DOT1L has emerged as an anticancer target for MLL-associated leukaemias; however, its functional role in solid tumours is largely unknown. Here we identify that DOT1L cooperates with c-Myc and p300 acetyltransferase to epigenetically activate epithelial–mesenchymal transition (EMT) regulators in breast cancer progression. DOT1L recognizes SNAIL, ZEB1 and ZEB2 promoters via interacting with the c-Myc-p300 complex and facilitates lysine-79 methylation and acetylation towards histone H3, leading to the dissociation of HDAC1 and DNMT1 in the regions. The upregulation of these EMT regulators by the DOT1L-c-Myc-p300 complex enhances EMT-induced breast cancer stem cell (CSC)-like properties. Furthermore, in vivo orthotopic xenograft models show that DOT1L is required for malignant transformation of breast epithelial cells and breast tumour initiation and metastasis. Clinically, DOT1L expression is associated with poorer survival and aggressiveness of breast cancers. Collectively, we suggest that cooperative effect of DOT1L and c-Myc-p300 is critical for acquisition of aggressive phenotype of breast cancer by promoting EMT/CSC.

The histone H3K27 demethylase, UTX, is a known component of the H3K4 methyltransferase MLL complex, but its functional association with H3K4 methylation in human cancers remains largely unknown. Here we demonstrate that UTX loss induces epithelial–mesenchymal transition (EMT)‐mediated breast cancer stem cell (CSC) properties by increasing the expression of the SNAIL, ZEB1 and ZEB2 EMT transcription factors (EMT‐TFs) and of the transcriptional repressor CDH1. UTX facilitates the epigenetic silencing of EMT‐TFs by inducing competition between MLL4 and the H3K4 demethylase LSD1. EMT‐TF promoters are occupied by c‐Myc and MLL4, and UTX recognizes these proteins, interrupting their transcriptional activation function. UTX decreases H3K4me2 and H3 acetylation at these promoters by forming a transcriptional repressive complex with LSD1, HDAC1 and DNMT1. Taken together, our findings indicate that UTX is a prominent tumour suppressor that functions as a negative regulator of EMT‐induced CSC‐like properties by epigenetically repressing EMT‐TFs. Synopsis UTX, a histone H3K27 demethylase, epigenetically silences EMT genes by facilitating LSD1‐dependent H3K4 demethylation and HDAC‐dependent histone deacetylation to inhibit EMT‐induced breast CSC properties. UTX suppresses EMT and CSC properties in breast cancer. UTX cooperates with LSD1 and HDAC1 to form a transcriptional repressive complex on EMT‐TF promoters.

EMBO Press is an editorially independent publishing platform for the development of EMBO scientific publications.

Histone methyltransferase NSD3 is frequently dysregulated in human cancers, yet the epigenetic role of NSD3 during cancer development remains elusive. Here we report that NSD3-induced methylation of H3K36 is crucial for breast tumor initiation and metastasis. In patients with breast cancer, elevated expression of NSD3 was associated with recurrence, distant metastasis, and poor survival. In vivo, NSD3 promoted malignant transformation of mammary epithelial cells, a function comparable to that of HRAS. Furthermore, NSD3 expanded breast cancer-initiating cells and promoted epithelial–mesenchymal transition to trigger tumor invasion and metastasis. Mechanistically, the long isoform (full-length transcript) of NSD3, but not its shorter isoform lacking a catalytic domain, cooperated with EZH2 and RNA polymerase II to stimulate H3K36me2/3-dependent transactivation of genes associated with NOTCH receptor cleavage, leading to nuclear accumulation of NICD and NICD-mediated transcriptional repression of E-cadherin. Furthermore, mice harboring primary and metastatic breast tumors with overexpressed NSD3 showed sensitivity to NOTCH inhibition. Together, our findings uncover the critical epigenetic role of NSD3 in the modulation of NOTCH-dependent breast tumor progression, providing a rationale for targeting the NSD3–NOTCH signaling regulatory axis in aggressive breast cancer.Significance: This study demonstrates the functional significance of histone methyltransferase NSD3 in epigenetic regulation of breast cancer stemness, EMT, and metastasis, suggesting NSD3 as an actionable therapeutic target in metastatic breast cancer.

Polycomb protein chromobox homolog 7 (CBX7) is involved in several biologic processes including stem cell regulation and cancer development, but its roles in breast cancer remain unknown. Here, we demonstrate that CBX7 negatively regulates breast tumor initiation. CD44 ⁺ /CD24 ^‐ /ESA ⁺ breast stem‐like cells showed diminished CBX7 expression. Furthermore, small hairpin RNA‐mediated CBX7 knockdown in breast epithelial and cancer cells increased the CD44 ⁺ /CD24 ^‐ /ESA ⁺ cell population and reinforced in vitro self‐renewal and in vivo tumor‐initiating ability. Similarly, CBX7 overexpression repressed these effects. We also found that CBX7 inhibits the Wnt/α‐catenin/T cell factor pathway by enhancing the expression of Dickkopf‐1 (DKK‐1), a Wnt antagonist. In particular, CBX7 increased DKK‐1 transcription by cooperating with p300 acetyltransferase and subsequently enhancing the histone acetylation of the DKK‐1 promoter. Furthermore, pharmacologic inhibition of DKK‐1 in CBX7‐overexpressing cells showed recovery of Wnt signaling and consequent rescue of the CD44 ⁺ /CD24 ^‐ /ESA ⁺ cell population. Taken together, these findings indicate that CBX7‐mediated epigenetic induction of DKK‐1 is crucial for the inhibition of breast tumorigenicity, suggesting that CBX7 could be a potential tumor suppressor in human breast cancer. —Kim, H.–Y., Park, J.–H., Won, H.–Y., Lee, J.–Y., Kong, G., CBX7 inhibits breast tumorigenicity through DKK‐1‐mediated suppression of the Wnt/β‐catenin pathway. FASEB J. 29, 300–313 (2015). www.fasebj.org

Despite the benefit of endocrine therapy, acquired resistance during or after treatment still remains a major challenge in estrogen receptor (ER)–positive breast cancer. We investigated the potential role of histone demethylase retinoblastoma-binding protein 2 (RBP2) in endocrine therapy resistance of breast cancer. Survival of breast cancer patients according to RBP2 expression was analyzed in three different breast cancer cohorts including METABRIC (n = 1980) and KM plotter (n = 1764). RBP2-mediated tamoxifen resistance was confirmed by in vitro sulforhodamine B (SRB) colorimetric, colony-forming assays, and in vivo xenograft models (n = 8 per group). RNA-seq analysis and receptor tyrosine kinase assay were performed to identify the tamoxifen resistance mechanism by RBP2. All statistical tests were two-sided. RBP2 was associated with poor prognosis to tamoxifen therapy in ER-positive breast cancer (P = .04 in HYU cohort, P = .02 in KM plotter, P = .007 in METABRIC, log-rank test). Furthermore, RBP2 expression was elevated in patients with tamoxifen-resistant breast cancer (P = .04, chi-square test). Knockdown of RBP2 conferred tamoxifen sensitivity, whereas overexpression of RBP2 induced tamoxifen resistance in vitro and in vivo (MCF7 xenograft: tamoxifen-treated control, mean [SD] tumor volume = 70.8 [27.9] mm³, vs tamoxifen-treated RBP2, mean [SD] tumor volume = 387.9 [85.1] mm³, P < .001). Mechanistically, RBP2 cooperated with ER co-activators and corepressors and regulated several tamoxifen resistance–associated genes, including NRIP1, CCND1, and IGFBP4 and IGFBP5. Furthermore, epigenetic silencing of IGFBP4/5 by RBP2-ER-NRIP1-HDAC1 complex led to insulin-like growth factor–1 receptor (IGF1R) activation. RBP2 also increased IGF1R-ErbB crosstalk and subsequent PI3K-AKT activation via demethylase activity–independent ErbB protein stabilization. Combinational treatment with tamoxifen and PI3K inhibitor could overcome RBP2-mediated tamoxifen resistance (RBP2-overexpressing cells: % cell viability [SD], tamoxifen = 89.0 [3.8]%, vs tamoxifen with BKM120 = 41.3 [5.6]%, P < .001). RBP2 activates ER-IGF1R-ErbB signaling cascade in multiple ways to induce tamoxifen resistance, suggesting that RBP2 is a potential therapeutic target for ER-driven cancer.