title: Transforming growth factor-beta stimulates production of insulin-like growth factor-binding protein-3 by human skin fibroblasts.
abstract: Human neonatal fibroblasts in monolayer culture produce insulin-like growth factor-binding protein-3 (IGFBP-3), the IGF-binding subunit of the circulating 140-kDa IGFBP complex. We now report that transforming growth factor-beta (TGF beta) is a potent stimulator of IGFBP-3 production by fibroblasts. After 72-h incubation with 1 ng/ml TGF beta, the levels of IGFBP-3 in conditioned medium were increased 5.8 +/- 1.2-fold (mean +/- SE; n = 9). Half-maximal stimulation of IGFBP-3 production was seen at 0.4 +/- 0.05 ng/ml TGF beta (n = 4). Coincubation of fibroblasts with TGF beta and either IGF-I or IGF-II at 50 ng/ml enhanced IGFBP-3 production 1.5- to 2-fold compared to TGF beta alone. As previously reported, fetal calf serum (FCS) stimulated IGFBP-3 production 5- to 6-fold; 1 ng/ml TGF beta increased the stimulated production of IGFBP-3 by FCS a further 2.5- to 3.5-fold. Acidification of FCS before addition enhanced the stimulation of IGFBP-3 compared to that caused by untreated FCS, but decreased further potentiation by TGF beta. This effect of acidified FCS was reversed by a neutralizing antibody to TGF beta. Similarly, the stimulation of IGFBP-3 levels by human serum or conditioned serum-free fibroblast medium was significantly increased by acidification of serum or medium before addition and was reversed by TGF beta antibody. These observations are consistent with acid-mediated activation of latent TGF beta added in serum or secreted by fibroblasts. Since IGFBP-3 is known to regulate IGF activity in fibroblasts, these results raise the possibility that TGF beta may modulate IGF actions in these cells by stimulating the production of IGFBP-3.
authors.affiliation: Department of Medicine, University of Sydney, New South Wales, Australia.
authors.forename: J L
authors.initials: JL
authors.lastname: Martin
authors.forename: R C
authors.initials: RC
authors.lastname: Baxter
mesh_terms: D000818:Animals; D001790:Blood Physiological Phenomena; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle / Q000097:blood / Q000196:embryology; D002452:Cell Count; D002478:Cells, Cultured; D003470:Culture Media; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008970:Molecular Weight; D012867:Skin / Q000166:cytology / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000097:blood / Q000494:pharmacology*
chemical_list: D002352:Carrier Proteins; D003470:Culture Media; D018969:Insulin-Like Growth Factor Binding Proteins; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I