Nucleosome-binding activities within JARID2 and EZH1 regulate the function of PRC2 on chromatin

Polycomb-repressive complex 2 (PRC2) comprises specific members of the Polycomb group of epigenetic modulators. PRC2 catalyzes methylation of histone H3 at Lys 27 (H3K27me3) through its Enhancer of zeste (Ezh) constituent, of which there are two mammalian homologs: Ezh1 and Ezh2. Several ancillary factors, including Jarid2, modulate PRC2 function, with Jarid2 facilitating its recruitment to target genes. Jarid2, like Ezh2, is present in poorly differentiated and actively dividing cells, while Ezh1 associates with PRC2 in all cells, including resting cells. We found that Jarid2 exhibits nucleosome-binding activity that contributes to PRC2 stimulation. Moreover, such nucleosome-binding activity is exhibited by PRC2 comprising Ezh1 (PRC2–Ezh1), in contrast to PRC2–Ezh2. The presence of Ezh1 helps to maintain PRC2 occupancy on its target genes in myoblasts where Jarid2 is not expressed. Our findings allow us to propose a model in which PRC2–Ezh2 is important for the de novo establishment of H3K27me3 in dividing cells, whereas PRC2–Ezh1 is required for its maintenance in resting cells.     

A complex Polycomb issue: the two faces of EZH2 in cancer

In the April 1, 2012, issue of Genes & Development, Simon and colleagues (pp. 651-656) demonstrated that the disruption of Ezh2 in mice is sufficient to cause T-acute lymphoblastic leukemia (T-ALL). Moreover, in concert with concurrent studies, the authors revealed that similar mechanisms are involved in human T-ALL. These data contrast with previous findings showing that increased EZH2 activity promotes cancer.     

Jarid2 and PRC2, partners in regulating gene expression

The Polycomb group proteins foster gene repression profiles required for proper development and unimpaired adulthood, and comprise the components of the Polycomb-Repressive Complex 2 (PRC2) including the histone H3 Lys 27 (H3K27) methyltransferase Ezh2. How mammalian PRC2 accesses chromatin is unclear. We found that Jarid2 associates with PRC2 and stimulates its enzymatic activity in vitro. Jarid2 contains a Jumonji C domain, but is devoid of detectable histone demethylase activity. Instead, its artificial recruitment to a promoter in vivo resulted in corecruitment of PRC2 with resultant increased levels of di- and trimethylation of H3K27 (H3K27me2/3). Jarid2 colocalizes with Ezh2 and MTF2, a homolog of Drosophila Pcl, at endogenous genes in embryonic stem (ES) cells. Jarid2 can bind DNA and its recruitment in ES cells is interdependent with that of PRC2, as Jarid2 knockdown reduced PRC2 at its target promoters, and ES cells devoid of the PRC2 component EED are deficient in Jarid2 promoter access. In addition to the well-documented defects in embryonic viability upon down-regulation of Jarid2, ES cell differentiation is impaired, as is Oct4 silencing.     

Co-expression of Bmi1 and EZH2 as an independent poor prognostic factor in esophageal squamous cell carcinoma

Bmi1 polycomb ring finger oncogene (Bmi1) and the enhancer of zeste homolog 2 (EZH2) are members of polycomb repressive complex (PRC) 1 and PRC2, respectively. PRC1 represses tumor suppressor genes such as p16INK4a and p14ARF in a PRC2-dependent manner. There have been few studies on Bmi1 or EZH2 expression in esophageal squamous cell carcinoma (ESCC). We investigated Bmi1 and EZH2 expression in 164 cases of ESCCs using immunohistochemistry, and evaluated the correlation with clinicopathologic features and their prognostic significance. Bmi1 and EZH2 were more highly expressed in tumor than in adjacent normal tissue (p<0.001). High expression of Bmi1 or EZH2 alone was not correlated with any clinicopathologic parameter and did not influence the prognosis. However, the group with high expression of both Bmi1 and EZH2 showed the poorest prognosis in overall survival (p=0.027) and disease-free survival (p=0.007). Also, it was an independent prognostic factor in overall survival (p=0.047). High expression of both Bmi1 and EZH2, not each alone, is an independent poor prognostic factor in ESCCs, supporting the repression of tumor suppressor gene by Bmi1 in an EZH2-dependent manner. This result suggests that both Bmi1 and EZH2, not each alone, could be potent candidates of new target therapy in ESCCs.     

胃癌中EZH2的表达及临床评估

目的：探讨EZH2在胃癌中的表达及其临床意义。方法：采用逆转录荧光PCR方法检测胃癌组织和配对的正常组织中EZH2的表达,分析EZH2与临床病理参数之间的关系。结果：53例标本中34例（64.15%,34/53）癌组织中EZH2表达增高,EZH2在胃癌组织中的表达明显高于配对正常组织（P〈0.05）。EZH2表达在低分化胃癌中表达明显高于高-中分化胃癌（P〈0.01）;EZH2表达在T3-T4期表达增高,明显高于T1-T2期（P〈0.05）;而EZH2的表达与性别、年龄等因素无关。结论：EZH2在胃癌组织表达增高,与分化程度及TNM分期有关,提供胃癌的进展和肿瘤形成;并预测胃癌治疗的预后方面,可能是一种新的生物标志物。     

前列腺癌中EZH2 mRNA及蛋白表达与细胞增殖的关系

目的 探讨EZH2 mRNA和蛋白在前列腺癌中的表达及其与肿瘤细胞增殖的关系.方法 通过组织芯片技术,应用原位杂交和免疫组化方法检测48例前列腺癌中EZH2 mRNA和蛋白的表达以及Ki-67增殖指数,同时检测15例良性前列腺增生组织(BPH)和12例高级别上皮内瘤变(HGPIN)中EZH2 mRNA和蛋白的表达.结果 前列腺癌组织中EZH2蛋白和mRNA阳性率分别为87.50%和81.25%,均高于BPH和HGPIN,差异有显著性(P<0.05).EZH2蛋白与mRNA表达之间差异无统计学意义(P>0.05).EZH2蛋白的表达与Gleason分级、TNM分期相关(P<0.05),与患者年龄和术前血清前列腺特异抗原(PSA)水平无关(P>0.05).EZH2 mRNA的表达与TNM分期相关(P<0.05),与患者年龄、术前PSA水平及Gleason分级无关(P>0.05).EZH2蛋白表达程度与Ki-67细胞增殖指数呈明显正相关(r=0.746,P<0.05).结论 EZH2 mRNA及其蛋白在前列腺癌中表达上调,通过促进肿瘤细胞增殖使得肿瘤发生、发展,有望成为预测前列腺癌恶性程度进程的参考指标.     

胃癌组织中EZH2和p53蛋白的表达及临床意义

目的探讨EZH2和p53蛋白在胃癌组织中的表达,及其在胃癌发生、发展过程中的作用和临床病理学意义。方法采用免疫组化EnVision法检测EZH2和p53蛋白在199例胃癌、25例高级别上皮内瘤变、24例低级别上皮内瘤变、46例肠上皮化生、17例慢性萎缩性胃炎和23例正常胃黏膜组织中的表达情况。结果在胃癌和上皮内瘤变组织中EZH2蛋白表达明显高于肠上皮化生、慢性萎缩性胃炎和正常胃黏膜组织。胃癌组织中EZH2蛋白的表达在进展期胃癌高于早期胃癌,差异有统计学意义。EZH2蛋白在胃癌组织中的表达与肿瘤的大小、淋巴结转移、组织学分期和临床分期均有关;但与患者的性别、年龄、肿瘤的部位、肿瘤的类型和分化以及患者的病死率均无关。p53蛋白在胃癌组织中表达最高,几乎不表达于其他病变和正常胃黏膜组织。p53表达水平与患者的年龄、性别、肿瘤大小、淋巴结转移、肿瘤分化、胃癌的类型和患者的生存情况相关。EZH2蛋白表达与p53蛋白表达之间呈正相关。结论 EZH2在胃癌中的表达增加与p53相关,提示胃癌中EZH2与p53可能相互协调,促进胃癌的发生、发展。     

Epigenetic remodeling and modification to preserve skeletogenesis in vivo

ABSTRACT

Current studies offer little insight on how epigenetic remodeling of bone-specific chromatin maintains bone mass in vivo. Understanding this gap and precise mechanism is pivotal for future therapeutic innovation to prevent bone loss. Recently, we found that low bone mass is associated with decreased H3K27 acetylation (activating histone modification) of bone specific gene promoters. Here, we aim to elucidate the epigenetic mechanisms by which a miRNA cluster controls bone synthesis and homeostasis by regulating chromatin accessibility and H3K27 acetylation. In order to decipher the epigenetic axis that regulates osteogenesis, we studied a drug inducible anti-miR-23a cluster (miR-23a Cl^ZIP) knockdown mouse model. MiR-23a cluster knockdown (heterozygous) mice developed high bone mass. These mice displayed increased expression of Runx2 and Baf45a, essential factors for skeletogenesis; and decreased expression of Ezh2, a chromatin repressor indispensable for skeletogenesis. ChIP assays using miR-23a Cl knockdown calvarial cells revealed a BAF45A-EZH2 epigenetic antagonistic mechanism that maintains bone formation. Together, our findings support that the miR-23a Cl connection with tissue-specific RUNX2-BAF45A-EZH2 function is a novel molecular epigenetic axis through which a miRNA cluster orchestrates chromatin modification to elicit major effects on osteogenesis in vivo.     

Protein kinase CK2 and regulation of Ca2+-ATPase activity in brain neuron chromatin in rats during aging

Protein kinase CK2 from neuronal chromatin phosphorylates myosin-like proteins isolated from rat brain chromatin. The protein kinase CK2 activator 1-ethyl-4,5-di(N-methylcarbamoyl)imidazole in vitro stimulated phosphorylation of myosin-like proteins and increased myosin-type Ca²⁺-ATPase activity in neuronal chromatin. After systemic administration this agent normalized Ca²⁺-ATPase activity of brain chromatin in aged rats.     

Nrf2通过调控EZH2的表达促进DMSO诱导的MEL细胞红系分化

目的 探讨Nrf2/EZH2通路参与DMSO诱导MEL细胞红系分化的作用及相关分子机制.方法 以MEL细胞为靶细胞,DMSO为刺激源,联苯胺染色法检测细胞红系分化情况;免疫印迹检测EZH2和Nrf2蛋白表达水平.结果 DMSO可显著诱导MEL细胞红系分化,同时EZH2和Nrf2表达水平也明显升高.通过使用Nrf2诱导剂TBHQ及Nrf2 shRNA,证明Nrf2调控MEL细胞中EZH2的表达.敲低Nrf2和EZH2的表达能够抑制DMSO诱导的MEL细胞红系分化.结论 Nrf2可通过调控EZH2的蛋白水平从而发挥促进MEL细胞红系分化的作用.     

Expanding the molecular spectrum of gene fusions in endometrial stromal sarcoma: Novel subunits of the chromatin remodeling complexes PRC2 and NuA4/TIP60 as alternative fusion partners

Endometrial stromal sarcomas (ESS) are morphologically and molecularly heterogeneous. We report novel gene fusions (EPC1::EED, EPC1::EZH2, ING3::PHF1) identified by targeted RNA sequencing in five cases. The ING3::PHF1-fusion positive ESS presented in a 58-year-old female as extrauterine mesocolonic, ovarian masses, and displayed large, monomorphic ovoid-to-epithelioid cells arranged in solid sheets. The patient remained alive with disease 13 months after surgery. The three ESS with EPC1::EED occurred in the uterine corpus in patients with a median age of 58 years (range 27–62 years). One tumor showed a uniform epithelioid nested morphology, while the other two were composed of monomorphic spindle cells in fascicles with elevated mitotic figures, focal tumor cell necrosis, and lymphovascular invasion. At a median follow-up of 20 months, two patients developed local recurrence, including one with concomitant distant metastasis, while one patient remained free of disease. All three patients were alive at the last follow-up. The EPC1::EZH2-fusion positive ESS presented in a 52-year-old female in the uterus, and displayed uniform spindled cells arranged in short fascicles, with focally elevated mitotic activity but without necrosis. The patient remained free of disease 3 months after surgery. All cases were diffusely positive for CD10; four diffusely express estrogen and progesterone receptors. Our study expands the molecular spectrum of EPC1 and PHF1-related gene fusions in ESS to include additional novel subunits of the PRC2 and/or NuA4/TIP60 complexes. These cases displayed a monomorphic epithelioid or spindled phenotype, spanning low-grade and high-grade cytomorphology, all expressing CD10 and commonly ER and PR, and are prone to local and/or distant spread.