Regulation of stanniocalcin in MDCK cells by hypertonicity and extracellular calcium

Differential display RT-PCR cloning method was applied to poly(A)(+) RNA isolated from Madin-Darby canine kidney (MDCK) cells in isotonic or hypertonic medium. A differentially expressed 360-bp PCR fragment was isolated, subcloned, sequenced, and used to screen an MDCK cDNA library constructed in lambdaZapII. A composite sequence of two overlapping cDNA clones provided 1,053 bp of sequence that was 93% identical to human stanniocalcin and corresponded 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 mammalian 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 activity. Furthermore, induction of the mRNA by hypertonicity is dependent on extracellular calcium and displays a threshold phenomenon. The data suggest that kidney stanniocalcin may have a role in the adaptation of kidney cells to osmotic stress, in a manner that is extracellular calcium dependent.