Intermediate-filament proteins in parathyroid glands and parathyroid adenomas

The intermediate-filament proteins of normal, hyperplastic, and adenomatous parathyroid glands were analyzed immunohistochemically and by immunoblotting with monospecific antibodies. In both normal and adenomatous parathyroid glands, we found keratins with molecular weights of 52, 45, and 40 kilodaltons (Nos. 8, 18, and 19, respectively). Vimentin proteins could be identified only in stromal cells, while glial fibrillary acidic protein was not found. In normal parathyroid glands, neurofilament positivity was seen only in nerve axons. In five of 15 parathyroid gland adenomas some keratin-positive cells expressed neurofilamentlike immunoreactivity also. In cytoskeletal extracts of one adenoma, the 200-kilodalton neurofilament protein was identified by immunoblotting. Thus it appears that some parathyroid gland adenoma cells may acquire neurofilament proteins and coexpress cytokeratin and neurofilament polypeptide in a way comparable with that reported in certain neuroendocrine tumors.