GITR overexpression on CD4+CD25+ HTLV-1 transformed cells: detection by massively parallel signature sequencing

MiR-150 in HTLV-1-infection and T-cell transformation

Human T-cell leukemia virus-1 (HTLV-1) is a retrovirus that persistently infects CD4+ T-cells, and is the causative agent of adult T-cell leukemia/lymphoma (ATLL), tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM) and several inflammatory diseases. T-cell transformation by HTLV-1 is driven by multiple interactions between viral regulatory proteins and host cell pathways that govern cell proliferation and survival. Studies performed over the last decade have revealed alterations in the expression of many microRNAs in HTLV-1-infected cells and ATLL cells, and have identified several microRNA targets with roles in the viral life cycle and host cell turnover. This review centers on miR-150-5p, a microRNA whose expression is temporally regulated during lymphocyte development and altered in several hematological malignancies. The levels of miR-150-5p are reduced in many HTLV-1-transformed- and ATLL-derived cell lines. Experiments in these cell lines showed that downregulation of miR-150-5p results in activation of the transcription factor STAT1, which is a direct target of the miRNA. However, data on miR-150-5p levels in freshly isolated ATLL samples are suggestive of its upregulation compared to controls. These apparently puzzling findings highlight the need for more in-depth studies of the role of miR-150-5p in HTLV-1 infection and pathogenesis based on knowledge of miR-150-5p-target mRNA interactions and mechanisms regulating its function in normal leukocytes and hematologic neoplasms.

Influenza-Activated ILC1s Contribute to Antiviral Immunity Partially Influenced by Differential GITR Expression

Innate lymphoid cells (ILCs) represent diversified subsets of effector cells as well as immune regulators of mucosal immunity and are classified into group 1 ILCs, group 2 ILCs, and group 3 ILCs. Group 1 ILCs encompass natural killer (NK) cells and non-NK ILCs (ILC1s) and mediate their functionality via the rapid production of IFN-γ and TNF-α. The current knowledge of ILC1s mainly associates them to inflammatory processes. Much less is known about their regulation during infection and their capacity to interact with cells of the adaptive immune system. The present study dissected the role of ILC1s during early influenza A virus infection, thereby revealing their impact on the antiviral response. Exploiting in vitro and in vivo H1N1 infection systems, a cross-talk of ILC1s with cells of the innate and the adaptive immunity was demonstrated, which contributes to anti-influenza immunity. A novel association of ILC1 functionality and the expression of the glucocorticoid-induced TNFR-related protein (GITR) was observed, which hints toward a so far undescribed role of GITR in regulating ILC1 responsiveness. Overexpression of GITR inhibits IFN-γ production by ILC1s, whereas partial reduction of GITR expression can reverse this effect, thereby regulating ILC1 functionality. These new insights into ILC1 biology define potential intervention targets to modulate the functional properties of ILC1s, thus contributing toward the development of new immune interventions against influenza.

Evaluation of T Regulatory Lymphocytes Transcription Factors in HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) Patients

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an aggressive neurological disease. The CD4⁺CD25⁺ T cell population plays pivotal roles in the maintenance of immunological tolerance and prevention of such autoimmune diseases. In the current study, proviral load (PVL), factor forkhead box p3 (Foxp3), and glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) gene expression and regulatory T cells (Tregs) counts of 21 HAM/TSP patients and 16 HTLV-1 healthy carriers (ACs) were measured using real-time PCR, TaqMan method, and flow cytometry. The demographic, history of disease, and severity of myelopathy were assessed by a checklist and the Osame motor disability score (OMDS). The mean OMDS for HAM/TSP was 4.82 ± 2.37 which had no significant correlation with Treg count or the expression of Foxp3, GITR, and PVL. The CD4⁺CD25⁺ cell counts had no significant differences between HAM/TSP and ACs. Findings revealed a higher PVL in HAM/TSPs (313.36 copies/10⁴) compared to ACs (144.93 copies/10⁴, p = 0.035). The Foxp3 and GITR mRNA levels were lower in HAM/TSP patients (11.78 and 13.80, respectively) than those in healthy carriers (18.44 and 21.00, p = 0.041 and 0.03, respectively). There was a significant correlation between Treg frequency and Foxp3 gene expression (R = 0.67, p = 0.006) and GITR and Foxp3 (R = 0.84, p = 0.042) in HAM/TSP patients. Furthermore, the transcription factors have strong correlations with CD4⁺CD25⁺ T cell frequencies. These findings suggest that HTLV-1 infection can modify the expression of main functional transcription factors, FOXP3 and GITR, which may lead to immune response deterioration of Tregs and consequently HAM/TSP manifestation.

Opportunistic Infections in Patients with HTLV-1 Infection

As an acquired immunodeficiency, human immunodeficiency virus (HIV) infection is primarily responsible for opportunistic infections in infected patients. However, opportunistic infections also occur in individuals with human T cell lymphotrophic virus type 1 (HTLV-1) infection. Here, we report opportunistic infections in two Japanese HTLV-1-seropositive patients. The first patient was a 67-year-old male, who had cytomegalovirus infection associated with esophagogastritis and terminal ileitis. The patient was HTLV-1-positive and was diagnosed with smoldering adult T cell leukemia (ATL). High levels of serum soluble IL-2 receptor (sIL-2R; 4,304 U/mL) and an increased percentage of CD4+CD25+ T cells (75.5%) in peripheral blood were also detected. The second patient was a 78-year-old female, a known asymptomatic HTLV-1 carrier, who presented with persistent herpes zoster, followed by Pneumocystis jirovecii pneumonia. Disease progression of smoldering ATL along opportunistic infections was observed with very high levels of serum sIL-2R (14,058 U/mL) and an increased percentage of CD4+CD25+ T cells (87.2%) in peripheral blood. In patients with suspected opportunistic infections, both HTLV-1 and HIV should be considered. In HTLV-1-positive patients, an increase in the CD4+CD25+ T cell subset may have its value as a prognostic marker.

Cell surface markers in HTLV-1 pathogenesis

The phenotype of HTLV-1-transformed CD4⁺ T lymphocytes largely depends on defined viral effector molecules such as the viral oncoprotein Tax. In this review, we exemplify the expression pattern of characteristic lineage markers, costimulatory receptors and ligands of the tumor necrosis factor superfamily, cytokine receptors, and adhesion molecules on HTLV-1-transformed cells. These molecules may provide survival signals for the transformed cells. Expression of characteristic surface markers might therefore contribute to persistence of HTLV-1-transformed lymphocytes and to the development of HTLV-1-associated disease.

Elevated cyclic AMP levels in T lymphocytes transformed by human T-cell lymphotropic virus type 1

Human T-cell lymphotropic virus type 1 (HTLV-1), the cause of adult T-cell leukemia/lymphoma (ATLL), transforms CD4(+) T cells to permanent growth through its transactivator Tax. HTLV-1-transformed cells share phenotypic properties with memory and regulatory T cells (T-reg). Murine T-reg-mediated suppression employs elevated cyclic AMP (cAMP) levels as a key regulator. This led us to determine cAMP levels in HTLV-1-transformed cells. We found elevated cAMP concentrations as a consistent feature of all HTLV-1-transformed cell lines, including in vitro-HTLV-1-transformed, Tax-transformed, and patient-derived cells. In transformed cells with conditional Tax expression, high cAMP levels coincided with the presence of Tax but were lost without it. However, transient ectopic expression of Tax alone was not sufficient to induce cAMP. We found specific downregulation of the cAMP-degrading phosphodiesterase 3B (PDE3B) in HTLV-1-transformed cells, which was independent of Tax in transient expression experiments. This is in line with the notion that PDE3B transcripts and cAMP levels are inversely correlated. Overexpression of PDE3B led to a decrease of cAMP in HTLV-1-transformed cells. Decreased expression of PDE3B was associated with inhibitory histone modifications at the PDE3B promoter and the PDE3B locus. In summary, Tax transformation and its continuous expression contribute to elevated cAMP levels, which may be regulated through PDE3B suppression. This shows that HTLV-1-transformed cells assume biological features of long-lived T-cell populations that potentially contribute to viral persistence.

MicroRNA miR-146a and further oncogenesis-related cellular microRNAs are dysregulated in HTLV-1-transformed T lymphocytes

Background

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent of a severe and fatal lymphoproliferative disease of mainly CD4⁺ T cell origin, adult T cell leukemia, which develops after prolonged viral persistence. Transformation of infected cells involves HTLV-1's oncoprotein Tax, which perturbs cell cycle regulation and modulates cellular gene expression. The latter function is also a hallmark of microRNAs, a rather new layer in the regulation of gene expression. Affecting e.g. proliferation, microRNAs constitute a potential target for viral interference on the way to persistence and transformation. Hence, we explored the interconnections between HTLV-1 and cellular microRNAs.

Results

We report that several microRNAs – miRs 21, 24, 146a, 155 and 223 – are deregulated in HTLV-1-transformed cells. They are all upregulated except for miR-223, which is downregulated. Each of those microRNAs has ties to cancer. Their expression pattern forms a uniform phenotype among HTLV-transformed cells when compared to HTLV-negative control cells. In particular, miR-146a expression was found to be directly stimulated by Tax via NF-κB-mediated transactivation of its promoter; a single NF-κB site proximal to the transcription start point was necessary and sufficient for this to happen. An in silico analysis of potential target genes revealed candidates that might be coregulated by two or more of the aforementioned overexpressed microRNAs.

Conclusion

These data demonstrate that cellular microRNAs are deregulated in HTLV-1-transformed T cells. In the case of miR-146a, this could be directly attributed to HTLV's oncoprotein Tax. Interference with cellular microRNAs may be crucial to maintaining persistence or may facilitate transformation of host cells.