POSTTRANSCRIPTIONAL REGULATION OF THE STANNIOCALCIN GENE BY CALCIUM

Stanniocalcin (STC) is a Ca2+-regulating hormone produced by the corpuscles of Stannius in bony fish. Calcium has been shown to stimulate STC synthesis at multiple levels including the level of gene expression. The purpose of this study was to determine the effects of Ca2+ on STC mRNA stability, The half-life of STC mRNA was measured in primary cultured trout corpuscles of Stannius cells maintained in either normal (1.2 mm) or high (1.9 mM) levels of extracellular calcium and treated with the transcriptional inhibitor alpha-amanitin. In cells maintained in 1.2 mM Ca2+, STC mRNA levels decreased progressively over time with an estimated half-life of similar to 71 h. However, message levels remained unchanged for up to 4 days in cells maintained in 1.9 mM Ca2+, indicating that the transcript had been stabilized in response to Ca2+ stimulation. Blocking transcription prior to exposing cells to high Ca2+ did not alter the stabilizing effects of the cation, indicating that synthesis and processing of the mRNA transcript were not involved in message stabilization. Inhibiting protein synthesis with cycloheximide also had no influence on the stabilizing effects of high calcium, The experiments involving cycloheximide further suggested that the mechanism of mRNA stabilization involved protein-nucleic acid interactions in the cytoplasm, whereby the polysomal complex protected the mRNA from degradation, These data demonstrate that the stimulatory effect of Ca2+ on STC gene expression is due, in part, to mRNA stabilization.