AJP - Renal Physiology, Vol 257, Issue 3 390-F398, Copyright © 1989 by American Physiological Society
Evidence that mouse renal proximal tubule cells produce nephrocalcin
D. Sirivongs, Y. Nakagawa, W. K. Vishny, M. J. Favus and F. L. Coe
Nephrology Program, Pritzker School of Medicine, University of Chicago, Illinois 60637.
Nephrocalcin (NC) is a glycoprotein inhibitor of calcium oxalate
monohydrate crystal growth present in urine and kidney tissue. To determine
if kidney cells can produce NC, we have isolated proximal tubules from
mouse kidney and cultured them in a serum-free medium containing
supplements. The tubules accumulate p-aminohippurate and respond with
increase in adenosine 3',5'-cyclic monophosphate to parathyroid hormone but
not to arginine vasopressin. They produce 1,25 dihydroxyvitamin D3 when 25
hydroxyvitamin D3 is added as substrate. Medium conditioned for 3 days
reacted by direct enzyme-linked immunosorbent assay (ELISA) with a rabbit
antiserum to human urinary NC; the same antiserum was localized to the
cells using immunoperoxidase staining. Using ion exchange and molecular
sieve chromatography, we purified a glycoprotein calcium oxalate
crystal-growth inhibitor the chromatographic behavior and amino acid and
carbohydrate compositions of which closely resembled that of purified human
urinary NC. Its dissociation constant toward the calcium oxalate crystal
was 0.4-10 X 10(-7) M. Purified fractions of the protein cross-reacted with
the antiserum tested by ELISA. Cultured proximal tubule cells produce a
molecule that resembles NC from human urine, rat urine, and rat kidneys;
proximal tubule is a probable site of NC production in vivo.
