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Breast cancer stem-like cells (BCSC) are crucial for metastasis but the underlying mechanisms remain elusive. Here, we report that tumor-infiltrating natural killer (NK) cells failed to limit metastasis and were not associated with improved therapeutic outcome of BCSC-rich breast cancer. Primary BCSCs were resistant to cytotoxicity mediated by autologous/allogeneic NK cells due to reduced expression of MICA and MICB, two ligands for the stimulatory NK cell receptor NKG2D. Furthermore, the downregulation of MICA/MICB in BCSCs was mediated by aberrantly expressed oncogenic miR20a, which promoted the resistance of BCSC to NK cell cytotoxicity and resultant lung metastasis. The breast cancer cell differentiation-inducing agent, all-trans retinoic acid, restored the miR20a-MICA/MICB axis and sensitized BCSC to NK cell-mediated killing, thereby reducing immune escape-associated BCSC metastasis. Together, our findings reveal a novel mechanism for immune escape of human BCSC and identify the miR20a-MICA/MICB signaling axis as a therapeutic target to limit metastatic breast cancer. Cancer Res; 74(20); 5746-57. Ó2014 AACR.

Highlights d SETD2-mediated EZH2-K735me1 licenses EZH2 destruction to impede PCa metastasis d Cancer-associated SETD2 mutation (R1523H) disrupts SETD2-EZH2 interaction d Metformin treatment might combat EZH2-high PCa by stimulating SETD2 expression

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