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J. Virol., 03 1996, 1415-1423, Vol 70, No. 3
S Michelson, P Turowski, L Picard, J Goris, MP Landini, A Topilko, B Hemmings, C Bessia, A Garcia and JL Virelizier
Human cytomegalovirus (CMV), a herpesvirus, is an important cause of
morbidity and mortality in immunocompromised patients. When studying
hyper-immediate-early events after contact between CMV virions and the cell
membrane, we observed a hypophosphorylation of cellular proteins within 10
min. This can be explained in part by our finding that purified CMV
contains serine/threonine protein phosphatase activities. Biochemical
analyses indicate that this protein phosphatase activity has all
characteristics of type 1 and 2A protein phosphatases (PP1 and PP2A).
Specifically, PP1 accounts for approximately 30% and PP2A accounts for the
remaining 70% of the phosphorylase phosphatase activity found. CMV produced
in astrocytoma cells stably expressing an amino-terminally tagged PP2A
catalytic subunit contained tagged enzyme, thus demonstrating the cellular
origin of CMV-associated PP2A. PP2A is specifically found inside the virus,
associated with the nucleocapsid fraction. Western blot (immunoblot)
analysis of purified virus revealed the presence of the catalytic subunits
of PP2A and PP1. Furthermore, the catalytic subunit of PP2A appears to be
complexed to the regulatory subunits PR65 and PR55, which is also the most
abundant configuration of this enzyme found in the host cells. Incubation
of virus with okadaic acid before contact of CMV with cells prevented
hypophosphorylation of cellular proteins, thus demonstrating the role of
CMV-associated phosphatases in this phenomenon. CMV can thus transport an
active enzyme from one cell to another.
Copyright © 1996, American Society for Microbiology
Human cytomegalovirus carries serine/threonine protein phosphatases PP1 and a host-cell derived PP2A
Unite d'Immunologie Virale, Institut Pasteur, Paris, France.
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