Promoter characterization of the human Na+/I- symporter.

The Na+/I- symporter (NIS) is the plasma membrane protein that mediates active iodide uptake into thyroid follicular cells. To understand the molecular mechanisms of human NIS (hNIS) gene regulation, the 2-kb immediate 5'-flanking region of hNIS was characterized. The tentative hNIS transcriptional start site was mapped to -375 nucleotide relative to the ATG site. Various 5'-genomic DNA fragments were tested for promoter activity in thyroid and nonthyroid cells. Our results indicate that the DNA regulatory elements in the 2-kb immediate 5'-flanking region were not sufficient to confer thyroid-selective transcription of the hNIS gene. In addition, hNIS minimal promoter was localized to a region of 144 bp that contains a 90-bp stretch of a highly conserved DNA fragment between hNIS and rat NIS.