EBV Conference 2008 Guangzhou - Baylor College of Medicine

91 (RegID: 1261)
Dinesh Verma
Institution: University of Florida
e-mail: dinesh75@ufl.edu
EPSTEIN-BARR VIRUS SM PROTEIN INHIBITS BHRF1 (VIRAL BCL-2) EXPRESSION BY
DOWNREGULATING THE EBV TRANSCRIPTIONAL ACTIVATOR R PROTEIN.
Dinesh Verma, Chen Ling, Nagaraja Tirumuru and Sankar Swaminathan
Posterabstract:
During primary infection and during reactivation from latent infection, EBV undergoes productive lytic
replication. The switch from latency to lytic replication is regulated by two EBV transcriptional activators;
BZLF1 (Z, Zta, EB1) and BRLF1(R, Rta). SM is an RNA-binding EBV protein expressed after Z and R
during the lytic cycle and is essential for virus production. SM enhances EBV mRNA accumulation via
multiple mechanisms that enhance target mRNA stability, processing and export. We have previously
compared EBV gene expression in the presence and absence of SM using an epithelial cell line carrying
an EBV recombinant deleted for SM. We found that most EBV genes are upregulated by SM, but one
gene, BHRF1, is highly downregulated. BHRF1 is an anti-apoptotic protein that is homologous to cellular
Bcl-2 and is expressed shortly after lytic EBV replication begins.
To ask whether the inhibitory effect of SM on BHRF1 expression was post-transcriptional, we measured
expression of BHRF1 from a heterologous promoter. SM was unable to decrease BHRF1 gene
expression from a CMV promoter, suggesting that the inhibitory effect was promoter-dependent. We
therefore analysed BHRF1 promoter activity with luciferase reporter assays and found that SM
downregulated BHRF1 promoter activity, but only in EBV-positive cells, suggesting involvement of other
EBV proteins in BHRF1 promoter inhibition by SM. We further demonstrate that SM downregulates R
protein and RNA levels in EBV positive cells and that the majority of BHRF1 promoter activity in 293
cells is R-dependent. Our results demonstrate that SM may inhibit BHRF1 promoter activity by
downregulating R expression during the lytic phase of EBV replication and may play a role in feedback
modulation of lytic cycle gene expression. Temporal modulation of BHRF1 levels during lytic replication
may thus be important for maintaining cell viability for a limited period during the early stage of EBV
replication.
EBV Conference 2008 Guangzhou
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