Insulin-like growth factor-I (IGF-1) receptor and IGF-I binding proteins in well-differentiated follicular and anaplastic human thyroid cancer cell lines

Insulin-like growth factor-I (IGF-I) has been identified in various tissues and cell lines in recent studies. In cancer tissues and papillary human thyroid cancer cell line, IGF-I may play an important role in stimulating cellular proliferation and differentiation through endocrine, paracrine, and autocrine mechanisms. In this study, we used RO82 W-1 (well-differentiated human thyroid cancer cell line) and SW 579 (anaplastic human thyroid cancer cell line) cell lines to study the role of IGF-I in the regulation of human thyroid cancer cell growth. The presence of IGF-I receptor was verified in both cell lines by ¹²⁵I labeled IGF-I binding inhibition assay. The binding affinity of IGF-I in both cell lines at 4°C was higher than at 25°C and 37°C. IGF-I could be identified in the cytosolic portion of the RO82 W-1 cell line by using immunocytochemical staining. In [³H] thymidine incorporation studies, IGF-I was shown to stimulate proliferation in both cell lines. About 60% of the thymidine incorporation increment was demonstrated. After the cells were cultured with serum-free RPMI 1640 culture medium, IGF-I binding proteins with a molecular weight of about 41 Kd were verified as secreted by both cell lines. From the results of the [³H] thymidine incorporation and IGF-I binding proteins secretion studies, IGF-I was shown to play a role in the regulation of human thyroid cancer cells. Both cell lines used in the study can secrete IGF-I binding proteins. Regulatory effects of these binding proteins in human thyroid cancer cells require further investigation.