IMMUNOCYTOCHEMICAL DETECTION OF P53 IN HUMAN THYROID CARCINOMAS IS ASSOCIATED WITH MUTATION AND IMMORTALIZATION OF CELL-LINES

Mutations in the tumor suppressor gene p53 are the most common mutatio ns found in human cancers. In thyroid cancers, p53 mutations generally are found only in poorly differentiated and undifferentiated tumors a nd in cell lines. To determine the prevalence of p53 mutations in thyr oid neoplasms and thyroid cell lines, we screened 58 thyroid tissues a nd 3 thyroid cell lines. p53 primers bracketing exons 4, 5/6, 7, and 8 were used to amplify genomic DNA using the PCR. Mutations were screen ed by denaturing gradient gel electrophoresis and confirmed by sequenc ing. The two papillary thyroid cancer cell lines and the follicular th yroid carcinoma cell line (positive control) had transitions (CGT->CAT ) in exon 8, codon 273, resulting in the replacement of arginine with histidine. No normal thyroid tissues or primary tumors from which the cell lines were derived demonstrated exon 8 mutations, using this tech nique. p53 immunocytochemistry demonstrated a progression of p53 immun opositivity between synchronous and metachronous neoplasms, parallelin g the neoplastic progression from a benign adenoma to primary carcinom a, regional, and distant metastasis and ultimately, the cell lines, wh ere intense immunopositivity is noted. In addition, fluorescence in si tu hybridization, using probes specific for the p53 locus, revealed th e presence of 3 homologues of p53 in the follicular cell line and 2 ho mologues in the papillary and Hurthle cell lines. These results sugges t that a point mutation present in a small number of original tumor ce lls and amplification of the mutant allele may be responsible for immo rtalizing well-differentiated thyroid cancer cells into cell lines.