The Human T-Lymphotropic Virus Type 1 Tax Protein Inhibits Nonsense-Mediated mRNA Decay by Interacting with INT6/EIF3E and UPF1

Human T-cell leukemia virus type 1 (HTLV-1) expression depends on the concerted action of Tax, which drives transcription of the viral genome, and Rex, which favors expression of incompletely spliced mRNAs and determines a 2-phase temporal pattern of viral expression. In the present study, we investigated the Rex dependence of the complete set of alternatively spliced HTLV-1 mRNAs. Analyses of cells transfected with Rex-wild-type and Rex-knockout HTLV-1 molecular clones using splice site-specific quantitative reverse transcription (qRT)-PCR revealed that mRNAs encoding the p30Tof, p13, and p12/8 proteins were Rex dependent, while the p21rex mRNA was Rex independent. These findings provide a rational explanation for the intermediate-late temporal pattern of expression of the p30tof, p13, and p12/8 mRNAs described in previous studies. All the Rex-dependent mRNAs contained a 75-nucleotide intronic region that increased the nuclear retention and degradation of a reporter mRNA in the absence of other viral sequences. Selective 2=-hydroxyl acylation analyzed by primer extension (SHAPE) analysis revealed that this sequence formed a stable hairpin structure. Cell cycle synchronization experiments indicated that mitosis partially bypasses the requirement for Rex to export Rex-dependent HTLV-1 transcripts. These findings indicate a link between the cycling properties of the host cell and the temporal pattern of viral expression/latency that might influence the ability of the virus to spread and evade the immune system. IMPORTANCEHTLV-1 is a complex retrovirus that causes two distinct pathologies termed adult T-cell leukemia/lymphoma and tropical spastic paraparesis/HTLV-1-associated myelopathy in about 5% of infected individuals. Expression of the virus depends on the concerted action of Tax, which drives transcription of the viral genome, and Rex, which favors expression of incompletely spliced mRNAs and determines a 2-phase temporal pattern of virus expression. The findings reported in this study revealed a novel cisacting regulatory element and indicated that mitosis partially bypasses the requirement for Rex to export Rex-dependent HTLV-1 transcripts. Our results add a layer of complexity to the mechanisms controlling the expression of alternatively spliced HTLV-1 mRNAs and suggest a link between the cycling properties of the host cell and the temporal pattern of viral expression/ latency that might influence the ability of the virus to spread and evade the immune system. H uman T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia-lymphoma (ATLL) (1) and tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM) (2). Accumulating evidence also supports an association between HTLV-1 infection and a number of chronic inflammatory diseases, including uveitis, arthropathy, and infective dermatitis (3).HTLV-1 produces many alternatively spliced transcripts coding for virion components and regulatory and accessory proteins ( Fig. 1) (4). The gag, pro, and pol genes are expre...

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“…The hbz sp1 mRNA exhibited a half-life of about 1 h (Fig. 3E), which is consistent with a recent study by Mocquet et al (35).…”

Section: Resultssupporting

confidence: 81%

Expression of Alternatively Spliced Human T-Cell Leukemia Virus Type 1 mRNAs Is Influenced by Mitosis and by a Novel cis -Acting Regulatory Sequence

Cavallari

Rende

Bona

et al. 2016

J Virol

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“…Such a possibility was not apparent from an analysis of HAM/TSP cells cultured ex vivo or from HTLV-1-infected rabbits as in both cases mRNA levels of Tax and HBZ exhibited somewhat divergent patterns (37,38). However, the abundance of these transcripts may not reflect the outputs of HTLV-1 sense and antisense transcription in that complex events occurring during infection and involving multiple HTLV-1 genes likely influence the abundance of viral RNA (43)(44)(45). Furthermore, the cellular environment may influence viral mRNA stability, which is supported by a substantial increase in the stability of the Tax transcript following T-cell stimulation (46).…”

Section: Discussionmentioning

confidence: 87%

Permissive Sense and Antisense Transcription from the 5′ and 3′ Long Terminal Repeats of Human T-Cell Leukemia Virus Type 1

Laverdure

Polakowski

Hoang

et al. 2016

J Virol

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Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus, and, as such, its genome becomes chromosomally integrated following infection. The resulting provirus contains identical 5= and 3= peripheral long terminal repeats (LTRs) containing bidirectional promoters. Antisense transcription from the 3= LTR regulates expression of a single gene, hbz, while sense transcription from the 5= LTR controls expression of all other viral genes, including tax. Both the HBZ and Tax proteins are implicated in the development of adult T-cell leukemia (ATL), a T-cell malignancy caused by HTLV-1 infection. However, these proteins appear to harbor opposing molecular functions, indicating that they may act independently and at different time points prior to leukemogenesis. Here, we used bidirectional reporter constructs to test whether transcriptional interference serves as a mechanism that inhibits simultaneous expression of Tax and HBZ. We found that sense transcription did not interfere with antisense transcription from the 3= LTR and vice versa, even with strong transcription emanating from the opposing direction. Therefore, bidirectional transcription across the provirus might not restrict hbz or tax expression. Single-cell analyses revealed that antisense transcription predominates in the absence of Tax, which transactivates viral sense transcription. Interestingly, a population of Taxexpressing cells exhibited antisense but not activated sense transcription. Consistent with the ability of Tax to induce cell cycle arrest, this population was arrested in G 0 /G 1 phase. These results imply that cell cycle arrest inhibits Tax-mediated activation of sense transcription without affecting antisense transcription, which may be important for long-term viral latency. IMPORTANCEThe chromosomally integrated form of the retrovirus human T-cell leukemia virus type 1 (HTLV-1) contains identical DNA sequences, known as long terminal repeats (LTRs), at its 5= and 3= ends. The LTRs modulate transcription in both forward (sense) and reverse (antisense) directions. We found that sense transcription from the 5= LTR does not interfere with antisense transcription from the 3= LTR, allowing viral genes encoded on opposite DNA strands to be simultaneously transcribed. Two such genes are tax and hbz, and while they are thought to function at different times during the course of infection to promote leukemogenesis of infected T cells, our results indicate that they can be simultaneously transcribed. We also found that the ability of Tax to induce cell cycle arrest inhibits its fundamental function of activating viral sense transcription but does not affect antisense transcription. This regulatory mechanism may be important for long-term HTLV-1 infection. R etroviruses express their proviral genome by taking advantage of the host cell transcription machinery. Following reverse transcription and integration within the infected cell genome, the 5= and 3= flanking regions of provirus comprise identical regions, termed long terminal repeats (LT...

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“…Retrovirus activity is also observed in the post-transcriptional control of gene expression. Retroviruses induce the degradation of cellular mRNA to obtain better access to the cell's translational mechanisms, thus disrupting the host's immune processes and inducing neoplastic transformations in cells (Mocquet et al 2012).…”

Section: Discussionmentioning

confidence: 99%

Polymorphism and expression of the tumour necrosis factor-alpha (TNF-alpha) gene in non-infected cows and in cows naturally infected with the bovine leukaemia virus (BLV)

Bojarojć-Nosowicz¹,

Brym²,

Kaczmarczyk³

et al. 2016

Vet. Med. - Czech

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ABSTRACT:The objective of this study was to determine the influence of TNF-alpha gene polymorphism at position -824 A > G on TNF-alpha gene expression in BLV-positive animals with aleukaemic (AL) and persistent lymphocytosis (PL) forms of enzootic bovine leukosis (EBL) and in BLV-negative cows. Polymorphism of the TNFalpha gene at position -824 A > G had a complex influence on TNF-alpha gene expression in cows infected with BLV. In animals with various TNF-alpha genotypes, mRNA levels were stable and similar, but significant differences were noted in the percentages of PBMCs expressing membrane TNF-alpha (mTNF-alpha) protein (PBMCs that were positive for mTNF-alpha). In healthy cows, significant differences in TNF-alpha gene expression were not noted at any of the analysed levels. BLV infection and EBL progression resulted in differential TNF-alpha gene expression at both mRNA and protein levels, but the differences in the amount of the transcript and the percentages of mTNF-alpha+ cells exhibited a reverse trend. The lowest mRNA levels and the highest percentage of PBMCs expressing mTNF-alpha protein were determined in BLV-positive cows. These complex results regarding TNF-alpha gene expression in BLV-positive cows could be attributed to the presence of virus or viral protein/ proteins modifying the expression of the TNF-alpha gene.

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The Human T-Lymphotropic Virus Type 1 Tax Protein Inhibits Nonsense-Mediated mRNA Decay by Interacting with INT6/EIF3E and UPF1

Cited by 73 publications

References 67 publications

Expression of Alternatively Spliced Human T-Cell Leukemia Virus Type 1 mRNAs Is Influenced by Mitosis and by a Novel cis -Acting Regulatory Sequence

Expression of Alternatively Spliced Human T-Cell Leukemia Virus Type 1 mRNAs Is Influenced by Mitosis and by a Novel cis -Acting Regulatory Sequence

Permissive Sense and Antisense Transcription from the 5′ and 3′ Long Terminal Repeats of Human T-Cell Leukemia Virus Type 1

Polymorphism and expression of the tumour necrosis factor-alpha (TNF-alpha) gene in non-infected cows and in cows naturally infected with the bovine leukaemia virus (BLV)

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