No abstract

SUMMARY Upon activation by the ligands Gas6 and Protein S, TAM receptor tyrosine kinases promote phagocytic clearance of apoptotic cells and downregulate immune responses initiated by Toll-like receptors and type I interferons (IFNs). Many enveloped viruses display the phospholipid phosphatidylserine on their membranes, through which they bind Gas6 and Protein S and engage TAM receptors. We find that ligand-coated viruses activate TAM receptors on dendritic cells (DCs), dampen type I IFN signaling, and thereby evade host immunity and promote infection. Upon virus challenge, TAM-deficient DCs display type I IFN responses that are elevated in comparison to wild-type cells. As a consequence, TAM-deficient DCs are relatively resistant to infection by flaviviruses and pseudotyped retroviruses, but infection can be restored with neutralizing type I IFN antibodies. Correspondingly, a TAM kinase inhibitor antagonizes the infection of wild-type DCs. Thus, TAM receptors are engaged by viruses in order to attenuate type I IFN signaling and represent potential therapeutic targets.

Azurin, a copper-containing redox protein released by the pathogenic bacterium Pseudomonas aeruginosa, is highly cytotoxic to the human breast cancer cell line MCF-7, but is less cytotoxic toward p53-negative (MDA-MB-157) or nonfunctional p53 cell lines like MDD2 and MDA-MB-231. The purpose of this study was to investigate the underlying mechanism of the action of bacterial cupredoxin azurin in the regression of breast cancer and its potential chemotherapeutic efficacy. Azurin enters into the cytosol of MCF-7 cells and travels to the nucleus, enhancing the intracellular levels of p53 and Bax, thereby triggering the release of mitochondrial cytochrome c into the cytosol. This process activates the caspase cascade (including caspase-9 and caspase-7), thereby initiating the apoptotic process. Our results indicate that azurininduced cell death stimuli are amplified in the presence of p53. In vivo injection of azurin in immunodeficient mice harboring xenografted human breast cancer cells in the mammary fat pad leads to statistically significant regression (85%, P ¼ 0.0179, Kruskal-Wallis Test) of the tumor. In conclusion, azurin blocks breast cancer cell proliferation and induces apoptosis through the mitochondrial pathway both in vitro and in vivo, thereby suggesting a potential chemotherapeutic application of this bacterial cupredoxin for the treatment of breast cancer.

Ebola virus (EBOV) infects several cell types and while viral entry is known to be pH dependent; the exact entry pathway(s) remains unknown. To gain insights into EBOV entry, the role of several inhibitors of clathrin-mediated endocytosis in blocking infection mediated by HIV pseudotyped with the EBOV envelope glycoprotein (EbGP) was examined. Wild type HIV and envelope-minus HIV pseudotyped with Vesicular Stomatitis Virus glycoprotein (VSVg) were used as controls to assess cell viability after inhibiting clathrin pathway. Inhibition of clathrin pathway using dominant-negative Eps15; siRNA-mediated knockdown of clathrin heavy chain; chlorpromazine and sucrose blocked EbGP pseudotyped HIV infection. Also, both chlorpromazine and Bafilomycin A1 inhibited entry of infectious EBOV. Sensitivity of EbGP pseudotyped HIV as well as infectious EBOV to inhibitors of clathrin suggests that EBOV uses clathrin-mediated endocytosis as an entry pathway. Furthermore, since chlorpromazine inhibits EBOV infection, novel therapeutic modalities could be designed based on this lead compound.