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J. Virol., Jul 1997, 5080-5087, Vol 71, No. 7
HW Amtoft, AB Sorensen, C Bareil, J Schmidt, A Luz and FS Pedersen
Murine retrovirus SL3-3 is highly T lymphomagenic. Its pathogenic
properties are determined by the transcriptional enhancer of the U3 repeat
region which shows preferential activity in T cells. Within the U3 repeats,
the major determinant of T-cell specificity has been mapped to binding
sites for the AML1 transcription factor family (also known as the core
binding factor [CBF], polyomavirus enhancer binding protein 2 [PEBP2], and
SL3-3 enhancer factor 1 [SEF-1]). SL3-3 viruses with AML1 site mutations
have lost a major determinant of T-cell-specific enhancer function but have
been found to retain a lymphomagenic potential, although disease induction
is slower than for the SL3-3 wild type. To compare the specificities and
mechanisms of disease induction of wild-type and mutant viruses, we have
examined lymphomas induced by mutant viruses harboring transversions of
three consecutive base pairs critical to AML1 site function (B. Hallberg,
J. Schmidt, A. Luz, F. S. Pedersen, and T. Grundstrom. J. Virol.
65:4177-4181, 1991). Our results show that the mutated AML1 sites are
genetically stable during lymphomagenesis and that ecotropic provirus
numbers in DNA of tumors induced by wild-type and mutant viruses fall
within the same range. Moreover, proviruses were found to be integrated at
the c-myc locus in similar proportions of wild-type and mutant
SL3-3-induced tumors, and the mutated AML1 sites of proviruses at c-myc are
unaltered. In some cases, however, including one c-myc-integrated provirus,
a single-base pair change was detected in a second, weaker AML1 binding
site. By DNA rearrangement analysis of the T-cell receptor beta-locus,
tumors induced by the AML1 site mutants are found to be of the T-cell type.
Thus, although the AML1 site mutants have weakened T-cell-specific
enhancers they are T-lymphomagenic, and wild-type- and mutant-virus-
induced tumor DNAs are similar with respect to the number of overall
ecotropic and c-myc-integrated clonal proviruses. The SL3-3 wild-type and
AML1 site mutant viruses may therefore induce disease by similar
mechanisms.
Copyright © 1997, American Society for Microbiology
Stability of AML1 (core) site enhancer mutations in T lymphomas induced by attenuated SL3-3 murine leukemia virus mutants
Department of Molecular and Structural Biology, University of Aarhus, Aarhus C, Denmark.
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