1. Fetuin and alpha-2HS glycoprotein induce alkaline phosphatase in epiphyseal growth plate chondrocytes.
- Author
-
Ishikawa Y, Wu LN, Valhmu WB, and Wuthier RE
- Subjects
- Amino Acid Sequence, Animals, Ascorbic Acid pharmacology, Chickens, Drug Synergism, Enzyme Induction, Membrane Proteins biosynthesis, Molecular Sequence Data, Phosphatidylinositols metabolism, alpha-Fetoproteins isolation & purification, Alkaline Phosphatase biosynthesis, Fibronectins pharmacology, Growth Plate enzymology, alpha-Fetoproteins pharmacology
- Abstract
A previously described chondrocyte alkaline phosphatase induction factor (CAP-IF) for chicken epiphyseal growth plate chondrocytes has been purified to SDS-PAGE homogeneity from fetal bovine serum by ammonium sulfate precipitation and by dye-ligand affinity (Affi-Gel Blue and Reactive Green-19 agarose) and hydroxyapatite column chromatographies. As determined by immunoprecipitation of [35S]methionine-labeled cellular proteins after 3 day treatment, this highly purified CAP-IF increases the level of AP and certain other membrane proteins 2- to 3-fold over control values. The pure protein of apparent 64.5 kDa molecular weight has been identified as fetuin by N-terminal amino acid sequencing. This was confirmed by the finding that high alkaline phosphatase (AP)-inducing activity is present in fetuin prepared by the Spiro method. However, fetuins prepared by the Pedersen or Deutsch procedures are inactive. At least half of the CAP-IF activity of fetuin was irreversibly destroyed by treatment with EDTA and addition of Zn2+ did not reactivate the EDTA-treated fetuin. Ascorbate synergistically enhanced the effect of fetuin on chondrocyte AP activity by over 8-fold during 3 day exposure. Because of the very high homology between fetuin and the A-chain of alpha 2-HS glycoprotein, we also tested and found that alpha 2HS glycoproteins from human serum and bovine bone are both strong AP inducers. Our findings suggest that the AP-inducing activity resides in a labile, cystatin/Zn(2+)-binding domain common to these related serum glycoproteins. These proteins appear to play a role in enhancing AP expression in normal growth plate cartilage differentiation.
- Published
- 1991
- Full Text
- View/download PDF