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J. Virol., Jun 1997, 4671-4678, Vol 71, No. 6
F Anouja, R Wattiez, S Mousset and P Caillet-Fauquet
Autonomous parvoviruses exert lytic and cytostatic effects believed to
contribute to their antineoplastic activity. Studies with inducible clones
have demonstrated a direct involvement of parvovirus nonstructural proteins
(NS) in oncolysis. Human and rat fibroblasts have been stably transfected
with MVM(p) (minute virus of mice prototype strain) NS genes cloned under
the control of a hormone- inducible promoter. Dexamethasone-induced
synthesis of the NS proteins in sensitive transformed cells results in cell
killing within a few days. From these sensitive cell lines have been
isolated some NS- resistant clones that also prove resistant to MVM(p)
infection, suggesting that cell factors modulate NS cytotoxicity. We have
previously reported that factors involved in cell cycle regulation may
contribute to this modulation, since NS toxicity requires cell
proliferation and correlates with a cell cycle perturbation leading to an
arrest in phase S/G2. In addition to its role in cytotoxicity, NS1 can
regulate transcription driven by parvovirus and nonparvovirus promoters.
Since phosphorylation is a critical event in controlling the activity of
many proteins, notably transcription factors and cell cycle- regulated
proteins, we have examined the effect of NS1 on the synthesis and
phosphorylation of cell proteins. Our results indicate that NS1 interferes,
within 7 h of induction, with phosphorylation of a protein of about 14 kDa
(p14). Cell synchronization has enabled us to show that phosphorylation of
this protein occurs in early S phase and is prevented when NS1 is induced.
This early effect of NS1 on p14 phosphorylation may be directly linked to
cytotoxicity and is probably related to the previously reported inhibition
of cell DNA synthesis. Late in the induction period (24 h), NS1 also alters
the synthesis of a 50-kDa protein and a 35-kDa protein (p50 and p35,
respectively). Microsequencing of p35 reveals sequence homology with
beta-tubulin. These effects of NS1, observed only in NS1-sensitive cell
lines, may be related to the protein's cytotoxicity.
Copyright © 1997, American Society for Microbiology
The cytotoxicity of the parvovirus minute virus of mice nonstructural protein NS1 is related to changes in the synthesis and phosphorylation of cell proteins
Departement de Biologie Moleculaire, Universite Libre de Bruxelles, Rhode-St-Genese, Belgium.
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