REDUCED EXPRESSION OF RETINOIC ACID RECEPTOR-BETA PROTEIN (RAR-BETA) IN HUMAN PAPILLARY THYROID-CARCINOMA - IMMUNOHISTOCHEMICAL AND WESTERN-BLOT STUDY

Aims: To investigate the role of retinoic acid receptor beta (RAR beta ) in thyroid carcinogenesis, we have investigated its expression in hu man thyroid samples by combined immunohistochemistry and Western blott ing. Methods and results: Fifty-eight paraffin-embedded thyroid sample s (40 normal or benign tissues, 16 papillary and two follicular carcin omas) were analysed by immunohistochemistry using a specific monoclona l antibody. Western blotting was also carried out on 11 selected sampl es (seven normal or benign tissues, three papillary carcinomas and one follicular carcinoma) and two human ovarian carcinomas as controls. R AR beta immunostaining was nuclear and limited to the normal epithelia l thyroid tissue. A dramatic decrease in RAR beta immunostaining was o bserved in all the papillary carcinomas and in one follicular carcinom a. The other follicular carcinoma exhibited strong RAR beta immunostai ning, By immunoblotting, a 51 kDa signal corresponding to the RAR beta was observed in nuclear extracts from normal thyroids and for one fol licular carcinoma. However, this signal was lacking in the papillary c arcinomas. These results were in complete agreement with the observati ons obtained by immunohistochemistry on the same samples. Conclusion: We present here the first demonstration of RAR beta protein in normal human thyroid follicular cells. In addition, we found that its express ion is decreased in papillary thyroid carcinoma.