Significance of P53 in human thyroid tumors.

Mutational changes in the p53 tumor suppressor gene are the most frequent genetic alterations in human malignant tumors. Studies have shown a correlation of p53 expression in breast cancer with tumor prognosis. In contrast to mutational activation of ras and GSP in thyroid tumors, little is known about the role of p53 in thyroid tumor development. Therefore thyroid tumors and thyroid tumor cell lines were studied for the presence of p53 mutations. Snap-frozen tissues from 57 differentiated thyroid carcinomas (DTCs) and 5 goiters were studied by immunohistochemical methods. A panel of six antibodies (pAb 240, 421, 1620, 1801, DO7, and CM1) was employed by using the ABC technique. Five cell lines from DTCs (FTC133, 236, 238, PTC337, MTC164) were examined by the same technique. Additionally, genomic DNA from the cells was amplified by the polymerase chain reaction (PCR) and the PCR product studied for p53 mutations (R273H) by mutation-specific oligonucleotide hybridization (MOH) and temperature gradient gel electrophoresis (TGGE) for the p53 exon 8. None of the benign thyroid tumors and 7 of 57 (12%) DTCs strongly express p53 with a heterogeneous distribution in the tumor tissue. All seven patients have metastatic disease or dedifferentiated tumors G3 (three of seven). CM1 was positive in two cell lines (FTC-133, PTC-337), questionable in FTC-238, and negative in FTC-236 and MTC-164. All three follicular cell lines, however, and the original tumor tissue showed the same p53 mutation (R273H) in MOH analysis and TGGE. P53 mutations are rare in thyroid tumors, but the presence of p53 mutations indicates a poor prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Highly efficient transactivation by the yeast Kluyveromyces lactis transcription factor LAC9 and its inhibition by the negative regulator GAL80 in mammalian cells.

Expression of the LAC9 gene from the yeast Kluyveromyces lactis in HepG2 human hepatoblastoma cells efficiently induced luciferase expression from reporter plasmids containing the four LAC9 binding sites from the K. lactis GAL1-GAL10 gene linked to a basal promoter. Induction was approximately 100fold and was dependent on the presence of the UAS sequence and an intact reading frame in the LAC9 gene. Additional cotransfection of constructs expressing the K. lactis GAL80 gene reduced luciferase activity by up to 98%. This inhibition was not affected by addition of 14mM galactose to the medium. No further yeast-specific factors appear necessary for efficient inhibition of LAC9 by GAL80, but additional gene products may be required for activation by galactose.