VITAMIN-D-DEPENDENT TRANSCRIPTIONAL REGULATION OF THE INTESTINAL PLASMA-MEMBRANE CALCIUM-PUMP

The vitamin D hormone, 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3], was shown to increase intestinal plasma membrane calcium pump (PMCA) gene expression. The present study was done to determine whether gene tran scription is involved in this process. Nuclei were isolated from duode na of vitamin-D-deficient chicks given 1,25(OH)(2)D-3 intracardially a t various times before experiment. The abundance of PMCA RNA in the nu clear and total cellular fractions, measured by a ribonuclease protect ion assay, was significantly increased above control values at 1.5 hr. and maximized at 3 hr. post-dose. As shown, cross-contamination of nu clear PMCA RNA by cytosolic RNA cannot account for these results. Thes e studies are the first to show that 1,25(OH)(2)D-3 regulates expressi on of a plasma membrane calcium pump gene by increasing the rate of tr anscription. (C) 1995 Academic Press, Inc.