IMMUNOCYTOCHEMICAL CHARACTERIZATION OF 2 THYROID MEDULLARY CARCINOMA CELL-LINES IN-VITRO

The immunocytochemical characterization of cell lines originating from thyroid medullary carcinoma, i.e. human TT cells and rat rMTC 6-23 ce lls, was undertaken. The immunocytochemical studies were supplemented by ultrastructural studies, including ultrastructural immunocytochemis try, and by radioimmunological estimation of calcitonin secretion to t he medium. In rMTC 6-23 cells (subcultures 24 to 30), no hormone prese nce was demonstrated immunocytochemically, which corresponded to the a bsence of secretory granules at the ultrastructural level. Of various proteins sought, only neuron-specific enolase could be demonstrated. N evertheless, the cells secreted calcitonin into the medium. TT cells ( passages 145 to 160) produced secretory granules. The granules contain ed calcitonin, calcitonin gene-related peptide, somatostatin, neuroten sin, met-enkephalin, leu-enkephalin, gastrin releasing peptide, parath yroid hormone-related protein, functional proteins of the chromogranin group and synaptophysin. Other functional proteins found in the cytos ol of TT cells included non-specific enolase, calbindin and tyrosine h ydroxylase. Receptor for calcitriol was localized in the cell nucleus. Marker proteins were localized in the cytosol (carcinoembryonic antig en) and in the cell skeleton (cu-tubulin, cytokeratin). Following chan ges in ionized calcium levels in the medium, changes in calcitonin sec retion and in immunocytochemical detectability of some hormones and fu nctional proteins were observed. TT cells demonstrated the expression of numerous hormones and functional proteins associated with calcitoni n secretion. Further, the cells in their ultrastructure, immunocytoche mical and secretory characteristics, resemble more closely normal para follicular cells of the thyroid and, in our opinion, represent a more appropriate model for functional studies.