Interaction of insulin-like growth factor I with porcine thyroid cells cultured in monolayer

• Published in: Endocrinology (Philadelphia) Vol. 121; no. 2; p. 749
• Main Authors: Saji, M, Tsushima, T, Isozaki, O, Murakami, H, Ohba, Y, Sato, K, Arai, M, Mariko, A, Shizume, K
• Format: Journal Article
• Language: English
• Published: United States 01.08.1987
• Subjects: Animals; Binding, Competitive; Cell Division; Cells, Cultured; Cyclic AMP - biosynthesis; DNA - biosynthesis; Insulin - analogs & derivatives; Insulin - metabolism; Insulin - pharmacology; Insulin-Like Growth Factor I - metabolism; Insulin-Like Growth Factor I - pharmacology; Insulin-Like Growth Factor II - metabolism; Insulin-Like Growth Factor II - pharmacology; Iodine Radioisotopes; Kinetics; Receptor, Insulin - metabolism; Receptors, Somatomedin; Somatomedins - metabolism; Swine; Thyroid Gland - drug effects; Thyroid Gland - metabolism
• ISSN: 0013-7227
• DOI: 10.1210/endo-121-2-749

The interaction of insulin-like growth factor I (IGF-I) with porcine thyroid cells cultured in monolayer was studied. Specific binding of [125I]iodo-IGF-I to thyroid cells was a reversible process dependent on the time and temperature of incubation. A steady state was achieved in 18 h at 4 C and averaged 14.2 +/- 2% (mean +/- SD)/10(6) cells. Binding of [125I]iodo-IGF-I was inhibited by unlabeled IGF-I; half-maximal inhibition occurred at concentrations of 2-5 ng/ml. Multiplication-stimulating activity (rat IGF-II) and pork insulin had relative potencies of 1:20 and 1:300 compared with IGF-I. Scatchard analysis of binding data revealed a single class of IGF-I receptors with a Ka of 4.3 X 10(10) M-1, 49,000 binding sites were estimated per cell. Affinity cross-linking and autoradiography demonstrated the presence of type I IGF receptors. Thyroid cells also had specific receptors for insulin, but specific binding of [125I]iodoinsulin (2.03 +/- 0.03%/10(6) cells) was much lower than that of [125I]iodo-IGF-I. Preincubation of thyroid cells with IGF-I or insulin caused a concentration-dependent decrease in [125I]iodo-IGF-I binding due to an apparent loss of receptors. Preincubation with epidermal growth factor, fibroblast growth factor, platelet-derived growth factor, or TSH did not alter subsequent binding of [125I]iodo-IGF-I. Low concentrations of IGF-I stimulated DNA synthesis and proliferation of thyroid cells and acted synergistically with epidermal growth factor. Multiplication-stimulating activity and insulin had relative potencies in stimulating DNA synthesis comparable to their abilities to inhibit the binding of [125I]iodo-IGF-I to thyroid cells, suggesting that their effects are mediated primarily by IGF-I receptors. Preincubation with IGF-I did not alter cAMP responsiveness to TSH. We, thus, demonstrated the presence of functional and regulated IGF-I receptors on porcine thyroid cells.