Phosphorylation Of Enhancer Of Zeste Homolog 2 Research Articles

MiR-4448/Girdin/Akt/AMPK axis inhibits EZH2-mediated EMT and tumorigenesis in small-cell lung cancer.

Small-cell lung cancer (SCLC) shows high enhancer of zeste homolog 2 (EZH2) expressions. EZH2-mediated epigenetics promote epithelial-mesenchymal transition (EMT), enhancing invasive and metastatic potential in malignancies. MicroRNAs (miRNAs), small noncoding RNAs, modulate EMT, determining tumor phenotypes. However, the association between miRNAs and EZH2 in SCLC remains to be clarified-we aimed to identify a novel tumorigenic mechanism through miRNAs, EZH2, and EMT in SCLC, leading to future therapeutic applications. We analyzed EZH2 and E-cadherin expressions in lung cancer cell lines and tumor tissues from 34 SCLC patients and confirmed EZH2 siRNA-mediated EMT inhibition. miRNA expression profiles were compared between EZH2 knockdown SCLC cells and negative control SCLC cells using miRNA array. We identified a target miRNA of EZH2 showing expressional differences in EZH2-knockdown cells and analyzed the impact of the miRNA on EZH2-mediated EMT and tumorigenesis. All SCLC cells showed increased EZH2 and decreased E-cadherin expressions. SCLC tissues had higher EZH2 and lower E-cadherin expressions than other lung cancer tissues. miRNA array revealed that miR-4448 expression increased in EZH2-knockdown SCLC cells. miR-4448 overexpression reduced tumor cell growth and prevented EMT. miR-4448 bound to the 3'UTR of the girdin gene and suppressed its expression, thereby decreasing Akt phosphorylation at Ser473. Attenuated Akt phosphorylation resulted in AMP-activated protein kinase (AMPK) phosphorylation at Thr172 and 183, enhancing EZH2 phosphorylation at Thr311. SCLC characterized high EZH2 expression and promoted EMT, compared with non-small cell lung cancer. miR-4448 inhibited Girdin expression, reducing Akt phosphorylation, and enhancing AMPK and EZH2 phosphorylation. Eventually, miR-4448 prevented EZH2-mediated EMT and tumorigenesis by modulating the Girdin/Akt/AMPK axis in SCLC. miR-4448 might be a potential SCLC inhibitor.

Abstract 6981: p38-mediated EZH2 phosphorylation at T367 regulates HER2 pathway in triple negative breast cancer

Abstract Background: Triple negative breast carcinomas (TNBC) are highly aggressive tumors with limited effective treatments. Clinical studies showed that targeting low HER2 levels in TNBC with anti-HER2 agents has survival benefit. Enhancer of Zeste Homolog 2 (EZH2) is a lysine methyltransferase component of the Polycomb Repressive Complex2 that regulates differentiation genes in normal and neoplastic cells. EZH2 phosphorylation at T416 was shown to maintain the TNBC phenotype. We have reported that p38-induced EZH2-T367 phosphorylation enhances metastasis and that high pEZH2-T367 expression is significantly associated with human TNBC tumors compared to other breast cancer subtypes. In this study we tested the hypothesis that pEZH2-T367 may regulate the HER2 pathway in TNBC and that inhibition of pEZH2-T367 may upregulate HER2 signaling, with clinical implications. Methods: MDA-MB-231 (mesenchymal-like TNBC) and CCN6KO cells derived from MMTV-Cre;Ccn6fl/fl (CCN6KO) TNBC mouse model generated in our lab were transduced with vector or EZH2 shRNA knockdown (KD). MDA-MB-231 EZH2 KD cells were rescued with lentivirus containing EZH2-wild-type (WT) or T367A phosphorylation-deficient mutant. Gene and protein expression was analyzed by RNA sequencing, q-RT-PCR, immunoblot and immunohistochemistry. Vector and EZH2-KD rescue MDA-MB-231 cells were treated with anti-HER2 (trastuzumab or pertuzumab 100 ug/ml) followed by Hoestch proliferation assays. TNBC cells were treated with vehicle, EZH2 inhibitor (EPZ-6438, 20uM), p38 inhibitor (p38i, SB202190, 20uM), EPZ+p38i, anti-HER2 (100 ug/ml), and EPZ+p38i+anti-HER2, followed by Hoestch cell proliferation assays. Results: EZH2-T367A deregulates the expression of a 94-gene network of HER2 pathway genes including EREG, SERPINB5, MERTK, IL6R, SOCS3, and FASCN1 compared to EZH2-WT. EZH2-T367A increased protein levels of HER2, EREG, and PP2AB, a major HER2 regulator and was sufficient to sensitize TNBC cells to the anti-proliferative effects of anti-HER2. Supporting the role of pEZH2-T367, we found that the combination of p38i and EPZ significantly sensitizes TNBC cells to anti-HER2 therapies. Conclusions: We demonstrate that T367 phosphorylation mediates the effect of EZH2 on HER2 signaling in TNBC. Our data support a role for pEZH2-T367 in maintaining the HER2-negative phenotype in and suggest that blocking this phosphorylation event may render TNBC tumors amenable to anti-HER2 treatment strategies. Citation Format: Maria E. Gonzalez, Ahmad Eido, Celina G. Kleer. p38-mediated EZH2 phosphorylation at T367 regulates HER2 pathway in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6981.

Diabetes Promotes Myocardial Fibrosis via AMPK/EZH2/PPAR-γ Signaling Pathway.

Diabetes-induced cardiac fibrosis is one of the main mechanisms of diabetic cardiomyopathy. As a common histone methyltransferase, enhancer of zeste homolog 2 (EZH2) has been implicated in fibrosis progression in multiple organs. However, the mechanism of EZH2 in diabetic myocardial fibrosis has not been clarified. In the current study, rat and mouse diabetic model were established, the left ventricular function of rat and mouse were evaluated by echocardiography and the fibrosis of rat ventricle was evaluated by Masson staining. Primary rat ventricular fibroblasts were cultured and stimulated with high glucose (HG) in vitro. The expression of histone H3 lysine 27 (H3K27) trimethylation, EZH2, and myocardial fibrosis proteins were assayed. In STZ-induced diabetic ventricular tissues and HG-induced primary ventricular fibroblasts in vitro, H3K27 trimethylation was increased and the phosphorylation of EZH2 was reduced. Inhibition of EZH2 with GSK126 suppressed the activation, differentiation, and migration of cardiac fibroblasts as well as the overexpression of the fibrotic proteins induced by HG. Mechanical study demonstrated that HG reduced phosphorylation of EZH2 on Thr311 by inactivating AMP-activated protein kinase (AMPK), which transcriptionally inhibited peroxisome proliferator-activated receptor γ (PPAR-γ) expression to promote the fibroblasts activation and differentiation. Our data revealed an AMPK/EZH2/PPAR-γ signal pathway is involved in HG-induced cardiac fibrosis.

EZH2 T367 phosphorylation activates p38 signaling through lysine methylation to promote breast cancer progression

SummaryTriple-negative breast cancers (TNBCs) are frequently poorly differentiated with high propensity for metastasis. Enhancer of zeste homolog 2 (EZH2) is the lysine methyltransferase of polycomb repressive complex 2 that mediates transcriptional repression in normal cells and in cancer through H3K27me3. However, H3K27me3-independent non-canonical functions of EZH2 are incompletely understood. We reported that EZH2 phosphorylation at T367 by p38α induces TNBC metastasis in an H3K27me3-independent manner. Here, we show that cytosolic EZH2 methylates p38α at lysine 139 and 165 leading to enhanced p38α stability and that p38 methylation and activation require T367 phosphorylation of EZH2. Dual inhibition of EZH2 methyltransferase and p38 kinase activities downregulates pEZH2-T367, H3K27me3, and p-p38 pathways in vivo and reduces TNBC growth and metastasis. These data uncover a cooperation between EZH2 canonical and non-canonical mechanisms and suggest that inhibition of these pathways may be a potential therapeutic strategy.

Abstract 5365: Repositioning nicardipine as a novel targeted therapy for chemoresistant prostate cancer

Abstract Background: It is imperative to develop novel therapeutics to overcome chemoresistance, a major obstacle in the clinical management of prostate cancer (PCa) and other cancers. Drug repositioning is being pursued as an attractive approach due to its potentially lower overall development costs and shorter timelines. The purpose of this study is to investigate the preclinical efficacy and mechanism of action of nicardipine, an FDA-approved hypertension drug, as a new treatment against chemoresistant prostate cancer. Methods: A panel of FDA-approved non-oncology drugs was screened for their selectivity and potency to inhibit chemoresistant PCa cells using a two-tier phenotypic screening platform (Theranostics, 2021, 11(14): 6873-6890). The mechanism of action of potential candidate(s) was evaluated using in silico docking, cellular and molecular assays in ARCaPE-shEPLIN and C4-2B-TaxR, two independent chemoresistant PCa cell lines. The in vivo efficacy was evaluated in clinically-relevant xenograft models of PCa. Results: Nicardipine exhibited high selectivity and potency against chemoresistant PCa cells via effectively inducing apoptosis and cell cycle arrest. The IC50 of nicardipine was determined as 0.5 μM and 2.1 μM in ARCaPE-shEPLIN and C4-2B-TaxR cells, respectively. Mechanically, nicardipine targeted a novel non-canonical enhancer of zeste homolog 2 (EZH2) signal pathway in chemoresistant PCa cells. Specifically, nicardipine might bind embryonic ectoderm development (EED), interrupt the integrity and stability of the polycomb repressive complex 2 (PRC2), reduce the phosphorylation and expression of EZH2, and subsequently inhibit downstream effectors including signal transducer and activator of transcription 3 (Stat3), S-phase kinase-associated protein 2 (SKP2), ATP binding cassette B1 (ABCB1) and survivin. In animal models, as a monotherapy, nicardipine significantly suppressed the intratibial growth of chemoresistant C4-2B-TaxR xenografts, with an average PSA level of 43.47 ng/ml, 36.63 ng/ml, and 28.78 ng/ml for the vehicle control, docetaxel, and nicardipine groups at the endpoint, respectively (p < 0.05 between the nicardipine group and the vehicle control or docetaxel groups). As a combination regime, nicardipine synergistically enhanced the efficacy of docetaxel against the intratibial growth of C4-2 xenografts, with an average PSA level of 79.17 ng/ml, 49.04 ng/ml, 42.80 ng/ml, and 23.23 ng/ml for the vehicle control, docetaxel, nicardipine, and combination groups at the endpoint, respectively (p < 0.0001 or 0.01 between the combination group and the vehicle control or docetaxel groups, respectively). Conclusion: These results demonstrated that, for the first time, nicardipine could be a novel EED inhibitor that has the potential to be promptly tested in PCa patients to overcome chemoresistance and improve clinical outcomes. Citation Format: Xin Li, Alira Danaher, Jason M. Wu, Yifei Wu, Zhong-Ru Xie, Nicholas Cook, Nathan Bowen, Daqing Wu. Repositioning nicardipine as a novel targeted therapy for chemoresistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5365.

Abstract PD3-03: EZH2 T367 phosphorylation activates p38 signaling through lysine methylation to promote breast cancer progression

Abstract Introduction: Triple negative breast cancers (TNBC) are frequently poorly differentiated with higher propensity for metastasis than all other subtypes. Enhancer of Zeste Homolog 2 (EZH2) is a lysine methyltransferase that mediates transcriptional repression of pro-differentiation genes in normal and neoplastic cells. The oncogenic role of EZH2 through H3K27me3 is well established. However, non-canonical H3K27me3-independent functions are unclear. We have reported that p38 phosphorylates T367 of EZH2, increasing TNBC metastasis. Recent reports show that EZH2 can regulate signaling pathways through direct methylation of proteins suggesting the hypothesis that EZH2 may methylate p38 in TNBC. Methods: Human tissue samples from 16 primary invasive breast carcinomas and matched distant metastasis arrayed in tissue microarrays were interrogated for pEZH2 T367 and p-p38 by immunohistochemistry. To study p38 methylation, we performed LC-MS/MS analyses GST-p38α, and GST-EZH2 were each incubated with or without recombinant PRC2 complex (EZH2/E ED/SUZ12/RbAp48/AEBP2) and S-adenosyl methionine methyl donor. MDA-MB-231, mouse and human primary TNBC cells and murine 4T1 cells were used in funcional assays in vitro and in vivo. EZH2 knockdown and rescue was carried out using lentiviral transduction of EZH2 with pBabe-myc-EZH2 (wild-type) or pBabe-myc-EZH2 (T367A). We developed p38 methylation mutants: HA-p38a K139A, HA-p38a K165A, and HA-p38a K130A/K165K. To investigate the importance of EZH2 and p38 enzymatic activities we used the EZH2 methyltransferase inhibitors GSK-343 and EPZ-6438 and the p38 inhibitor SB202190 in vitro and in vivo. For animal studies, MDA-MB-231 and 4T1 cells were orthotopically injected into the right inguinal mammary fat pad of eight-week old NOD/SCID or BALBc mice, respectively. When tumors reached 100 mm3 mice were treated 5 days/week by intraperitoneal injection with SB202190 (1mg/kg/day), EPZ-6438 (10mg/kg/day), combination of SB202190 and EPZ-6438, or control. We monitored tumor growth for 50 days, and harvested primary tumors, lungs, and sites of metastasis for histopathology, Western blot, and immunohistochemistry. Primary xenografts from the control and treatment groups were subjected to RNA sequencing. Results: EZH2 methylates p38 at lysines 139 and 165 leading to enhanced p38 stability and increased invasion, and p38 activation requires T367 phosphorylation of EZH2. Dual inhibition of EZH2 methyltransferase and p38 kinase activities downregulates pEZH2 T367, H3K27me3, and p-p38 in vivo, reduces TNBC growth and metastasis, and results in gene expression changes towards a better differentiated phenotype. pEZH2 T367 and p-p38 proteins are significantly coexpressed in human primary and metastatic breast cancer. Conclusions: We provide direct evidence that EZH2 methylates p38 with resultant p38 activation, and that EZH2 phosphorylation at T367 is important for this function. Dual targeting of EZH2 methyltransferase and p38 kinase activities with specific inhibitors reduces breast cancer growth and metastasis indicating a cooperation between EZH2 canonical and non-canonical mechanisms and suggesting therapeutic strategies. Citation Format: Maria E Gonzalez, Shilpa R. Tekula, Talha Anwar, Shoshana A. Leflein, Celina G. Kleer. EZH2 T367 phosphorylation activates p38 signaling through lysine methylation to promote breast cancer progression [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD3-03.

Chromatin-Independent Interplay of NFATc1 and EZH2 in Pancreatic Cancer.

Background: The Nuclear Factor of Activated T-cells 1 (NFATc1) transcription factor and the methyltransferase Enhancer of Zeste Homolog 2 (EZH2) significantly contribute to the aggressive phenotype of pancreatic ductal adenocarcinoma (PDAC). Herein, we aimed at dissecting the mechanistic background of their interplay in PDAC progression. Methods: NFATc1 and EZH2 mRNA and protein expression and complex formation were determined in transgenic PDAC models and human PDAC specimens. NFATc1 binding on the Ezh2 gene and the consequences of perturbed NFATc1 expression on Ezh2 transcription were explored by Chromatin Immunoprecipitation (ChIP) and upon transgenic or siRNA-mediated interference with NFATc1 expression, respectively. Integrative analyses of RNA- and ChIP-seq data was performed to explore NFATc1-/EZH2-dependent gene signatures. Results: NFATc1 targets the Ezh2 gene for transcriptional activation and biochemically interacts with the methyltransferase in murine and human PDAC. Surprisingly, our genome-wide binding and expression analyses do not link the protein complex to joint gene regulation. In contrast, our findings provide evidence for chromatin-independent functions of the NFATc1:EZH2 complex and reveal posttranslational EZH2 phosphorylation at serine 21 as a prerequisite for robust complex formation. Conclusion: Our findings disclose a previously unknown NFATc1-EZH2 axis operational in the pancreas and provide mechanistic insights into the conditions fostering NFATc1:EZH2 complex formation in PDAC.

Intermittent High Glucose Elevates Nuclear Localization of EZH2 to Cause H3K27me3-Dependent Repression of KLF2 Leading to Endothelial Inflammation

Epigenetic mechanisms have emerged as one of the key pathways promoting diabetes-associated complications. Herein, we explored the role of enhancer of zeste homolog 2 (EZH2) and its product histone 3 lysine 27 trimethylation (H3K27me3) in high glucose-mediated endothelial inflammation. To examine this, we treated cultured primary endothelial cells (EC) with different treatment conditions—namely, constant or intermittent or transient high glucose. Intermittent high glucose maximally induced endothelial inflammation by upregulating transcript and/or protein-level expression of ICAM1 and P-selectin and downregulating eNOS, KLF2, and KLF4 protein levels. We next investigated the underlining epigenetic mechanisms responsible for intermittent hyperglycemia-dependent endothelial inflammation. Compared with other high glucose treatment groups, intermittent high glucose-exposed EC exhibited an increased level of H3K27me3 caused by reduction in EZH2 threonine 367 phosphorylation and nuclear retention of EZH2. Intermittent high glucose also promoted polycomb repressive complex-2 (PRC2) assembly and EZH2′s recruitment to histone H3. Abrupt enrichment of H3K27me3 on KLF2 and KLF4 gene promoters caused repression of these genes, further supporting endothelial inflammation. In contrast, reducing H3K27me3 through small molecule and/or siRNA-mediated inhibition of EZH2 rescued KLF2 level and inhibited endothelial inflammation in intermittent high glucose-challenged cultured EC and isolated rat aorta. These findings indicate that abrupt chromatin modifications cause high glucose-dependent inflammatory switch of EC.

LncRNA UCA1 Antagonizes Arsenic-Induced Cell Cycle Arrest through Destabilizing EZH2 and Facilitating NFATc2 Expression

Arsenic (As) is a widespread metalloid contaminant, and its internal exposure is demonstrated to cause serious detrimental health problems. Albeit considerable studies are performed to interrogate the molecular mechanisms responsible for As-induced toxicities, the exact mechanisms are not fully understood yet, especially at the epigenetic regulation level. In the present study, it is identified that long non-coding RNA (lncRNA) urothelial cancer associated 1 (UCA1) alleviates As-induced G2/M phase arrest in human liver cells. Intensive mechanistic investigations illustrate that UCA1 interacts with enhancer of zeste homolog 2 (EZH2) and accelerates the latter's protein turnover rate under normal and As-exposure conditions. The phosphorylation of EZH2 at the Thr-487 site by cyclin dependent kinase 1 (CDK1) is responsible for As-induced EZH2 protein degradation, and UCA1 enhances this process through increasing the interaction between CDK1 and EZH2. As a consequence, the cell cycle regulator nuclear factor of activated T cells 2 (NFATc2), a downstream target of EZH2, is upregulated to resist As-blocked cell cycle progress and cytotoxicity. In conclusion, the findings decipher a novel prosurvival signaling pathway underlying As toxicity from the perspective of epigenetic regulation: UCA1 facilitates the ubiquitination of EZH2 to upregulate NFATc2 and further antagonizes As-induced cell cycle arrest.

ZMYND8 preferentially binds phosphorylated EZH2 to promote a PRC2-dependent to -independent function switch in hypoxia-inducible factor–activated cancer

Both gene repressor (Polycomb-dependent) and activator (Polycomb-independent) functions of the Polycomb protein enhancer of zeste homolog 2 (EZH2) are implicated in cancer progression. EZH2 protein can be phosphorylated at various residues, such as threonine 487 (T487), by CDK1 kinase, and such phosphorylation acts as a Polycomb repressive complex 2 (PRC2) suppression "code" to mediate the gene repressor-to-activator switch of EZH2 functions. Here we demonstrate that the histone reader protein ZMYND8 is overexpressed in human clear cell renal cell carcinoma (ccRCC). ZMYND8 binds to EZH2, and their interaction is largely enhanced by CDK1 phosphorylation of EZH2 at T487. ZMYND8 depletion not only enhances Polycomb-dependent function of EZH2 in hypoxia-exposed breast cancer cells or von Hippel-Lindau (VHL)-deficient ccRCC cells, but also suppresses the FOXM1 transcription program. We further show that ZMYND8 is required for EZH2-FOXM1 interaction and is important for FOXM1-dependent matrix metalloproteinase (MMP) gene expression and EZH2-mediated migration and invasion of VHL-deficient ccRCC cells. Our results identify a previously uncharacterized role of the chromatin reader ZMYND8 in recognizing the PRC2-inhibitory phosphorylation "code" essential for the Polycomb-dependent to -independent switch of EZH2 functions. They also reveal an oncogenic pathway driving cell migration and invasion in hypoxia-inducible factor-activated (hypoxia or VHL-deficient) cancer.

Pharmacological inhibition of noncanonical EED-EZH2 signaling overcomes chemoresistance in prostate cancer.

Rationale: Chemoresistance is a major obstacle in prostate cancer (PCa) treatment. We sought to understand the underlying mechanism of PCa chemoresistance and discover new treatments to overcome docetaxel resistance.Methods: We developed a novel phenotypic screening platform for the discovery of specific inhibitors of chemoresistant PCa cells. The mechanism of action of the lead compound was investigated using computational, molecular and cellular approaches. The in vivo toxicity and efficacy of the lead compound were evaluated in clinically-relevant animal models.Results: We identified LG1980 as a lead compound that demonstrates high selectivity and potency against chemoresistant PCa cells. Mechanistically, LG1980 binds embryonic ectoderm development (EED), disrupts the interaction between EED and enhancer of zeste homolog 2 (EZH2), thereby inducing the protein degradation of EZH2 and inhibiting the phosphorylation and activity of EZH2. Consequently, LG1980 targets a survival signaling cascade consisting of signal transducer and activator of transcription 3 (Stat3), S-phase kinase-associated protein 2 (SKP2), ATP binding cassette B 1 (ABCB1) and survivin. As a lead compound, LG1980 is well tolerated in mice and effectively suppresses the in vivo growth of chemoresistant PCa and synergistically enhances the efficacy of docetaxel in xenograft models.Conclusions: These results indicate that pharmacological inhibition of EED-EZH2 interaction is a novel strategy for the treatment of chemoresistant PCa. LG1980 and its analogues have the potential to be integrated into standard of care to improve clinical outcomes in PCa patients.

Methylation of EZH2 by PRMT1 regulates its stability and promotes breast cancer metastasis.

Enhancer of zeste homolog 2 (EZH2), a key histone methyltransferase and EMT inducer, is overexpressed in diverse carcinomas, including breast cancer. However, the molecular mechanisms of EZH2 dysregulation in cancers are still largely unknown. Here, we discover that EZH2 is asymmetrically dimethylated at R342 (meR342-EZH2) by PRMT1. meR342-EZH2 was found to inhibit the CDK1-mediated phosphorylation of EZH2 at T345 and T487, thereby attenuating EZH2 ubiquitylation mediated by the E3 ligase TRAF6. We also demonstrate that meR342-EZH2 resulted in a decrease in EZH2 target gene expression, but an increase in breast cancer cell EMT, invasion and metastasis. Moreover, we confirm the positive correlations among PRMT1, meR342-EZH2 and EZH2 expression in the breast cancer tissues. Finally, we report that high expression levels of meR342-EZH2 predict a poor clinical outcome in breast cancer patients. Our findings may provide a novel diagnostic target and promising therapeutic target for breast cancer metastasis.

A partially disordered region connects gene repression and activation functions of EZH2

Enhancer of Zeste Homolog 2 (EZH2) is the catalytic subunit of Polycomb Repressive Complex 2 (PRC2), which minimally requires two other subunits, EED and SUZ12, for enzymatic activity. EZH2 has been traditionally known to mediate histone H3K27 trimethylation, a hallmark of silent chromatin. Emerging evidence indicates that EZH2 also activates gene expression in cancer cells in a context distinct from canonical PRC2. The molecular mechanism underlying the functional conversion of EZH2 from a gene repressor to an activator is unclear. Here, we show that EZH2 harbors a hidden, partially disordered transactivation domain (TAD) capable of interacting with components of active transcription machinery, mimicking archetypal acidic activators. The EZH2 TAD comprises the SRM (Stimulation-Responsive Motif) and SANT1 (SWI3, ADA2, N-CoR, and TFIIIB 1) regions that are normally involved in H3K27 methylation. The crystal structure of an EZH2-EED binary complex indicates that the EZH2 TAD mediates protein oligomerization in a noncanonical PRC2 context and is entirely sequestered. The EZH2 TAD can be unlocked by cancer-specific EZH2 phosphorylation events to undergo structural transitions that may enable subsequent transcriptional coactivator binding. The EZH2 TAD directly interacts with the transcriptional coactivator and histone acetyltransferase p300 and activates gene expression in a p300-dependent manner in cells. The corresponding TAD may also account for the gene activation function of EZH1, the paralog of EZH2. Distinct kinase signaling pathways that are known to abnormally convert EZH2 into a gene activator in cancer cells can now be understood in a common structural context of the EZH2 TAD.

Blocking immunosuppressive neutrophils deters pY696-EZH2-driven brain metastases.

The functions of immune cells in brain metastases are unclear because the brain has traditionally been considered "immune privileged." However, we found that a subgroup of immunosuppressive neutrophils is recruited into the brain, enabling brain metastasis development. In brain metastatic cells, enhancer of zeste homolog 2 (EZH2) is highly expressed and phosphorylated at tyrosine-696 (pY696)-EZH2 by nuclear-localized Src tyrosine kinase. Phosphorylation of EZH2 at Y696 changes its binding preference from histone H3 to RNA polymerase II, which consequently switches EZH2's function from a methyltransferase to a transcription factor that increases c-JUN expression. c-Jun up-regulates protumorigenic inflammatory cytokines, including granulocyte colony-stimulating factor (G-CSF), which recruits Arg1+- and PD-L1+ immunosuppressive neutrophils into the brain to drive metastasis outgrowth. G-CSF-blocking antibodies or immune checkpoint blockade therapies combined with Src inhibitors impeded brain metastasis in multiple mouse models. These findings indicate that pY696-EZH2 can function as a methyltransferase-independent transcription factor to facilitate the brain infiltration of immunosuppressive neutrophils, which could be clinically targeted for brain metastasis treatment.

LncRNA UCA1 Antagonizes Arsenic-Induced Cell Cycle Arrest through Destabilizing EZH2 and Facilitating NFATc2 Expression.

Arsenic (As) is a widespread metalloid contaminant, and its internal exposure is demonstrated to cause serious detrimental health problems. Albeit considerable studies are performed to interrogate the molecular mechanisms responsible for As‐induced toxicities, the exact mechanisms are not fully understood yet, especially at the epigenetic regulation level. In the present study, it is identified that long non‐coding RNA (lncRNA) urothelial cancer associated 1 (UCA1) alleviates As‐induced G2/M phase arrest in human liver cells. Intensive mechanistic investigations illustrate that UCA1 interacts with enhancer of zeste homolog 2 (EZH2) and accelerates the latter's protein turnover rate under normal and As‐exposure conditions. The phosphorylation of EZH2 at the Thr‐487 site by cyclin dependent kinase 1 (CDK1) is responsible for As‐induced EZH2 protein degradation, and UCA1 enhances this process through increasing the interaction between CDK1 and EZH2. As a consequence, the cell cycle regulator nuclear factor of activated T cells 2 (NFATc2), a downstream target of EZH2, is upregulated to resist As‐blocked cell cycle progress and cytotoxicity. In conclusion, the findings decipher a novel prosurvival signaling pathway underlying As toxicity from the perspective of epigenetic regulation: UCA1 facilitates the ubiquitination of EZH2 to upregulate NFATc2 and further antagonizes As‐induced cell cycle arrest.

CDK2-mediated site-specific phosphorylation of EZH2 drives and maintains triple-negative breast cancer

Triple-negative breast cancer (TNBC), which lacks estrogen receptor α (ERα), progesterone receptor, and human epidermal growth factor receptor 2 (HER2) expression, is closely related to basal-like breast cancer. Previously, we and others report that cyclin E/cyclin-dependent kinase 2 (CDK2) phosphorylates enhancer of zeste homolog 2 (EZH2) at T416 (pT416-EZH2). Here, we show that transgenic expression of phospho-mimicking EZH2 mutant EZH2T416D in mammary glands leads to tumors with TNBC phenotype. Coexpression of EZH2T416D in mammary epithelia of HER2/Neu transgenic mice reprograms HER2-driven luminal tumors into basal-like tumors. Pharmacological inhibition of CDK2 or EZH2 allows re-expression of ERα and converts TNBC to luminal ERα-positive, rendering TNBC cells targetable by tamoxifen. Furthermore, the combination of either CDK2 or EZH2 inhibitor with tamoxifen effectively suppresses tumor growth and markedly improves the survival of the mice bearing TNBC tumors, suggesting that the mechanism-based combination therapy may be an alternative approach to treat TNBC.

CDK5/FBW7-dependent ubiquitination and degradation of EZH2 inhibits pancreatic cancer cell migration and invasion

Pancreatic cancer is one of the most lethal cancer types. Enhancer of zeste homolog 2 (EZH2) is an oncogenic protein overexpressed in pancreatic cancer, and EZH2 could be a potential therapeutic target for the treatment of pancreatic cancer. Although significant progress has been made toward understanding the function and deregulation of EZH2 in cancer cells, the posttranslational regulation of EZH2 in cancer cells is still unclear. F-box and WD repeat domain-containing 7 (FBW7) acts as a tumor suppressor by targeting multiple oncoprotein substrates for ubiquitination and degradation. Here we demonstrate that EZH2 is a bona fide substrate of FBW7 in pancreatic cancer cells. We provide evidence that the activated CDK5 kinase is involved in the EZH2 phosphorylation that is required for FBW7-mediated degradation. We further show that FBW7 suppresses EZH2 activity and inhibits tumor migration and invasion via degradation of EZH2 in pancreatic cancer cells. Furthermore, immunohistochemistry analysis revealed that expression of EZH2 protein negatively correlates with FBW7 protein levels in a cohort of human pancreatic cancer specimens. Collectively, our findings demonstrate that FBW7 is a novel E3 ligase of EZH2 that regulates the EZH2 protein level in pancreatic cancer and represents a viable strategy for effective treatment of pancreatic cancer.

LncRNA MALAT1 promotes development of mantle cell lymphoma by associating with EZH2

BackgroundMantle cell lymphoma (MCL) is considered an aggressive subtype of non-Hodgkin’s lymphoma with variable treatment responses. There is an urgent need to identify novel markers with prognostic and therapeutic value for MCL. Long non-coding RNAs (lncRNAs) have emerged as key regulators in cancers, including MCL. Metastasis-associated lung adenocarcinoma transcript 1(MALAT1), a lncRNA located at pathognomonic translocation site of t (11; 14) of MCL. MALAT1 is known to be overexpressed in solid tumors and hematologic malignancies. However, the pathological role and clinical relevance of MALAT1 in MCL are not completely understood.MethodsWe quantified MALAT1 in MCL samples (40) and CD19+ B cells by quantitative real time polymerase chain reaction (qRT-PCR) and correlated levels with clinical outcome. We silenced MALAT1 in MCL cell lines and analyzed cells in tumorigenic assays and formation of transcription complexes.ResultsWe found that the expression of MALAT1 was elevated in human MCL tumors and cell lines as compared to normal controls, and the elevated levels of MALAT1 correlated with higher MCL international prognostic index (MIPI) and reduced overall survival. MCL with knockdown of MALAT1 showed impaired cell proliferation, facilitated apoptosis and produced fewer clonogenic foci. The increased expression of p21 and p27 upon MALAT1 knockdown was regulated by enhancer of zeste homolog 2 (EZH2). Moreover, decreased phosphorylation of EZH2 at T350 attenuated the binding to MALAT1.ConclusionsOur findings illuminate the oncogenic role of MALAT1, which may serve as a novel biomarker and as a therapeutic target in MCL.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-016-1100-9) contains supplementary material, which is available to authorized users.

Abstract 4481: Phosphorylation regulates EZH2 neoplastic functions in triple-negative breast cancer

Abstract Background: Triple negative (estrogen receptor, progesterone receptor, HER2-neu negative) breast cancers (TNBC) comprise 15% of all breast cancers but are responsible for a disproportionately high number of deaths. Overexpression of the histone methyltransferase EZH2 (Enhancer of Zeste Homolog 2) is an independent prognostic biomarker significantly associated with poorly-differentiated TNBCs and poor patient outcome. We previously identified a novel link between EZH2 and the p38 mitogen-activated protein kinase, an important mediator of progression and metastasis of TNBC. We found that EZH2 binds to p38, and that EZH2 and activated p38 are concordantly expressed in the metastases of breast cancer patients. Based on these data and previous in vitro studies, we hypothesized that p38 MAPK may also regulate EZH2 through phosphorylation in breast cancer. We further hypothesized that this phosphorylation event may be important for EZH2 contribution to malignancy. Methods: In order to test this hypothesis, we performed knockdown rescue experiments in triple-negative breast cancer cell lines MDA-MB-231 and MDA-MB-436. Stable knockdown of EZH2 was achieved using shRNA targeting the 3’UTR. Knockdown of EZH2 was rescued by reintroduction of myc-EZH2 (WT) or a T367A-EZH2 phosphorylation-deficient mutant. Cell lines were then used in functional assays of proliferation, migration, and invasion. In order to further interrogate the importance of this phosphorylation event, we developed a phospho-specific EZH2 T367 antibody. Results: p38-mediated phosphorylation of EZH2 at T367 contributes to the migratory and invasive properties of TNBC. Mechanistically, phosphorylation by p38 does not affect binding to other PRC2 members but may affect EZH2 activity. We are currently investigating the relevance of pEZH2 as a biomarker of breast cancer survival with our new antibody. Conclusions: We provide evidence that p38 phosphorylation of EZH2 at T367 contributes to malignancy of triple-negative breast cancers. Our data suggest a new mechanism by which EZH2 is regulated and may offer an additional mechanism by which EZH2 contributes to TNBC progression. Citation Format: Talha Anwar, Caroline Arellano-Garcia, Boris Burman, Celina G. Kleer. Phosphorylation regulates EZH2 neoplastic functions in triple-negative breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4481.

PCAF-primed EZH2 acetylation regulates its stability and promotes lung adenocarcinoma progression.

Enhancer of zeste homolog 2 (EZH2) is a key epigenetic regulator that catalyzes the trimethylation of H3K27 and is modulated by post-translational modifications (PTMs). However, the precise regulation of EZH2 PTMs remains elusive. We, herein, report that EZH2 is acetylated by acetyltransferase P300/CBP-associated factor (PCAF) and is deacetylated by deacetylase SIRT1. We identified that PCAF interacts with and acetylates EZH2 mainly at lysine 348 (K348). Mechanistically, K348 acetylation decreases EZH2 phosphorylation at T345 and T487 and increases EZH2 stability without disrupting the formation of polycomb repressive complex 2 (PRC2). Functionally, EZH2 K348 acetylation enhances its capacity in suppression of the target genes and promotes lung cancer cell migration and invasion. Further, elevated EZH2 K348 acetylation in lung adenocarcinoma patients predicts a poor prognosis. Our findings define a new mechanism underlying EZH2 modulation by linking EZH2 acetylation to its phosphorylation that stabilizes EZH2 and promotes lung adenocarcinoma progression.