RelB NF-κB Represses Estrogen Receptor α Expression via Induction of the Zinc Finger Protein Blimp1

Aberrant constitutive expression of NF-κB subunits, reported in more than 90% of breast cancers and multiple other malignancies, plays pivotal roles in tumorigenesis. Higher RelB subunit expression was demonstrated in estrogen receptor alpha (ERα)-negative breast cancers versus ERα-positive ones, due in part to repression of RelB synthesis by ERα signaling. Notably, RelB promoted a more invasive phenotype in ERα-negative cancers via induction of the BCL2 gene. We report here that RelB reciprocally inhibits ERα synthesis in breast cancer cells, which contributes to a more migratory phenotype. Specifically, RelB is shown for the first time to induce expression of the zinc finger repressor protein Blimp1 (B-lymphocyte-induced maturation protein), the critical mediator of B- and T-cell development, which is transcribed from the PRDM1 gene. Blimp1 protein repressed ERα (ESR1) gene transcription. Commensurately higher Blimp1/PRDM1 expression was detected in ERα-negative breast cancer cells and primary breast tumors. Induction of PRDM1 gene expression was mediated by interaction of Bcl-2, localized in the mitochondria, with Ras. Thus, the induction of Blimp1 represents a novel mechanism whereby the RelB NF-κB subunit mediates repression, specifically of ERα, thereby promoting a more migratory phenotype.