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Journal of Virology, June 1999, p. 5110-5122, Vol. 73, No. 6
Center for Immunology, Departments of
Pathology and Molecular Microbiology,1 and
Lauren V. Ackerman Laboratory of Surgical
Pathology,2 Washington University School of
Medicine, St. Louis, Missouri
Received 10 November 1998/Accepted 4 March 1999
Several gammaherpesviruses contain open reading frames encoding
proteins homologous to mammalian D-type cyclins. In this study, we
analyzed the expression and function of the murine gammaherpesvirus 68 (
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
The Murine Gammaherpesvirus 68 v-Cyclin Gene Is an
Oncogene That Promotes Cell Cycle Progression in Primary
Lymphocytes
HV68) viral cyclin (v-cyclin). The
HV68 v-cyclin gene was expressed in lytically infected fibroblasts as a leaky-late mRNA of
approximately 0.9 kb encoding a protein of approximately 25 kDa. To
evaluate the effect of the
HV68 v-cyclin on cell cycle progression
in primary lymphocytes and to determine if the
HV68 v-cyclin gene is
an oncogene, we generated transgenic mice by using the lck
proximal promoter to express the
HV68 v-cyclin in early T cells.
Expression of the
HV68 v-cyclin significantly increased the number
of thymocytes in cell culture, as determined by measuring both DNA
content and incorporation of 5-bromo-2-deoxyuridine following in vivo
pulse-labeling. Expression of the
HV68 v-cyclin interfered with
normal thymocyte maturation, as shown by increased numbers of
CD4+ CD8+ double-positive thymocytes and
decreased numbers of CD4+ or CD8+
single-positive and T-cell-receptor-bright thymocytes and splenocytes in transgenic mice. Despite increased numbers of cycling thymocytes,
HV68-v-cyclin-transgenic mice did not have proportionately
increased thymocyte numbers, and staining by terminal
deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling
demonstrated increased apoptosis in the thymi of v-cyclin-transgenic
mice. Fifteen of 38
HV68-v-cyclin-transgenic mice developed
high-grade lymphoblastic lymphoma between 3 and 12 months of age. We
conclude that (i) the
HV68 v-cyclin is expressed as a leaky-late
gene in lytically infected cells, (ii) expression of the
HV68
v-cyclin in thymocytes promotes cell cycle progression and inhibits
normal T-cell differentiation, and (iii) the
HV68 v-cyclin gene is
an oncogene.
*
Corresponding author. Mailing address: Center for
Immunology, Departments of Pathology and Molecular Microbiology,
Washington University School of Medicine, Box B118, 660 S. Euclid Ave.,
St. Louis, MO 63110-1093. Phone for Samuel H. Speck: (314) 362-0367. Fax: (314) 362-4096. E-mail: speck{at}pathbox.wustl.edu.
Phone for Herbert W. Virgin IV: (314) 362-9223. Fax: (314) 362-4096. E-mail: virgin{at}immunology.wustl.edu.
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