Bortezomib induction of C/EBPβ mediates Epstein-Barr virus lytic activation in Burkitt lymphoma.

Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Blood (Impact Factor: 9.78). 03/2011; 117(23):6297-303. DOI: 10.1182/blood-2011-01-332379
Source: PubMed

ABSTRACT Epstein-Barr virus (EBV) is associated with a variety of lymphoid malignancies. Bortezomib activates EBV lytic gene expression. Bortezomib, a proteasome inhibitor, leads to increased levels of CCAAT/enhancer-binding proteinβ (C/EBPβ) in a variety of tumor cell lines. C/EBPβ activates the promoter of the EBV lytic switch gene ZTA. Bortezomib treatment leads to increased binding of C/EBP to previously recognized binding sites in the ZTA promoter. Knockdown of C/EBPβ inhibits bortezomib activation of EBV lytic gene expression. Bortezomib also induces the unfolded protein response (UPR), as evidenced by increases in ATF4, CHOP10, and XBP1s and cleavage of ATF6. Thapsigargin, an inducer of the UPR that does not interfere with proteasome function, also induces EBV lytic gene expression. The effects of thapsigargin on EBV lytic gene expression are also inhibited by C/EBPβ knock-down. Therefore, C/EBPβ mediates the activation of EBV lytic gene expression associated with bortezomib and another UPR inducer.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Bortezomib is an FDA-approved proteasome inhibitor, and oncolytic HSV-1 (oHSV) is a promising therapeutic approach for cancer. We tested the impact of combining bortezomib with oHSV for anti-tumor efficacy. The synergistic interaction between oHSV and bortezomib was calculated using Chou-Talalay analysis. Viral replication was evaluated using plaque assay and immune fluorescence. Western-blot assays were used to evaluate induction of ER stress and unfolded protein response (UPR). Inhibitors targeting Hsp90 were utilized to investigate the mechanism of cell killing. Anti-tumor efficacy in vivo was evaluated using subcutaneous and intracranial tumor xenografts of glioma and head and neck cancer. Survival was analyzed by Kaplan-Meier curves and two-sided log rank test. Combination treatment with bortezomib and oHSV, 34.5ENVE, displayed strong synergistic interaction in ovarian cancer, head & neck cancer, glioma, and malignant peripheral nerve sheath tumor (MPNST) cells. Bortezomib treatment induced ER stress, evident by strong induction of Grp78, CHOP, PERK and IRE1α (western blot analysis) and the UPR (induction of hsp40, 70 and 90). Bortezomib treatment of cells at both sublethal and lethal doses increased viral replication (p value <0.001), but inhibition of Hsp90 ablated this response, reducing viral replication and synergistic cell killing. The combination of bortezomib and 34.5ENVE significantly enhanced anti-tumor efficacy in multiple different tumor models in vivo. The dramatic synergy of bortezomib and 34.5ENVE is mediated by bortezomib- induced UPR and warrants future clinical testing in patients.
    Clinical Cancer Research 05/2014; · 8.19 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Autophagy is a catabolic pathway that helps cells to survive in stressful conditions. Cells also use autophagy to clear microbiological infections but, on the other hand, microbes have learned how to manipulate the autophagic pathway for their own benefit. The experimental evidence obtained in this study suggests that the autophagic flux is blocked at the final steps during the reactivation of EBV from latency. This is indicated by the level of LC3II that does not increase in the presence of bafilomycin and by the lack of colocalization of autophagosomes with lysosomes, which correlates with a reduced Rab7 expression.. Since the inhibition of the early phases of autophagy impaired EBV replication and viral particles were observed in autophagic vescicles in the cytoplasm of producing cells, we suggest that EBV exploits the autophagic machinery for its transportation, in order to enhance viral production. The autophagic block was not mediated by ZEBRA, an immediate early EBV lytic gene, whose transfection in Ramos, Akata and 293 cells promoted a complete autophagic flux, The block occurred only when the complete set of EBV lytic genes was expressed. We suggest that the inhibition of the early autophagic steps or finding strategies to overcome the autophagic block, allowing viral degradation into the lysosomes, could be potentially exploited to manipulate EBV replication.
    Journal of Virology 08/2014; · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The combination of relative nutrient deprivation and dysregulation of protein synthesis make malignant cells especially prone to protein misfolding. Endoplasmic reticulum stress, which results from protein misfolding within the secretory pathway, has a profound effect on cancer cell proliferation and survival. In this review, we examine the evidence implicating endoplasmic reticulum dysfunction in the pathology of cancer and discuss how recent findings may help to identify novel therapeutic targets.
    Cancer cell 05/2014; 25(5):563-573. · 25.29 Impact Factor