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Evaluation of transcriptional activity of the oestrogen receptor with sodium iodide symporter as an imaging reporter gene

BackgroundOestrogen receptors are ligand-dependent transcription factors whose activity is modulated either by oestrogens or by an alternative signalling pathway. Oestrogen receptors interact via a specific DNA-binding domain, the oestrogen responsive element (ERE), in the promoter region of sensitive genes. This binding leads to an initiation of gene expression and hormonal effects. ObjectiveTo determine the transcriptional activity of the oestrogen receptor, we developed a molecular imaging system using sodium iodide symporter (NIS) as a reporter gene. MethodsThe NIS reporter gene was placed under the control of an artificial ERE derived from pERE-TA-SEAP and named as pERE-NIS. pERE-NIS was transferred to MCF-7, human breast cancer cells, which highly expressed oestrogen receptor-&agr; with lipofectamine. Stably expressing cells were generated by selection with G418 for 14 days. After treatment of 17&bgr;-oestradiol and tamoxifen with serial doses, the 125I uptake was measured for the determination of NIS expression. The inhibition of NIS activity was performed with 50 μmol·l−1 potassium perchlorate. ResultsThe MCF7/pERE-NIS treated with 17&bgr;-oestradiol accumulated 125I up to 70–80% higher than did non-treated cells. NIS expression was increased according to increasing doses of 17&bgr;-oestradiol. MCF7/pERE-NIS treated with tamoxifen also accumulated 125I up to 50% higher than did non-treated cells. Potassium perchlorate completely inhibited 125I uptake. When MDA-MB231 cells, the oestrogen receptor-negative breast cancer cells, were transfected with pERE-NIS, 125I uptake of MDA-MB-231/pERE-NIS did not increase. ConclusionThis pERE-NIS reporter system is sufficiently sensitive for monitoring transcriptional activity of the oestrogen receptor. Therefore, cis-enhancer reporter systems with ERE will be applicable to the development of a novel selective oestrogen receptor modulator with low toxicity and high efficacy.