POINT MUTATIONS IN THE THYROTROPIN RECEPTOR IN HUMAN THYROID-TUMORS

The mechanism of the impaired response to thyrotropin (TSH) in thyroid tumor cells was investigated by searching for structural changes in t he TSH receptor (TSH-R) in neoplastic thyroid tissues in humans. Total RNA was prepared from 34 thyroid tissue samples (four normal, six ade noma, six follicular cancer, and 18 papillary cancer) and reverse-tran scribed into single-stranded cDNA, which was then used as a template f or the polymerase chain reaction and subjected to single-strand confor mation polymorphism (SSCP) analysis. Two fragments, FRAG (468-692) (nu cleotides 468 to 692, corresponding to the mid-portion of the receptor extracellular domain) and FRAG (2044-2295) (nucleotides 2044 to 2295, corresponding to the COOH-terminal, cytoplasmic domain of the TSH-R c DNA) showed differences in electrophoretic mobility among the various thyroid tissue samples. Direct sequencing revealed Phe(197) (TTC) --> Ile(ATC), and Asp(219) (GAT) --> Glu(GAG) substitutions in FRAG (468-6 92) from two papillary cancers. Three types of substitution were ident ified in FRAG (2044-2295): Asn(715) (AAC) --> Asp(GAC) from one papill ary cancer, Lys(723) (AAG) --> Met(ATG) from one papillary cancer, and Asp(727) (GAC) --> Glu(GAG) from one normal tissue sample, one follic ular cancer, and four papillary cancers. These results suggest that th ere exist structural changes in TSH-R in some cases of thyroid neoplas tic tissue.