BAG6 promotes PINK1 signaling pathway and is essential for mitophagy.

Bcl-2-associated athanogen-6 (BAG6) is a nucleocytoplasmic shuttling protein involved in protein quality control. We previously demonstrated that BAG6 is essential for autophagy by regulating the intracellular localization of the acetyltransferase EP300, and thus, modifying accessibility to its substrates (TP53 in the nucleus and autophagy-related proteins in the cytoplasm). Here, we investigated BAG6 localization and function in the cytoplasm. First, we demonstrated that BAG6 is localized in the mitochondria. Specifically, BAG6 is expressed in the mitochondrial matrix under basal conditions, and translocates to the outer mitochondrial membrane after mitochondrial depolarization with carbonyl cyanide m-chlorophenyl hydrazine, a mitochondrial uncoupler that induces mitophagy. In SW480 cells, the deletion of BAG6 expression abrogates its ability to induce mitophagy and PINK1 accumulation. On the reverse, its ectopic expression in LoVo colon cancer cells, which do not express endogenous BAG6, reduces the size of the mitochondria, induces mitophagy, leads to the activation of the PINK1/PARKIN pathway and to the phospho-ubiquitination of mitochondrial proteins. Finally, BAG6 contains two LIR (LC3-interacting Region) domains specifically found in receptors for selective autophagy and responsible for the interaction with LC3 and for autophagosome selectivity. Site-directed mutagenesis showed that BAG6 requires wild-type LIRs domains for its ability to stimulate mitophagy. In conclusion, we propose that BAG6 is a novel mitophagy receptor or adaptor that induces PINK1/PARKIN signaling and mitophagy in a LIR-dependent manner.

HIV-1 Env induces pexophagy and an oxidative stress leading to uninfected CD4+ T cell death.

The immunodeficiency observed in HIV-1-infected patients is mainly due to uninfected bystander CD4+ T lymphocyte cell death. The viral envelope glycoproteins (Env), expressed at the surface of infected cells, play a key role in this process. Env triggers macroautophagy/autophagy, a process necessary for subsequent apoptosis, and the production of reactive oxygen species (ROS) in bystander CD4+ T cells. Here, we demonstrate that Env-induced oxidative stress is responsible for their death by apoptosis. Moreover, we report that peroxisomes, organelles involved in the control of oxidative stress, are targeted by Env-mediated autophagy. Indeed, we observe a selective autophagy-dependent decrease in the expression of peroxisomal proteins, CAT and PEX14, upon Env exposure; the downregulation of either BECN1 or SQSTM1/p62 restores their expression levels. Fluorescence studies allowed us to conclude that Env-mediated autophagy degrades these entire organelles and specifically the mature ones. Together, our results on Env-induced pexophagy provide new clues on HIV-1-induced immunodeficiency.Abbreviations: Ab: antibodies; AF: auranofin; AP: anti-proteases; ART: antiretroviral therapy; BafA1: bafilomycin A1; BECN1: beclin 1; CAT: catalase; CD4: CD4 molecule; CXCR4: C-X-C motif chemokine receptor 4; DHR123: dihydrorhodamine 123; Env: HIV-1 envelope glycoproteins; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; GFP-SKL: GFP-serine-lysine-leucine; HEK: human embryonic kidney; HIV-1: type 1 human immunodeficiency virus; HTRF: homogeneous time resolved fluorescence; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; NAC: N-acetyl-cysteine; PARP: poly(ADP-ribose) polymerase; PEX: peroxin; ROS: reactive oxygen species; siRNA: small interfering ribonucleic acid; SQSTM1/p62: sequestosome 1.

HIV-1 Vpr inhibits autophagy during the early steps of infection of CD4 T cells.

BACKGROUND INFORMATION: Autophagy is induced during HIV-1 entry into CD4 T cells by the fusion of the membranes triggered by the gp41 envelope glycoprotein. This anti-HIV-1 mechanism is inhibited by the viral infectivity factor (Vif) neosynthesized after HIV-1 integration to allow viral replication. However, autophagy is very rapidly controlled after HIV-1 entry by a still unknown mechanism. As HIV-1 viral protein R (Vpr) is the only auxiliary protein found within the virion in substantial amount, we studied its capability to control the early steps of HIV-1 envelope-mediated autophagy. RESULTS: We demonstrated that ectopic Vpr inhibits autophagy in both the Jurkat CD4 T cell line and HEK.293T cells. Interestingly, Vpr coming from the virus also blocks autophagy in CD4 T cells, the main cell target of HIV-1. Furthermore, Vpr decreases the expression level of two essential autophagy proteins (ATG), LC3B and Beclin-1, and an important autophagy-related protein, BNIP3 as well as the level of their mRNA. We also demonstrated in HEK.293T cells that Vpr degrades the FOXO3a transcription factor through the ubiquitin proteasome system. CONCLUSION: Vpr, the only well-expressed HIV-1 auxiliary protein incorporated into viruses, is able to negatively control autophagy induced during HIV-1 entry into CD4 T cells. SIGNIFICANCE: We provide insights of how HIV-1 controls autophagy very early after its entry into CD4 T cells and discovered a new function of Vpr. These results open the route to a better understanding of the roles of Vpr during HIV-1 infection through FOXO3a degradation and could be important to consider additional therapies that counteract the role of Vpr on autophagy.

[LAP (LC3-associated phagocytosis): phagocytosis or autophagy?] / La phagocytose associée à LC3 (LAP) - Phagocytose ou autophagie ?

Phagocytosis and macroautophagy, named here autophagy, are two essential mechanisms of lysosomal degradation of diverse cargos into membrane structures. Both mechanisms are involved in immune regulation and cell survival. However, phagocytosis triggers degradation of extracellular material whereas autophagy engulfs only cytoplasmic elements. Furthermore, activation and maturation of these two processes are different. LAP (LC3-associated phagocytosis) is a form of phagocytosis that uses components of the autophagy pathway. It can eliminate (i) pathogens, (ii) immune complexes, (iii) threatening neighbouring cells, dead or alive, and (iv) cell debris, such as POS (photoreceptor outer segment) and the midbody released at the end of mitosis. Cells have thus optimized their means of elimination of dangerous components by sharing some fundamental elements coming from the two main lysosomal degradation pathways.

TITLE: La phagocytose associée à LC3 (LAP) - Phagocytose ou autophagie ? ABSTRACT: Phagocytose et macroautophagie, appelée ici autophagie, sont deux mécanismes essentiels de dégradation lysosomale de divers cargos englobés dans des structures membranaires. Ils sont tous deux impliqués dans la régulation du système immunitaire et la survie cellulaire. Cependant, la phagocytose permet l'ingestion de matériel extracellulaire alors que l'autophagie dégrade des composants intra-cytoplasmiques, avec des mécanismes d'activation et de maturation différents. La LAP (LC3-associated phagocytosis) est une forme particulière de phagocytose qui utilise certains éléments de l'autophagie. Elle permet l'élimination de pathogènes, de complexes immuns, de cellules avoisinantes, mortes ou vivantes, constituant un danger pour l'organisme, et de débris cellulaires, tels que les segments externes des photorécepteurs (POS, photoreceptor outer segment), ou la pièce centrale du pont intercellulaire produit en fin de mitose. Les cellules ont ainsi « optimisé ¼ leurs moyens d'éliminer les composés potentiellement dangereux en partageant certains éléments essentiels des deux voies de dégradation lysosomale.

Peptides derived from evolutionarily conserved domains in Beclin-1 and Beclin-2 enhance the entry of lentiviral vectors into human cells.

Autophagy-related proteins such as Beclin-1 are involved in an array of complex processes, including antiviral responses, and may also modulate the efficiency of gene therapy viral vectors. The Tat-Beclin-1 (TB1) peptide has been reported as an autophagy-inducing factor inhibiting the replication of pathogens such as HIV, type 1 (HIV-1). However, autophagy-related proteins are also essential for the early steps of HIV-1 infection. Therefore, we examined the effects of the Beclin-1 evolutionarily conserved domain in TB1 on viral transduction and autophagy in single-round HIV infection or with nonreplicative HIV-1-derived lentiviral vectors. TB1 enhanced transduction with various pseudotypes but without inducing the autophagy process. TB1 augmented the transduction of human CD34+ hematopoietic stem/progenitor cells while maintaining their capacity to engraft in vivo into humanized mice. TB1 was as effective as other transduction additives and functioned by enhancing the adhesion and fusion of viral particles with target cells but not their aggregation. We also found that the N-terminal L1 loop was critical for TB1 transduction-enhancing activity. Interestingly, the Tat-Beclin-2 (TB2) peptide, derived from the human Beclin-2 protein, was even more potent than TB1 in promoting viral transduction and infection. Taken together, our findings suggest that the TB1 and TB2 peptides enhance the viral entry step. Tat-Beclin peptides therefore represent a new family of viral transduction enhancers for potential use in gene therapy.

HIV-1 viral infectivity factor interacts with microtubule-associated protein light chain 3 and inhibits autophagy.

OBJECTIVE: Autophagy, an important antiviral process triggered during HIV-1 entry by gp41-dependent membrane fusion, is repressed in infected CD4+ T cells by an unknown mechanism. The aim of this study was to identify the role of viral infectivity factor (Vif) in the autophagy blockade. DESIGN/METHODS: To determine the role of Vif in autophagy inhibition, we used cell lines that express CD4 and CXCR4 and primary CD4+ T cells. Pull-down experiments, immunoprecipitation assays and computational analyses were performed to analyze the interaction between Vif and microtubule-associated protein light chain 3B (LC3B), a major autophagy component, in presence or absence of the antiviral host factor apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G), after HIV-1 infection or ectopic expression of Vif. Autophagy was analyzed after infection by viruses expressing Vif (NL4.3) or not (NL4.3[DELTA]Vif), or after exogenous Vif expression. RESULTS: We demonstrate that the C-terminal part of Vif interacts directly with LC3B, independently of the presence of APOBEC3G.Vif binds to pro-LC3 and autophagy-related protein 4-cleaved LC3 forms, and glycine 120, the amino acid conjugated to phosphatidylethanolamine on autophagosomes, is required. Importantly, we evidence that Vif inhibits autophagy during HIV-1 infection. Indeed, autophagy is detected in target cells infected by NL4.3[DELTA]Vif, but prevented in cells infected by NL4.3. Furthermore, autophagy triggered in NL4.3[DELTA]Vif-infected cells is inhibited when Vif is expressed in trans but is still active when target cells express a mutant of Vif that binds weakly to LC3B. CONCLUSION: Our study unveils that Vif inhibits autophagy independently of its action on APOBEC3G and, therefore, suggest a new function of this viral protein in restricting innate antiviral mechanisms.

MAPK14/p38α confers irinotecan resistance to TP53-defective cells by inducing survival autophagy.

Recently we have shown that the mitogen-activated protein kinase (MAPK) MAPK14/p38α is involved in resistance of colon cancer cells to camptothecin-related drugs. Here we further investigated the cellular mechanisms involved in such drug resistance and showed that, in HCT116 human colorectal adenocarcinoma cells in which TP53 was genetically ablated (HCT116-TP53KO), overexpression of constitutively active MAPK14/p38α decreases cell sensitivity to SN-38 (the active metabolite of irinotecan), inhibits cell proliferation and induces survival-autophagy. Since autophagy is known to facilitate cancer cell resistance to chemotherapy and radiation treatment, we then investigated the relationship between MAPK14/p38α, autophagy and resistance to irinotecan. We demonstrated that induction of autophagy by SN38 is dependent on MAPK14/p38α activation. Finally, we showed that inhibition of MAPK14/p38α or autophagy both sensitizes HCT116-TP53KO cells to drug therapy. Our data proved that the two effects are interrelated, since the role of autophagy in drug resistance required the MAPK14/p38α. Our results highlight the existence of a new mechanism of resistance to camptothecin-related drugs: upon SN38 induction, MAPK14/p38α is activated and triggers survival-promoting autophagy to protect tumor cells against the cytotoxic effects of the drug. Colon cancer cells could thus be sensitized to drug therapy by inhibiting either MAPK14/p38 or autophagy.

Autophagy in HIV-induced T cell death.

HIV infection leads to progressive CD4 T cell depletion, resulting in the development of AIDS. The mechanisms that trigger T cell death after HIV infection are still not fully understood, but a lot of data indicate that apoptosis of uninfected CD4 lymphocytes plays a major role. HIV directly modulates cell death using various strategies in which several viral proteins, in particular the envelope glycoproteins (Env), play an essential role. Importantly, Env, expressed on infected cells, triggers autophagy in uninfected CD4 T cells, leading to their apoptosis. Furthermore, HIV, like other viruses, has evolved strategies to inhibit this autophagic process in HIV-infected cells. This discovery further increases the level of complexity of the cellular processes involved in HIV-induced pathology. Interestingly, HIV protease inhibitors, currently used in highly active antiretroviral therapy (HAART), are able to induce autophagy in cancer cells, leading to a recent repositioning of these drugs as anticancer agents. This review presents an overview of the relationship between HIV, HAART, and autophagy.

Differential role of autophagy in CD4 T cells and macrophages during X4 and R5 HIV-1 infection.

BACKGROUND: HIV-1 can infect and replicate in both CD4 T cells and macrophages. In these cell types, HIV-1 entry is mediated by the binding of envelope glycoproteins (gp120 and gp41, Env) to the receptor CD4 and a coreceptor, principally CCR5 or CXCR4, depending on the viral strain (R5 or X4, respectively). Uninfected CD4 T cells undergo X4 Env-mediated autophagy, leading to their apoptosis, a mechanism now recognized as central to immunodeficiency. METHODOLOGY/PRINCIPAL FINDINGS: We demonstrate here that autophagy and cell death are also induced in the uninfected CD4 T cells by HIV-1 R5 Env, while autophagy is inhibited in productively X4 or R5-infected CD4 T cells. In contrast, uninfected macrophages, a preserved cell population during HIV-1 infection, do not undergo X4 or R5 Env-mediated autophagy. Autophagosomes, however, are present in macrophages exposed to infectious HIV-1 particles, independently of coreceptor use. Interestingly, we observed two populations of autophagic cells: one highly autophagic and the other weakly autophagic. Surprisingly, viruses could be detected in the weakly autophagic cells but not in the highly autophagic cells. In addition, we show that the triggering of autophagy in macrophages is necessary for viral replication but addition of Bafilomycin A1, which blocks the final stages of autophagy, strongly increases productive infection. CONCLUSIONS/SIGNIFICANCE: Taken together, our data suggest that autophagy plays a complex, but essential, role in HIV pathology by regulating both viral replication and the fate of the target cells.

HIV-1 gp41 fusogenic function triggers autophagy in uninfected cells.

Cell-expressed HIV-1 envelope glycoproteins (gp120 and gp41, called Env) induce autophagy in uninfected CD4 T cells, leading to their apoptosis, a mechanism most likely contributing to immunodeficiency. The presence of CD4 and CXCR4 on target cells is required for this process, but Env-induced autophagy is independent of CD4 signaling. Here we demonstrate that CXCR4-mediated signaling pathways are not directly involved in autophagy and cell death triggering. Indeed, cells stably expressing mutated forms of CXCR4, unable to transduce different Gi-dependent and -independent signals, still undergo autophagy and cell death after coculture with effector cells expressing Env. After gp120 binding to CD4 and CXCR4, the N terminus fusion peptide (FP) of gp41 is inserted into the target membrane, and gp41 adopts a trimeric extended pre-hairpin intermediate conformation, target of HIV fusion inhibitors such as T20 and C34, before formation of a stable six-helix bundle structure and cell-to-cell fusion. Interestingly, Env-mediated autophagy is triggered in both single cells (hemifusion) and syncytia (complete fusion), and prevented by T20 and C34. The gp41 fusion activity is responsible for Env-mediated autophagy since the Val2Glu mutation in the gp41 FP totally blocks this process. On the contrary, deletion of the C-terminal part of gp41 enhances Env-induced autophagy. These results underline the major role of gp41 in inducing autophagy in the uninfected cells and indicate that the entire process leading to HIV entry into target cells through binding of Env to its receptors, CD4 and CXCR4, is responsible for autophagy and death in the uninfected, bystander cells.

Involvement of autophagy in viral infections: antiviral function and subversion by viruses.

Autophagy is a cellular process involved in the degradation and turn-over of long-lived proteins and organelles, which can be subjected to suppression or further induction in response to different stimuli. According to its essential role in cellular homeostasis, autophagy has been implicated in several pathologies including cancer, neurodegeneration and myopathies. More recently, autophagy has been described as a mechanism of both innate and adaptive immunity against intracellular bacteria and viruses. In this context, autophagy has been proposed as a protective mechanism against viral infection by degrading the pathogens into autolysosomes. This is strengthened by the fact that several proteins involved in interferon (IFN) signalling pathways are linked to autophagy regulation. However, several viruses have evolved strategies to divert IFN-mediated pathways and autophagy to their own benefit. This review provides an overview of the autophagic process and its involvement in the infection by different viral pathogens and of the connections existing between autophagy and proteins involved in IFN signalling pathways.

Autophagy is involved in T cell death after binding of HIV-1 envelope proteins to CXCR4.

HIV-1 envelope glycoproteins (Env), expressed at the cell surface, induce apoptosis of uninfected CD4+ T cells, contributing to the development of AIDS. Here we demonstrate that, independently of HIV replication, transfected or HIV-infected cells that express Env induced autophagy and accumulation of Beclin 1 in uninfected CD4+ T lymphocytes via CXCR4. The same phenomena occurred in a T cell line and in transfected HEK.293 cells that expressed both wild-type CXCR4 and a truncated form of CD4 that is unable to bind the lymphocyte-specific protein kinase Lck. Env-mediated autophagy is required to trigger CD4+ T cell apoptosis since blockade of autophagy at different steps, by either drugs (3-methyladenine and bafilomycin A1) or siRNAs specific for Beclin 1/Atg6 and Atg7 genes, totally inhibited the apoptotic process. Furthermore, CD4+ T cells still underwent Env-mediated cell death with autophagic features when apoptosis was inhibited. These results suggest that HIV-infected cells can induce autophagy in bystander CD4+ T lymphocytes through contact of Env with CXCR4, leading to apoptotic cell death, a mechanism most likely contributing to immunodeficiency.

[Negative regulation of the JAK/STAT: pathway implication in tumorigenesis]. / Les régulations négatives de la voie JAK/STAT: implication dans la tumorigenèse.

Cytokines, hormones or growth factors induce a variety of biological responses including proliferation, differentiation and apoptosis. After binding to their specific cell surface receptors, these stimuli induce the activation of a number of signaling pathways including the activation of JAK (JAnus Kinase) proteins by auto and transphosphorylation. Activated JAK phosphorylate the receptor chains on tyrosines, creating docking sites for cytoplasmic transcription factors named STAT (Signal Transducers and Activators of Transcription). Furthermore, the JAK phosphorylate the STAT which form dimers and migrate to the nucleus where they bind to specific DNA sequences leading to the activation of transcription. The multiplicity of JAK (4 members) and STAT (7 members) and their associations with multiple possible partners allow the formation of various STAT homo and heterodimers and STAT-containing transcriptional complexes. Each of these complexes lead to the specific regulation of gene transcription. Negative regulation of the JAK/STAT signaling pathway is crucial to switch off the cytokine/growth factors' signal. Three families of proteins : the phosphotyrosine phosphatases (SHPs, CD45, PTP1B/TC-PTP), the SOCS proteins (Suppressors Of Cytokine Signaling) and the PIAS (Protein Inhibitor of Activated STAT) are involved in this process. These proteins act at various levels of the JAK/STAT pathway. Thus, tyrosine-phosphatases dephosphorylate activated JAK, STAT or cytokine receptors. PIAS interact with activated STAT and inhibit their DNA binding or their transactivating capacity, probably in relation with their intrinsic SUMO E3-ligase activity. The tyrosine phosphatases and the PIAS are constitutively present in the cell and represent a first level of regulation. The SOCS, which represent a second level of JAK/STAT negative control, are induced by cytokines and exert a negative feed-back loop. Indeed, they interact with activated JAK or with phosphorylated receptors, inhibiting the recruitment of STAT, the activation of the JAK enzymatic activity, or inducing the proteasome-dependant degradation of activated JAK or receptors.

Mitochondria-dependent apoptosis in T-cell homeostasis.

T-cell homeostasis is maintained by balancing the proliferation and destruction of lymphocytes at multiple steps during the life of an individual. Regulated mitochondria-dependent apoptosis is essential for both the development and the subsequent maintenance of the immune system, in that it keeps the total number of lymphocytes constant. Firstly, during thymic development, sequential stages of T-cell maturation require strict control of T-cell selection, and secondly, apoptosis is essential in controlling the massive expansion of antigen-specific T-cells after their activation. Failure in each of these steps can lead to pathologies, while drugs that target apoptosis could have therapeutic benefit.

Interferons alpha and gamma induce p53-dependent and p53-independent apoptosis, respectively.

Type I interferon (IFN) enhances the transcription of the tumor suppressor gene p53. To elucidate the molecular mechanism mediating IFN-induced apoptosis, we analysed programmed cell death in response to type I (IFNalpha) or type II (IFNgamma) treatment in relation to p53 status. In two cell lines (MCF-7, SKNSH), IFNalpha, but not IFNgamma, enhanced apoptosis in a p53-dependent manner. Furthermore, only IFNalpha upregulated p53 as well as p53 target genes (Noxa, Mdm2 and CD95). The apoptotic response to IFNalpha decreased in the presence of ZB4, an anti-CD95 antibody, suggesting that CD95 is involved in this process. When p53 was inactivated by the E6 viral protein or the expression of a p53 mutant, IFNalpha-induced apoptosis and p53 target genes upregulation were abrogated. Altogether these results demonstrate that p53 plays a pivotal role in the IFNalpha-induced apoptotic response. IFNalpha-induced PML was unable to recruit p53 into nuclear bodies and its downregulation by siRNA did not alter CD95 expression. In contrast, IFNgamma-induced apoptosis is p53-independent. CD95 and IFN-regulatory factor 1 (IRF1) are directly upregulated by this cytokine. Apoptotic response to IFNgamma is decreased in the presence of ZB4 and strongly diminished by IRF1 siRNA, implicating both CD95 and IRF1 in IFNgamma-induced apoptotic response. Taken together, these results show that in two different cell lines, IFNalpha and IFNgamma, induce p53-dependent -independent apoptosis, respectively.

The exonuclease ISG20 is directly induced by synthetic dsRNA via NF-kappaB and IRF1 activation.

Many interferon (IFN)-stimulated genes are also induced by double-stranded RNA (dsRNA), a component closely associated with the IFN system in the context of virus-host interactions. Recently, we demonstrated that the IFN-induced 3' --> 5' exonuclease ISG20 possesses antiviral activities against RNA viruses. Here we show that ISG20 induction by synthetic dsRNA (pIpC) is stronger and faster than its induction by IFN. Two families of transcription factors are implicated in the transcriptional activation of ISG20 by dsRNA. Initially, the NF-kappaB factors p50 and p65 bind and activate the kappaB element of the Isg20 promoter. This is followed by IRF1 binding to the ISRE. As pIpC often induces protein movements in the cells, we questioned whether it could influence ISG20 localization. Interestingly and contrary to IFN, dsRNA induces a nuclear matrix enrichment of the ISG20 protein. dsRNA induction of ISG20 via NF-kappaB and its antiviral activity led us to suggest that ISG20 could participate in the cellular response to virus infection.

Hyaluronan, a major non-protein glycosaminoglycan component of the extracellular matrix in human bone marrow, mediates dexamethasone resistance in multiple myeloma.

Originating from a post-switch memory B cell or plasma cell compartment in peripheral lymphoid tissues, malignant multiple myeloma (MM) cells accumulate in the bone marrow of patients with MM. In this favourable microenvironment, their growth and survival are dependent upon both soluble factors and physical cell-to-cell and cell-to-extracellular-matrix contacts. In this study, hyaluronan (HA), a major non-protein glycosaminoglycan component of the extracellular matrix in mammalian bone marrow, acted as a survival factor against dexamethasone (Dex)-induced apoptosis in MM cell lines. These effects were mediated through an interleukin 6 (IL-6) autocrine pathway, involving signal transducers and activators of transcription-3 phosphorylation on IL-6-dependent XG-1 and XG-6 cell lines. HA promoted accumulation of IL-6 in the culture medium without affecting IL-6 gene expression, suggesting that HA protects, stabilizes and concentrates IL-6 close to its site of secretion, thus favouring its autocrine activity. In contrast, in the IL-6-independent RPMI8226 cell line, HA survival effect was mediated through a gp80-IL-6 receptor-independent pathway, resulting in the upregulation of Bcl-2 anti-apoptotic protein expression and nuclear factor-kappaB activation. Taken together, these data suggest that HA antagonizes Dex-induced apoptosis of MM cells by favouring the autocrine activity of different cytokines or growth factors. As HA is a major component of the bone marrow extracellular matrix, these findings support the idea that HA could play a major role in the survival of MM cells in vivo, and could explain why MM cells accumulate in the bone marrow of patients with MM and escape conventional chemotherapy.

[Interferon : antiviral mechanisms and viral escape]. / Interféron: une barrière antivirale efficace qui a ses faiblesses.

15 % of human cancers have virus origin, meaning that viruses are the second cause of cancers after tabagism. The knowledge of antiviral mechanisms is essential for treatment and prevention of infection evolution towards cancers. Interferons (IFNs) are a large family of multifunctional cytokines. They are involved in regulation of cell growth and modulation of immune response. But, all these functions seem to converge toward the most important of them : the antiviral activity. IFN secretion is the first event induced by viral infection, and will act on specific receptors on neighbour cells and prevent their infection by inducing numbers of antiviral genes. Although few of them are well known like the PKR, the 2-5OAS/RNase L pathway and the Mx proteins, many others need extensive studies to understand the wide range of IFN effect. Viruses have evolved to circumvent the IFN antiviral activity, and are able not only to divert the cellular machinery but also to lure the antiviral mechanisms of the host cell. The purpose of this review is to describe the many antiviral pathways and proteins induced by IFNs and to summarize the strategies of viral escape.

ISG20, a new interferon-induced RNase specific for single-stranded RNA, defines an alternative antiviral pathway against RNA genomic viruses.

Interferons (IFNs) encode a family of secreted proteins that provide the front-line defense against viral infections. Their diverse biological actions are thought to be mediated by the products of specific but usually overlapping sets of cellular genes induced in the target cells. We have recently isolated a new human IFN-induced gene that we have termed ISG20, which codes for a 3' to 5' exonuclease with specificity for single-stranded RNA and, to a lesser extent, for DNA. In this report, we demonstrate that ISG20 is involved in the antiviral functions of IFN. In the absence of IFN treatment, ISG20-overexpressing HeLa cells showed resistance to infections by vesicular stomatitis virus (VSV), influenza virus, and encephalomyocarditis virus (three RNA genomic viruses) but not to the DNA genomic adenovirus. ISG20 specifically interfered with VSV mRNA synthesis and protein production while leaving the expression of cellular control genes unaffected. No antiviral effect was observed in cells overexpressing a mutated ISG20 protein defective in exonuclease activity, demonstrating that the antiviral effects were due to the exonuclease activity of ISG20. In addition, the inactive mutant ISG20 protein, which is able to inhibit ISG20 exonuclease activity in vitro, significantly reduced the ability of IFN to block VSV development. Taken together, these data suggested that the antiviral activity of IFN against VSV is partly mediated by ISG20. We thus show that, besides RNase L, ISG20 has an antiviral activity, supporting the idea that it might represent a novel antiviral pathway in the mechanism of IFN action.