RET rearrangements in radiation-induced papillary thyroid carcinomas: high prevalence of topoisomerase I sites at breakpoints and microhomology-mediated end joining in ELE1 and RET chimeric genes.
Children exposed to radioactive iodine after the Chernobyl reactor accident frequently developed papillary thyroid carcinomas (PTC). The predominant molecular lesions in these tumors are rearrangements of the RET receptor tyrosine kinase gene. Various types of RET rearrangements have been described. More than 90% of PTC with RET rearrangement exhibit a PTC1 or PTC3 type of rearrangement with an inversion of the H4 or ELE1 gene, respectively, on chromosome 10. To obtain closer insight into the mechanisms underlying PTC3 inversions, we analyzed the genomic breakpoints of 22 reciprocal and 4 nonreciprocal ELE1 and RET rearrangements in 26 post-Chernobyl tumor samples. In contrast to previous assumptions, an accumulation of breakpoints at the two Alu elements in the ELE1 sequence was not observed. Instead, breakpoints are distributed in the affected introns of both genes without significant clustering. When compared to the corresponding wildtype sequences, the majority of breakpoints (92%) do not contain larger deletions or insertions. Most remarkably, at least one topoisomerase I site was found exactly at or in close vicinity to all breakpoints, indicating a potential role for this enzyme in the formation of DNA strand breaks and/or ELE1 and RET inversions. The presence of short regions of sequence homology (microhomologies) and short direct and inverted repeats at the majority of breakpoints furthermore indicates a nonhomologous DNA end-joining mechanism in the formation of chimeric ELE1/Ret and Ret/ELE1 genes.
Klugbauer
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S
Institute of Pathology, Ludwig Maximilians University of Munich, Thalkirchner Strasse 36, D-80337 Munich, Germany.
Pfeiffer
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P
Gassenhuber
H
H
Beimfohr
C
C
Rabes
H M
HM
D001483:Base Sequence; D002291:Carcinoma, Papillary / Q000235:genetics*; D007446:Chromosome Inversion; D002879:Chromosomes, Human, Pair 10 / Q000235:genetics; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000235:genetics; D029721:Drosophila Proteins; D005091:Exons; D015321:Gene Rearrangement / Q000528:radiation effects; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D009381:Neoplasms, Radiation-Induced / Q000235:genetics*; D056918:Nuclear Receptor Coactivators; D015513:Oncogene Proteins / Q000235:genetics; D009857:Oncogenes / Q000528:radiation effects; D016133:Polymerase Chain Reaction; D011210:Power Plants; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051096:Proto-Oncogene Proteins c-ret; D018788:Radioactive Hazard Release; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D011995:Recombination, Genetic / Q000528:radiation effects; D017384:Sequence Deletion; D013964:Thyroid Neoplasms / Q000235:genetics*; D014157:Transcription Factors; D014455:Ukraine
D004273:DNA, Neoplasm; D029721:Drosophila Proteins; C111382:NCOA4 protein, human; D056918:Nuclear Receptor Coactivators; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; D004264:DNA Topoisomerases, Type I