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Mol. Cell. Biol., Mar 1995, 1522-1535, Vol 15, No. 3
WJ Fredericks, N Galili, S Mukhopadhyay, G Rovera, J Bennicelli, FG Barr and FJ Rauscher 3rd
Alveolar rhabdomyosarcomas are pediatric solid tumors with a hallmark
cytogenetic abnormality: translocation of chromosomes 2 and 13 [t(2;13)
(q35;q14)]. The genes on each chromosome involved in this translocation
have been identified as the transcription factor-encoding genes PAX3 and
FKHR. The NH2-terminal paired box and homeodomain DNA-binding domains of
PAX3 are fused in frame to COOH-terminal regions of the chromosome
13-derived FKHR gene, a novel member of the forkhead DNA- binding domain
family. To determine the role of the fusion protein in transcriptional
regulation and oncogenesis, we identified the PAX3-FKHR fusion protein and
characterized its function(s) as a transcription factor relative to
wild-type PAX3. Antisera specific to PAX3 and FKHR were developed and used
to examine PAX3 and PAX3-FKHR expression in tumor cell lines. Sequential
immunoprecipitations with anti-PAX3 and anti-FKHR sera demonstrated
expression of a 97-kDa PAX3-FKHR fusion protein in the t(2;13)-positive
rhabdomyosarcoma Rh30 cell line and verified that a single polypeptide
contains epitopes derived from each protein. The PAX3-FKHR protein was
localized to the nucleus in Rh30 cells, as was wild-type PAX3, in
t(2;13)-negative A673 cells. In gel shift assays using a canonical PAX
binding site (e5 sequence), we found that DNA binding of PAX3-FKHR was
significantly impaired relative to that of PAX3 despite the two proteins
having identical PAX DNA-binding domains. However, the PAX3-FKHR fusion
protein was a much more potent transcriptional activator than PAX3 as
determined by transient cotransfection assays using e5-CAT reporter
plasmids. The PAX3-FKHR protein may function as an oncogenic transcription
factor by enhanced activation of normal PAX3 target genes.
Copyright © 1995, American Society for Microbiology
The PAX3-FKHR fusion protein created by the t(2;13) translocation in alveolar rhabdomyosarcomas is a more potent transcriptional activator than PAX3
Wistar Institute, University of Pennsylvania School of Medicine, Philadelphia 19104.
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