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J. Virol., 05 1997, 3580-3587, Vol 71, No. 5
MA Hardwicke and PA Schaffer
The herpes simplex virus type 1 (HSV-1) genome contains three origins of
DNA replication, one copy of oriL and two copies of oriS. Although oriL and
oriS are structurally different, they have extensive nucleotide sequence
similarity and can substitute for each other to initiate viral DNA
replication. A fundamental question that remains to be answered is why the
HSV-1 genome contains two types of origin. We have recently identified a
novel glucocorticoid response element (GRE) within oriL that is not present
in oriS and have shown by gel mobility shift assays that purified
glucocorticoid receptor (GR), as well as GR present in cellular extracts,
can bind to the GRE in oriL. To determine whether glucocorticoids and the
GRE affect the efficiency of oriL- dependent DNA replication, we performed
transient DNA replication assays in the presence and absence of
dexamethasone (DEX). Because HSV- 1 is a neurotropic virus and establishes
latency in cells of neural origin, these tests were conducted in PC12
cells, which assume the properties of sympathetic neurons when
differentiated with nerve growth factor (NGF). In NGF-differentiated PC12
cells, oriL-dependent DNA replication was enhanced 5-fold by DEX, whereas
in undifferentiated cells, DEX enhanced replication approximately 2-fold.
Notably, the enhancement of oriL function by DEX was abolished when the GRE
was mutated. NGF-induced differentiation alone had no effect. In contrast
to oriL, oriS-dependent DNA replication was reduced approximately 5- fold
in NGF-differentiated PC12 cells and an additional 4-fold in differentiated
cells treated with DEX. In undifferentiated PC12 cells, DEX had only a
minor inhibitory effect (approximately 2-fold) on oriS function. Although
the cis-acting elements that mediate the NGF- and DEX-specific repression
of oriS-dependent DNA replication are unknown, a functional GRE is critical
for the DEX-induced enhancement of oriL function in NGF-differentiated PC12
cells. The enhancement of oriL- dependent DNA replication by DEX in
differentiated PC12 cells suggests the possibility that glucocorticoids,
agents long recognized to enhance reactivation of latent herpesvirus
infections, act through the GRE in oriL to stimulate viral DNA replication
and reactivation in terminally differentiated neurons in vivo.
Copyright © 1997, American Society for Microbiology
Differential effects of nerve growth factor and dexamethasone on herpes simplex virus type 1 oriL- and oriS-dependent DNA replication in PC12 cells
Dana-Farber Cancer Institute, Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
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