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

Abstract

The gene for plasma membrane calcium pump isoform1 (PMCA1) is expressed in calcium-transporting epithelia and bone mesenchymal cells and is upregulated 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 was performed using mobility shift analysis (EMSA) and nuclear extracts from COS-1 cells expressing human VDR (hVDR) and RXRalpha (hRXRalpha). 1,25-(OH)(2)D(3) induced transrepression of the entire 1.7-kb hPMCA1 promoter and of one promoter deletion construct in ROS 17/2.8 cells but not MDBK cells when assayed by luciferase reporter gene assays. Three additional hPMCA1 promoter deletion constructs were unaffected by 1,25-(OH)(2)D(3) in either cell line. While hVDR and hRXRalpha were capable of complexing with a rat osteocalcin DR3 VDRE, EMSA analysis of the potential VDRE from the hPMCA1 gene did not show interaction of either nuclear receptor. Our results indicate tissue-specific sensitivity of the promoter region of the hPMCA1 gene to direct transcriptional downregulation by 1,25-(OH)(2)D(3) and suggest that any positive regulatory VDRE must lie outside of the 1.7-kb core promoter.