Specific antiviral effect of violaceoid E on bovine leukemia virus

Bovine leukemia virus (BLV) infection has spread worldwide causing significant economic losses in the livestock industry. In countries with a high prevalence of BLV, minimizing economic losses is challenging; thus, research into various countermeasures is important for improving BLV control. Because anti-BLV drugs have not been developed, the present study explored a promising chemical compound with anti-BLV activity. Initially, screening of a chemical compound library revealed that violaceoid E (vioE), which is isolated from fungus, showed antiviral activity. Further analysis demonstrated that the antiviral effect of vioE inhibited transcriptional activation of BLV. Cellular thermal shift assay and pulldown assays provided evidence for a direct interaction between vioE and the viral transactivator protein, Tax. These data indicate that interference with Tax-dependent transcription could be a novel target for development of anti-BLV drugs. Therefore, it is suggested that vioE is a novel antiviral compound against BLV.

Analysis of Nucleotide Sequence of Tax, miRNA and LTR of Bovine Leukemia Virus in Cattle with Different Levels of Persistent Lymphocytosis in Russia

Bovine Leukemia Virus (BLV) is the etiological agent of enzootic bovine leucosis (EBL), a lymphoproliferative disease of the bovine species. In BLV-infected cells, the long terminal repeat (LTR), the viral Tax protein and viral miRNAs promote viral and cell proliferation as well as tumorigenesis. Although their respective roles are decisive in BLV biology, little is known about the genetic sequence variation of these parts of the BLV genome and their impact on disease outcome. Therefore, the objective of this study was to assess the relationship between disease progression and sequence variation of the BLV Tax, miRNA and LTR regions in infected animals displaying either low or high levels of persistent lymphocytosis (PL). A statistically significant association was observed between the A(+187)C polymorphism in the downstream activator sequence (DAS) region in LTR (p-value = 0.00737) and high lymphocytosis. Our study also showed that the mutation A(−4)G in the CAP site occurred in 70% of isolates with low PL and was not found in the high PL group. Conversely, the mutations G(−133)A/C in CRE2 (46.7%), C(+160)T in DAS (30%) and A(310)del in BLV-mir-B4-5p, A(357)G in BLV-mir-B4-3p, A(462)G in BLV-mir-B5-5p, and GA(497–498)AG in BLV-mir-B5-3p (26.5%) were often seen in isolates with high PL and did not occur in the low PL group. In conclusion, we found several significant polymorphisms among BLV genomic sequences in Russia that would explain a progression towards higher or lower lymphoproliferation. The data presented in this article enabled the classification between two different genotypes; however, clear association between genotypes and the PL development was not found.

Bovine leukemia virus tax gene/Tax protein polymorphism and its relation to Enzootic Bovine Leukosis

Bovine leukemia virus (BLV) is an oncogenic retrovirus of the Deltaretrovirus genus, which causes persistent infection in its natural hosts – cattle, zebu, and water buffalo with diverse clinical manifestations through the defeat of B-cells. The BLV proviral genome, along with structural genes (gag, pro, pol, and env), includes nonstructural ones (R3, G4, tax, rex, AS, pre-miRs (for miRNAs). We have shown in our previous data the association of some pre-miRs-B’ (for BLV miRNA) alleles with leukocyte (WBC – white blood cell) number in BLV-infected cows. Multifunctional properties of Tax protein have led us to an assumption that tax gene/Tax protein could have too population variations related to WBC counts. Here we report about several tax alleles/Tax protein variants, which have a highly significant association with an increase or a decrease of WBC number in BLV-infected cows. We have provided evidence that Tax A, H variants (tax b, c, d, f, e alleles) are correlated with reduced WBC counts at the level of BLV-negative groups of animals and thus could be the feature of the aleukemic (AL) form of BLV infection. We suggest this finding could be used in BLV testing for the presence of Tax A, H in the proviral DNA consider such strains of BLV as AL ones, and because of this, minimize the clinical losses due to BLV infection in cattle.

Non-cytotoxic 1,2,3-triazole tethered fused heterocyclic ring derivatives display Tax protein inhibition and impair HTLV-1 infected cells

Human T cell lymphotropic virus type 1 (HTLV-1) is a human retrovirus that infects approximately 10-20 million people worldwide and causes an aggressive neoplasia (adult T-cell leukemia/lymphoma - ATL). Therapeutic approaches for the treatment of ATL have variable effectiveness and poor prognosis, thus requiring strategies to identify novel compounds with activity on infected cells. In this sense, we initially screened a small series of 25 1,2,3-triazole derivatives to discover cell proliferation inhibitors and apoptosis inducers in HTLV-1-infected T-cell line (MT-2) for further assessment of their effect on viral tax activity through inducible-tax reporter cell line (Jurkat LTR-GFP). Eight promising compounds (02, 05, 06, 13, 15, 21, 22 and 25) with activity ≥70% were initially selected, based on a suitable cell-based assay using resazurin reduction method, and evaluated towards cell cycle, apoptosis and Tax/GFP expression analyses through flow cytometry. Compound 02 induced S phase cell cycle arrest and compounds 05, 06, 22 and 25 promoted apoptosis. Remarkably, compounds 22 and 25 also reduced GFP expression in an inducible-tax reporter cell, which suggests an effect on Tax viral protein. More importantly, compounds 02, 22 and 25 were not cytotoxic in human hepatoma cell line (Huh-7). Therefore, the discovery of 3 active and non-cytotoxic compounds against HTLV-1-infected cells can potentially contribute, as an initial promising strategy, to the development process of new drugs against ATL.

Transcriptional activation of long terminal repeat of bovine leukemia virus by bovine heat shock factor 1

Bovine leukemia virus (BLV) causes enzootic bovine leukosis (EBL). The BLV genome encodes Tax protein, a transcriptional activator of viral gene expression that binds to the BLV long terminal repeat (LTR). Heat shock factor 1 (HSF1) is a known regulator of the heat shock response proteins, including heat shock proteins. In the present study, the BLV LTR was investigated for interaction of heat shock element (HSE) with HSF1 and the viral Tax protein. It could be confirmed that a functional HSE is well conserved in different BLV strains. The LTR transcriptional activity, as measured by luciferase reporter assay, was upregulated by bovine HSF1 - without Tax expression - in feline CC81 cells. The HSF1 activated LTR transcription by binding to the HSE. LTR-activation was lost upon HSE removal from the LTR and upon expression of a mutant HSF1 lacking the DNA-binding domain. We conclude that BLV LTR is activated to a basal level by host transcriptional factor HSF1, but without Tax protein involvement.

[Inhibition of proliferation of adult T-cell leukemia cells by celastrol]

We studied the effect of celastrol on the proliferation and apoptosis of adult T-cell leukemia (ATL) cells. After treating adult T-cell leukemia cell lines with different concentrations of celastrol, we analyzed the cell proliferation by MTT and colony formation assays. Flow cytometry was conducted to detect cell apoptosis by Annexin V-FITC/PI staining. Western blotting and dual-luciferase reporter assay were done to study the mechanism how celastrol suppressed the growth of adult T-cell leukemia cells. Celastrol could significantly inhibit the proliferation of adult T-cell leukemia cells, and induce apoptosis of ATL cells. With the increase of the concentration of celastrol, the ratio of Bax/Bcl-2 protein was up-regulated. The Caspase-3/7 protein was cleaved and activated after treatment with celastrol. Moreover, the expression of HTLV-1-encoded viral protein Tax was significantly inhibited in the celastrol treated cells. Taken together, these results indicated that celastrol effectively inhibited the proliferation of adult T-cell leukemia cells by regulating the expression of Bcl-2 family protein, and induced cell apoptosis by activating Caspase dependent pathway. In addition, celastrol could inhibit the expression of viral protein Tax. This study will provide an experimental basis for the clinical application of celastrol in the treatment of adult T-cell leukemia.

L233P mutation of the Tax protein strongly correlated with leukemogenicity of bovine leukemia virus

The bovine leukemia virus (BLV) Tax protein is believed to play a crucial role in leukemogenesis by the virus. BLV usually causes asymptomatic infections in cattle, but only one-third develop persistent lymphocytosis that rarely progress after a long incubation period to lymphoid tumors, namely enzootic bovine leucosis (EBL). In the present study, we demonstrated that the BLV tax genes could be divided into two alleles and developed multiplex PCR detecting an L233P mutation of the Tax protein. Then, in order to define the relationship between the Tax protein and leukemogenicity, we examined 360 tumor samples randomly collected from dairy or breeding cattle in Japan, of which Tax proteins were categorized, for age at the time of diagnosis of EBL. The ages of 288 animals (80.0%) associated with L233-Tax and those of 70 animals (19.4%) with P233-Tax individually followed log-normal distributions. Only the two earliest cases (0.6%) with L233-Tax disobeyed the log-normal distribution. These findings suggest that the animals affected by EBL were infected with the virus at a particular point in life, probably less than a few months after birth. Median age of those with P233-Tax was 22 months older than that with L233-Tax and geometric means exhibited a significant difference (P<0.01). It is also quite unlikely that viruses carrying the particular Tax protein infect older cattle. Here, we conclude that BLV could be divided into two categories on the basis of amino acid at position 233 of the Tax protein, which strongly correlated with leukemogenicity.