Molecular analysis of radiation-induced thyroid carcinomas in humans
Title: Molecular analysis of radiation-induced thyroid carcinomas in humans
Author: Rabes, Hartmut M
Reference: International Congress Series, 1236, p.207-215, Jul 2002
doi: 10.1016/S0531-5131(01)00750-6
Keywords: Papillary thyroid carcinoma; Gene rearrangement; RET; NTRK1; Genotype/phenotype correlations
Abstract: Correlations have been found between radiation exposure and thyroid carcinoma development, particularly in children. Recent studies on a large cohort of radiation-induced papillary thyroid carcinomas (PTC) after the Chernobyl reactor accident disclosed a common type of underlying genetic alteration. A high prevalence of rearrangements of the receptor tyrosine kinase (TK) c-RET was observed, besides some rearrangements involving NTRK1. Radiation-induced RET rearrangements in PTC consist most frequently of fusions to the H4 gene (RET/PTC1) or to the ELE1 (ARA70) gene (RET/PTC3). Both fusions are formed by balanced paracentric inversions on chromosome 10. An analysis of the fused genes in ELE1/RET rearrangements revealed DNA double-strand breaks spread over a distance of about 2.3 kb in two introns and the interposed exon of ELE1, exon 11 and intron 11 of RET, without significant clustering in these parts of the genes. Topoisomerase I sites were found exactly at or in close vicinity to all breakpoints, suggesting a role for this enzyme in formation of DNA strand breaks or inversions. The genes fuse at short regions of sequence homology and short direct or inverted repeats (microhomology-mediated DNA end joining). A minority of PTC cases contain novel types of RET rearrangement, with RIα, GOLGA2, HTIF, HTIF homolog, RFG8, ELKS, KTN1 and PCM-1 as the 5′-fused genes. These novel types of gene fusions are formed by interchromosomal translocation. The formation of these rare types of rearrangement seems to be highly related to radiation as they have rarely been found in sporadic PTC. All RET gene fusions seem to act similarly on RET function: The strict physiological control of RET TK activity is suspended through constitutive activation by 5′-fused parts of genes containing coiled-coil domains with dimerization potential. RET expression in thyrocytes, which under normal conditions, lack RET TK activity apparently triggers clonal expansion and early invasion of the affected cells. RET-fused genes, some of which are transcriptional coactivators, are important determinators of the peculiar phenotype of the tumour and for its clinical course. This is most significant in RET/PTC3 rearrangements with ELE1 as the RET-fused gene: this type of rearrangement leads more often to the phenotype of a solid variant of PTC, and to rapid tumour development and early lymph node metastasis. Up to now, no other genetic aberration has more frequently been observed in PTC than RET rearrangement, thus suggesting that RET rearrangement represents a genetic marker lesion of radiation history in the development of a PTC.
URL: http://www.sciencedirect.com/science/article/pii/S0531513101007506