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J Virol, July 1998, p. 5745-5756, Vol. 72, No. 7
Department of Molecular and Structural
Biology1 and
Department of Medical
Microbiology and Immunology,2 University of
Aarhus, DK-8000 Aarhus C, Denmark, and
Institute of Molecular
Virology3 and
Institute of
Pathology,4 GSF-Research Center for Environment
and Health, D-85764 Neuherberg, Germany
Received 17 November 1997/Accepted 9 April 1998
Akv is an endogenous, ecotropic murine leukemia virus (MuLV) of the
AKR strain. It has served as a prototype nonpathogenic or
weakly pathogenic reference virus for studies of closely related potent
lymphomagenic viruses such as the T-lymphomagenic SL3-3. We here report
that Akv and an Akv mutant (Akv1-99) with only one copy of the 99-bp
transcriptional enhancer induce malignant lymphomas with nearly 100%
incidence and mean latency periods of 12 months after injection into
newborn NMRI mice. Molecular analysis of tumor DNA showed that the
majority of the tumors were of the B-cell type. Sequence analysis of
proviral transcriptional enhancers in DNA of B-cell lymphomas revealed
conservation of the enhancer sequence, as well as a lack of sequence
duplications of the Akv1-99 variant, while the repeat copy number in
Akv was subject to fluctuations. In support of a B-cell specificity of the Akv enhancer, a murine plasmacytoma cell line was found to sustain
three- to fivefold-higher transient transcriptional activity upon the
Akv and Akv1-99 enhancers than upon the enhancer of the T-lymphomagenic
SL3-3 MuLV. Thus, the overall picture is that Akv MuLV possesses a
B- lymphomagenic potential and that the second copy of the 99-bp
sequence seems to be of minor importance for this potential. However,
in one animal the lymphomas induced by Akv1-99 were of the T-cell type.
Among the 24 tumors analyzed only this one harbored a clonal proviral
integration in the c-myc locus. This provirus had undergone
a duplication of a 113-bp sequence of the enhancer region, partly
overlapping with the 99-bp repeat of Akv, as well as a few single
nucleotide alterations within and outside the repeats. Taken together
with previous studies, our results suggest that T- versus
B-lymphomagenic specificity of the enhancer is governed by more than
one nucleotide difference and that alterations in binding sites for
transcription factors of the AML1 and nuclear-factor-1 families may
contribute to this specificity.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
B-Cell Lymphoma Induction by Akv Murine Leukemia
Viruses Harboring One or Both Copies of the Tandem Repeat in the
U3 Enhancer
*
Corresponding author. Mailing address: Department of
Molecular and Structural Biology, University of Aarhus, C. F. Møllers Allé, Bldg. 130, DK-8000 Aarhus C, Denmark. Phone: 45 8942 3188. Fax: 45 86 196500. E-mail: fsp{at}mbio.aau.dk.
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