New breakpoints in both the H4 and RET genes create a variant of PTC-1 in a post-Chernobyl papillary thyroid carcinoma

Two main types of RET/PTC oncogene, named RET/ PTC-1 and 3, occur in papill ary thyroid carcinomas especially in those from Belarus children after the Chernobyl nuclear accident, Several variants of RET/ PTC-3 have also been f ound, having different break points with respect to the classical RET/PTC-3 . To our knowledge, no variant of RET/PTC-1 has been described up to now. We found a post-Chernobyl papillary thyroid carcinoma with an RET/PTC-1 rea rrangement characterized by a transcript longer than expected, Sequence ana lysis of the PCR product obtained after RT-PCR revealed new fusion points b etween H4 and RET genes. The genomic sequence showed new breakpoints in bot h H4 intronic and in RET exonic regions. The RET gene breakpoint occurred w ithin exon 11, at variance with the classical form of RET/PTC-1, in which i t is in intron 11. As a consequence of this new fusion point, the transcrip t included 132 nucleotides of exon 11, coding for 44 amino acids of RET pro tein. Regarding the H4 gene, the classical breakpoint is in the first intro n and the cDNA contains a fragment of 339 nucleotides, in our case the cDNA had a longer fragment of H4 involving a total of 1266 nucleotides, Sequenc ing of genomic DNA revealed a rearrangement breakpoint at position 886 of a new H4 intron located downstream of the 1266 coding region. Furthermore, a s a consequence of the activation of a cryptic splicing site, 132 nucleotid es of this intron were spliced between the H4 and RET genes, Sequence analy sis of the new chimera showed that the original frames of H4 and RET were j oint with the intronic sequence without disruption of the open reading fram e (ORF), Moreover, the genomic DNA of this case showed transforming activit y in the DNA-mediated transfection assay using NIH-3T3 cells. In conclusion, we describe here the first variant of RET/PTC-1 oncogene, wh ich we have termed 'long'-PTC-1, characterized by new breakpoints of both g enes involved in the rearrangement and having transforming activity, Simila r to previously reported PTC-3 variants, long-PTC-1 has been found in a pos t-Chernobyl papillary thyroid carcinoma confirming that RET/PTC rearrangeme nts other than the classical forms (RET/PTC-1 and -3) are specifically asso ciated with radiation-induced papillary thyroid cancer.