Redox events in HTLV-1 Tax-induced apoptotic T-cell death

Glutathione reductase system changes in HTLV-1 infected patients

During chronic HTLV-1 infections oxidative stress occurs and contributes in viral pathogenesis. Glutaredoxin (Grx) system is one of the most effective antioxidant components. The system maintains the cellular redox and scavenges reactive oxygen species through the function of glutathione reductase (GR) enzyme, NADPH and reduced glutathione (GSH). This study was performed to investigate potential changes in GR gene expression and activity as well as GSH level, and their association with the viral load in HTLV-1 infection. Forty HTLV-1 seropositive patients divided into two groups: asymptomatic carriers (N = 20) and HAM/TSP (N = 20) with the same number of age and sex-matched healthy controls were recruited in this study. GR cellular gene expression and viral load in PBMCs were determined using Real-time PCR Technique. Enzyme activity and GSH level in sera were measured by commercial kits based on manufacturer's provided protocols. GR gene expression and GR enzyme activity, as well as GSH level, were significantly lower in HTLV-1 patients. A negative correlation between viral load and GR gene expression/enzyme activity was observed in HAM/TSP group. Similarly, a negative relationship between viral load and GSH levels was observed in both carrier and HAM/TSP groups. We also found that in profound complicated condition of HTLV-1 infection, HAM/TSP, Grx system components activity was significantly decreased compared to the controls. Such observation was not the case in clinically healthy HTLV-1 carriers. These findings may shed a light on the conditions contributing in pathogenesis of the complications and exacerbation of the disease in the HAM/TSP cases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-022-00758-y.

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.

Association between serum zinc and copper levels and antioxidant defense in subjects infected with human T-lymphotropic virus type 1

Introduction

Copper (Cu) and zinc (Zn) are important trace elements that are also structural ions of superoxide dismutase (SOD), which reduce oxidative stress. Zinc deficiency and excess copper have been reported to be associated with inflammation. The human T-lymphotropic virus type 1 (HTLV-1) is a retrovirus, which is believed to cause systemic inflammation. The aim of this study is to measure levels of Zn, Cu, SOD, and prooxidant–antioxidant balance (PAB) in HTLV-1-positive patients and investigate the association between serum Zn and Cu concentrations and levels of oxidative stress in them.

Methods

The serum samples of 1,116 subjects who had participated in the “Mashhad Stroke and Heart Atherosclerotic Disorder” study, including 279 HTLV-1-positive and 837 HTLV-1-negative patients, were used. Levels of Zn, Cu, SOD, and PAB were measured.

Results

Zinc and SOD levels were lower in the HTLV-1-positive group; however, the difference was statistically significant only for the level of SOD (P=0.003). On the other hand, levels of copper and PAB were significantly higher in HTLV-1 positive subjects; P=0.004 and P=0.002, respectively.

Conclusion

In HTLV-infected patients, serum Zn concentration is lower and Cu concentration is higher than healthy controls. This altered situation might be either primary or secondary to HTLV-1 infection, which should be investigated in larger studies. We showed that SOD is significantly lower in HTLV-1-infected subjects. As in some other viruses that evolve different mechanisms to potentiate virus replication by changing the physiologic condition of host cells, HTLV-1 too probably decreases the activity of copper–zinc SOD1 by suppressing its gene.

HTLV-1 infection-induced motor dysfunction, memory impairment, depression, and brain tissues oxidative damage in female BALB/c mice

AIMS

The HTLV-1 infection is associated with a neuro-inflammatory disease. In the present study, the behavioral consequences and brain oxidative damages were evaluated in HTLV-1-infected BALB/c mice.

MATERIAL AND METHODS

20 female BALB/c mice were divided into two groups comprising control and HTLV-1-infected. The HTLV-1-infected group was inoculated with a 10⁶ MT-2 HTLV-1-infected cell line. Two months later, the behavioral tests were conducted. Finally, oxidative stress was assessed in the cortex and hippocampus tissues.

KEY FINDINGS

In the HTLV-1-infected group, running time and latency to fall, travel distance and time spent in the peripheral zone, total crossing number and total traveled distance in open field test, the latency of entrance into the dark compartment in the passive avoidance test, the new object exploration percentage, and discrimination ratio were significantly lower than in the control group. The immobility time, time spent in the dark compartment in passive avoidance test, and total exploration time significantly increased in the HTLV-1-infected group compared to the control group. In the cortical tissue of the HTLV-1 group, the malondialdehyde levels were elevated while the total thiol levels decreased in comparison to the control group. The activity of superoxide dismutase in the cortical and hippocampal tissues, and catalase activity in cortical tissue significantly decreased in the HTLV-1 group in comparison to the control group.

SIGNIFICANCE

The HTLV-1 infection seems to induce depression-like behavior, motor dysfunction, disruption in working and fear memory and also oxidative stress in the cortex and hippocampus.

Structure and properties of slow-resorbing nanofibers obtained by (co-axial) electrospinning as tissue scaffolds in regenerative medicine

With the rapid advancement of regenerative medicine technologies, there is an urgent need for the development of new, cell-friendly techniques for obtaining nanofibers—the raw material for an artificial extracellular matrix production. We investigated the structure and properties of PCL₁₀ nanofibers, PCL₅/PCL₁₀ core-shell type nanofibers, as well as PCL₅/PCL_Ag nanofibres prepared by electrospinning. For the production of the fiber variants, a 5–10% solution of polycaprolactone (PCL) (M_w = 70,000–90,000), dissolved in a mixture of formic acid and acetic acid at a ratio of 70:30 m/m was used. In order to obtain fibers containing PCL_Ag 1% of silver nanoparticles was added. The electrospin was conducted using the above-described solutions at the electrostatic field. The subsequent bio-analysis shows that synthesis of core-shell nanofibers PCL₅/PCL₁₀, and the silver-doped variant nanofiber core shell PCL₅/PCL_Ag, by using organic acids as solvents, is a robust technique. Furthermore, the incorporation of silver nanoparticles into PCL₅/PCL_Ag makes such nanofibers toxic to model microbes without compromising its biocompatibility. Nanofibers obtained such way may then be used in regenerative medicine, for the preparation of extracellular scaffolds: (i) for controlled bone regeneration due to the long decay time of the PCL, (ii) as bioscaffolds for generation of other types of artificial tissues, (iii) and as carriers of nanocapsules for local drug delivery. Furthermore, the used solvents are significantly less toxic than the solvents for polycaprolactone currently commonly used in electrospin, like for example chloroform (CHCl₃), methanol (CH₃OH), dimethylformamide (C₃H₇NO) or tetrahydrofuran (C₄H₈O), hence the presented here electrospin technique may allow for the production of multilayer nanofibres more suitable for the use in medical field.

Tax-1 and Tax-2 similarities and differences: focus on post-translational modifications and NF-κB activation

Although human T cell leukemia virus type 1 and 2 (HTLV-1 and HTLV-2) share similar genetic organization, they have major differences in their pathogenesis and disease manifestation. HTLV-1 is capable of transforming T lymphocytes in infected patients resulting in adult T cell leukemia/lymphoma whereas HTLV-2 is not clearly associated with lymphoproliferative diseases. Numerous studies have provided accumulating evidence on the involvement of the viral transactivators Tax-1 versus Tax-2 in T cell transformation. Tax-1 is a potent transcriptional activator of both viral and cellular genes. Tax-1 post-translational modifications and specifically ubiquitylation and SUMOylation have been implicated in nuclear factor-kappaB (NF-κB) activation and may contribute to its transformation capacity. Although Tax-2 has similar protein structure compared to Tax-1, the two proteins display differences both in their protein–protein interaction and activation of signal transduction pathways. Recent studies on Tax-2 have suggested ubiquitylation and SUMOylation independent mechanisms of NF-κB activation. In this present review, structural and functional differences between Tax-1 and Tax-2 will be summarized. Specifically, we will address their subcellular localization, nuclear trafficking and their effect on cellular regulatory proteins. A special attention will be given to Tax-1/Tax-2 post-translational modification such as ubiquitylation, SUMOylation, phosphorylation, acetylation, NF-κB activation, and protein–protein interactions involved in oncogenecity both in vivo and in vitro.

Anti-apoptotic effect of Tax: an NF-κB path or a CREB way?

The NF-κB pathway is intimately linked to the survival of mammalian cells, and its activation by Tax has consequently been considered important for human T-cell leukemia/lymphoma virus type 1 (HTLV-1)-infected cell resistance to death. Very little emphasis has been given to other mechanisms, although Tax regulates the expression and activity of several cellular genes. The finding that CREB protein is activated in HTLV-1 infected cells underlines the possibility that other mechanisms of survival may be implicated in HTLV-1 infection. Indeed, CREB activation or overexpression plays a role in normal hematopoiesis, as well as in leukemia development, and CREB is considered as a survival factor in various cell systems. A better understanding of the different molecular mechanisms used by Tax to counteract cell death will also help in the development of new therapeutic strategies for HTLV-1 associated diseases.

HTLV-1 Tax: Linking transformation, DNA damage and apoptotic T-cell death

The human T-cell leukemia virus type I (HTLV-1) is the causative agent of adult T-cell leukemia (ATL), an aggressive CD4-positive T-cell neoplasia. The HTLV-1 proto-oncogene Tax, a potent transcriptional activator of cellular and viral genes, is thought to play a pivotal role in the transforming properties of the virus by deregulating intracellular signaling pathways. During the course of HTLV-1 infection, the dysregulation of cell-cycle checkpoints and the suppression of DNA damage repair is tightly linked to the activity of the viral oncoprotein Tax. Tax activity is associated with production of reactive oxygen intermediates (ROS), chromosomal instability and DNA damage, apoptotic cell death and cellular transformation. Changes in the intracellular redox status induced by Tax promote DNA damage. Tax-mediated DNA damage is believed to be essential in initiating the transformation process by subjecting infected T cells to genetic changes that eventually promote the neoplastic state. Apoptosis and immune surveillance would then exert the necessary selection pressure for eliminating the majority of virally infected cells, while escape variants acquiring a mutator phenotype would constitute a subpopulation of genetically altered cells prone to neoplasia. While the potency of Tax-activity seems to be a determining factor for the observed effects, the cooperation of Tax with other viral proteins determines the fate and progression of HTLV-1-infected cells through DNA damage, apoptosis, survival and transformation.

Diametrically opposed effects of hypoxia and oxidative stress on two viral transactivators

Background

Many pathogens exist in multiple physiological niches within the host. Differences between aerobic and anaerobic conditions are known to alter the expression of bacterial virulence factors, typically through the conditional activity of transactivators that modulate their expression. More recently, changes in physiological niches have been shown to affect the expression of viral genes. For many viruses, differences in oxygen tension between hypoxia and normoxia alter gene expression or function. Oxygen tension also affects many mammalian transactivators including AP-1, NFkB, and p53 by affecting the reduced state of critical cysteines in these proteins. We have recently determined that an essential cys-x-x-cys motif in the EBNA1 transactivator of Epstein-Barr virus is redox-regulated, such that transactivation is favoured under reducing conditions. The crucial Tat transactivator of human immunodeficiency virus (HIV) has an essential cysteine-rich region, and is also regulated by redox. Contrary to EBNA1, it is reported that Tat's activity is increased by oxidative stress. Here we have compared the effects of hypoxia, oxidative stress, and cellular redox modulators on EBNA1 and Tat.

Results

Our results indicate that unlike EBNA1, Tat is less active during hypoxia. Agents that generate hydroxyl and superoxide radicals reduce EBNA1's activity but increase transactivation by Tat. The cellular redox modulator, APE1/Ref-1, increases EBNA1's activity, without any effect on Tat. Conversely, thioredoxin reductase 1 (TRR1) reduces Tat's function without any effect on EBNA1.

Conclusions

We conclude that oxygen partial pressure and oxidative stress affects the functions of EBNA1 and Tat in a dramatically opposed fashion. Tat is more active during oxidative stress, whereas EBNA1's activity is compromised under these conditions. The two proteins respond to differing cellular redox modulators, suggesting that the oxidized cysteine adduct is a disulfide bond(s) in Tat, but sulfenic acid in EBNA1. The effect of oxygen partial pressure on transactivator function suggests that changes in redox may underlie differences in virus-infected cells dependent upon the physiological niches they traffic to.

Oxidative damage in dengue fever

Oxidative stress may be important in the pathogenesis of dengue infection. Using accurate markers of oxidative damage, we assessed the extent of oxidative damage in dengue patients. The levels of hydroxyeicosatetraenoic acid products (HETEs), F(2)-isoprostanes (F(2)-IsoPs), and cholesterol oxidation products (COPs) were measured in 28 adult dengue patients and 28 age-matched study controls during the febrile, defervescent, and convalescent stages of infection. We compared the absolute and the percentage change in these markers in relation to key clinical parameters and inflammatory markers. The levels of total HETEs and total HETEs/arachidonate, total F(2)-IsoPs/arachidonate, and COPs/cholesterol were higher during the febrile compared to the convalescent level. Total HETEs correlated positively with admission systolic blood pressure (r=0.52, p<0.05), whereas an inverse relationship was found between 7beta-hydroxycholesterol and systolic and diastolic blood pressure (r=-0.61 and -0.59, respectively, p<0.01). The urinary F(2)-IsoP level was higher in urine during the febrile stage compared to the convalescent level. Despite lower total cholesterol levels during the febrile stage compared to convalescent levels, a higher percentage of cholesterol was found as COPs (7beta-, 24-, and 27-hydroxycholesterol). The levels of platelet-activating factor-acetylhydrolase activity, vascular cellular adhesion molecule-1, tumor necrosis factor-alpha, and high-sensitivity C-reactive protein were higher during the febrile stage compared to their convalescent levels (p<0.01). Markers of oxidative damage are altered during the various stages of dengue infection.

Molecular mechanisms of cellular transformation by HTLV-1 Tax

The HTLV Tax protein is crucial for viral replication and for initiating malignant transformation leading to the development of adult T-cell leukemia. Tax has been shown to be oncogenic, since it transforms and immortalizes rodent fibroblasts and human T-lymphocytes. Through CREB, NF-kappaB and SRF pathways Tax transactivates cellular promoters including those of cytokines (IL-13, IL-15), cytokine receptors (IL-2Ralpha) and costimulatory surface receptors (OX40/OX40L) leading to upregulated protein expression and activated signaling cascades (e.g. Jak/STAT, PI3Kinase, JNK). Tax also stimulates cell growth by direct binding to cyclin-dependent kinase holenzymes and/or inactivating tumor suppressors (e.g. p53, DLG). Moreover, Tax silences cellular checkpoints, which guard against DNA structural damage and chromosomal missegregation, thereby favoring the manifestation of a mutator phenotype in cells.

Relevance of CREB phosphorylation in the anti-apoptotic function of human T-lymphotropic virus type 1 tax protein in serum-deprived murine fibroblasts

The human T-cell leukemia virus type 1 (HTLV-1) Tax transactivator is thought to play a primary role in the development of HTLV-1-mediated diseases. Using a murine fibroblast model, we previously showed that Tax reduces apoptosis induced by serum starvation by preventing cytochrome c release from the mitochondria. As Tax can enhance the transcriptional activity of nuclear factor NF-kB and cAMP-responsive element binding protein/activating transcription factor-1 (CREB/ATF-1), we investigated the relevance of these routes in the anti-apoptotic effects of Tax. Results showed that a Tax mutant retaining CREB/ATF-1 transactivating activity protects murine fibroblasts from serum-depletion-induced apoptosis, while two CREB/ATF-1-defective mutants did not. Treatment with forskolin, an activator of CREB, significantly attenuated cytochrome c release and Bax translocation in response of serum deprivation. In analogy to forskolin treatment, Tax expression results in sustained phosphorylation of CREB at Ser(133) during serum starvation. Considered together, these results underscore a primary role of CREB transcriptional activation in preventing apoptosis triggered by growth factor withdrawal, and suggest that Tax might in part function by affecting the phosphorylation state of CREB.

Two discrete events, human T-cell leukemia virus type I Tax oncoprotein expression and a separate stress stimulus, are required for induction of apoptosis in T-cells

Background

It is poorly understood why many transforming proteins reportedly enhance both cell growth (transformation) and cell death (apoptosis). At first glance, the ability to transform and the ability to engender apoptosis seem to be contradictory. Interestingly, both abilities have been widely reported in the literature for the HTLV-I Tax protein.

Results

To reconcile these apparently divergent findings, we sought to understand how Tax might cause apoptosis in a Jurkat T-cell line, JPX-9. Tax expression can be induced equally by either cadmium (Cd) or zinc (Zn) in JPX-9 cells. Surprisingly, when induced by Zn, but not when induced by Cd, Tax-expression produced significant apoptosis. Under our experimental conditions, Zn but not Cd, induced SAPK (stress activated protein kinase)/JNK (Jun kinase) activation in cells. We further showed that transient over-expression of Tax-alone or Jun-alone did not induce cell death. On the other hand, co-expression of Tax plus Jun did effectively result in apoptosis.

Conclusion

We propose that Tax-expression alone in a T-cell background insufficiently accounts for apoptosis. On the other hand, Tax plus activation of a stress kinase can induce cell death. Thus, HTLV-I infection/transformation of cells requires two discrete events (i.e. oncoprotein expression and stress) to produce apoptosis.

Robust singular value decomposition analysis of microarray data

In microarray data there are a number of biological samples, each assessed for the level of gene expression for a typically large number of genes. There is a need to examine these data with statistical techniques to help discern possible patterns in the data. Our technique applies a combination of mathematical and statistical methods to progressively take the data set apart so that different aspects can be examined for both general patterns and very specific effects. Unfortunately, these data tables are often corrupted with extreme values (outliers), missing values, and non-normal distributions that preclude standard analysis. We develop a robust analysis method to address these problems. The benefits of this robust analysis will be both the understanding of large-scale shifts in gene effects and the isolation of particular sample-by-gene effects that might be either unusual interactions or the result of experimental flaws. Our method requires a single pass and does not resort to complex "cleaning" or imputation of the data table before analysis. We illustrate the method with a commercial data set.