Efficient transfer of HTLV-1 tax gene in various primary and immortalized cells using a flap lentiviral vector

Human T lymphotropic virus type 1 increases T lymphocyte migration by recruiting the cytoskeleton organizer CRMP2

Recruitment of virus-infected T lymphocytes into the CNS is an essential step in the development of virus-associated neuroinflammatory diseases, notably myelopathy induced by retrovirus human T leukemia virus-1 (HTLV-1). We have recently shown the key role of collapsin response mediator protein 2 (CRMP2), a phosphoprotein involved in cytoskeleton rearrangement, in the control of human lymphocyte migration and in brain targeting in animal models of virus-induced neuroinflammation. Using lymphocytes cloned from infected patients and chronically infected T cells, we found that HTLV-1 affects CRMP2 activity, resulting in an increased migratory potential. Elevated CRMP2 expression accompanies a higher phosphorylation level of CRMP2 and its more pronounced adhesion to tubulin and actin. CRMP2 forms, a full length and a shorter, cleaved one, are also affected. Tax transfection and extinction strategies show the involvement of this viral protein in enhanced full-length and active CRMP2, resulting in prominent migratory rate. A role for other viral proteins in CRMP2 phosphorylation is suspected. Full-length CRMP2 confers a migratory advantage possibly by preempting the negative effect of short CRMP2 we observe on T lymphocyte migration. In addition, HTLV-1-induced migration seems, in part, supported by the ability of infected cell to increase the proteosomal degradation of short CRMP2. Finally, gene expression in CD69(+) cells selected from patients suggests that HTLV-1 has the capacity to influence the CRMP2/PI3K/Akt axis thus to positively control cytoskeleton organization and lymphocyte migration. Our data provide an additional clue to understanding the infiltration of HTLV-1-infected lymphocytes into various tissues and suggest that the regulation of CRMP2 activity by virus infection is a novel aspect of neuroinflammation.

Anti-Tax antibody levels in asymptomatic carriers, oligosymptomatic carriers, patients with rheumatologic disease or with HAM/TSP do not correlate with HTLV-1 proviral load

BACKGROUND

HTLV-1 infects millions of people around the world and induces myelopathy (HAM/TSP), adult T-cell leukemia (ATL) or other inflammatory or rheumatologic diseases. The host-virus interaction causes asymptomatic carriers to develop HAM/TSP. Biomarkers are needed to predict patients who are at risk for HAM/TSP. Tax is highly immunogenic and is a major target protein recognized by cytotoxic T lymphocytes. Anti-Tax antibodies are involved in HAM/TSP pathogenesis.

OBJECTIVES

To assess anti-Tax IgG reactivity with a flow cytometry assay (FCA) using an infection/transfection system with Vaccinia virus and pLW44/Tax-expressing Tax and to correlate the anti-Tax response and the HTLV-1 proviral load.

STUDY DESIGN

: We enrolled 81 individuals: 9 HTLV-1 seronegative (NP) and 72 HTLV-1 positive (23 HTLV-1 asymptomatic carriers (AC), 12 oligosymptomatic patients (OL), 7 with rheumatologic diseases (DR) and 30 with HAM/TSP (HT)). Anti-Tax reactivity was assessed by FCA, and HTLV-1 proviral load was measured with real time PCR.

RESULTS

The HT and DR groups showed greater anti-Tax IgG reactivity (p<0.001 and p<0.05 comparing HT to the OL and AC group, respectively; p<0.05 comparing DR to the OL group), and the reactivity in the DR+HT group was significantly different when compared to the AC group (p<0.05) and to the OL group (p<0.001). The proviral load was higher in the HT group compared to the OL (p<0.001) and in the HT+DR group compared to OL (p<0.001). There was no correlation between anti-Tax IgG reactivity and proviral load in any of the HTLV-1-infected groups.

CONCLUSION

These findings suggest that although anti-Tax IgG reactivity and the HTLV-1 proviral load are important markers of the development of HTLV-1-associated diseases, their levels are not correlated.

Diagnostic tool based on an HTLV-1-Tax expression system in eukaryotic cells using a poxvirus vector

Human T-lymphotropic virus 1 (HTLV-1) induces an immune-mediated inflammatory disease affecting the nervous system that eventually is accompanied by ocular, rheumatic and dermatologic manifestations (HTLV-1 associated myelopathy/tropical spastic paraparesis, or HAM/TSP). Proviral load and HTLV-1 protein expression, mainly of Tax, is correlated with disease progression and induction of host-virus equilibrium breakdown that, reportedly, involves the presence of Tax-specific cytotoxic T lymphocytes (CTL), T regulatory cells and anti-Tax antibodies. Based on knowledge of anti-Tax antibodies as markers of disease progression, the objectives of this study were both to design an infection/transfection system using the Vaccinia virus and a tax-encoding plasmid for the expression of Tax protein as well as to use this cell support to evaluate anti-Tax IgG by flow cytometry. The flow cytometry assay was standardized using pooled sera from each test group (negative, asymptomatic and HAM/TSP patients). The HAM/TSP group presented higher IgG anti-Tax reactivity (above 70%) than the asymptomatic group (nearly 40% reactivity). The data indicate that the infection/transfection system is useful for assessing Tax expression. This is a promising assay for use as a diagnostic tool to detect IgG anti-Tax and monitor HTLV-1 infected individuals.

Cell context-dependent involvement of ATR in early stages of retroviral replication

Retroviral DNA integration leaves behind a single-strand DNA discontinuity at each virus:host DNA junction. It has long been proposed that cellular proteins detect and repair the integrated DNA and that failure to do so might lead to apoptotic cell death, but their identity remains unknown. PIKK family members ATM, DNA-PKcs and ATR have all been proposed to be important for HIV-1 replication, but these findings turned out to be very controversial. In order to clarify their role in retroviral replication, we analyzed the effect of pharmacological inhibitors and of a dominant-negative version of ATR on the replication of retroviruses in cell lines relevant to HIV-1 infection. Our data show that ATR and probably other PIKKs as well are involved in retroviral replication in some but not all cell lines and that ATR increases the frequency of retroviral transduction by a mechanism other than the enhancement of infected cell survival.

Alteration of blood-brain barrier integrity by retroviral infection

The blood–brain barrier (BBB), which forms the interface between the blood and the cerebral parenchyma, has been shown to be disrupted during retroviral-associated neuromyelopathies. Human T Lymphotropic Virus (HTLV-1) Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) is a slowly progressive neurodegenerative disease associated with BBB breakdown. The BBB is composed of three cell types: endothelial cells, pericytes and astrocytes. Although astrocytes have been shown to be infected by HTLV-1, until now, little was known about the susceptibility of BBB endothelial cells to HTLV-1 infection and the impact of such an infection on BBB function. We first demonstrated that human cerebral endothelial cells express the receptors for HTLV-1 (GLUT-1, Neuropilin-1 and heparan sulfate proteoglycans), both in vitro, in a human cerebral endothelial cell line, and ex vivo, on spinal cord autopsy sections from HAM/TSP and non-infected control cases. In situ hybridization revealed HTLV-1 transcripts associated with the vasculature in HAM/TSP. We were able to confirm that the endothelial cells could be productively infected in vitro by HTLV-1 and that blocking of either HSPGs, Neuropilin 1 or Glut1 inhibits this process. The expression of the tight-junction proteins within the HTLV-1 infected endothelial cells was altered. These cells were no longer able to form a functional barrier, since BBB permeability and lymphocyte passage through the monolayer of endothelial cells were increased. This work constitutes the first report of susceptibility of human cerebral endothelial cells to HTLV-1 infection, with implications for HTLV-1 passage through the BBB and subsequent deregulation of the central nervous system homeostasis. We propose that the susceptibility of cerebral endothelial cells to retroviral infection and subsequent BBB dysfunction is an important aspect of HAM/TSP pathogenesis and should be considered in the design of future therapeutics strategies.

The blood–brain barrier (BBB) forms the interface between the blood and the central nervous system (CNS). BBB disruption is considered to be a key event in the pathogenesis of retroviral-associated neurological diseases. The present paper deals with the susceptibility of the endothelial cells (i.e., one of the main cellular components of BBB) to retroviral infection, and with the impact of infection in BBB function. This study focuses on the Human T-Lymphotropic Virus (HTLV-1), which infects 20 million people worldwide, and is the etiological agent of a neurodegenerative disease called HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). We first demonstrated that the cerebral endothelial cells express the receptors for the retrovirus in vitro, and on spinal cord autopsy sections from non-infected and HAM/TSP patients. We found on these latter that vascular-like structures were infected and confirmed in vitro that the endothelial cells could be productively infected by HTLV-1. We demonstrated that such an infection impairs BBB properties in vitro, as well as tight junctions, that are cell adhesion structures. This study is the first to demonstrate the impact of HTLV-1 infection on human BBB integrity; such a susceptibility has to be considered in the design of future therapeutics strategies.

High frequency of CD4+FoxP3+ cells in HTLV-1 infection: inverse correlation with HTLV-1-specific CTL response

Evidence from population genetics, gene expression microarrays, and assays of ex vivo T-cell function indicates that the cytotoxic T lymphocyte (CTL) response to human T-lymphotropic virus type 1 (HTLV-1) controls the level of HTLV-1 expression and the proviral load. The rate at which CTLs kill autologous HTLV-1–infected lymphocytes differs significantly among infected people, but the reasons for such variation are unknown. Here, we demonstrate a strong negative cor-relation between the frequency of CD4⁺FoxP3⁺ Tax⁻ regulatory T cells (T_regs) in the circulation and the rate of CTL-mediated lysis of autologous HTLV-1–infected cells ex vivo. We propose that the frequency of CD4⁺FoxP3⁺ Tax⁻ T_regs is one of the chief determinants of the efficiency of T cell–mediated immune control of HTLV-1.

DC-SIGN facilitates fusion of dendritic cells with human T-cell leukemia virus type 1-infected cells

Interactions between the oncogenic retrovirus human T-cell leukemia virus type 1 (HTLV-1) and dendritic cells (DCs) are poorly characterized. We show here that monocyte-derived DCs form syncytia and are infected upon coculture with HTLV-1-infected lymphocytes. We examined the role of DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN), a C-type lectin expressed in DCs, in HTLV-1-induced syncytium formation. DC-SIGN is known to bind with high affinity to various viral envelope glycoproteins, including human immunodeficiency virus (HIV) and hepatitis C virus, as well as to the cellular receptors ICAM-2 and ICAM-3. After cocultivating DCs and HTLV-1-infected cells, we found that anti-DC-SIGN monoclonal antibodies (MAbs) were able to decrease the number and size of HTLV-1-induced syncytia. Moreover, expression of the lectin in epithelial-cell lines dramatically enhanced the ability to fuse with HTLV-1-positive cells. Interestingly, in contrast to the envelope (Env) glycoproteins of HIV and other viruses, that of HTLV-1 does not bind directly to DC-SIGN. The facilitating role of the lectin in HTLV-1 syncytium formation is mediated by its interaction with ICAM-2 and ICAM-3, as demonstrated by use of MAbs directed against these adhesion molecules. Altogether, our results indicate that DC-SIGN facilitates HTLV-1 infection and fusion of DCs through an ICAM-dependent mechanism.

Muscle wasting induced by HTLV-1 tax-1 protein: an in vitro and in vivo study

Besides tropical spastic paraparesis/human T-cell leukemia virus type-1 (HTLV-1)-associated myelopathy, the human retrovirus HTLV-1 causes inflammatory disorders such as myositis. Although the pathogenesis of HTLV-1-associated myositis is primarily unknown, a direct effect of cytokines or viral proteins in myocytotoxicity is suspected. We have developed an in vitro cell culture model to study the interactions between primary human muscle cells and HTLV-1 chronically infected cells. When HTLV-1-infected cell lines were added to differentiated muscle cultures, cytopathic changes such as fiber shrinking were observed as early as 1 day after contact. This was accompanied by alterations in desmin and vimentin organization, occurring in the absence of muscle cell infection but with Tax-1 present in myotubes. Cytopathic changes were also observed when infected culture supernatants were added to the muscle cells. Fiber atrophy and cytoskeletal disorganization were confirmed in muscle biopsies from two HTLV-1-infected patients with myositis. Transduction of cultured muscle cells with a lentiviral vector containing the HTLV-1 Tax gene reproduced such effects in vitro. The present data indicate that the myocytotoxicity that is observed in HTLV-1-associated myopathies can be due to a direct effect of the Tax-1 protein expressed in infected inflammatory cells, in the absence of muscle cell infection.

Extensive editing of a small fraction of human T-cell leukemia virus type 1 genomes by four APOBEC3 cytidine deaminases

In the absence of the human immunodeficiency virus type 1 (HIV-1) Vif protein, the host-cell cytidine deaminases APOBEC3F and -3G are co-packaged along with virion RNA. Upon infection of target cells, nascent single-stranded DNA can be edited extensively, invariably giving rise to defective genomes called G-->A hypermutants. Although human T-cell leukemia virus type 1 (HTLV-1) replicates in the same cell type as HIV-1, it was shown here that HTLV-1 is relatively resistant to the antiviral effects mediated by human APOBEC3B, -3C, -3F and -3G. Nonetheless, a small percentage of genomes (0.1<f<5 %) were edited extensively: up to 97 % of cytidine targets were deaminated. In contrast, hypermutated HTLV-1 genomes were not identified in peripheral blood mononuclear cell DNA from ten patients with non-malignant HTLV-1 infection. Thus, although HTLV-1 DNA can indeed be edited by at least four APOBEC3 cytidine deaminases in vitro, they are conspicuously absent in vivo.

Inactivation of hTERT transcription by Tax

Telomerase expression is the hallmark of tumor cells in which this ribonucleoprotein complex preserves chromosome integrity by maintaining telomere length and thereby prevents cell death. However, recent data support a role of the combination of p53 and telomerase inactivation in initiating genetic instability that promotes malignant transformation. Through its pleiotropic effects on infected T-cell metabolism, the human T-cell leukemia virus type 1 (HTLV-1) oncoprotein Tax plays a central role in leukemogenesis. Here, we show that Tax inhibits human telomerase reverse transcriptase (hTERT) transcription, which is the rate-limiting factor of telomerase activity. This inhibitory effect, that occurs in competition with c-Myc through a canonical c-Myc binding site within the hTERT promoter, results in a decreased telomerase activity of Tax-expressing cells. This is the first demonstration of hTERT inhibition by an oncogene. Tax, which is only expressed in preleukemic cells, triggers infected T-cell cycle and keeps these cells cycling while inactivating p53. We propose that, in combination with these effects, hTERT repression by Tax at an early phase of carcinogenesis might contribute to the massive ploidy changes associated with the development of HTLV-1-associated malignancies.