Pterostilbene induces accumulation of autophagic vacuoles followed by cell death in HL60 human leukemia cells.

Pterostilbene, a naturally occurring structural analog of resveratrol, has been reported to exert antiproliferative and proapoptotic effects in various cancer types. Recently, it has been demonstrated to induce both autophagy and apoptosis in human bladder and breast cancer cell lines. The aim of this study was to evaluate the effects of pterostilbene on HL60 human leukemia cells. Cell morphology was examined using confocal and electron microscopy. Cell viability was determined by MTT, neutral red uptake and trypan blue exclusion assays. LC3 processing was studied based on Western blotting and immunofluorescence analyses. Flow cytometry was used to study cell cycle distribution, phosphatidylserine externalization, caspase activation, disruption of mitochondrial membrane potential and intracellular production of reactive oxygen species. DNA degradation was examined by gel electrophoresis. We found that treatment of HL60 cells with pterostilbene at the IC90 concentration resulted in the G0/G1 cell cycle arrest. Pterostilbene induced conversion of cytosolic LC3-I to membrane-bound LC3-II and accumulation of large LC3-positive vacuolar structures. Pterostilbene also led to phosphatidylserine externalization, internucleosomal DNA fragmentation, caspase activation and disruption of mitochondrial membrane potential. Moreover, it did not induce oxidative stress. Our results suggest that pterostilbene induces accumulation of autophagic vacuoles followed by cell death in HL60 cells.

Bovine herpesvirus 1 interferes with TAP-dependent peptide transport and intracellular trafficking of MHC class I molecules in human cells.

Bovine herpesvirus 1 (BoHV-1), the cause of infectious bovine rhinotracheitis and infectious pustular vulvovaginitis in cattle, establishes a lifelong infection, despite the presence of antiviral immunity in the host. BoHV-1 has been shown to elude the host immune system, but the viral gene products responsible for this interference have not yet been identified. Studies aiming at the identification of BoHV-1-encoded immune evasion genes have been hampered by the lack of bovine-specific immunological reagents. Some of the immune evasion molecules identified for other herpesviruses are host species specific; others can act across the species barrier. In this study, experiments were performed to investigate whether BoHV-1 can infect human cells and interfere with antigen processing and presentation in these cells. A human melanoma cell line, Mel JuSo, appeared to be permissive for BoHV-1 infection. BoHV-1 induced expression of major viral glycoproteins at the surface of these cells and produced progeny virus up to 10(5) plaque forming units per ml. BoHV-1 infection resulted in impaired intracellular transport of human MHC class I molecules and inhibition of human TAP. These data indicate that the BoHV-1-encoded molecule(s) that block antigen presentation in bovine cells are able to interact with homologous components of the human MHC class I presentation pathway. The fact that immune evasion by BoHV-1 can be studied in human cells will facilitate the identification of the BoHV-1 gene products involved in this process. Moreover, the data presented here suggest that the BoHV-1 encoded inhibitors of antigen presentation represent potential immune suppressive agents for use in humans.

The extracellular part of glycoprotein E of bovine herpesvirus 1 is sufficient for complex formation with glycoprotein I but not for cell-to-cell spread.

Glycoproteins gE and gI of bovine herpesvirus 1 (BHV-1) are type I transmembrane proteins that can form a complex that is involved in cell-to-cell spread mechanisms. The extracellular domains of both proteins have cysteine-rich regions that are also found in the homologous proteins of other alpha-herpesviruses. The extracellular domain of gE has two conserved cysteine-rich regions: C1 and C2. The other conserved regions in gE are located between C2 and transmembrane region and in the cytoplasmic domain of gE. We studied the complex formation between gE and gI using a series of truncated gE proteins and a full length form and a secreted form of gI. All proteins were expressed in recombinant baculoviruses. To analyse the complex formation between these polypeptides we used monoclonal antibodies (MAbs 67 and 75) that specifically react with the gE/gI complex and not with separately expressed glycoproteins gE and gI alone. This analysis showed that the BHV-1 gE/gI complex can be formed in insect cells after a co-infection with baculoviruses expressing gE and gI in their full length form. When secreted forms of gE and gI were expressed after co-infection, the gE/gI complex was still formed and could also be detected in the tissue culture medium. This gE/gI complex was also formed after mixing the tissue culture media of insect cells expressing the secreted form or gE or gI separately. The smallest part of gE that still formed a complex is encoded by the first 246 residues of gE. This extracellular domain contains only the C1 region, showing that the C2 region is not essential for gE/gI complex formation. Shorter forms of gE encoding the C1 region did not form a detectable complex. We also found that the formation of gE/gI complex is not sufficient for normal cell-to-cell spread of BHV-1. A recombinant BHV-1 gE TM-virus, expressing a truncated glycoprotein E from which the transmembrane and cytoplasmic domain were removed, forms plaques as small as a gE null mutant.