Correction: The interferon stimulated gene 20 protein (ISG20) is an innate defense antiviral factor that discriminates self versus non-self translation

[This corrects the article DOI: 10.1371/journal.ppat.1008093.].

Is the HTLV-1 Retrovirus Targeted by Host Restriction Factors?

Human T cell leukemia virus type 1 (HTLV-1), the etiological agent of adult T cell leukemia/lymphoma (ATLL) and of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), was identified a few years before Human Immunodeficiency Virus (HIV). However, forty years later, our comprehension of HTLV-1 immune detection and the host immune responses to HTLV-1 is far more limited than for HIV. In addition to innate and adaptive immune responses that rely on specialized cells of the immune system, host cells may also express a range of antiviral factors that inhibit viral replication at different stages of the cycle, in a cell-autonomous manner. Multiple antiviral factors allowing such an intrinsic immunity have been primarily and extensively described in the context HIV infection. Here, we provide an overview of whether known HIV restriction factors might act on HTLV-1 replication. Interestingly, many of them do not exert any antiviral activity against HTLV-1, and we discuss viral replication cycle specificities that could account for these differences. Finally, we highlight future research directions that could help to identify antiviral factors specific to HTLV-1.

A novel domain within the CIL regulates egress of IFITM3 from the Golgi and reveals a regulatory role of IFITM3 on the secretory pathway

The InterFeron-Induced TransMembrane proteins (IFITMs) are members of the dispanin/CD225 family that act as broad viral inhibitors by preventing viral-to-cellular membrane fusion. In this study, we uncover egress from the Golgi as an important step in the biology of IFITM3 by identifying the domain that regulates this process and that similarly controls the egress of the dispanins IFITM1 and PRRT2, protein linked to paroxysmal kinesigenic dyskinesia. In the case of IFITM3, high levels of expression of wild-type, or mutations in the Golgi egress domain, lead to accumulation of IFITM3 in the Golgi and drive generalized glycoprotein trafficking defects. These defects can be relieved upon incubation with Amphotericin B, compound known to relieve IFITM-driven membrane fusion defects, as well as by v-SNARE overexpression, suggesting that IFITM3 interferes with membrane fusion processes important for Golgi functionalities. The comparison of glycoprotein trafficking in WT versus IFITMs-KO cells indicates that the modulation of the secretory pathway is a novel feature of IFITM proteins. Overall, our study defines a novel domain that regulates the egress of several dispanin/CD225 members from the Golgi and identifies a novel modulatory function for IFITM3.

Nipah virus W protein harnesses nuclear 14-3-3 to inhibit NF-κB-induced proinflammatory response

Nipah virus (NiV) is a highly pathogenic emerging bat-borne Henipavirus that has caused numerous outbreaks with public health concerns. It is able to inhibit the host innate immune response. Since the NF-κB pathway plays a crucial role in the innate antiviral response as a major transcriptional regulator of inflammation, we postulated its implication in the still poorly understood NiV immunopathogenesis. We report here that NiV inhibits the canonical NF-κB pathway via its nonstructural W protein. Translocation of the W protein into the nucleus causes nuclear accumulation of the cellular scaffold protein 14-3-3 in both African green monkey and human cells infected by NiV. Excess of 14-3-3 in the nucleus was associated with a reduction of NF-κB p65 subunit phosphorylation and of its nuclear accumulation. Importantly, W-S449A substitution impairs the binding of the W protein to 14-3-3 and the subsequent suppression of NF-κB signaling, thus restoring the production of proinflammatory cytokines. Our data suggest that the W protein increases the steady-state level of 14-3-3 in the nucleus and consequently enhances 14-3-3-mediated negative feedback on the NF-κB pathway. These findings provide a mechanistic model of W-mediated disruption of the host inflammatory response, which could contribute to the high severity of NiV infection.

Microbial Biofilms: Human T-cell Leukemia Virus Type 1 First in Line for Viral Biofilm but Far Behind Bacterial Biofilms

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). To date, it is the unique published example of a virus able to form a biofilm at the surface of infected cells. Deeply studied in bacteria, bacterial biofilms represent multicellular assemblies of bacteria in contact with a surface and shielded by the extracellular matrix (ECM). Microbial lifestyle in biofilms, either viral or bacterial, is opposed structurally and physiologically to an isolated lifestyle, in which viruses or bacteria freely float in their environment. HTLV-1 biofilm formation is believed to be promoted by viral proteins, mainly Tax, through remodeling of the ECM of the infected cells. HTLV-1 biofilm has been linked to cell-to-cell transmission of the virus. However, in comparison to bacterial biofilms, very little is known on kinetics of viral biofilm formation or dissemination, but also on its pathophysiological roles, such as escape from immune detection or therapeutic strategies, as well as promotion of leukemogenesis. The switch between production of cell-free isolated virions and cell-associated viral biofilm, although not fully apprehended yet, remains a key step to understand HTLV-1 infection and pathogenesis.

SQSTM-1/p62 potentiates HTLV-1 Tax-mediated NF-κB activation through its ubiquitin binding function

The NF-κB pathway is constitutively activated in adult T cell leukemia, an aggressive malignancy caused by Human T Leukemia Virus type 1 (HTLV-1). The viral oncoprotein Tax triggers this constitutive activation by interacting with the ubiquitin-rich IKK complex. We previously demonstrated that Optineurin and TAX1BP1, two members of the ubiquitin-binding, Sequestosome-1 (SQSTM-1/p62)-like selective autophagy receptor family, are involved in Tax-mediated NF-κB signaling. Here, using a proximity-dependent biotinylation approach (BioID), we identify p62 as a new candidate partner of Tax and confirm the interaction in infected T cells. We then demonstrate that p62 knock-out in MEF cells as well as p62 knock-down in HEK293T cells significantly reduces Tax-mediated NF-κB activity. We further show that although p62 knock-down does not alter NF-κB activation in Jurkat T cells nor in infected T cells, p62 does potentiate Tax-mediated NF-κB activity upon over-expression in Jurkat T cells. We next show that p62 associates with the Tax/IKK signalosome in cells, and identify the 170–206 domain of p62 as sufficient for the direct, ubiquitin-independent interaction with Tax. However, we observe that this domain is dispensable for modulating Tax activity in cells, and functional analysis of p62 mutants indicates that p62 could potentiate Tax activity in cells by facilitating the association of ubiquitin chains with the Tax/IKK signalosome. Altogether, our results identify p62 as a new ubiquitin-dependent modulator of Tax activity on NF-κB, further highlighting the importance of ubiquitin in the signaling activity of the viral Tax oncoprotein.

The interferon stimulated gene 20 protein (ISG20) is an innate defense antiviral factor that discriminates self versus non-self translation

ISG20 is a broad spectrum antiviral protein thought to directly degrade viral RNA. However, this mechanism of inhibition remains controversial. Using the Vesicular Stomatitis Virus (VSV) as a model RNA virus, we show here that ISG20 interferes with viral replication by decreasing protein synthesis in the absence of RNA degradation. Importantly, we demonstrate that ISG20 exerts a translational control over a large panel of non-self RNA substrates including those originating from transfected DNA, while sparing endogenous transcripts. This activity correlates with the protein's ability to localize in cytoplasmic processing bodies. Finally, these functions are conserved in the ISG20 murine ortholog, whose genetic ablation results in mice with increased susceptibility to viral infection. Overall, our results posit ISG20 as an important defense factor able to discriminate the self/non-self origins of the RNA through translation modulation.

[Viral oncogenesis and genomic instability: the centr(osom)al connection]

Currently, more than 10% of human cancers are associated with viral infection. Studies on oncoviruses led to the development of clinical intervention strategies and elucidated fundamental cellular events altered upon cell transformation. Cancer cells exhibit several hallmarks including genomic instability, defined as a high frequency of mutations including gain or loss of chromosomes. The centrosome is an organelle that governs mitotic chromosome segregation and that functions as a signaling platform downstream of the DNA damage response. Here, we review the current literature to highlight how oncoviruses induce genomic instability via the deregulation of the centrosome. Viral interference with the centrosome duplication cycle, leading to centrosome amplification, is illustrated, with a special emphasis on mechanisms shared by several viral families. In addition, we discuss how oncoviruses could alter the signaling functions of the centrosome, and we comment on the bibliographic gaps that could be addressed by future research.

Viral oncogenesis and genomic instability: the centr(osom)al connection

Currently, more than 10% of human cancers are associated with viral infection. Studies on oncoviruses led to the development of clinical intervention strategies and elucidated fundamental cellular events altered upon cell transformation. Cancer cells exhibit several hallmarks including genomic instability, defined as a high frequency of mutations including gain or loss of chromosomes. The centrosome is an organelle that governs mitotic chromosome segregation and that functions as a signaling platform downstream of the DNA damage response. Here, we review the current literature to highlight how oncoviruses induce genomic instability via the deregulation of the centrosome. Viral interference with the centrosome duplication cycle, leading to centrosome amplification, is illustrated, with a special emphasis on mechanisms shared by several viral families. In addition, we discuss how oncoviruses could alter the signaling functions of the centrosome, and we comment on the bibliographic gaps that could be addressed by future research.

TRAF3 Is Required for NF-κB Pathway Activation Mediated by HTLV Tax Proteins

Human T-cell leukemia viruses type 1 (HTLV-1) and type 2 (HTLV-2) share a common genome organization and expression strategy but have distinct pathological properties. HTLV-1 is the etiological agent of Adult T-cell Leukemia (ATL) and of HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP), whereas HTLV-2 does not cause hematological disorders and is only sporadically associated with cases of subacute myelopathy. Both HTLV genomes encode two regulatory proteins that play a pivotal role in pathogenesis: the transactivating Tax-1 and Tax-2 proteins and the antisense proteins HBZ and APH-2, respectively. We recently reported that Tax-1 and Tax-2 form complexes with the TNF-receptor associated factor 3, TRAF3, a negative regulator of the non-canonical NF-κB pathway. The NF-κB pathway is constitutively activated by the Tax proteins, whereas it is inhibited by HBZ and APH-2. The antagonistic effects of Tax and antisense proteins on NF-κB activation have not yet been fully clarified. Here, we investigated the effect of TRAF3 interaction with HTLV regulatory proteins and in particular its consequence on the subcellular distribution of the effector p65/RelA protein. We demonstrated that Tax-1 and Tax-2 efficiency on NF-κB activation is impaired in TRAF3 deficient cells obtained by CRISPR/Cas9 editing. We also found that APH-2 is more effective than HBZ in preventing Tax-dependent NF-κB activation. We further observed that TRAF3 co-localizes with Tax-2 and APH-2 in cytoplasmic complexes together with NF-κB essential modulator NEMO and TAB2, differently from HBZ and TRAF3. These results contribute to untangle the mechanism of NF-κB inhibition by HBZ and APH-2, highlighting the different role of the HTLV-1 and HTLV-2 regulatory proteins in the NF-κB activation.

STLV-1 co-infection is correlated with an increased SFV proviral load in the peripheral blood of SFV/STLV-1 naturally infected non-human primates

Simian T-Leukemia Virus type 1 and Simian Foamy Virus infect non-human primates. While STLV-1, as HTLV-1, causes Adult T-cell Leukemia/lymphoma, SFV infection is asymptomatic. Both retroviruses can be transmitted from NHPs to humans through bites that allow contact between infected saliva and recipient blood. Because both viruses infect CD4+ T-cells, they might interfere with each other replication, and this might impact viral transmission. Impact of STLV-1 co-infection on SFV replication was analyzed in 18 SFV-positive/STLV-1-negative and 18 naturally SFV/STLV-1 co-infected Papio anubis. Even if 9 animals were found STLV-1-positive in saliva, STLV-1 PVL was much higher in the blood. SFV proviruses were detected in the saliva of all animals. Interestingly, SFV proviral load was much higher in the blood of STLV-1/SFV co-infected animals, compared to STLV-1-negative animals. Given that soluble Tax protein can enter uninfected cells, we tested its effect on foamy virus promoter and we show that Tax protein can transactivate the foamy LTR. This demonstrates that true STLV-1 co-infection or Tax only has an impact on SFV replication and may influence the ability of the virus to be zoonotically transmitted as well as its ability to promote hematological abnormalities.

Foamy viruses infect a lot of mammalian hosts including non-human primates (NHP) and humans. Foamy infection is not associated with disease, although a recent report described hematological abnormalities in infected humans. Some NHP species are also naturally infected with another retrovirus i.e. Simian T lymphotropic virus type 1, while humans are infected with the Human T lymphotropic virus type 1 counterpart. Both viruses cause leukemia. Here we report that natural foamy/STLV-1 co-infection is associated with a higher foamy virus proviral load in blood. Co-infected animals might therefore present a higher risk of developing hematological disease.

How to Control HTLV-1-Associated Diseases: Preventing de Novo Cellular Infection Using Antiviral Therapy

Five to ten million individuals are infected by Human T-cell Leukemia Virus type 1 (HTLV-1). HTLV-1 is transmitted through prolonged breast-feeding, by sexual contacts and by transmission of infected T lymphocytes through blood transfusion. One to ten percent of infected carriers will develop a severe HTLV-1-associated disease: Adult-T-cell leukemia/lymphoma (ATLL), or a neurological disorder named Tropical Spastic Paraparesis/HTLV-1 Associated Myelopathy (TSP/HAM). In vivo, HTLV-1 is mostly detected in CD4⁺ T-cells, and to a lesser extent in CD8⁺ T cells and dendritic cells. There is a strong correlation between HTLV-1 proviral load (PVL) and clinical status of infected individuals. Thus, reducing PVL could be part of a strategy to prevent or treat HTLV-1-associated diseases among carriers. Treatment of ATLL patients using conventional chemotherapy has very limited benefit. Some chronic and acute ATLL patients are, however, efficiently treated with a combination of interferon α and zidovudine (IFN-α/AZT), to which arsenic trioxide is added in some cases. On the other hand, no efficient treatment for TSP/HAM patients has been described yet. It is therefore crucial to develop therapies that could either prevent the occurrence of HTLV-1-associated diseases or at least block the evolution of the disease in the early stages. In vivo, reverse transcriptase (RT) activity is low in infected cells, which is correlated with a clonal mode of viral replication. This renders infected cells resistant to nucleoside RT inhibitors such as AZT. However, histone deacetylase inhibitors (HDACi) associated to AZT efficiently induces viral expression and prevent de novo cellular infection. In asymptomatic STLV-1 infected non-human primates, HDACi/AZT combination allows a strong decrease in the PVL. Unfortunately, rebound in the PVL occurs when the treatment is stopped, highlighting the need for better antiviral compounds. Here, we review previously used strategies targeting HTLV-1 replication. We also tested a series of HIV-1 RT inhibitors in an in vitro anti-HTLV-1 screen, and report that bis-POM-PMEA (adefovir dipivoxil) and bis-POC-PMPA (tenofovir disoproxil) are much more efficient compared to AZT to decrease HTLV-1 cell-to-cell transmission in vitro. Our results suggest that revisiting already established antiviral drugs is an interesting approach to discover new anti-HTLV-1 drugs.

Correction: Dendritic cell maturation, but not type I interferon exposure, restricts infection by HTLV-1, and viral transmission to T-cells

[This corrects the article DOI: 10.1371/journal.ppat.1006353.].

Dendritic cell maturation, but not type I interferon exposure, restricts infection by HTLV-1, and viral transmission to T-cells

Human T lymphotropic Virus type 1 (HTLV-1) is the etiological agent of Adult T cell Leukemia/Lymphoma (ATLL) and HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). Both CD4⁺ T-cells and dendritic cells (DCs) infected with HTLV-1 are found in peripheral blood from HTLV-1 carriers. We previously demonstrated that monocyte-derived IL-4 DCs are more susceptible to HTLV-1 infection than autologous primary T-cells, suggesting that DC infection precedes T-cell infection. However, during blood transmission, breast-feeding or sexual transmission, HTLV-1 may encounter different DC subsets present in the blood, the intestinal or genital mucosa respectively. These different contacts may impact HTLV-1 ability to infect DCs and its subsequent transfer to T-cells. Using in vitro monocyte-derived IL-4 DCs, TGF-β DCs and IFN-α DCs that mimic DCs contacting HTLV-1 in vivo, we show here that despite their increased ability to capture HTLV-1 virions, IFN-α DCs restrict HTLV-1 productive infection. Surprisingly, we then demonstrate that it is not due to the antiviral activity of type–I interferon produced by IFN-α DCs, but that it is likely to be linked to a distinct trafficking route of HTLV-1 in IL-4 DCs vs. IFN-α DCs. Finally, we demonstrate that, in contrast to IL-4 DCs, IFN-α DCs are impaired in their capacity to transfer HTLV-1 to CD4 T-cells, both after viral capture and trans-infection and after their productive infection. In conclusion, the nature of the DCs encountered by HTLV-1 upon primo-infection and the viral trafficking route through the vesicular pathway of these cells determine the efficiency of viral transmission to T-cells, which may condition the fate of infection.

Human T-Lymphotropic Virus type 1 (HTLV-1) is the etiological agent of Adult T-cell Leukemia/Lymphoma (ATLL) and HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). In chronically infected patients, the provirus is mainly detected in the CD4⁺ T-cell population. However, beside lymphocytes, HTLV-1 infects blood or monocyte-derived dendritic cells (DCs) in vitro. Moreover, we previously showed that DCs are more susceptible to HTLV-1 infection than autologous T-cells, suggesting that DCs might be the first cells to be infected upon primo-infection, and important intermediaries for the viral spread to surrounding lymphocytes. Interestingly, different DC subsets are found in the blood or in the mucosa, the two entry routes used by HTLV-1 during infection of new individuals. In this study, we show for the first time that the different DC subsets are not equally susceptible to HTLV-1 infection. Furthermore we demonstrate that DC subsets with an increased ability to capture HTLV-1 virion are restricted to HTLV-1 productive infection. This restriction is linked to DC maturation but not to the antiviral activity of IFN-α produced by resistant DCs. Finally, we demonstrate that efficient viral transmission to T-cells is dependent upon DC productive infection rather than trans-infection. Altogether, our results indicate that the nature of the DCs encountered by HTLV-1 upon primo-infection determines the efficiency of viral transmission to T-cells, which may condition the fate of infection.

ADAR1 enhances HTLV-1 and HTLV-2 replication through inhibition of PKR activity

Background

The role of innate immunity in general and of type I interferon (IFN-I) in particular in HTLV-1 pathogenesis is still a matter of debate. ADAR1-p150 is an Interferon Stimulated Gene (ISG) induced by IFN-I that can edit viral RNAs. We therefore investigated whether it could play the role of an anti-HTLV factor.

Results

We demonstrate here that ADAR1 is also expressed in the absence of IFN stimulation in activated primary T-lymphocytes that are the natural target of this virus and in HTLV-1 or HTLV-2 chronically infected T-cells. ADAR1 expression is also increased in primary lymphocytes obtained from HTLV-1 infected individuals. We show that ADAR1 enhances HTLV-1 and HTLV-2 infection in T-lymphocytes and that this proviral effect is independent from its editing activity. ADAR1 expression suppresses IFN-α inhibitory effect on HTLV-1 and HTLV-2 and acts through the repression of PKR phosphorylation.

Discussion

This study demonstrates that two interferon stimulated genes, i.e. PKR and ADAR1 have opposite effects on HTLV replication in vivo. The balanced expression of those proteins could determine the fate of the viral cycle in the course of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0093-9) contains supplementary material, which is available to authorized users.

Alpha interferon restricts human T-lymphotropic virus type 1 and 2 de novo infection through PKR activation

Type I interferon (IFN-I) inhibits the replication of different viruses. However, the effect of IFN-I on the human T-lymphotropic virus type 1 (HTLV-1) viral cycle is controversial. Here, we investigated the consequences of IFN-α addition for different steps of HTLV-1 and HTLV-2 infection. We first show that alpha interferon (IFN-α) efficiently impairs HTLV-1 and HTLV-2 de novo infection in a T cell line and in primary lymphocytes. Using pseudotyped viruses expressing HTLV-1 envelope, we then show that cell-free infection is insensitive to IFN-α, demonstrating that the cytokine does not affect the early stages of the viral cycle. In contrast, intracellular levels of Gag, Env, or Tax protein are affected by IFN-α treatment in T cells, primary lymphocytes, or 293T cells transfected with HTLV-1 or HTLV-2 molecular clones, demonstrating that IFN-α acts during the late stages of infection. We show that IFN-α does not affect Tax-mediated transcription and acts at a posttranscriptional level. Using either small interfering RNA (siRNA) directed against PKR or a PKR inhibitor, we demonstrate that PKR, whose expression is induced by interferon, plays a major role in IFN-α-induced HTLV-1/2 inhibition. These results indicate that IFN-α has a strong repressive effect on the HTLV-1 and HTLV-2 viral cycle during de novo infection of cells that are natural targets of the viruses.

Combination of arsenic and interferon-α inhibits expression of KSHV latent transcripts and synergistically improves survival of mice with primary effusion lymphomas

Background

Kaposi sarcoma-associated herpesvirus (KSHV) is the etiologic agent of primary effusion lymphomas (PEL). PEL cell lines infected with KSHV, but negative for Epstein-Barr virus have a tumorigenic potential in non-obese diabetic/severe combined immunodeficient mice and result in efficient engraftment and formation of malignant ascites with notable abdominal distension, consistent with the clinical manifestations of PEL in humans.

Methodology/Principal Findings

Using this preclinical mouse model, we demonstrate that the combination of arsenic trioxide and interferon-alpha (IFN) inhibits proliferation, induces apoptosis and downregulates the latent viral transcripts LANA-1, v-FLIP and v-Cyc in PEL cells derived from malignant ascites. Furthermore, this combination decreases the peritoneal volume and synergistically increases survival of PEL mice.

Conclusion/Significance

These results provide a promising rationale for the therapeutic use of arsenic/IFN in PEL patients.

[Human retrovirus XMRV: The end of an exciting story?]

Viruses represent an important cause of cancer in humans: infections are estimated to account for close to one cancer case out of five.With the ongoing discovery of new infectious agents, this number should be raising in the near future. In 2006, the discovery of a new _-retrovirus in prostate cancer biopsies launched an intense research activity: could this new xenotropic MLV-related virus (XMRV) be the cause of prostate cancer? Five years later, the initial enthusiasm of retrovirologists has dramatically diminished. One by one, arguments favouring the hypothesis of human infection with XMRV are being refuted. The aim of this review article is to present the discovery of XMRV and to analyze recent data arguing against its existence in humans. A synthetic interpretation of XMRV literature will then be suggested.

HTLV-1 and innate immunity

Innate immunity plays a critical role in the host response to a viral infection. The innate response has two main functions. First, it triggers effector mechanisms that restrict the infection. Second, it primes development of the adaptive response, which completes the elimination of the pathogen or of infected cells. In vivo, HTLV-1 infects T lymphocytes that participate in adaptive immunity but also monocytes and dendritic cells that are major players in innate immunity. Herein, we will review the interplay between HTLV-1 and innate immunity. Particular emphasis is put on HTLV-1-induced alteration of type-I interferon (IFN-I) function. In vitro, the viral Tax protein plays a significant role in the alteration of IFN synthesis and signaling. Despite this, IFN-I/AZT treatment of Adult T-cell Leukemia/Lymphoma (ATLL) patients leads to complete remission. We will discuss a model in which exogenous IFN-I could act both on the microenvironment of the T-cells to protect them from infection, and also on infected cells when combined with other drugs that lead to Tax down-regulation/degradation.

NRP/Optineurin Cooperates with TAX1BP1 to potentiate the activation of NF-kappaB by human T-lymphotropic virus type 1 tax protein

Nuclear factor (NF)-κB is a major survival pathway engaged by the Human T-Lymphotropic Virus type 1 (HTLV-1) Tax protein. Tax1 activation of NF-κB occurs predominantly in the cytoplasm, where Tax1 binds NF-κB Essential Modulator (NEMO/IKKγ) and triggers the activation of IκB kinases. Several independent studies have shown that Tax1-mediated NF-κB activation is dependent on Tax1 ubiquitination. Here, we identify by co-immunoprecipitation assays NEMO-Related Protein (NRP/Optineurin) as a binding partner for Tax1 in HTLV-1 infected and Tax1/NRP co-expressing cells. Immunofluorescence studies reveal that Tax1, NRP and NEMO colocalize in Golgi-associated structures. The interaction between Tax1 and NRP requires the ubiquitin-binding activity of NRP and the ubiquitination sites of Tax1. In addition, we observe that NRP increases the ubiquitination of Tax1 along with Tax1-dependent NF-κB signaling. Surprisingly, we find that in addition to Tax1, NRP interacts cooperatively with the Tax1 binding protein TAX1BP1, and that NRP and TAX1BP1 cooperate to modulate Tax1 ubiquitination and NF-κB activation. Our data strongly suggest for the first time that NRP is a critical adaptor that regulates the assembly of TAX1BP1 and post-translationally modified forms of Tax1, leading to sustained NF-κB activation.

Oncogenic viruses (i.e., viruses that can induce cancer) have usually been found to deregulate several cellular signaling pathways controlling cell survival and proliferation. Among those, the NF-κB pathway is particularly important. In this study, we focus on the Human T-Lymphotropic Virus type 1 (HTLV-1), which infects immune T cells, and is associated with the development of a severe hematological disease, termed adult T cell leukemia. The viral Tax oncoprotein is known to activate the NF-κB pathway, but the precise mechanism is still under investigation. In cells, proteins can undergo modifications that can modulate their function. In the case of Tax, a modified form of the protein (ubiquitinated Tax) is able to activate the NF-κB pathway. Our aim was to identify cellular proteins that participate in the modification of Tax, and in turn in the regulation of its function. We show for the first time that the cellular protein NRP/Optineurin interacts with Tax and increases its ubiquitination, thus leading to an enhanced NF-κB activation. We further demonstrate that TAX1BP1, another cellular protein that had been previously identified as a partner of Tax, also participates in this regulation. Thus, this study uncovers new actors of the virally induced cell signaling.

HTLV gene regulation: because size matters, transcription is not enough

Despite being discovered in animals in the early 20th century, the scientific interest in retroviruses was boosted with the discovery of human retroviruses (human T-leukemia/lymphoma virus [HTLV] and HIV), which are responsible for significant morbidity and mortality. HTLV was identified more than 25 years ago as the etiological agent of adult T-cell leukemia/lymphoma. It was then shown to be a complex retrovirus, given that it not only encodes the characteristic retroviral Gag, Pol and Env proteins, but also regulatory and accessory proteins. Since the first studies documenting the role of these proteins in viral expression, the picture has become increasingly more complex. Indeed, owing to the limited size of its genome that contains overlapping open-reading frames, HTLV has evolved unique ways to regulate its expression. Retroviral expression was originally thought to be mainly controlled through the regulation of transcription from the 5 long-terminal repeats, but we now know that the 3 long-terminal repeats also serve as promoters. Regulation of splicing and mRNA export, and post-translational modifications of viral protein also play a major role. This review discusses the latest insights gained into the field of HTLV gene expression.

[Viruses and interferon: mechanisms of interferon induction and strategies to escape interferon response]

Pathogen intrusion triggers an immediate host response leading in most cases to the elimination of the microbe. Type-I interferons (IFN-a/b) production and release is a major event in innate antiviral immunity through the establishment of an antiviral state in neighbouring cells. IFN production depends on the interaction between viral PAMPs (pathogen-associated molecular patterns) and their corresponding cellular sensors-also called PRRs (pattern recognition receptors)-either from membranous (Toll-like receptors) or cytosolic (RIG-I helicase) origin. Activated PRRs can recruit downstream partners in order to activate the IRF-3/7, AP1 and NF-jB transcription factors which drive the synthesis of IFN-a/b and inflammatory cytokines. Following binding to their cognate receptor, they activate a signaling cascade (Jak/STAT pathway) that leads to the synthesis of proteins endowed with antiviral or immunomodulatory properties. However, viruses have evolved diverse strategies to escape the IFN response.

Laticola dae n. sp. (Monogenea: Diplectanidae) from Epinephelus maculatus (Perciformes: Serranidae) off New Caledonia

Laticola dae n. sp. is described from specimens collected from the gill-filaments of the highfin grouper Epinephelus maculatus, a coral reef fish caught off Nouméa, New Caledonia, South Pacific. The species is characterised by a spoon-shaped sclerotised male copulatory organ, with four thin walls and 73-[Formula: see text]m in outer length, and a sclerotised vagina in form of a disc, 16-[Formula: see text]m in diameter, with a smaller hemisphere on one side. Laticola Yang et al., 2006 was described to accommodate diplectanids from Lates calcarifer (Centropomidae); this is the first Laticola described from a serranid. Other diplectanids, including several species of Pseudorhabdosynochus Yamaguti, 1958, were also found on the same species of fish; specimens of L. dae represented about half of the diplectanids collected; all other species were rare.