Insulin-like growth factors in sheep thyroid cells: action, receptors and production.
Sheep thyroid cells cultured in serum-free medium were used to study the biologic activity, binding, and production of the insulin-like growth factors (IGFs). IGF-I, IGF-II, and insulin stimulated thyroid cell division. Abundant, specific IGF receptors on sheep thyroid cell membranes were identified by binding displacement studies. Maximal specific binding of [125I]-labeled IGF-I and IGF-II to 25 micrograms of membrane protein averaged 21% and 27% respectively. The presence of type I and type II IGF receptors was confirmed by polyacrylamide gel electrophoresis of [125I]IGFs covalently cross-linked to cell membranes. Under reducing conditions, [125I]IGF-I bound to a moiety of approximate Mr = 135,000 and [125I]IGF-II to a moiety of approximate Mr = 260,000. Cross-linking of [125I]IGF-I to medium conditioned by thyroid cells indicated the presence of four IGF binding proteins with apparent Mr = 34,000, 26,000, 19,000 and 14,000. Thyroid cells also secreted IGF-I and II into the medium. IGF synthesis was enhanced consistently by recombinant growth hormone. These data indicate that sheep thyroid cells are a site for IGF action, binding, and production and provide further evidence that IGFs may modulate thyroid gland growth in an autocrine or paracrine manner.
Bachrach
L K
LK
Department of Pediatrics, Stanford University Medical Center, CA 94305.
Eggo
M C
MC
Hintz
R L
RL
Burrow
G N
GN
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D011972:Receptor, Insulin / Q000378:metabolism*; D017451:Receptors, Somatomedin; D012756:Sheep; D013002:Somatomedins / Q000378:metabolism*; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology
D007328:Insulin; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013972:Thyrotropin; D011972:Receptor, Insulin