Data from FOXP3 Controls an miR-146/NF-κB Negative Feedback Loop That Inhibits Apoptosis in Breast Cancer Cells

<div>Abstract<p>FOXP3 functions not only as the master regulator in regulatory T cells, but also as an X-linked tumor suppressor. The tumor-suppressive activity of FOXP3 has been observed in tumor initiation, but its role during tumor progression remains controversial. Moreover, the mechanism of FOXP3-mediated tumor-suppressive activity remains largely unknown. Using chromatin immunoprecipitation (ChIP) sequencing, we identified a series of potential FOXP3-targeted miRNAs in MCF7 cells. Notably, FOXP3 significantly induced the expression of miR-146a/b. <i>In vitro</i>, FOXP3-induced miR-146a/b prevented tumor cell proliferation and enhanced apoptosis. Functional analyses <i>in vitro</i> and <i>in vivo</i> revealed that FOXP3-induced miR-146a/b negatively regulates NF-κB activation by inhibiting the expression of <i>IRAK1</i> and <i>TRAF6</i>. In ChIP assays, FOXP3 directly bound the promoter region of miR-146a but not of miR-146b, and FOXP3 interacted directly with NF-κB p65 to regulate an miR-146–NF-κB negative feedback regulation loop in normal breast epithelial and tumor cells, as demonstrated with luciferase reporter assays. Although FOXP3 significantly inhibited breast tumor growth and migration <i>in vitro</i> and metastasis <i>in vivo</i>, FOXP3-induced miR-146a/b contributed only to the inhibition of breast tumor growth. These data suggest that miR-146a/b contributes to FOXP3-mediated tumor suppression during tumor growth by triggering apoptosis. The identification of a FOXP3–miR-146–NF-κB axis provides an underlying mechanism for disruption of miR-146 family member expression and constitutive NF-κB activation in breast cancer cells. Linking the tumor suppressor function of FOXP3 to NF-κB activation reveals a potential therapeutic approach for cancers with FOXP3 defects. <i>Cancer Res; 75(8); 1703–13. ©2015 AACR</i>.</p></div>