Duplication of U3 sequences in the long terminal repeat of mink cell focus-inducing viruses generates redundancies of transcription factor binding sites important for the induction of thymomas
Document Type
Journal ArticlePublication Date
2003-02-14Keywords
Animals; Animals, Newborn; Binding Sites; *Cell Transformation, Viral; Enhancer Elements (Genetics); Gene Expression Regulation, Viral; Genes, myc; Mice; Mice, Inbred AKR; Mink Cell Focus-Inducing Viruses; Molecular Sequence Data; Recombination, Genetic; Retroviridae Infections; Terminal Repeat Sequences; Thymoma; Thymus Neoplasms; Transcription Factors; Tumor Virus InfectionsLife Sciences
Medicine and Health Sciences
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Show full item recordAbstract
The ability of mink cell focus-inducing (MCF) viruses to induce thymomas is determined, in part, by transcriptional enhancers in the U3 region of their long terminal repeats (LTRs). To elucidate sequence motifs important for enhancer function in vivo, we injected newborn mice with MCF 1dr (supF), a weakly pathogenic, molecularly tagged (supF) MCF virus containing only one copy of a sequence that is present as two copies (known as the directly repeated [DR] sequence) in the U3 region of MCF 247 and analyzed LTRs from supF-tagged proviruses in two resulting thymomas. Tagged proviruses integrated upstream and in the reverse transcriptional orientation relative to c-myc provided the focus of our studies. These proviruses are thought to contribute to thymoma induction by enhancer-mediated deregulation of c-myc expression. The U3 region in a tagged LTR in one thymoma was cloned and sequenced. Relative to MCF 1dr (supF), the cloned U3 region contained an insertion of 140 bp derived predominantly from the DR sequence of the injected virus. The inserted sequence contains predicted binding sites for transcription factors known to regulate the U3 regions of various murine leukemia viruses. Similar constellations of binding sites were duplicated in two proviral LTRs integrated upstream from c-myc in a second thymoma. We replaced the U3 sequences in an infectious molecular clone of MCF 247 with the cloned proviral U3 sequences from the first thymoma and generated an infectious chimeric virus, MCF ProEn. When injected into neonatal AKR mice, MCF ProEn was more pathogenic than the parental virus, MCF 1dr (supF), as evidenced by the more rapid onset and higher incidence of thymomas. Molecular analyses of the resultant thymomas indicated that the U3 region of MCF ProEn was genetically stable. These data suggest that the arrangement and/or redundancy of transcription factor binding sites generated by specific U3 sequence duplications are important to the biological events mediated by MCF proviruses integrated near c-myc that contribute to transformation.Source
J Virol. 2003 Mar;77(5):3326-33.
DOI
10.1128/JVI.77.5.3326-3333.2003Permanent Link to this Item
http://hdl.handle.net/20.500.14038/33643PubMed ID
12584358Related Resources
ae974a485f413a2113503eed53cd6c53
10.1128/JVI.77.5.3326-3333.2003