EBV Conference 2008 Guangzhou - Baylor College of Medicine

216 (RegID: 1166)
Jade Yee
Institution: Imperial College London
e-mail: jade.yee@imperial.ac.uk
LATENT EBV PROTECTS BL CELLS FROM APOPTOSIS BY AT LEAST TWO DISTINCT
PATHWAYS
Jade Yee, Goran Gregorovic, Paul J Farrell, Robert E White and Martin J Allday, Imperial College London
Posterabstract:
Most EBV-negative Burkitt’s lymphoma (BL) cell lines rapidly undergo apoptosis in response to various
cytotoxic drugs including the cyclin-dependent-kinase inhibitor roscovitine, the DNA cross-linking agent
cisplatin and the mitotic spindle poison nocodazole. Previous reports have shown that the latent infection
of these BL cells with EBV significantly increased their resistance to apoptosis. This protection is
dependent on the co-expression of EBNA3A and EBNA3C, which downregulate the pro-apoptotic protein
Bim, but is independent of the tumour suppressor p53 (Anderton et. al., 2008). However, using the
calcium ionophore ionomycin as the apoptosis-inducing agent, another pathway by which BL cells
undergo apoptosis has been identified. This is independent of both Bim and p53, but can also be blocked
by latent EBV.
In order to identify the EBV latent gene(s) responsible for the protection against ionomycin-induced
apoptosis, the response of a panel of BL cells expressing restricted sets of viral latent genes was assessed.
It was determined that EBNA1, EBNA2, the LMPs and full-length EBNA-LP are not required for this
phenotype. Protection was also independent of EBNA3A, EBNA3B or EBNA3C. Experiments conducted
using BL cells recently established using new recombinant knockout and revertant EBV-BACs, showed
that EBER1, EBER2 and the complete EBNA3 locus are not required for ionomycin-resistance. We also
confirmed that this EBV-mediated protection of BL cells did not involve the induction of the viral lytic
cycle. Recombinant EBVs are being constructed to determine the role of BHRF1 and the BHRF1-miRNA
cluster in the cellular response to ionomycin. Real-time quantitative RT-PCR and Western blot analyses
indicate that the pro-apoptotic protein Noxa is consistently induced in BL cells sensitive to ionomycin.
The data suggest that EBV confers resistance against ionomycin-induced apoptosis by inhibiting the
accumulation of Noxa, via a yet to be identified mechanism.
EBV Conference 2008 Guangzhou
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