THE DNA REARRANGEMENT THAT GENERATES THE TRK-T3 ONCOGENE INVOLVES A NOVEL GENE ON CHROMOSOME-3 WHOSE PRODUCT HAS A POTENTIAL COILED-COIL DOMAIN

Oncogenic rearrangements of the NTRK1 gene (also designated TRKA), enc oding one of the receptors for the nerve growth factor, are frequently detected in thyroid carcinomas, Such rearrangements fuse the NTRK1 ty rosine kinase domain to 5'-end sequences belonging to different genes, In previously reported studies we have demonstrated that NTRK1 oncoge nic activation involves two genes, TPM3 and TPR, both localized simila rly to the receptor tyrosine kinase, on the q arm of chromosome 1. Her e we report the characterization of a novel NTRK1-derived thyroid onco gene, named TRK-T3. A cDNA clone, capable of transforming activity, wa s isolated from a transformant cell line. Sequence analysis revealed t hat TRK-T3 contains 1,412 nucleotides of NTRK1 preceded by 598 nucleot ides belonging to a novel gene that we have named TFG (TRK-fused gene) . The TRK-T3 amino acid sequence displays, within the TFG region, a co iled-coil motif that could endow the oncoprotein with the capability t o form complexes. The TRK-T3 oncogene encodes a 68-kDa cytoplasmic pro tein reacting with NTRK1-specific antibodies. By sedimentation gradien t experiments the TRK-T3 oncoprotein was shown to form, in vivo, multi meric complexes, most likely trimers or tetramers. The. TFG gene is ub iquitously expressed and is located on chromosome 3. The breakpoint pr oducing the TRK-T3 oncogene occurs, within exons of both the TFG gene and the NTRK1 gene and produces a chimeric exon that undergoes alterna tive splicing. Molecular analysis of the NTRK1 rearranged fragments in dicated that the chromosomal rearrangement is reciprocal and balanced and involves loss of a few nucleotides of germ line sequences.