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

Abstract

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 sequencing, we identified a series of potential FOXP3-targeted microRNAs (miRs) in MCF7 cells. Notably, FOXP3 significantly induced the expression of miR-146a/b. In vitro, FOXP3-induced miR-146a/b prevented tumor cell proliferation and enhanced apoptosis. Functional analyses in vitro and in vivo revealed that FOXP3-induced miR-146a/b negatively regulate NF-κB activation by inhibiting the expression of IRAK1 and TRAF6. In chromatin immunoprecipitation 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 in vitro and metastasis in vivo, FOXP3-induced miR-146a/b contributed only to the inhibition of breast tumor growth. These data suggest that miR-146a/b contribute 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.

Silencing of CD24 Enhances the PRIMA-1–Induced Restoration of Mutant p53 in Prostate Cancer Cells

“…At 0 and 24 hours, cell cycle progression was determined by propidium iodide (PI) staining and flow cytometry, as described previously (6). At 5 days, apoptosis was detected by flow cytometry based on cell binding to Annexin V (561012, BD Biosciences) and 7-aminoactinomycin (7-AAD; 555816, BD Biosciences) (32). …”

miR-146b antagomir–treated human Tregs acquire increased GVHD inhibitory potency

“…Although TRAF6 is a target of both miR-146a and miR-146b-5p in many cell types such as dendritic cells and cancer cells, 19,43 knockdown of miR-146a increased tTreg TRAF6 expression in mice, but not human, tTregs 31 and increased TRAF6 in murine tTregs were not responsible for enhanced tTreg function. 25 We observed that miR146b-5p directly targeted TRAF6 39-UTR sites in human Tregs and that knockdown of miR-146b-5p enhanced FoxP3 expression and Treg function in vitro and in vivo.…”

“…[15][16][17][18] The miR-146 family includes 2 main members, miR-146a and miR-146b, which are both highly expressed and play important roles in cell proliferation and function in diverse cell types, including T and B cells. Studies of breast cancer cells have shown a Foxp3-dependant increase in the expression of miR-146b and, to a lesser extent, miR-146a, 19 which results in reduced breast cancer cell proliferation and enhanced apoptosis via negative regulation of nuclear factor kB (NF-kB). Even though they share the same seed regions, posttranscriptional processing mechanisms and consequently functions may be distinct due to different genomic locations (chromosomes 5 and 10, respectively).…”

Sexual dimorphism in cancer

“…Furthermore, in breast and prostate cancer Foxp3 inhibits NFkB activation, through a Foxp3-miR-146-NFkB axis, which promotes tumor suppression and apoptosis 128 .…”