Autocrine role of insulin-like growth factor (IGF)-I in a human thyroid cancer cell line.

An established cell line (TC-cell, clone 78) derived from human thyroid papillary cancer cells was investigated for production of peptide growth factors. The cells had specific binding sites for insulin-like growth factor-I (IGF-I) and responded to this growth factor with increased proliferation. Culture medium conditioned by TC cells was found to contain insulin-like growth factor (IGF)-I and IGF-binding protein(s). Furthermore, reverse transcription-polymerase chain reaction revealed expression of IGF-I mRNA. When monoclonal antibody to IGF-I receptors (alpha IR3) was added, the growth of TC cells cultured in serum-free medium was significantly reduced. The growth rate of the cells was restored when the antibody was removed from the medium. These results strongly suggest that TC cells produce IGF-I, which is involved in the regulation of their own growth.