Caractérisation moléculaire de la protéine antibiotique P1 du phage AP205

La recrudescence de maladies infectieuses et le nombre grandissant de bactéries résistantes aux antibiotiques sont des problèmes majeurs de santé publique. Ainsi, le développement d’une nouvelle catégorie d’agents antimicrobiens est de plus en plus pressant. Nous nous sommes tournés vers les bactériophages afin d’en connaître davantage sur les moyens qu’ils utilisent pour tuer les bactéries. Cependant, jusqu’à maintenant il existe très peu de connaissances sur leur activité bactéricide. Nous avons donc caractérisé le mode d’action de la protéine de lyse P1 du phage AP205 à l’aide d’approches in vitro et in vivo. Ce phage a pour hôte Acinetobacter. La protéine P1 cible un élément essentiel à la survie bactérienne, la paroi de peptidoglycane. En fait, nous avons découvert qu’elle inhibe plusieurs enzymes impliquées au niveau de cette voie synthèse. Nous espérons que les connaissances acquises sur cette protéine antibiotique contribueront au développement d’une nouvelle classe d’agents antimicrobiens.The constant increase of infectious diseases and bacterial resistance to antibiotics are major problems of public health. Thus, development of a new class of antimicrobial agents is very urgent. We have decided to explore bacteriophages to learn more about the way they kill bacteria. Therefore, until now, the knowledge about this bactericidal activity is limited. We have characterized the inhibition mechanism of P1 lysis protein from phage AP205 using in vitro and in vivo approaches. The host of this phage is Acinetobacter. The P1 lysis protein targets an essential element for the bacterial survival, the bacterial cell wall. Actually, we hope that knowledge about this protein will contribute to the development of a new class of antibiotics

Epstein-Barr Virus Interferes with the Amplification of IFNα Secretion by Activating Suppressor of Cytokine Signaling 3 in Primary Human Monocytes

Epstein-Barr virus is recognized to cause lymphoproliferative disorders and is also associated with cancer. Evidence suggests that monocytes are likely to be involved in EBV pathogenesis, especially due to a number of cellular functions altered in EBV-infected monocytes, a process that may affect efficient host defense. Because type I interferons (IFNs) are crucial mediators of host defense against viruses, we investigated the effect of EBV infection on the IFNalpha pathway in primary human monocytes.Infection of monocytes with EBV induced IFNalpha secretion but inhibited the positive feedback loop for the amplification of IFNalpha. We showed that EBV infection induced the expression of suppressor of cytokine signaling 3 (SOCS3) and, to a lesser extent, SOCS1, two proteins known to interfere with the amplification of IFNalpha secretion mediated by the JAK/STAT signal transduction pathway. EBV infection correlated with a blockage in the activation of JAK/STAT pathway members and affected the level of phosphorylated IFN regulatory factor 7 (IRF7). Depletion of SOCS3, but not SOCS1, by small interfering RNA (siRNA) abrogated the inhibitory effect of EBV on JAK/STAT pathway activation and significantly restored IFNalpha secretion. Finally, transfection of monocytes with the viral protein Zta caused the upregulation of SOCS3, an event that could not be recapitulated with mutated Zta.We propose that EBV protein Zta activates SOCS3 protein as an immune escape mechanism that both suppresses optimal IFNalpha secretion by human monocytes and favors a state of type I IFN irresponsiveness in these cells. This immunomodulatory effect is important to better understand the aspects of the immune response to EBV

Role of the extracellular matrix proteins in the resistance of SP6.5 uveal melanoma cells toward cisplatin

Uveal melanoma is the most frequent primary intraocular tumor in the adult population. This malignancy has a high mortality rate and responds poorly to existing chemotherapy. Recently, the tumor environment has been found to exert a profound influence on drug response through cell interaction with components from the extracellular matrix (ECM). In the present study, we investigated whether individual components from the ECM may affect cell survival and/or cell death induced by the cytotoxic agent cisplatin on the SP6.5 uveal melanoma cell line. Tumor cells were shown by immunofluorescence analyses to be surrounded by the ECM proteins fibronectin (FN), type IV collagen (CIV) and laminin (LM), both at the primary and metastatic sites. Binding of SP6.5 cells to FN, LM and CIV is primarily dictated by the expression of membrane bound integrins from the beta1 family as revealed by cell adhesion assays conducted on ECM-coated culture plates. Analysis of cell death by flow cytometry demonstrated that culturing SP6.5 cells in the presence of FN, CIV and LM, substantially reduced the percentage of cells undergoing apoptosis after cisplatin treatment when compared with those seeded on a non-permissive matrix. These results suggest that adhesion of the SP6.5 uveal melanoma cells to the ECM proteins FN, CIV and LM might therefore confer resistance to the chemotherapeutic agent cisplatin. The cellular resistance induced by the ECM proteins toward cisplatin could explain in part the local recurrence of metastasis derived from uveal melanoma often observed clinically after chemotherapy