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| THE CALCIUM-OXALATE CRYSTAL-GROWTH INHIBITOR PROTEIN PRODUCED BY MOUSE KIDNEY CORTICAL-CELLS IN CULTURE IS OSTEOPONTIN |
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| Author(s): WORCESTER EM, BLUMENTHAL SS, BESHENSKY AM, LEWAND DL |
| Source: JOURNAL OF BONE AND MINERAL RESEARCH Volume: 7 Issue: 9 Pages: 1029-1036 Published: SEP 1992 |
| Times Cited: 96 References: 31 |
| Abstract: Urine contains proteins that inhibit the growth of calcium oxalate (CaOx) crystals and may prevent the formation of kidney stones. We have identified a potent crystal growth inhibitor in the conditioned media from primary cultures of mouse kidney cortical cells. Conditioned media, incubated with the kidney cells for 6-72 h, was assayed for crystal growth inhibition; inhibitory activity increased 15-fold by 24 h. Inhibitory activity was purified from serum-free media containing proteinase inhibitors using anion-exchange and gel-filtration chromatography. A single band of molecular weight 80,000 daltons was seen after SDS-polyacrylamide gel electrophoresis. The sequence of the N-terminal 21 amino acids of this protein matched that of osteopontin (OP), a phosphoprotein initially isolated from bone matrix. Antisera raised to fusion proteins produced by plasmids containing the N-terminal or C-terminal portions of OP cDNA also cross-reacted with the protein purified from cell culture media on western blots. The effect of the purified protein on the growth of CaOx crystals was measured using a constant composition assay. A 50% inhibition of growth occurred at a protein concentration of 0.85-mu-g/ml, and the dissociation constant of the protein with respect to CaOx crystal was 3.7 x 10(-8) M. The concentration of OP in mouse urine, measured using antibodies raised to the purified protein, was approximately 8-mu-g/ml. We conclude that OP is synthesized by kidney cortical tubule cells and functions as a crystal growth inhibitory protein in urine. |
| Document Type: Article |
| Language: English |
| Reprint Address: WORCESTER, EM (reprint author), ZABLOCKI VET ADM MED CTR, NEPHROL SECT 111K, 5000 W NATL AVE, MILWAUKEE, WI 53295 USA |
Addresses:
1. MED COLL WISCONSIN, DEPT MED, MILWAUKEE, WI 53226 USA |
| Publisher: BLACKWELL SCIENCE INC, 350 MAIN ST, MALDEN, MA 02148 |
| Subject Category: Endocrinology & Metabolism |
| IDS Number: JN951 |
| ISSN: 0884-0431 |
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