Production of carrier proteins for insulin‐like growth factors (IGFs) by rat osteoblastic cells Regulation by IGF I and cortisol

Abstract

A bone-derived rat cell line, PyMS, releases IGF I and IGF carrier proteins which are similar to those found in rat serum. Western blot analysis of culture media conditioned by hormone-treated cells shows that growth hormone and IGF I stimulate and cortisol inhibits production of IGF carrier proteins in vitro. A glycosylated carrier protein species of 49-42 kDa is closely related to the subunits of the growth hormone-dependent carrier protein complex found in rat serum. In addition, rhIGF I rapidly induces a 32 kDa, non-glycosylated IGF-binding protein whose accumulation is markedly increased by cortisol.Insulin-like growth factor I; Carrier protein; Cortisol; (Bone cell)

A unique receptor-independent mechanism by which insulinlike growth factor I regulates the availability of insulinlike growth factor binding proteins in normal and transformed human fibroblasts.

“…Nevertheless, our observations may be related to other in vivo and in vitro studies. IGF-I-"inducible" 28-32-kD IGFBPs have been described in fetal and neonatal human fibroblast cultures (15,42), rat osteoblast-like cells (18), rodent muscle cells (14), and rabbit articular chondrocytes (16). The 36-kD IGFBP may represent 36-kD human IGFBP-2, which is increased in plasma during subcutaneous infusion of IGF-I in healthy adults (12).…”

“…Subcutaneous infusion of IGF-I in healthy adults also raises serum levels of IGFBP-2 (12). Moreover, IGF-I stimulates the release of various IGFBPs, including IGFBP-3, in cultured cells (13)(14)(15)(16)(17)(18) IGFs were iodinated by a modification ofthe chloramine T method to a specific activity of 150-300 MCi/Mg (26). Cell cultures.…”

Regulation of binding proteins for insulin-like growth factors (IGF) in humans. Increased expression of IGF binding protein 2 during IGF I treatment of healthy adults and in patients with extrapancreatic tumor hypoglycemia.

“…However, they have also been detected in interstitial and cerebrospinal fluid (2, 4,5) and in media of cultured cells or organ explants (2, [6][7][8].…”

“…They prolong the half-life of the IGFs in the circulation (9,10) and protect the organism against acute insulinlike effects of the IGFs (10,11). In the interstitial fluid they may modulate the bioavailability of locally secreted IGFs to IGF target cells (7,8,(12)(13)(14). Finally, they appear to be involved in specific IGF targeting (11,15).…”

Effects of IGF-I and -II, IGF binding protein-3 (IGFBP-3), and transforming growth factor-beta (TGF-beta) on growth and apoptosis of human osteosarcoma Saos-2/B-10 cells: lack of IGF-independent IGFBP-3 effects

“…The air-dried ®lters were washed in Tris-buffered saline (TBS; 0.15 mol/l NaCl and 0.01 mol/l Tris, pH 4), containing 0.1% Tween 20 and then incubated with 125 I-labeled IGF-II (4 Â 10 6 cXpXmX per plastic bag) for 6 h at room temperature. After washing with TBS containing 0.1% Tween 20, the ®lters were exposed for 1 day at 280 8C to an X-ray ®lm (Kodak X-OMAT AR) in cassettes equipped with intensifying screens as described (18). For immunoblot analysis, 30 ml media aliquots were loaded per lane and electrophoresed under reducing conditions.…”