The promoter region of the human PMCA1 gene mediates transcriptional downregulation by 1,25-dihydroxyvitamin D-3

The gene for plasma membrane calcium pump isoform 1 (PMCA1) is expressed in calcium-transporting epithelia and bone mesenchymal cells and is upregulat ed to 1,25-(OH)(2)D-3 in those tissues. A candidate sequence for a vitamin D response element (VDRE) is present within a 1.7-kb promoter region of the human PMCA1 (hPMCA1) gene, We studied hPMCA1 promoter activity in MDBK and ROS 17/2.8 cell lines as PMCA1 mRNA expression is upregulated by 1,25-(OH) (2)D-3 in both. Structural analysis of the putative hPMCA1 VDRE sequence wa s performed using mobility shift analysis (EMSA) and nuclear extracts from COS-l cells expressing human VDR (hVDR) and RXR alpha (hRXR alpha). 1,25-(O H)(2)D-3 induced transrepression of the entire 1.7-kb hPMCA1 promoter and o f one promoter deletion construct in ROS 17/2.8 cells but not MDBK cells wh en assayed by luciferase reporter gene assays. Three additional hPMCA1 prom oter deletion constructs were unaffected by 1,25-(OH)(2)D-3 in either cell line. While hVDR and hRXR alpha were capable of complexing with a rat osteo calcin DR3 VDRE, EMSA analysis of the potential VDRE from the hPMCA1 gene d id not show interaction of either nuclear receptor. Our results indicate ti ssue-specific sensitivity of the promoter region of the hPMCA1 gene to dire ct transcriptional downregulation by 1,25-(OH)(2)D-3 and suggest that any p ositive regulatory VDRE must lie outside of the 1.7-kb core promoter. (C) 2 000 Academic Press.