Abstract A077: Post-transcriptional regulation of CXCR4 by the tristetraprolin/HuR axis in breast cancer

Abstract

Abstract Chemokine receptors can direct tumors to distant organs and tissues along a gradient of their respective ligands. One such chemokine receptor is CXCR4 which has been implicated in breast cancer metastasis, notably to the lung, bone, and lymph nodes, where its chemokine ligand, CXCL12, is highly expressed. Expression of the receptor or its ligand is associated with a poor prognosis. Here, we report that aberrations in the post-transcriptional regulation of the CXCR4/CXCL12 signaling pathway play a pivotal role in the metastatic phenotype of breast cancer cells. We show, utilizing 3′UTR reporter assays, that CXCR4 3′UTR contains an AU-rich element that confers instability to its mRNA and presents it as a prospective target for RNA binding proteins. Indeed, immunoprecipitation of TTP- and HuR-bound mRNA and RNA shift revealed CXCR4 mRNA is a novel target of both proteins suggesting post-transcriptional regulation of the chemokine receptor. We demonstrate correlation between the aberrant TTP/HuR axis and increased CXCR4 expression and metastasis in Tumor Cancer Genome Atlas (TCGA) breast cancer patient data. Furthermore, real-time PCR and western blotting techniques showed that CXCR4 mRNA and protein levels were significantly higher in the invasive breast cancer cell line MDA-MB-231 compared to the non-invasive MCF7 or normal cell lines. Using MDA-MB-231 cells as a model of invasive breast cancer, we attempted to normalize the aberrant TTP/HuR axis by a miR-29a inhibitor which led to de-suppression of TTP expression. This triggered increased instability of CXCR4 mRNA, a down regulation of CXCR4 expression, and a subsequent reduction in the migratory potential of MDA-MB-231 cells. The anti-invasive and anti-migratory effect was similarly obtained by knockdown of HuR and CXCR4. Further regulation of CXCR4 by TTP and HuR was substantiated by mRNA decay assays and 3′UTR reporter experiments. Our findings indicate that CXCR4 is a novel target of post-transcriptional regulation by the RNA binding proteins TTP and HuR and that restoration of a normal balance between TTP and HuR may offer a novel therapeutic approach in the control of metastatic breast cancer. Citation Format: Norah A. Al-Souhibani, Maha Al-Ghamidi, Wijdan Al-Ahmadi, Khalid SA Khabar. Post-transcriptional regulation of CXCR4 by the tristetraprolin/HuR axis in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A077.