title: Interaction of insulin-like growth factor I with porcine thyroid cells cultured in monolayer.
abstract: 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.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002455:Cell Division; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis; D004247:DNA / Q000096:biosynthesis; D007328:Insulin / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000378:metabolism / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007700:Kinetics; D011972:Receptor, Insulin / Q000378:metabolism; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*; D013552:Swine; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*
chemical_list: D007328:Insulin; D007457:Iodine Radioisotopes; D017451:Receptors, Somatomedin; D013002:Somatomedins; C008147:insulin, iodo-; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D004247:DNA; D000242:Cyclic AMP; D011972:Receptor, Insulin