTLV-1-transformed T cells remains incompletely understood. In the present study, we showed that the autophagy molecule Beclin1 not only executed a cytoprotective function through induction of autophagy but also played a pivotal role in maintaining Tax-induced activation of two key survival factors, NF-κB and Stat3. Silencing Beclin1 in HTLV-1-transformed T cells resulted in diminished activities of NF-κB and Stat3 as well as impaired growth. In Beclin1-depleted cells, Tax failed to activate NF-κB and Stat3 at its full capacity. In addition, we showed that Beclin1 interacted with the catalytic subunits of IKK. Further, we observed that selective inhibition of IKK repressed the activities of both NF-κB and Stat3 in the context of HTLV-1-transformation of T cells. Our data, therefore, unveiled a key role of Beclin1 in maintaining persistent activities of both NF-κB and Stat3 in the pathogenesis of HTLV-1-mediated oncogenesis.

Developing an in vitro model of T cell type of large granular lymphocyte leukemia.

We developed a strategy that can prolong in vitro growth of T cell type of large granular lymphocyte (T-LGL) leukemia cells. Primary CD8+ lymphocytes from T-LGL leukemia patients were stably transduced with the retroviral tax gene derived from human T cell leukemia virus type 2. Expression of Tax overrode replicative senescence and promoted clonal expansion of the leukemic CD8+ T cells. These cells exhibit features characteristic of leukemic LGL, including resistance to FasL-mediated apoptosis, sensitivity to the inhibitors of sphingosine-1-phosphate receptor and IκB kinases as well as expression of cytotoxic gene products such as granzyme B, perforin and IFNγ. Collectively, these results indicate that this leukemia cell model can duplicate the main phenotype and pathophysiological characteristics of the clinical isolates of T-LGL leukemia. This model should be useful for investigating molecular pathogenesis of the disease and for developing new therapeutics targeting T-LGL leukemia.

Interferon |[gamma]| is a STAT1-dependent direct inducer of BCL6 expression in imatinib-treated chronic myeloid leukemia cells

B-cell CLL/lymphoma 6 (BCL6) exerts oncogenic effects in several human hematopoietic malignancies including chronic myeloid leukemia (CML), where BCL6 expression was shown to be essential for CML stem cell survival and self-renewal during imatinib mesylate (IM) treatment. As several lines of evidence suggest that interferon γ (IFNγ) production in CML patients might have a central role in the response to tyrosine kinase inhibitor (TKI) therapy, we analyzed if IFNγ modulates BCL6 expression in CML cells. Although separate IFNγ or IM treatment only slightly upregulated BCL6 expression, combined treatment induced remarkable BCL6 upregulation in CML lines and primary human CD34+ CML stem cells. We proved that during combined treatment, inhibition of constitutive signal transducer and activator of transcription (STAT) 5 activation by IM allowed the specific enhancement of the STAT1 dependent, direct upregulation of BCL6 by IFNγ in CML cells. By using colony-forming assay, we found that IFNγ enhanced the ex vivo colony or cluster-forming capacity of human CML stem cells in the absence or presence of IM, respectively. Furthermore, inhibition of the transcriptional repressor function of BCL6 in the presence of IM and IFNγ almost completely blocked the cluster formation of human CML stem cells. On the other hand, by using small interfering RNA knockdown of BCL6, we demonstrated that in an IM-treated CML line the antiapoptotic effect of IFNγ was independent of BCL6 upregulation. We found that IFNγ also upregulated several antiapoptotic members of the BCL2 and BIRC gene families in CML cells, including the long isoform of MCL1, which proved to be essential for the antiapoptotic effect of IFNγ in an IM-treated CML line. Our results suggest that combination of TKIs with BCL6 and MCL1 inhibitors may potentially lead to the complete eradication of CML stem cells.

Tid1, the Mammalian Homologue of Drosophila Tumor Suppressor Tid56, Mediates Macroautophagy by Interacting with Beclin1-containing Autophagy Protein Complex.

Background: Tid1 is a human DnaJ protein and has a role in regulating cellular signaling pathways. Results: Tid1 increases autophagic flux by interacting with the autophagy protein complex. Conclusion: Tid1 is a novel mediator of macroautophagy. Significance: As a new member of autophagy pathway, Tid1 may have a crucial role in participating in a broad range of biological aspects. One of the fundamental functions of molecular chaperone proteins is to selectively conjugate cellular proteins, targeting them directly to lysosome. Some of chaperones, such as the stress-induced Hsp70, also play important roles in autophagosome-forming macroautophagy under various stress conditions. However, the role of their co-chaperones in autophagy regulation has not been well defined. We here show that Tid1, a DnaJ co-chaperone for Hsp70 and the mammalian homologue of the Drosophila tumor suppressor Tid56, is a key mediator of macroautophagy pathway. Ectopic expression of Tid1 induces autophagy by forming LC3+ autophagosome foci, whereas silencing Tid1 leads to drastic impairment of autophagy as induced by nutrient deprivation or rapamycin. In contrast, Hsp70 is dispensable for a role in nutrient deprivation-induced autophagy. The murine Tid1 can be replaced with human Tid1 in murine fibroblast cells for induction of autophagy. We further show that Tid1 increases autophagy flux by interacting with the Beclin1-PI3 kinase class III protein complex in response to autophagy inducing signal and that Tid1 is an essential mediator that connects IκB kinases to the Beclin1-containing autophagy protein complex. Together, these results reveal a crucial role of Tid1 as an evolutionarily conserved and essential mediator of canonical macroautophagy.

Foxp3-dependent transformation of human primary CD4+ T lymphocytes by the retroviral protein tax.

The retroviral Tax proteins of human T cell leukemia virus type 1 and 2 (HTLV-1 and -2) are highly homologous viral transactivators. Both viral proteins can immortalize human primary CD4+ memory T cells, but when expressed alone they rarely transform T cells. In the present study, we found that the Tax proteins displayed a differential ability to immortalize human CD4+Foxp3+ T cells with characteristic expression of CTLA-4 and GITR. Because epidermal growth factor receptor (EGFR) was reportedly expressed and activated in a subset of CD4+Foxp3+ T cells, we introduced an activated EGFR into Tax-immortalized CD4+Foxp3+ T cells. We observed that these modified cells were grown independently of exogenous IL-2, correlating with a T cell transformation phenotype. In Tax-immortalized CD4+Foxp3- T cells, ectopic expression of Foxp3 was a prerequisite for Tax transformation of T cells. Accordingly, treatment of the transformed T cells with erlotinib, a selective inhibitor of EGFR, induced degradation of EGFR in lysosome, consequently causing T cell growth inhibition. Further, we identified autophagy as a crucial cellular survival pathway for the transformed T cells. Silencing key autophagy molecules including Beclin1, Atg5 and PI3 kinase class III (PI3KC3) resulted in drastic impairment of T cell growth. Our data, therefore, unveiled a previously unidentified role of Foxp3 in T cell transformation, providing a molecular basis for HTLV-1 transformation of CD4+Foxp3+ T cells.

HBZ RNA may promote cell survival against clastogenic damages and thereby contributes to the development of leukemic ATL cells

HTLV-1, the first tumorigenic retrovirus identified in humans, causes adult-T cell leukemia in about 5% of the infected individuals with a long latency period > 40 years. The mechanism of ATL has been extensively studied with emphasis on the role of regulatory factors encoded by the viral genome including Tax, Rex, p30 p12, p8 and p13. However, the recent discovery of a new gene HBZ (HTLV-1 basic ZIP factor) encoded by the minus strand of the virus has added a new layer to the research. HBZ helps the establishment of T-cell leukemia in mice when expressed in T-lineage cells as a transgene (demonstrated by Satou et al. in 2011). HBZ seems to exert its functions by two forms – as protein and as regulatory RNA. We hypothesized that HBZ may be responsible for the accumulation in ATL precursor cells of chromosomal damages that would arrest the cell cycle progression in normal cells. We observed that HBZ-transduced mouse and human cells become resistant to apoptotic cell death or replicative senescence that is caused by clastogenic agents including arsenic trioxide. This is accompanied by the suppression of check-point mechanisms. Importantly, this function of HBZ seems mediated by the RNA form, rather than by the HBZ-protein. The nature of the RNA form of HBZ remains largely uncharacterized at the moment and our data adds new layer leading to the comprehensive understanding of how HTLV-1 causes malignant transformation of human T cells.