MOLECULAR AND CYTOGENETIC CHARACTERIZATION OF A T(1-10-21) TRANSLOCATION IN THE HUMAN PAPILLARY THYROID-CANCER CELL-LINE TPC-1 EXPRESSING THE RET H4 CHIMERIC TRANSCRIPT/

Background. Activation of the ret proto-oncogene by three different ch romosomal rearrangements occurs in up to 25% of papillary thyroid carc inomas. We developed a rapid screening technique to detect ret rearran gements in human interphase and metaphase cells on the basis of multic olor fluorescence in situ hybridization (FISH) of locus-specific DNA p robes. Methods. DNA from individual clones representing the respective ends of a yeast artificial chromosome (YAC) contig spanning the entir e ret gene locus were labeled with either digoxigenin (visualized in r ed) or biotin (green) and hybridized to normal human lymphocytes and t he papillary thyroid cancer cell line TPC-1 expressing the ret/H4 chim eric transcript. Further detailed analysis was performed with whole ch romosome painting probes and locus-specific probes (YACs, P1s, DNA rep eat probes) on tumor metaphase spreads. Results. Hybridization of the YACs to unrearranged ret loci in normal human lymphocyte interphase nu clei showed two yellow domains because of probe overlap. Hybridization to TPC-1 interphase nuclei showed one yellow domain, and 1 red and 1 green domain separated by a large physical distance. Further analysis of metaphase spreads revealed a complex translocation t(1;10;21)(1pter > 1q31::21q22.1 > 21qter; 10q11.2 > 10pter::1q31 > 1qter; 21pter > 21 q22.1;;10q21.2 > 10q11.2::10q21.2 > 10qter) and loss of the H4 gene lo cus on the nontranslocated chromosome 10. Conclusions. Break point spa nning probes can reliably detect ret rearrangements in interphase nucl ei. Locus-specific and whole chromosome painting probes can be used to further characterize complex rearrangements by fluorescence in situ h ybridization to metaphase spreads. The papillary thyroid cancer cell l ine TPC-1 carries the paracentric inversion 10q inv(10)(q11.2q21) and a complex t(q; 10; 21) translocation. Deletion of the H4 gene on the c hromosome 10 not involved in the t(1; 10; 21) translocation suggests l ack of normal H4 expression in the TPC-1 cell line. Further studies wi ll have to address the role of the H4 gene product in tumor genesis an d progression.