Insulin-like growth factor (IGF) binding proteins and insulin-like growth factor secretion by cultured chondrocyte cells: identification, characterization and ontogeny during cell differentiation.
Insulin-like growth factor binding proteins (IGF BP) and insulin-like growth factors (IGF) secretion by differentiating chondrocytes, derived from mouse embryonic limb bud and responsive to both IGF-I and -II [23], was investigated. The Western ligand blot analysis of the conditioned medium (CM) from days 1, 3, 5 and 7 of culture revealed the secretion of IGF BP of approx. 35-40, 28-30 and 24-26 kDa. The 35-40 kDa protein which comigrated with the 40 kDa protein in CM of trophoblast cells identified as IGF BP-3. The 28-30 kDa protein was identified as IGF BP-2 by Western immunoblotting with alpha-IGF BP-2 antisera. The 24-26 kDa protein was consistent with the nonglycosylated form of IGF BP-4. Secretion of three IGF BPs were increased with the age of the culture. This suggested that the major IGF BP secreted by differentiating chondrocytes in culture are IGF BP-2, -3 and -4. All three of these IGF BPs were stimulated by both IGF-I and -II. IGF-I was approx. 2-fold more potent than IGF-II. The investigation of the localized production of IGF revealed that chondrocytes, similar to IGF BP, secreted IGF-II in differentiation dependent manner. No IGF-I secretion was identified. Examination of the secretion of solubilized IGF-II receptor by the chondrocytes, in contrast to trophoblasts, failed to reveal the presence of IGF-II receptor in the CM. This suggested that, unlike many other cells, including trophoblasts, chondrocytes do not secrete solubilized IGF-II receptor. In summary, the present results suggested an interactive autocrine/paracrine action of IGF BP and IGF-II in the chondrocytes, while the IGF-I action is predominantly endocrine.
Bhaumick
B
B
Department of Medicine, University of Saskatchewan, Saskatoon, Canada.
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis / Q000096:biosynthesis* / Q000378:metabolism; D002356:Cartilage / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D004622:Embryo, Mammalian; D018971:Insulin-Like Growth Factor Binding Protein 2; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000096:biosynthesis* / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000032:analysis / Q000096:biosynthesis* / Q000494:pharmacology; D007457:Iodine Radioisotopes; D051379:Mice; D008970:Molecular Weight; D011869:Radioligand Assay; D017527:Receptor, IGF Type 2 / Q000032:analysis
D002352:Carrier Proteins; D018971:Insulin-Like Growth Factor Binding Protein 2; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D007457:Iodine Radioisotopes; D017527:Receptor, IGF Type 2; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II