Stanniocalcin 2 is positively and negatively controlled by 1,25(OH)(2)D(3) and PTH in renal proximal tubular cells.

We have previously identified a second mammalian stanniocalcin (STC2) in humans and demonstrated that STC2 inhibits phosphate uptake in an opossum renal proximal tubular cell line (opossum kidney (OK) cells). However, the regulation of Stc2 gene expression in OK cells is not well understood. In this study, we identified the opossum Stc2 cDNA sequence. The opossum STC2 amino acid sequence had 78.8% homology with human STC2, and has a conserved putative N-linked glycosylation site. Next, we investigated the regulation of Stc2 gene expression by the classical calcium and phosphate-regulating factors 1,25(OH)(2)D(3) and PTH in OK cells. In western blot analysis using affinity-purified anti-STC2 antibody, the secretion of STC2 protein was stimulated by 1,25(OH)(2)D(3) in a dose-dependent manner. By contrast, PTH suppressed the induction of STC2 protein secretion by 1,25(OH)(2)D(3). Real-time PCR analysis revealed that Stc2 mRNA expression was increased by 1,25(OH)(2)D(3) in a dose- and time-dependent manner. In addition, actinomycin D, an RNA synthesis inhibitor, prevented the effects of 1,25(OH)(2)D(3) on Stc2 gene expression. On the other hand, PTH and phorbol 12,13-myristic acetate, a specific PKC activator, but not 8-bromo-cyclic AMP, a specific PKA activator, reduced the mRNA levels of Stc2. In addition, Gö6976, a specific PKC inhibitor, abolished the downregulation of Stc2 mRNA expression by PTH. Furthermore, we demonstrated that the renal Stc2 mRNA expression was increased by 1,25(OH)(2)D(3) and decreased by PTH in vivo. These results suggest that STC2 is positively and negatively controlled by 1,25(OH)(2)D(3) and PTH in renal proximal tubular cells.