Molecular Aspects of HTLV-1 Entry: Functional Domains of the HTLV-1 Surface Subunit (SU) and Their Relationships to the Entry Receptors

The initial step in retroviral infection involves specific interactions between viral envelope proteins (Env) and specific receptors on the surface of target cells. For many years, little was known about the entry receptors for HTLV-1. During this time, however, functional domains of the HTLV-1 Env were identified by analyzing the effects of neutralizing antibodies and specific mutations in Env on HTLV-1 infectivity. More recent studies have revealed that HTLV-1 infectivity involves interactions with three different molecules: heparan sulfate proteoglycans (HSPG), the VEGF-165 receptor Neuropilin 1 (NRP-1) and glucose transporter type 1 (GLUT1). Here, we revisit previously published data on the functional domains of Env in regard to the recent knowledge acquired about this multi-receptor complex. We also discuss the similarities and differences between HTLV-1 and other deltaretroviruses in regards to receptor usage

Involvement of microRNA machinery in retroviral replication

Les virus sont des parasites intracellulaires obligatoires, qui détournent la quasi-totalité des voies cellulaires. La voie des miRNA et du RNAi ne font pas exception. D'abord, les miRNA peuvent reconnaître les ARN viraux, permettant le recrutement de la machinerie du RNAi, en particulier AGO2, sur les messagers viraux, ce qui peut moduler la réplication du virus. Pendant ma thèse, nous avons identifié un nouveau moyen de recruter AGO2, sur les messagers viraux, qui n'impliquent pas les miRNA, ni sa capacité à induire l'extinction des gènes. Nous avons montré qu'AGO2 interagit avec GAG et se fixe aux ARN viraux par les séquences d'encapsidation. Ensuite, les virus peuvent moduler le répertoire de miRNA cellulaires, de sorte à créer un contexte favorable à sa propre réplication. Ainsi, nous avions pour objectif, d'identifier de nouveaux partenaires cellulaires de VIH. Nous avons alors analysé des données transcriptomiques, obtenues à partir de cellules infectées par VIH-1 ou VIH-2, et reconstitué des réseaux de régulations impliquant les facteurs de transcription et les miRNA. Nous avons montré que les modulations de miRNA dépendent du mode d'entrée du virus, en particulier de l'utilisation des co-récepteurs. De plus, l'approche de Biologie Intégrative que nous avons suivie, nous a permis de caractériser une nouvelle protéine cellulaire, capable de réguler l'expression du VIH et de restreindre sa réplication.Viruses are obligatory intracellular parasites that hijack many, if not all, cellular pathways. The RNA interference (RNAi) and the micro(mi)RNA pathways are no exceptions. First, cellular micro(mi)RNAs are able to recognize viral RNAs through imperfect micro-homologies. Similar to the miRNA-mediated repression of cellular translation, this recognition is thought to tether the RNAi machinery, in particular Argonaute(AGO)2, on viral messengers and eventually to modulate virus replication. During my PhD, we have unveiled another pathway by which AGO2 can interact with retroviral mRNAs without involving host miRNAs and translation repression. We have shown that AGO2 interacts with the retroviral GAG core proteins and preferentially binds unspliced retroviral RNAs through the RNA packaging sequences. The interaction between AGO2 and GAG, observed with both the Human Immunodeficiency Virus 1 (HIV-1) and the Primate Foamy Virus 1 (PFV-1), facilitates GAG multimerization and retroviral particle formation. Second, viruses modulate the miRNA repertoire presumably to create favorable conditions for viral replication. Hence, in order to identify novel cellular partners of HIV, we have analyzed transcriptomics data obtained from HIV1 and HIV-2-infected cells and reconstituted Transcription Factor- and miRNA-based regulation networks. Strikingly, we have noticed that the modulations of the transcriptome (coding and non-coding RNAs) depend on the mode of entry of the virus (i.e. co-receptor usage). Our in silico approach also helped us characterize a novel cellular protein able to regulate virus gene expression an

RNAi and retroviruses: are they in RISC?

International audienceRNA interference (RNAi) is a potent cellular system against viruses in various organisms. Although common traits are observed in plants, insects, and nematodes, the situation observed in mammals appears more complex. In mammalian somatic cells, RNAi is implicated in endonucleolytic cleavage mediated by artificially delivered small interfering RNAs (siRNAs) as well as in translation repression mediated by microRNAs (miRNAs). Because siRNAs and miRNAs recognize viral mRNAs, RNAi inherently limits virus production and participates in antiviral defense. However, several observations made in the cases of hepatitis C virus and retroviruses (including the human immunodeficiency virus and the primate foamy virus) bring evidence that this relationship is much more complex and that certain components of the RNAi effector complex [called the RNA-induced silencing complex (RISC)], such as AGO2, are also required for viral replication. Here, we summarize recent discoveries that have revealed this dual implication in virus biology. We further discuss their potential implications for the functions of RNAi-related proteins, with special emphasis on retrotransposition and genome stability

Retroviral GAG proteins recruit AGO2 on viral RNAs without affecting RNA accumulation and translation

International audienceCellular micro(mi)RNAs are able to recognize viral RNAs through imperfect micro-homologies. Similar to the miRNA-mediated repression of cellular translation, this recognition is thought to tether the RNAi machinery, in particular Argonaute 2 (AGO2) on viral messengers and eventually to modulate virus replication. Here, we unveil another pathway by which AGO2 can interact with retroviral mRNAs. We show that AGO2 interacts with the retroviral Group Specific Antigen (GAG) core proteins and preferentially binds unspliced RNAs through the RNA packaging sequences without affecting RNA stability or eliciting translation repression. Using RNAi experiments, we provide evidences that these interactions, observed with both the human immunodeficiency virus 1 (HIV-1) and the primate foamy virus 1 (PFV-1), are required for retroviral replication. Taken together, our results place AGO2 at the core of the retroviral life cycle and reveal original AGO2 functions that are not related to miRNAs and translation repression

Estrogen and retinoic acid antagonistically regulate several microRNA genes to control aerobic glycolysis in breast cancer cells.

International audienceIn addition to estrogen receptor modulators, retinoic acid and other retinoids are promising agents to prevent breast cancer. Retinoic acid and estrogen exert antagonistic regulations on the transcription of coding genes and we evaluated here whether these two compounds have similar effects on microRNAs. Using an integrative approach based on several bioinformatics resources together with experimental validations, we indeed found that retinoic acid positively regulates miR-210 and miR-23a/24-2 expressions and is counteracted by estrogen. Conversely, estrogen increased miR-17/92 and miR-424/450b expressions and is inhibited by retinoic acid. In silico functional enrichment further revealed that this combination of transcriptional/post-transcriptional regulations fully impacts on the molecular effects of estrogen and retinoic acid. Besides, we unveiled a novel effect of retinoic acid on aerobic glycolysis. We specifically showed that it increases extracellular lactate production, an effect counteracted by the miR-210 and the miR-23a/24-2, which simultaneously target lactate dehydrogenase A and B mRNAs. Together our results provide a new framework to better understand the estrogen/retinoic acid antagonism in breast cancer cells

Vitamin D induces interleukin-1β expression: paracrine macrophage epithelial signaling controls M. tuberculosis infection.

Although vitamin D deficiency is a common feature among patients presenting with active tuberculosis, the full scope of vitamin D action during Mycobacterium tuberculosis (Mtb) infection is poorly understood. As macrophages are the primary site of Mtb infection and are sites of vitamin D signaling, we have used these cells to understand the molecular mechanisms underlying modulation of the immune response by the hormonal form of vitamin D, 1,25-dihydroxyvitamin D (1,25D). We found that the virulent Mtb strain H37Rv elicits a broad host transcriptional response. Transcriptome profiling also revealed that the profile of target genes regulated by 1,25D is substantially altered by infection, and that 1,25D generally boosts infection-stimulated cytokine/chemokine responses. We further focused on the role of 1,25D- and infection-induced interleukin 1β (IL-1β) expression in response to infection. 1,25D enhanced IL-1β expression via a direct transcriptional mechanism. Secretion of IL-1β from infected cells required the NLRP3/caspase-1 inflammasome. The impact of IL-1β production was investigated in a novel model wherein infected macrophages were co-cultured with primary human small airway epithelial cells. Co-culture significantly prolonged survival of infected macrophages, and 1,25D/infection-induced IL-1β secretion from macrophages reduced mycobacterial burden by stimulating the anti-mycobacterial capacity of co-cultured lung epithelial cells. These effects were independent of 1,25D-stimulated autophagy in macrophages but dependent upon epithelial IL1R1 signaling and IL-1β-driven epithelial production of the antimicrobial peptide DEFB4/HBD2. These data provide evidence that the anti-microbial actions of vitamin D extend beyond the macrophage by modulating paracrine signaling, reinforcing its role in innate immune regulation in humans

Transcriptional repression of microRNA genes by PML-RARA increases expression of key cancer proteins in acute promyelocytic leukemia.

Micro(mi)RNAs are small noncoding RNAs that orchestrate many key aspects of cell physiology and their deregulation is often linked to distinct diseases including cancer. Here, we studied the contribution of miRNAs in a well-characterized human myeloid leukemia, acute promyelocytic leukemia (APL), targeted by retinoic acid and trioxide arsenic therapy. We identified several miRNAs transcriptionally repressed by the APL-associated PML-RAR oncogene which are released after treatment with all-trans retinoic acid. These coregulated miRNAs were found to control, in a coordinated manner, crucial pathways linked to leukemogenesis, such as HOX proteins and cell adhesion molecules whose expressions are thereby repressed by the chemotherapy. Thus, APL appears linked to transcriptional perturbation of miRNA genes, and clinical protocols able to successfully eradicate cancer cells may do so by restoring miRNA expression. The identification of abnormal miRNA biogenesis in cancer may therefore provide novel biomarkers and therapeutic targets in myeloid leukemias