Bortezomib induction of C/EBP mediates Epstein-Barr virus lytic activation in Burkitt lymphoma
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: Endoplasmic reticulum (ER) stress triggers a homeostatic cellular response in mammalian cells to ensure efficient folding, sorting, and processing of client proteins. In lytic-permissive lymphoblastoid cell lines (LCLs), pulse exposure to the chemical ER-stress inducer thapsigargin (TG) followed by recovery resulted in the activation of the EBV immediate-early (BRLF1, BZLF1), early (BMRF1), and late (gp350) genes, gp350 surface expression, and virus release. The protein phosphatase 1 a (PP1a)-specific phosphatase inhibitor Salubrinal (SAL) synergized with TG to induce EBV lytic genes; however, TG treatment alone was sufficient to activate EBV lytic replication. SAL showed ER-stress-dependent and -independent antiviral effects, preventing virus release in human LCLs and abrogating gp350 expression in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated B95-8 cells. TG resulted in sustained BCL6 but not BLIMP1 or CD138 expression, which is consistent with maintenance of a germinal center B-cell, rather than plasma-cell, phenotype. Microarray analysis identified candidate genes governing lytic replication in LCLs undergoing ER stress.Blood 08/2011; 118(20):5528-39. DOI:10.1182/blood-2011-04-347112 · 10.43 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Gamma herpesviruses (GHVs) are responsible for a substantial proportion of virus-associated human cancers, particularly in immunocompromised individuals. Methods that employ lytic activation of viruses latently infecting tumors represent a novel strategy of antineoplastic therapy. The proteasome inhibitor, bortezomib, has been shown to be a potent activator of GHV lytic cycle and has demonstrated activity in case reports of GHV-related malignancies. Although initial reports implicated the inhibition of the NF-κB pathway, more recent studies identify alternative pathways responsible for bortezomib-mediated lytic induction of GHVs and activity against the malignancies that harbor them. Further exploration of proteasome inhibition as an oncolytic strategy is warranted and will require clinical/translational trials to determine whether lytic induction of GHVs correlates with clinical response to bortezomib, and, if so, to optimize this oncolytic strategy.Current opinion in oncology 09/2011; 23(5):482-7. DOI:10.1097/CCO.0b013e3283499c37 · 3.76 Impact Factor
- Infectious Agents and Cancer 04/2012; 7(1). DOI:10.1186/1750-9378-7-S1-P32 · 2.07 Impact Factor