| Abstract: | The presence of IGF-I receptors was demonstrated in normal and neoplastic tissues of human thyroid. Binding of (125I)IGF-I to thyroid membranes was dependent on time and temperature of incubation, and maximal binding was achieved at 4 degree C and 18 h of incubation. (125I)IGI-I binding was dose-dependently displaced by unlabelled IGF-I; half-maximal inhibition occurred at concentrations of 10-20 milligrams. IGF-II and insulin had relative potencies of 5 and 1% compared with IGF-I. Scatchard analysis of binding data revealed a single class of IGF-I receptors with high affinity (Ka: 1.2-8.6 x 10(9) 1/mol) in normal thyroid tissues. Affinity cross-linking and autoradiography demonstrated the type IIGF receptors. Specific binding of (125I)IGF-1 in thyroid cancer tissues (9.69 +/- 2.07% per 200 micrograms protein; mean +/- SEM, N = 8) was significantly (p less than 0.05) higher than that in the surrounding normal tissues (3.03 +/- 0.35%, N = 8). In contrast there was no difference in the binding between adenoma tissues (4.19 +/- 0.53%, N = 5) and the adjacent normal tissues (2.94 +/- 0.24%, N = 5). The higher IGF-I binding in cancer tissues was due to an increase in the binding capacity without any change in the affinity. The presence of IGF-I receptors suggests a possible role of IGF-I and its receptors in the growth of thyroid cancer cells. |
