Nephrocalcin: biosynthesis by human renal carcinoma cells in vitro and in vivo

Renal carcinoma cells removed surgically from two patients (one primary tumor and one bone metastasis) were maintained in short-term culture. Media conditioned by these cells contained calcium oxalate monohydrate crystal growth inhibitor, a glycoprotein named nephrocalcin (NC). NC was also detected in both cell lines by an enzyme-linked immunosorbent assay using anti-NC antibody raised in rabbits. The glycoprotein was purified from the culture medium and found to have an amino acid composition similar to that of normal human urinary NC. However, NC from the renal carcinoma cells, isolated in multiple forms by DEAE-cellulose column chromatography, contained larger amounts of carbohydrate residues than normal NC. Purified NCs showed a dissociation constant of 10(-6) to 10(-8) M toward calcium oxalate monohydrate crystal. Three renal carcinoma cell lines maintained in long-term culture failed to produce NC. Our study demonstrates that NC is produced by renal cell carcinoma cells (in vitro) from primary and metastatic tumors. Preliminary data suggest that urinary levels of NC corresponded with disease progression in patients with metastatic disease, suggesting that NC may be useful clinically as a tumor marker.