Localization and expression of thyroid hormone receptors in normal and neoplastic human thyroid

The aim of this study was to investigate the regional expression of thyroid hormone nuclear receptor forms (TRα and TRβ) and isoform (TRα1 and TRβ2) mRNAs in normal and neoplastic (benignant and malignant) human thyroid tissue. Tumor specimens from patients with thyroid carcinomas (papillary: 5 cases; follicular: 5 cases; anaplastic: 2 cases), thyroid follicular adenomas (7 cases) and tissue from normal thyroid glands (12 cases) were analyzed by in situ hybridization and semiquantitative RT-PCR for the expression of TRα1 and β, as well as for the isoform α2 that does not bind the hormone. In normal tissues, TRα2 was expressed at lower levels compared to TRα1 (α1/α2=4.3). In papillary and follicular carcinomas, the expression of TRα1 and TRβ did not change as compared with normal thyroid tissue and adenomas (0.87±0.15 SD vs 0.89±0.17 densitometric units, DU, and 0.15±0.02 vs 0.14±0.03 DU, respectively). However, the expression of TRα2 was significantly higher in differentiated carcinomas compared to normal thyroid tissue and adenomas (0.47±0.05 vs 0.20±0.05 DU, p<0.05) with α1/α2=1.4. In anaplastic carcinoma all TRs were absent. We concluded that both normal and pathological thyroid tissues, with the exception of anaplastic carcinoma, express all TRs in thyreocites and that differentiated thyroid carcinomas are associated in enhancing the expression of TRα2 mRNA. ©2003, Editrice Kurtis.