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The 11 th International Workshop on KSHV & Related Agents, Birmingham, UK
Gene Expression I Abstract 65
KSHV ORF57 AND RNA EXPORT FACTORS: ROLES OF UAP56, URH49, RBM15,
AND OTT3 IN ORF57 EXPRESSION AND FUNCTION
Merlyn Deng 1 , Vladimir Majerciak 1 , Barbara K. Felber 2 , and Zhi-Ming Zheng 1
1HIV
and AIDS Malignancy Branch, National Cancer Institute, NIH, Bethesda, MD. USA.
2
Human Retrovirus Pathogenesis Section, Vaccine Branch, National Cancer Institute,
Frederick, MD, USA
Abstract
KSHV ORF57 promotes the expression of a subset of viral lytic genes at
posttranscriptional level and is essential for virus production. To investigate how ORF57
might function to promote RNA export of its targets, we examined the cellular export
factors UAP56, URH49, RBM15 and OTT3 for their possible roles in ORF57-enhanced
expression of KSHV ORF59. We found that reducing the expression of each of these
proteins with gene-specific siRNAs significantly reduced the expression of ORF59 in
cotransfection experiments. Surprisingly, we also found that all four proteins affected
ORF57 expression, indicating that the reduced ORF59 expression was likely due to the
reduction of ORF57. The effect became most severe when two genes were knocked down
simultaneously. To investigate whether the downregulation of ORF57 expression was due
to a reduction of ORF57 mRNA export, we fractionated the nuclear RNA from the
cytoplasmic RNA of cells transfected with an ORF57 expression vector and UAP56
and/URH49 siRNAs. A substantial reduction of cytoplasmic ORF57 RNA was observed
along with substantial accumulation of nuclear ORF57 RNA. A greater reduction of
cytoplasmic ORF57 RNA was noticed in double-knockdown cells. Although overexpression
of UAP56 had no effect on ORF57 or ORF59, the presence of RBM15 or OTT3 greatly
increased expression of ORF59, but suppressed ORF57 expression. Collectively, our data
suggest that ORF57 expression is controlled by the four RNA export factors analyzed.
The role of ORF57 is likely to substitute cellular RBM15 and OTT3 in promotion of ORF59
expression by sequestering them from RNA export machinery.
Presenting author Email: zhengt@exchange.nih.gov
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