Thyrotropin-induced expression of a gene for a ribosomal protein related to the trk oncogene.

By differential screening of an FRTL5 rat thyroid cell cDNA library, we isolated a clone (G7) corresponding to an mRNA transcript whose steady-state level is increased by thyrotropin (TSH) stimulation by a non-transcriptional mechanism. The nucleotide sequence of the G7 cDNA (0.85 kb) revealed homology with two other genes. First, there was 89% homology with the cDNA for a protein whose amino-terminal end forms the amino terminus of the chimeric tyrosine kinase human oncogene, trk-2h. Second, TSH-responsive G7 is 95% homologous with the 'surf-3' gene within the mouse surfeit locus which codes for the mouse L7a ribosomal protein. These findings are of interest in view of the frequent occurrence in thyroid cancers of an oncogene (PTC) that consists of an unidentified amino terminus linked to a downstream tyrosine kinase moiety.