Regulation of stanniocalcin in MDCK cells by hypertonicity and extracellular calcium

Differential display RT-PCR cloning method was applied to poly(A)(+) RNA is olated from Madin-Darby canine kidney (MDCK) cells in isotonic or hypertoni c medium. A differentially expressed 360-bp PCR fragment was isolated, subc loned, sequenced, and used to screen an MDCK cDNA library constructed in la mbda ZapII. A composite sequence of two overlapping cDNA clones provided 1, 053 bp of sequence that was 93% identical to human stanniocalcin and corres ponded to the 3'-end of the mRNA. Although the fish homolog of this hormone inhibits calcium uptake by the gill and intestine, the function of mammali an stanniocalcin remains unknown. Stanniocalcin cDNA probe hybridizes to a 4.4-kb mRNA that is induced eightfold by hypertonicity, in a manner that is dependent on medium organic osmolytes. The mRNA induction correlates with increased total cellular content of the protein and its concomitant release to the medium, consistent with secretion for autocrine or paracrine activi ty. Furthermore, induction of the mRNA by hypertonicity is dependent on ext racellular calcium and displays a threshold phenomenon. The data suggest th at kidney stanniocalcin may have a role in the adaptation of kidney cells t o osmotic stress, in a manner that is extracellular calcium dependent.