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 human thyroid samples by combined immunohistochemistry and Western blotting.

METHODS AND

RESULTS

Fifty-eight paraffin-embedded thyroid samples (40 normal or benign tissues, 16 papillary and two follicular carcinomas) were analysed by immunohistochemistry using a specific monoclonal antibody. Western blotting was also carried out on 11 selected samples (seven normal or benign tissues, three papillary carcinomas and one follicular carcinoma) and two human ovarian carcinomas as controls. RAR beta immunostaining was nuclear and limited to the normal epithelial thyroid tissue. A dramatic decrease in RAR beta immunostaining was observed in all the papillary carcinomas and in one follicular carcinoma. The other follicular carcinoma exhibited strong RAR beta immunostaining. By immunoblotting, a 51 kDa signal corresponding to the RAR beta was observed in nuclear extracts from normal thyroids and for one follicular carcinoma. However, this signal was lacking in the papillary carcinomas. These results were in complete agreement with the observations 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 expression is decreased in papillary thyroid carcinoma.