title: Insulin-like growth factor I (IGF-I) production and the presence of IGF-I receptors in rat medullary thyroid carcinoma cell line 6-23 (clone 6).
abstract: To clarify whether insulin-like growth factor I (IGF-I) is an autocrine growth factor of rat medullary thyroid carcinoma (MTC) cell line, 6-23 (clone 6), IGF-I binding to MTC cell membranes, IGF-I levels in the conditioned culture medium of MTC cells and the effects of IGF-I on methyl-[3H]thymidine incorporation to MTC cells were examined. Scatchard analysis of saturation binding studies revealed the association constant and the maximal binding capacity were 1.0 x 10(9) M-1 and 199 fmol/mg of membrane protein, respectively. The binding of [125I]IGF-I to MTC cell membranes was inhibited by unlabeled IGF-I, IGF-II and insulin; the relative potencies were IGF-I greater than IGF-II much greater than insulin, suggesting the presence of type I IGF receptors in MTC cells. IGF-I levels in the conditioned culture medium of MTC cells were 120 +/- 3 pM (mean + SE). IGF-I (10(-10) to 10(-8) M) dose-dependently stimulated methyl-[3H]thymidine incorporation to MTC cells. These findings suggest a possible role of IGF-I as an autocrine growth factor for MTC cells.
authors.affiliation: Division of Metabolism and Nutrition, International Center for Medical Research, Kobe, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Okimura
authors.forename: N
authors.initials: N
authors.lastname: Kitajima
authors.forename: T
authors.initials: T
authors.lastname: Uchiyama
authors.forename: H
authors.initials: H
authors.lastname: Yagi
authors.forename: H
authors.initials: H
authors.lastname: Abe
authors.forename: S
authors.initials: S
authors.lastname: Shakutsui
authors.forename: K
authors.initials: K
authors.lastname: Chihara
mesh_terms: D000818:Animals; D002277:Carcinoma / Q000473:pathology / Q000503:physiopathology*; D002455:Cell Division; D003470:Culture Media; D004273:DNA, Neoplasm / Q000096:biosynthesis; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000502:physiology; D051381:Rats; D011956:Receptors, Cell Surface / Q000502:physiology*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000096:biosynthesis*; D013964:Thyroid Neoplasms / Q000503:physiopathology*; D014407:Tumor Cells, Cultured
chemical_list: D003470:Culture Media; D004273:DNA, Neoplasm; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I