Reduced expression of retinoic acid receptor beta protein (RARβ) in human papillary thyroid carcinoma: immunohistochemical and Western blot study

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Abstract
To investigate the role of retinoic acid receptor beta (RARβ) in thyroid carcinogenesis, we have investigated its expression in human thyroid samples by combined immunohistochemistry and Western blotting. 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. RARβ immunostaining was nuclear and limited to the normal epithelial thyroid tissue. A dramatic decrease in RARβ immunostaining was observed in all the papillary carcinomas and in one follicular carcinoma. The other follicular carcinoma exhibited strong RARβ immunostaining. By immunoblotting, a 51 kDa signal corresponding to the RARβ 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. We present here the first demonstration of RARβ protein in normal human thyroid follicular cells. In addition, we found that its expression is decreased in papillary thyroid carcinoma.