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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.

The fundamental tenet that aging is irreversible has been challenged by the development of reprogramming technology that can restore molecular and cellular age by reversing the progression of aging. The use of cells from aged individuals as sources for reprogramming or transplantation creates a major barrier in stem cell therapy with respect to cell quality and quantity. Here, we investigated the molecular features underlying senescence and rejuvenation during aged cell reprogramming and identified novel factors that can overcome age-associated barriers. Enzymes, such as nicotinamide nucleotide transhydrogenase (NNT) and nicotinamide mononucleotide adenylyltransferase 3 (NMNAT3), that control mitochondrial NAD+ levels appear to be susceptible to aging. In aged cells, mitochondrial NAD+ levels decrease, accompanied by reduced SIRT3 activity; these changes severely impede cell fate transition. However, in cells collected from aged p16 knockout mice, which exhibit delayed cellular senescence, no changes in NNT or NMNAT3 expression were found. Importantly, restoring mitochondrial NAD+ levels by overexpressing NNT and NMNAT3 enhanced reprogramming efficiency of aged somatic cells and extended the lifespan of human mesenchymal stem cells by delaying replicative senescence. These results demonstrate that maintenance of mitochondrial NAD+ levels is critical for reversing the mechanisms of aging and ensuring that cells collected from aged individuals are of high quality.

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.

The polycomb protein MEL-18 has been proposed as a tumor suppressor in breast cancer; however, its functional relevance to the hormonal regulation of breast cancer remains unknown. Here, we demonstrated that MEL-18 loss contributes to the hormone-independent phenotype of breast cancer by modulating hormone receptor expression. In multiple breast cancer cohorts, MEL-18 was markedly downregulated in triple-negative breast cancer (TNBC). MEL-18 expression positively correlated with the expression of luminal markers, including estrogen receptor–α (ER-α, encoded by ESR1). MEL-18 loss was also associated with poor response to antihormonal therapy in ER-α–positive breast cancer. Furthermore, whereas MEL-18 loss in luminal breast cancer cells resulted in the downregulation of expression and activity of ER-α and the progesterone receptor (PR), MEL-18 overexpression restored ER-α expression in TNBC. Consistently, in vivo xenograft experiments demonstrated that MEL-18 loss induces estrogen-independent growth and tamoxifen resistance in luminal breast cancer, and that MEL-18 overexpression confers tamoxifen sensitivity in TNBC. MEL-18 suppressed SUMOylation of the ESR1 transactivators p53 and SP1, thereby driving ESR1 transcription. MEL-18 facilitated the deSUMOylation process by inhibiting BMI-1/RING1B-mediated ubiquitin-proteasomal degradation of SUMO1/sentrin-specific protease 1 (SENP1). These findings demonstrate that MEL-18 is a SUMO-dependent regulator of hormone receptors and suggest MEL-18 expression as a marker for determining the antihormonal therapy response in patients with breast cancer.

Liver fibrosis can be reversed by removing its causative injuries; however, the molecular mechanisms mediating the resolution of liver fibrogenesis are poorly understood. We investigate the role of a scaffold protein, A-Kinase Anchoring Protein 12 (AKAP12), during liver fibrosis onset, and resolution. Biliary fibrogenesis and fibrosis resolution was induced in wild-type (WT) or AKAP12-deficient C57BL/6 mice through different feeding regimens with 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing chow. AKAP12 expression in portal fibroblasts (PFs) and liver sinusoidal endothelial cells (LSECs) gradually decreased as fibrosis progressed but was restored after cessation of the fibrotic challenge. Histological analysis of human liver specimens with varying degrees of fibrosis of different etiologies revealed that AKAP12 expression diminishes in hepatic fibrosis from its early stages onward. AKAP12 KO mice displayed reduced fibrosis resolution in a DDC-induced biliary fibrosis model, which was accompanied by impaired normalization of myofibroblasts and capillarized sinusoids. RNA sequencing of the liver transcriptome revealed that genes related to ECM accumulation and vascular remodeling were mostly elevated in AKAP12 KO samples. Gene ontology (GO) and bioinformatic pathway analyses identified that the differentially expressed genes were significantly enriched in GO categories and pathways, such as the adenosine 3′,5′-cyclic monophosphate (cAMP) pathway. Knockdown of the AKAP12 gene in cultured primary PFs revealed that AKAP12 inhibited PF activation in association with the adenosine 3′,5′-cyclic monophosphate (cAMP) pathway. Moreover, AKAP12 knockdown in LSECs led to enhanced angiogenesis, endothelin-1 expression and alterations in laminin composition. Collectively, this study demonstrates that AKAP12-mediated regulation of PFs and LSECs has a central role in resolving hepatic fibrosis.