The Regulatory Role of CTCF in IL6 Gene Transcription Assessed in Breast Cancer Cell Lines

<b>Background:</b> Breast cancer (BrCa) patients with tumors expressing high interleukin-6 (IL6) levels have poor clinical outcomes. In BrCa, altered occupancy of CCCTC-binding factor (CTCF) within its DNA binding sites deregulates the expression of its targeted genes. In this study, we investigated whether CTCF contributes to the altered <i>IL6</i> expression in BrCa. <b>Methods/Results:</b> We performed CTCF gain- and loss-of-function assays in BrCa cell lines and observed an inverse correlation between <i>CTCF</i> and <i>IL6</i> expression levels. To understand how CTCF negatively regulates <i>IL6</i> gene expression, we performed luciferase gene reporter assays, site-directed mutagenesis assays, and chromatin immunoprecipitation assays. Our findings revealed that CTCF interacted with the <i>IL6</i> promoter, a form of regulation disrupted in a CpG methylation-independent fashion in MDA-MB-231 and Tamoxifen-resistant MCF7 cells. Data from TCGA and GEO databases allowed us to explore the clinical implications of our results. An inverse correlation between <i>CTCF</i> and <i>IL6</i> expression levels was seen in disease-free survival BrCa patients but not in patients who experienced cancer recurrence. <b>Conclusions:</b> Our findings provide evidence that the CTCF-mediated negative regulation of the <i>IL6</i> gene is lost in highly tumorigenic BrCa cells.