Affiliation:
1. Marjorie
B. Kovler Viral Oncology Laboratories, University of Chicago, Chicago,
Illinois 60637
Abstract
ABSTRACT
Herpes
simplex virus type 1 (HSV-1) infected cell protein 0 (ICP0) is a
multifunctional protein that functions as a promiscuous transactivator
and promotes the degradation of multiple cellular proteins. In vitro
studies indicated that it encodes two physically separated functional
E3 ubiquitin ligase domains. One, designated herpesvirus ubiquitin
ligase 1 (HUL-1), maps to a region encoded by exon 3 and is contained
between residues 543 and 680. Deletion of amino acids 621 to 625
abolishes this activity. The second, designated HUL-2, maps to the RING
finger domain present in ICP0 encoded by exon 2. Earlier studies have
shown that ICP0 stabilizes cyclins D1 and D3, and several lines of
investigation led to the hypothesis that this function of ICP0 is the
consequence of degradation of the E2 enzyme cdc34, known to be involved
in the proteasome-dependent degradation of D-type cyclins. Consistent
with this hypothesis, we have previously shown that cdc34 physically
interacts with ICP0 at or near aspartate 199 and at amino acids 621 to
625 and that the former site is required for effective ubiquitylation
and degradation of cdc34. Furthermore, the ICP0 HUL-1 domain promotes
the polyubiquitination of cdc34 in vitro. If the mechanism by which
D-type cyclins are salvaged in wild-type-infected cells is dependent on
polyubiquitination and consequent destruction of cdc34, than the mutant
virus R6701, which was constructed for these studies and lacks ICP0
residues 621 to 625, should destabilize the D cyclins and preclude the
degradation of cdc34. We report that ICP0 residues 621 to 625 are
essential for degradation of cdc34 in infected cells and for the
ICP0-mediated stabilization of D-type cyclins, that a mutation that
specifically disrupted the ring finger domain of the HUL-2 site had no
effect on the degradation of cdc34 in infected cells, and that deletion
of ICP0 residues 621 to 625 decreased the replicative capacity of the
virus in growth-arrested but not in dividing cells and resulted in
diminished pathogenicity on intracerebral inoculation of mice. We
conclude that the ICP0 HUL-1 domain acts in infected cells to degrade
cdc34 and that this function requires the interaction of cdc34 with
sequences in exons 2 and 3 but does not involve the HUL-2 RING finger
E3
domain.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology
Cited by
25 articles.
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