Journal of Virology, April 2001, p. 3391-3403, Vol. 75, No. 7
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.7.3391-3403.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261,1 and GenVec, Inc., Gaithersburg, Maryland 208782
Received 3 November 2000/Accepted 5 January 2001
Herpes simplex virus (HSV) ICP0 can effectively activate gene
expression from otherwise silent promoters contained on persisting viral genomes. However, the expression of high levels of ICP0, as from
ICP4
HSV type 1 (HSV-1) vectors, results in marked
toxicity. We have analyzed the results of ICP0 expressed from an
E1
E4
adenovirus vector (AdS.11E4ICP0) in
which ICP0 expression is controlled from the endogenous adenoviral E4
promoter. In this system, the expression level of ICP0 was reduced more
than 1,000-fold relative to the level of expression from HSV-1 vectors.
This low level of ICP0 did not affect cellular division or greatly
perturb cellular metabolism as assessed by gene expression array
analysis comparing the effects of HSV and adenovirus vector strains.
However, this amount of ICP0 was sufficient to quantitatively destroy
ND10 structures as measured by promyelocytic leukemia
immunofluorescence. The levels of adenovirus-expressed ICP0 were
sufficient to activate quiescent viral genomes in trans and
promote persistent transgene expression in cis. Moreover,
infection of complementing cells with AdS.11E4ICP0 promoted viral
growth and resulted in a 20-fold increase in the plaquing efficiency of
d109, a virus defective for all five immediate-early genes.
Thus, the low level expression of ICP0 from the E1
E4
adenovirus vector may increase the utility of
adenovirus vectors and also provides a means to efficiently quantify
and possibly propagate HSV vectors defective in ICP0. Importantly, the
results demonstrate that the activation function of ICP0 may not result from changes in cellular gene expression, but possibly as a direct consequence of an enzymatic function inherent to the protein that may
involve its action at ND10 resulting in the preferential activation of
viral genomes.
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