PROMOTER CHARACTERIZATION OF THE RAT NA+ I- SYMPORTER GENE/

The Na+/I- symporter is the molecule that mediates active iodide uptak e in the thyroid gland. A 16.4 kb genomic DNA fragment of the rat Na+/ I- symporter gene (rNIS) was isolated, restriction mapped and a 2 kb r egion immediate 5' to the ATG site was sequenced. The transcription st art site for rNIS was mapped to -98 nucleotide (nt) relative to the AT G translation initiation site. A series of 5' genomic DNA fragments ra nging from 233 bp to 8 kb were tested for promoter activity in both th yroid and non-thyroid cells. Our results indicate that the DNA regulat ory elements within 8 kb of the 5' flanking region of rNIS are not suf ficient to confer thyroid-selective transcription. However, consistent with the clinical observation that NIS expression is reduced in thyro id tumors, the rNIS promoter activity is suppressed in ret/PTC1 transf ormed NIH3T3 cells, compared to non-transformed NIH3T3 cells. (C) 1997 Academic Press.