Abstract 1235: The organic cation transporter SLC22A5 gene is regulated by the cooperative activity of the estrogen receptor and other transcription factors in breast cancer
Authors: Wang Chunyu , Mayer Julie Ann , DeNardo David G. , Brown Powel H. 
Published: February 2011

The solute carrier family 22 member 5 (SLC22A5) gene encodes a polyspecific organic cation transporter that is associated with many diseases. However, the regulation of SLC22A5 and its relationship with breast cancer is not clearly defined. In a previous global gene expression analysis from our group, SLC22A5 was identified as an estrogen-regulated gene. In this study, we investigated the molecular mechanism by which estrogen receptor (ER) and other transcription factors regulate SLC22A5 gene expression in breast cancer.

SLC22A5 is highly expressed in ER-positive breast cancer cell lines and ER-positive mammary tumor tissues compared to ER-negative cells and tissues. SLC22A5 expression is also correlated with the levels of ER expression in breast cancer cell lines and in mammary tumor tissue specimens. SLC22A5 mRNA expression is induced in MCF-7 breast cancer cells within half an hour after estrogen treatment and remains elevated for over 24 hours. Actinomycin D, but not cycloheximide, can inhibit this estrogen induction, indicating new protein synthesis is not needed for induction. These results suggest that estrogen directly activates SLC22A5 transcription. We next cloned the 6kb SLC22A5 promoter and luciferase experiments demonstrated that this portion of the SLC22A5 promoter is not responsive to estrogen treatment. However, we discovered that an intronic enhancer located approximately 9kb from the transcriptional start site confers estrogen responsiveness when inserted downstream of the SLC22A5 gene promoter-luciferase reporter construct. Several transcription factors binding sites, such as a cyclic adenosine monophosphate (cAMP) response element (CRE), an estrogen-response element (ERE), an activator protein-1 (AP-1) site and a half ERE, are juxtaposed in the middle of this intronic enhancer. Mutation or deletion of these elements abolishes the estrogen responsiveness. Chromatin-immunoprecipitation (ChIP) assay demonstrates the recruitment of the transcription factors onto the intronic enhancer region in an estrogen-dependent manner. We next investigated the effect of SLC22A5 knockdown on breast cancer cell growth. Results from these studies show that shRNA knockdown of SLC22A5 inhibits the proliferation of MCF-7 cells. This reduced proliferation is accompanied by decreased cyclin D1 levels.

These results suggest that SLC22A5 is an estrogen-induced gene that is involved in regulating breast cell growth. Our results also suggest that this estrogen induction is mediated by a complex intronic enhancer. This estrogen-induced gene may serve as a novel breast cancer biomarker that may be targeted for improved treatment and prevention of breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1235.