Intronic elements in the Na+/I- symporter gene (NIS) interact with retinoic acid receptors and mediate initiation of transcription.
Activity of the sodium/iodide symporter (NIS) in lactating breast is essential for iodide (I(-)) accumulation in milk. Significant NIS upregulation was also reported in breast cancer, indicating a potential use of radioiodide treatment. All-trans-retinoic acid (tRA) is a potent ligand that enhances NIS expression in a subset of breast cancer cell lines and in experimental breast cancer models. Indirect tRA stimulation of NIS in breast cancer cells is very well documented; however, direct upregulation by tRA-activated nuclear receptors has not been identified yet. Aiming to uncover cis-acting elements directly regulating NIS expression, we screened evolutionary-conserved non-coding genomic sequences for responsiveness to tRA in MCF-7. Here, we report that a potent enhancer in the first intron of NIS mediates direct regulation by tRA-stimulated nuclear receptors. In vitro as well as in vivo DNA-protein interaction assays revealed direct association between retinoic acid receptor-alpha (RARalpha) and retinoid-X-receptor (RXR) with this enhancer. Moreover, using chromatin immunoprecipitation (ChIP) we uncovered early events of NIS transcription in response to tRA, which require the interaction of several novel intronic tRA responsive elements. These findings indicate a complex interplay between nuclear receptors, RNA Pol-II and multiple intronic RAREs in NIS gene, and they establish a novel mechanistic model for tRA-induced gene transcription.
Alotaibi
Hani
H
Department of Molecular Biology and Genetics, Bilkent University, 06800 Bilkent, Ankara, Turkey.
Yaman
Elif
E
Salvatore
Domenico
D
Di Dato
Valeria
V
Telkoparan
Pelin
P
Di Lauro
Roberto
R
Tazebay
Uygar H
UH
D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D017124:Conserved Sequence; D004742:Enhancer Elements, Genetic; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D023281:Genomics; D006801:Humans; D007438:Introns; D012319:RNA Polymerase II / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D020218:Response Elements; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors / Q000378:metabolism; D027981:Symporters / Q000235:genetics*; D014158:Transcription, Genetic; D014212:Tretinoin / Q000494:pharmacology; D000099209:Sodium-Iodide Symporters
D012319:RNA Polymerase II; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D027981:Symporters; D014212:Tretinoin; D000099209:Sodium-Iodide Symporters; C000607071:RARA protein, human