İnsan Na+/I- simportır geni transkripsiyonunun düzenlenmesini kontrol eden yeni genetik elemanların belirlenmesi

The function of sodium iodide symporter (NIS) in mammary gland epithelial cells isessential for the accumulation of iodide in mother?s milk, which is the first source ofiodide for the synthesis of thyroid hormones in the newborn. In addition to thelactating mammary gland, NIS expression has been also detected in breast tumors.Several hormones and ligands have been implicated in the functional expression ofNIS in the mammary gland and breast cancer cell line models but the moleculardeterminants governing this expression are not yet identified. In this study we aimedto identify cis- and trans-acting elements regulating NIS expression in the breastcancer cell line MCF-7 in response to all-trans-retinoic acid (tRA), and to assess thepossible role of 17-β-estradiol (E2) in regulating the expression of NIS. Usingcomparative bioinformatics, we have identified several regions that were conservedin human, mouse and rat in the sequences flanking and including the NIS gene. Byusing luciferase reporter assays, we have established that conserved clusters 3 and 4respond to tRA in MCF-7. We have also shown that putative retinoic acid responseelements controlling tRA-induced NIS expression in MCF-7 are located in the firstintron of this gene. This tRA-responsive NIS expression was also correlated with theestrogen receptor status of mammary gland cell lines and we investigated roles ofERα in the regulation of NIS expression. We showed that the suppression ofendogenous ERα by RNA interference resulted in down-regulation of both basal andtRA-induced NIS expression in MCF-7, furthermore, we have also shown that (E2)is capable of up-regulating NIS expression in MCF-7. In the ERα negative cell lineMDA-MB-231, re-introduction of ERα resulted in NIS expression in a ligandindependent manner. The role of ERα in the regulation of NIS expression wassupported by the identification of an estrogen response element (ERE) in thepromoter of NIS, this ERE was conserved in human, mouse and rat. We have alsoshowed that this ERE could respond to E2 stimulation, and that ERα occupies theNIS promoter by binding to this novel element in vivo. These results indicate that E2and ERα contribute to the regulation of NIS in the breast cancer cell line MCF-7.iii