Characterization of insulin-like growth factor-binding proteins secreted by isolated sheep thyroid epithelial cells

Abstract

We have characterized the insulin-like growth factor-binding proteins (IGF-BPs) released by isolated sheep thyroid epithelial cells. Thyroid follicles were isolated with collagenase and cultured in Coon's modified F-12 M (0H medium) supplemented with insulin, cortisol, transferrin, glycyl-histidyl-lysine and somatostatin (5H medium) and TSH (6H medium). Conditioned 0H medium specifically bound both 125I-labelled IGF-I and -II, although binding capacity was reduced following acid-gel filtration to separate endogenous IGF-BP complexes, suggesting some destruction of BPs. The binding of 125I-labelled IGF-I or -II to conditioned (0H) medium was progressively displaced by increasing amounts of unlabelled homologous peptides, while fractionation on concanavalin A-Sepharose showed that the IGF-BPs consisted of both glycoprotein and non-glycoprotein components. The molecular sizes of the IGF-BPs were resolved by separation of 0H medium on SDS-PAGE and ligand blot analysis with 125I-labelled IGF-I or -II. Conditioned medium contained four specific binding species for IGF-II of 19, 30, 38 and 46 kDa; all but the smallest also binding radiolabelled IGF-I. Prior fractionation on concanavalin A-Sepharose showed that the 46 kDa binding species was a glycoprotein. Competition studies with increasing concentrations of unlabelled IGF-I or -II during ligand blotting suggested that the 46 and 30 kDa binding species had a greater affinity for IGF-II than IGF-I, while the 38 kDa had a greater relative affinity for IGF-I. Incubation of cells in 5H medium reduced the abundance of the 46 kDa binding protein, while incubation in 6H medium decreased the release of all binding protein species. Results show that isolated thyroid follicles released several forms of IGF-BP with differing relative affinities for IGF-I and -II. Gross changes seen in the presence of BPs between 0H, 5H and 6H media suggest acute hormonal control of release.

Presence and possible role of vascular endothelial growth factor in thyroid cell growth and function

“…Multiple growth factors including FGF-2, transforming growth factor (TGF ), epidermal growth factor (EGF) and the insulin-like growth factors (IGFs) and their associated binding proteins (IGFBPs) have been found in thyroid tissues. These growth factors have been implicated in the regulation of thyroid growth during goitre formation, and also modulate the metabolic effects of TSH on thyroid cells (Westermark et al 1983, Bachrach et al 1985, Morris et al 1988, Wang et al 1990, Cowin et al 1992, Logan et al 1992. Proliferation of endothelial cells, expansion of vascular spaces and increase in local blood flow are all hallmarks of iodine-deficient goitre (Denef et al 1989).…”

Effects of insulin-like growth factor I on growth, epithelial barrier and iodide transport in polarized pig thyrocyte monolayers

“…Secretion of several types of IGF binding proteins by thyrocytes has been demonstrated (16)(17)(18). Studies on mesenchymal as well as epithelial cells shows that the expression of general, as well as tissuespecific functions is influenced by the cellular organiza¬ tion, cell-cell contact and cell-substrate interaction (19)(20)(21)(22).…”

Interactive effects of nutrients and hormones on the expression of insulin‐like growth factor binding protein‐1 (IGFBP‐1) mRNA and peptide, and IGF I release from isolated adult rat hepatocytes

“…To examine the number and molecular size of IGFBPs released from cultured rat hepatocytes, the conditioned medium from control cultures, and following incubation with hormones and nutrient combinations, was subjected to ligand blot analysis as previously described (Wang et al, 1990). Briefly, 50 p1 of whole conditioned medium was mixed with 10 pl 2 x modified sample electrophoresis buffer (Laemmli, 1970) and loaded on 8% SDS polyacrylamide gels under nonreducing conditions.…”