title: Sequestration and secretion of insulin-like growth factor-I by bovine aortic endothelial cells.
abstract: Endothelial cells elaborate growth promoting activities in culture medium that support limited smooth muscle cell and fibroblast growth in vitro in the absence of serum. We investigated whether insulin-like growth factor-I (IGF-I) was synthesized and secreted by bovine aortic endothelial cells in vitro. Subconfluent endothelial cell cultures in serum-free medium secreted severalfold higher IGF-I levels than confluent cultures by acid-sizing chromatography and IGF-I radioimmunoassay. The IGF-I secretory level was not sustained during a second serum-free incubation. In contrast, secretion of IGF binding proteins persisted and was maintained at constant levels throughout the same observation periods. Analysis of poly(A+)RNA by northern blots revealed hybridization of an IGF-I cDNA to a 7.5- to 7.0-kb transcript and superinduction of the 7.5-7.0-kb mRNA by the translational inhibitor, cyclohexamide. However, no endogenously labeled IGF-I was detected in conditioned media after incubation of cultures with [35S]cysteine or [3H]leucine. When cultures were incubated in the presence of serum supplemented with IGF-I, subconfluent cultures sequestered and released more IGF-I than confluent cultures. We concluded that the majority of IGF-I secreted in vitro was sequestered from serum.
authors.affiliation: Department of Neurological Surgery, University of Washington, Seattle.
authors.forename: C M
authors.initials: CM
authors.lastname: Gajdusek
authors.forename: Z
authors.initials: Z
authors.lastname: Luo
authors.forename: M R
authors.initials: MR
authors.lastname: Mayberg
mesh_terms: D000818:Animals; D001011:Aorta; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000235:genetics; D011863:Radioimmunoassay
chemical_list: D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I