Latency Reversing Agents: Kick and Kill of HTLV-1?

Human T-cell leukemia virus type 1 (HTLV-1), the cause of adult T-cell leukemia/lymphoma (ATLL), is a retrovirus, which integrates into the host genome and persistently infects CD4+ T-cells. Virus propagation is stimulated by (1) clonal expansion of infected cells and (2) de novo infection. Viral gene expression is induced by the transactivator protein Tax, which recruits host factors like positive transcription elongation factor b (P-TEFb) to the viral promoter. Since HTLV-1 gene expression is repressed in vivo by viral, cellular, and epigenetic mechanisms in late phases of infection, HTLV-1 avoids an efficient CD8+ cytotoxic T-cell (CTL) response directed against the immunodominant viral Tax antigen. Hence, therapeutic strategies using latency reversing agents (LRAs) sought to transiently activate viral gene expression and antigen presentation of Tax to enhance CTL responses towards HTLV-1, and thus, to expose the latent HTLV-1 reservoir to immune destruction. Here, we review strategies that aimed at enhancing Tax expression and Tax-specific CTL responses to interfere with HTLV-1 latency. Further, we provide an overview of LRAs including (1) histone deacetylase inhibitors (HDACi) and (2) activators of P-TEFb, that have mainly been studied in context of human immunodeficiency virus (HIV), but which may also be powerful in the context of HTLV-1.

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Kinetic Analysis of Human T-Cell Leukemia Virus Type 1 Gene Expression in Cell Culture and Infected Animals

Journal of Virology ◽

10.1128/jvi.02315-08 ◽

2009 ◽

Vol 83 (8) ◽

pp. 3788-3797 ◽

Cited By ~ 38

Author(s):

Min Li ◽

Matthew Kesic ◽

Han Yin ◽

Lianbo Yu ◽

Patrick L. Green

Keyword(s):

Gene Expression ◽

T Cell ◽

Proviral Load ◽

Leukemia Virus ◽

Viral Gene ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell

ABSTRACT Human T-cell leukemia virus type 1 (HTLV-1) infection causes adult T-cell leukemia and is associated with a variety of lymphocyte-mediated disorders. It has been hypothesized that a highly regulated pattern of HTLV-1 gene expression is critical for virus survival and disease pathogenesis. In this study, real-time reverse transcriptase PCR was used to determine the kinetics of viral gene expression in cells transiently transfected with an HTLV-1 proviral plasmid, in newly infected human peripheral blood mononuclear cells (PBMCs), and in PBMCs from newly infected rabbits. The HTLV-1 gene expression profiles in transiently transfected and infected cells were similar; over time, all transcripts increased and then maintained stable levels. gag/pol, tax/rex, and env mRNA were detected first and at the highest levels, whereas the expression levels of the accessory genes, including the antisense Hbz, were significantly lower than the tax/rex levels (ranging from 1 to 4 logs depending on the specific mRNA). In infected rabbits, tax/rex and gag/pol mRNA levels peaked early after inoculation and progressively decreased, which correlated inversely with the proviral load and host antibody response against viral proteins. Interestingly, Hbz mRNA was detectable at 1 week postinfection and increased and stabilized. The expression levels of all other HTLV-1 genes in infected rabbit PBMCs were at or below our limit of detection. This analysis provides insight into viral gene expression under various in vitro and in vivo experimental conditions. Our in vivo data indicate that in infected rabbits, Hbz mRNA expression over time directly correlates with the proviral load, which provides the first evidence linking Hbz expression to proviral load and the survival of the virus-infected cell in the host.

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Human T-Cell Leukemia Virus Type 1 Tax Enhances Serum Response Factor DNA Binding and Alters Site Selection

Journal of Virology ◽

10.1128/jvi.02179-06 ◽

2007 ◽

Vol 81 (11) ◽

pp. 6089-6098 ◽

Cited By ~ 9

Author(s):

Heather Y. Winter ◽

Susan J. Marriott

Keyword(s):

Gene Expression ◽

T Cell ◽

Serum Response Factor ◽

Leukemia Virus ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

T Cell Leukemia Virus ◽

Serum Response

ABSTRACT Human T-cell leukemia virus type I (HTLV-1) is the etiological agent of adult T-cell leukemia. The viral transforming protein Tax regulates the transcription of viral and cellular genes by interacting with cellular transcription factors and coactivators. The effects of Tax on cellular gene expression have an important impact on HTLV-1-mediated cellular transformation. Expression of the c-fos cellular oncogene is regulated by serum response factor (SRF), and Tax is known to induce c-fos gene expression by activating SRF-responsive transcription. SRF activates cellular gene expression by binding to a consensus DNA sequence (CArG box) located within a serum response element (SRE). Since SRF activates transcription of many growth regulatory genes, this pathway is likely to have a significant impact on Tax-mediated transformation. Here we demonstrate that Tax interacts with SRF and enhances the binding of SRF to SREs located in the c-fos, Nur77, and viral promoters. Also, we establish that in the presence of Tax, SRF selects more divergent CArG box sequences than in the absence of Tax, revealing a novel mechanism for regulating SRF-responsive gene expression. Finally, increased association of SRF with chromatin and specific promoters was observed in Tax-expressing cells, correlating with increased c-fos and Nur77 mRNA levels in Tax-expressing cells. These results suggest that Tax activates SRF-responsive transcription by enhancing its binding affinity to multiple different SRE sequences.

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Preferential selection of human T-cell leukemia virus type I provirus integration sites in leukemic versus carrier states

Blood ◽

10.1182/blood-2004-11-4350 ◽

2005 ◽

Vol 106 (3) ◽

pp. 1048-1053 ◽

Cited By ~ 49

Author(s):

Keitarou Doi ◽

Xiaolin Wu ◽

Yuko Taniguchi ◽

Jun-ichirou Yasunaga ◽

Yorifumi Satou ◽

...

Keyword(s):

T Cell ◽

Leukemia Virus ◽

Leukemic Cells ◽

Viral Gene ◽

Type I ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

Integration Sites

Abstract Human T-cell leukemia virus type I (HTLV-I) is a causative agent of neoplastic disease, adult T-cell leukemia (ATL). Although the encoding viral proteins play an important role in oncogenesis, the role of the HTLV-I proviral integration site remains unsolved. We determined the integration sites of HTLV-I proviruses in ATL cells and HTLV-I–infected cells in asymptomatic carriers. In carrier and ATL cells, HTLV-I provirus was integrated into the transcriptional unit at frequencies of 26.8% (15/56) and 33.9% (20/59), respectively, which were equivalent to the frequency calculated based on random integration (33.2%). In addition, HTLV-I provirus was prone to integration near the transcriptional start sites in leukemic cells (P = .006), and the transcriptional direction of the provirus was in accordance with that of integrated cellular genes in 70% of cases. More importantly, the integration sites in the carrier cells favored the alphoid repetitive sequences (11/56; 20%) whereas in leukemic cells they disfavored these sequences (2/59; 3.4%). Taken together, during natural course from carrier to onset of ATL, HTLV-I–infected cells with integration sites favorable for viral gene transcription are susceptible to malignant transformation due to increased viral gene expression.

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Differential Transcriptional Activation by Human T-Cell Leukemia Virus Type 1 Tax Mutants Is Mediated by Distinct Interactions with CREB Binding Protein and p300

Molecular and Cellular Biology ◽

10.1128/mcb.18.4.2392 ◽

1998 ◽

Vol 18 (4) ◽

pp. 2392-2405 ◽

Cited By ~ 80

Author(s):

Françoise Bex ◽

Min-Jean Yin ◽

Arsène Burny ◽

Richard B. Gaynor

Keyword(s):

Gene Expression ◽

T Cell ◽

Transcriptional Activation ◽

Leukemia Virus ◽

T Cell Leukemia ◽

Creb Binding Protein ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

Creb Pathway

ABSTRACT The human T-cell leukemia virus type 1 Tax protein transforms human T lymphocytes, which can lead to the development of adult T-cell leukemia. Tax transformation is related to its ability to activate gene expression via the ATF/CREB and the NF-κB pathways. Transcriptional activation of these pathways is mediated by the actions of the related coactivators CREB binding protein (CBP) and p300. In this study, immunocytochemistry and confocal microscopy were used to localize CBP and p300 in cells expressing wild-type Tax or Tax mutants that are able to selectively activate gene expression from either the NF-κB or ATF/CREB pathway. Wild-type Tax colocalized with both CBP and p300 in nuclear bodies which also contained ATF-1 and the RelA subunit of NF-κB. However, a Tax mutant that selectively activates gene expression from only the ATF/CREB pathway colocalized with CBP but not p300, while a Tax mutant that selectively activates gene expression from only the NF-κB pathway colocalized with p300 but not CBP. In vitro and in vivo protein interaction studies indicated that the integrity of two independent domains of Tax delineated by these mutants was involved in the direct interaction of Tax with either CBP or p300. These studies are consistent with a model in which activation of either the NF-κB or the ATF/CREB pathway by specific Tax mutants is mediated by distinct interactions with related coactivator proteins.

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

Cancers ◽

10.3390/cancers13205066 ◽

2021 ◽

Vol 13 (20) ◽

pp. 5066

Author(s):

Said M. Elshafae ◽

Nicole A. Kohart ◽

Justin T. Breitbach ◽

Blake E. Hildreth ◽

Thomas J. Rosol

Keyword(s):

T Cell ◽

Zoledronic Acid ◽

Tumor Growth ◽

Bone Tumors ◽

Viral Gene ◽

Mrna Levels ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Adult T Cell Leukemia

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.

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HTLV-1 bZIP factor: the key viral gene for pathogenesis

Retrovirology ◽

10.1186/s12977-020-0511-0 ◽

2020 ◽

Vol 17 (1) ◽

Cited By ~ 7

Author(s):

Masao Matsuoka ◽

Jean-Michel Mesnard

Keyword(s):

T Cells ◽

T Cell ◽

Viral Gene ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

Bzip Factor ◽

Infected Cells

AbstractHuman T cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia-lymphoma (ATL) and inflammatory diseases. The HTLV-1 bZIP factor (HBZ) gene is constantly expressed in HTLV-1 infected cells and ATL cells. HBZ protein suppresses transcription of the tax gene through blocking the LTR recruitment of not only ATF/CREB factors but also CBP/p300. HBZ promotes transcription of Foxp3, CCR4, and T-cell immunoreceptor with Ig and ITIM domains (TIGIT). Thus, HBZ is critical for the immunophenotype of infected cells and ATL cells. HBZ also functions in its RNA form. HBZ RNA suppresses apoptosis and promotes proliferation of T cells. Since HBZ RNA is not recognized by cytotoxic T cells, HTLV-1 has a clever strategy for avoiding immune detection. HBZ plays central roles in maintaining infected T cells in vivo and determining their immunophenotype.

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Regulation of Human T-Cell Leukemia Virus Type 1 Gene Expression by Sp1 and Sp3 Interaction with TRE-1 Repeat III

DNA and Cell Biology ◽

10.1089/dna.2006.25.262 ◽

2006 ◽

Vol 25 (5) ◽

pp. 262-276 ◽

Cited By ~ 6

Author(s):

Jing Yao ◽

Christian Grant ◽

Edward Harhaj ◽

Michael Nonnemacher ◽

Timothy Alefantis ◽

...

Keyword(s):

Gene Expression ◽

T Cell ◽

Virus Type ◽

Leukemia Virus ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

T Cell Leukemia Virus

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Induction of Lactoferrin Gene Expression in Myeloid or Mammary Gland Cells by Human T-Cell Leukemia Virus Type 1 (HTLV-1) Tax: Implications for Milk-Borne Transmission of HTLV-1

Journal of Virology ◽

10.1128/jvi.00409-06 ◽

2006 ◽

Vol 80 (14) ◽

pp. 7118-7126 ◽

Cited By ~ 4

Author(s):

Masako Moriuchi ◽

Hiroyuki Moriuchi

Keyword(s):

Gene Expression ◽

T Cell ◽

Leukemia Virus ◽

Gene Promoter ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

Lactoferrin Gene ◽

Mcf 7

ABSTRACT Human T-cell leukemia virus type 1 (HTLV-1), the causative agent of adult T-cell leukemia, is transmitted vertically via breastfeeding. We have previously demonstrated that lactoferrin, a major milk protein, enhances HTLV-1 replication, at least in part by upregulating the HTLV-1 long terminal repeat promoter. We now report that HTLV-1 infection can induce lactoferrin gene expression. Coculture with HTLV-1-infected MT-2 cells increased the levels of lactoferrin mRNA in myeloid-differentiated HL-60 cells, as well as MCF-7 cells, models of two probable sources (neutrophils and mammary epithelium) of lactoferrin in breast milk. MT-2 cell coculture could be replaced with cell-free culture supernatants of MT-2 cells to exert the same effect. Furthermore, extracellularly administered Tax protein also induced lactoferrin gene expression at physiologically relevant concentrations. In transient-expression assays, Tax transactivated the lactoferrin gene promoter in HL-60 or MCF-7 cells. Experiments with Tax mutants, as well as site-directed mutants of the lactoferrin promoter reporters, indicated that the NF-κB transactivation pathway is critical for Tax induction of the lactoferrin gene promoter activity in myeloid-differentiated HL-60 cells, but not in MCF-7 cells. These results suggest that HTLV-1 infection may be able to induce expression of lactoferrin in a paracrine manner in the lactic compartment. Our findings, in conjunction with our previous study, implicate that mutual interaction between HTLV-1 and lactoferrin would benefit milk-borne transmission of this virus.

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Discovery and Characterization of a Hidden Retroviral Enhancer by Viral DNA-capture-seq Approach

10.21203/rs.3.rs-141856/v1 ◽

2021 ◽

Author(s):

Misaki Matsuo ◽

Takaharu Ueno ◽

Kazuaki Monde ◽

Benjy Jek Yang Tan ◽

Paola Miyazato ◽

...

Keyword(s):

T Cell ◽

Gene Transcription ◽

High Throughput Sequencing ◽

Antisense Transcription ◽

Viral Gene ◽

T Cell Leukemia ◽

Cell Leukemia ◽

Cell Leukemia Virus Type ◽

Human T Cell ◽

Dna Capture

Abstract Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus that causes a cancer of infected cells called adult T-cell leukemia (ATL). There is both sense and antisense transcription from the integrated provirus. Sense transcription tends to be suppressed, but antisense transcription is constitutively active in vivo even in proviruses lacking the 5’ long terminal repeat (LTR), a known viral enhancer and promoter. Various efforts have been made to elucidate the regulatory mechanism of HTLV-1 provirus for several decades; however, it remains unknown how HTLV-1 antisense transcription is maintained. Here, using proviral DNA-capture followed by high-throughput sequencing, we found a previously unidentified viral enhancer not in the LTR but in the middle of the HTLV-1 provirus. The host transcription factors, SRF and ELK-1, bind to this enhancer region both in cell lines and in freshly isolated ATL cells. HTLV-1 containing mutations in the SRF- and ELK-1-binding sites markedly decreased chromatin openness at the viral enhancer, viral gene transcription, and enhancing effects on host gene transcription near the viral integration site. Aberrant host genome transcription was observed at nearby integration sites in defective proviruses containing the enhancer in ATL cells. This finding reveals how the exogenous retrovirus achieves persistent infection in the host via the internal viral enhancer and resolves certain long-standing questions concerning HTLV-1 infection. We anticipate that the DNA-capture-seq approach can be applied to analyze regulatory mechanisms of other oncogenic viruses integrated into the host cellular genome.

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