Expression of p53 and MDM2 Proteins in Thyroid Carcinomas

Lee, Chang Hun

Abstract

The nuclear protein p53 is a tumor suppressor gene product that functions in pathways of cell cycle control and in the repair of damaged DNA. The MDM2 gene codes for a cellular protein that can complex the p53 gene product and negatively regulate its function. Interestingly an autoregulatory feedback loop is set up to regulate the activity of p53 protein and MDM2 gene expression. To evaluate the role of p53 and MDM2 proteins in thyroid carcinogenesis, the author tried immunohistochemical studies in the paraffin embedded sections of 58 thyroid carcinoma cases, including 30 papillary carcinomas, 20 follicular carcinomas, and 8 undifferentiated carcinomas. p53 protein expression was found in 8 cases (26.7%) of papillary carcinomas. It was found in all the cases of undifferentiated carcinomas and not found in the follicular carcinomas. The staining intensity and the frequency scores were more prominent in undifferentiated carcinomas. MDM2 protein expression was found in only 6 cases of papillary carcinomas. It was not expressed in follicular carcinomas or undifferentiated carcinomas. The staining intensity is less than moderate and the frequency score was usually focal. In papillary carcinomas, the correlation of p53 and MDM2 expression was insignificant. In conclusion, p53 may play a major role in tumorigenesis or the progression of undifferentiated carcinomas, but not in the other carcinomas. As compared with papillary carcinomas, follicular carcinomas are regarded as taking a different carcinogenetic pathway. The overexpression of p53 and MDM2 proteins in papillary carcinomas is presumed not to be necessarily correlated with the p53-MDM2 complex formation.