Characterization of the upstream enhancer of the rat sodium/iodide symporter gene.
We previously demonstrated the presence of an enhancer that is located between nucleotides - 2264 and - 2495 in the 5' flanking region of the rat sodium/iodide symporter (NIS) gene (Ohno et al., 1999). When attached to NIS or heterologous promoters, this 232 bp fragment, which we call NUE, is able to stimulate transcription in a thyroid-specific and cAMP-dependent manner. A paired-domain transcription factor Pax8 binds to this enhancer and can stimulate the transcription in non-thyroid cells that do not normally support the NUE activities. Cotransfection of PKA, a downstream effector of cAMP, further potentiates the Pax8-mediated transactivation. However, this transcriptional machinery containing pax8 seems to require contributions from the neighboring cis-acting element that is similar to CRE/AP-1 consensus sequences. Modification of this putative CRE/AP-1 site not only represses the NUE transcriptional activities by 90% in FRTL-5 cells, but also nullifies the synergistic effect of PKA on pax8-mediated transactivation in HeLa cells. In this report, we have further characterized the putative CRE/AP-1 site within the NIS upstream enhancer using gel mobility shift assay. An oligonucleotide probe with NIS CRE/AP-1 sequence produced complex binding patterns in both FRTL-5 and HeLa cell, reflecting the presence of diverse classes of binding factors. When compared with CRE or AP-1 elements in other genes, the mobility shift pattern of NIS CRE/AP-1 was similar to those of collagenase TRE, c-Jun TRE, and somatostatin CRE, but the relative intensities of the binding complexes were quite different. This observation raises a possibility that the NIS CRE/AP-site is regulated by a novel mechanism.
Chun
J T
JT
Department of Biochemistry and Molecular Biology, Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli, Italy. chun@alpha.szn.it
Di Lauro
R
R
D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D000242:Cyclic AMP / Q000494:pharmacology; D004742:Enhancer Elements, Genetic / Q000187:drug effects*; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D007455:Iodine / Q000378:metabolism; D051381:Rats; D027981:Symporters / Q000235:genetics*; D013972:Thyrotropin / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000737:chemistry / Q000378:metabolism; D014158:Transcription, Genetic; D000099209:Sodium-Iodide Symporters
D000242:Cyclic AMP; D007455:Iodine; D027981:Symporters; D013972:Thyrotropin; D018808:Transcription Factor AP-1; D000099209:Sodium-Iodide Symporters