组蛋白H3K27去甲基化酶与肿瘤发生

组蛋白甲基化是一种重要的表观遗传学修饰,在基因表达调节方面发挥着重要的作用.组蛋白H3赖氨酸27三甲基化（H3K27me3）是一种抑制性组蛋白标记,可被去甲基化酶UTX和JMJD3催化而移去甲基.UTX和JMJD3通过激活HOX基因而参与细胞分化和多能细胞抑制过程.在多种肿瘤中检测到UTX和JMJD3突变或表达下降,同时多种基因启动子区H3K27me3含量增多.UTX和JMJD3均被看作肿瘤抑制基因,其中UTX调节了RB依赖的细胞命运控制,而JMJD3通过激活INK4b-ARF-INK4a位点而参与了癌基因诱导的衰老.组蛋白H3K27去甲基化酶与肿瘤发生的研究使我们对癌症发展过程有了更好的理解,同时也为癌症诊断和治疗提供了新靶点.     

组蛋白去甲基酶UTX在发育和疾病中的作用

UTX(ubiquitously transcribed tetratricopeptide repeat,X chromosome)是抑制性组蛋白H3K27me3的特异性去甲基化酶,和甲基转移酶PRC2共同调控H3K27me3。此外,UTX也是组蛋白H3K4甲基转移酶MLL3/MLL4的组成部分。UTX参与胚胎发育、HOX基因的表达和重编程等生命过程。在歌舞伎综合征中,UTX突变是关键的致病因素。同时,UTX作为肿瘤抑制因子参与多种实体肿瘤和血液肿瘤的产生。该文总结了UTX在正常发育和疾病发生中的作用及近期研究的重大突破,并结合我们的研究探讨了UTX对体细胞重编程的影响。     

MER-ERK信号通路调控H3K27me3甲基化酶和去甲基化酶基因表达的研究

在人的某些癌症细胞中,组蛋白H3K27me3甲基化酶EZH2基因存在过表达的现象,很多研究已经证明,这可能是受MEK ERK信号通路调控的.为了确定这种调控模式在小鼠细胞系中是否同样存在,以及MEK ERK信号通路是否同时调控H3K27me3甲基化酶EZH1基因和去甲基化酶UTX、JMJD3基因的表达,用RT PCR和Western印迹方法检测不同浓度的MEK ERK抑制剂U0126（0、10、20、40 μmol/L）对C2C12、C127、NIH3T3三种小鼠细胞系处理后,EZH1、EZH2基因和UTX、JMJD3基因表达变化.结果显示：MEK-ERK抑制剂处理后,3种细胞中EZH1和EZH2基因的表达与对照相比都有不同程度的降低,其中EZH2基因表达变化在C2C12、NIH3T3两种细胞达到显著水平(P<0.05). H3K27me3去甲基化酶UTX、JMJD3基因在3种细胞中表达均有升高,JMJD3升高达到显著水平（P<0.05).因此,在小鼠细胞系MEK ERK信号通路可能参与调控EZH2、JMJD3基因的表达,但对EZH1、UTX基因的表达调控作用不明显.
关键词MEK ERK信号通路;     

PI3K/AKT信号通路调控Myogenin和MCK基因的表达

骨骼肌分化过程受多个信号通路调控, PI3K/AKT信号通路是其中最重要的信号转导通路之一。PI3K/AKT信号通路可以调控骨骼肌分化, 但在染色质水平上的调控机制还不是很清楚。文章以小鼠成肌细胞(C2C12)为研究材料, 采用免疫印迹、染色质免疫共沉淀(Chromatin immunoprecipitation, ChIP)、定量PCR (Q-PCR)的方法研究PI3K/AKT信号通路调控Myogenin和MCK基因的表达。研究发现, C2C12细胞分化过程中添加PI3K/AKT信号通路激活剂处理24 h, Myogenin和MCK蛋白表达水平显著升高, 组蛋白H3K27me3去甲基化酶UTX的表达也升高, H3K27me3在Myogenin基因启动子区和MCK基因启动子及增强子区的富集与对照组相比显著降低。用PI3K/AKT信号通路抑制剂处理, 结果相反。因此, PI3K/AKT信号通路可能通过调控组蛋白去甲基化酶UTX的表达活性改变靶基因的H3K27me3的富集进而调控骨骼肌分化。     

EZH2-Mediated H3K27me3 Is Involved in Epigenetic Repression of Deleted in Liver Cancer 1 in Human Cancers

Enhancer of zeste homolog 2 (EZH2), the histone methyltransferase of the Polycomb Repressive complex 2 catalyzing histone H3 lysine 27 tri-methylation (H3K27me3), is frequently up-regulated in human cancers. In this study, we identified the tumor suppressor Deleted in liver cancer 1 (DLC1) as a target of repression by EZH2-mediated H3K27me3. DLC1 is a GTPase-activating protein for Rho family proteins. Inactivation of DLC1 results in hyper-activated Rho/ROCK signaling and is implicated in actin cytoskeleton reorganization to promote cancer metastasis. By chromatin immunoprecipitation assay, we demonstrated that H3K27me3 was significantly enriched at the DLC1 promoter region of a DLC1-nonexpressing HCC cell line, MHCC97L. Depletion of EZH2 in MHCC97L by shRNA reduced H3K27me3 level at DLC1 promoter and induced DLC1 gene re-expression. Conversely, transient overexpression of GFP-EZH2 in DLC1-expressing Huh7 cells reduced DLC1 mRNA level with a concomitant enrichment of EZH2 on DLC1 promoter. An inverse relation between EZH2 and DLC1 expression was observed in the liver, lung, breast, prostate, and ovarian cancer tissues. Treating cancer cells with the EZH2 small molecular inhibitor, 3-Deazaneplanocin A (DZNep), restored DLC1 expression in different cancer cell lines, indicating that EZH2-mediated H3K27me3 epigenetic regulation of DLC1 was a common mechanism in human cancers. Importantly, we found that DZNep treatment inhibited HCC cell migration through disrupting actin cytoskeleton network, suggesting the therapeutic potential of DZNep in targeting cancer metastasis. Taken together, our study has shed mechanistic insight into EZH2-H3K27me3 epigenetic repression of DLC1 and advocated the significant pro-metastatic role of EZH2 via repressing tumor and metastasis suppressors.     

Jumonji C Domain Protein JMJ705-Mediated Removal of Histone H3 Lysine 27 Trimethylation Is Involved in Defense-Related Gene Activation in Rice

Histone methylation is an important epigenetic modification in chromatin function, genome activity, and gene regulation. Dimethylated or trimethylated histone H3 lysine 27 (H3K27me2/3) marks silent or repressed genes involved in developmental processes and stress responses in plants. However, the role and the mechanism of the dynamic removal of H3K27me2/3 during gene activation remain unclear. Here, we show that the rice (Oryza sativa) Jumonji C (jmjC) protein gene JMJ705 encodes a histone lysine demethylase that specifically reverses H3K27me2/3. The expression of JMJ705 is induced by stress signals and during pathogen infection. Overexpression of the gene reduces the resting level of H3K27me2/3 resulting in preferential activation of H3K27me3-marked biotic stress-responsive genes and enhances rice resistance to the bacterial blight disease pathogen Xanthomonas oryzae pathovar oryzae. Mutation of the gene reduces plant resistance to the pathogen. Further analysis revealed that JMJ705 is involved in methyl jasmonate–induced dynamic removal of H3K27me3 and gene activation. The results suggest that JMJ705 is a biotic stress-responsive H3K27me2/3 demethylase that may remove H3K27me3 from marked defense-related genes and increase their basal and induced expression during pathogen infection.     

Polycomb (PcG) Proteins, BMI1 and SUZ12, Regulate Arsenic-induced Cell Transformation

Inorganic arsenic is a well-documented human carcinogen associated with cancers of the skin, lung, liver, and bladder. However, the underlying mechanisms explaining the tumorigenic role of arsenic are not well understood. The present study explored a potential mechanism of cell transformation induced by arsenic exposure. Exposure to a low dose (0.5 μm) of arsenic trioxide (As(2)O(3)) caused transformation of BALB/c 3T3 cells. In addition, in a xenograft mouse model, tumor growth of the arsenic-induced transformed cells was dramatically increased. In arsenic-induced transformed cells, polycomb group (PcG) proteins, including BMI1 and SUZ12, were activated resulting in enhanced histone H3K27 tri-methylation levels. On the other hand, tumor suppressor p16(INK4a) and p19(ARF) mRNA and protein expression were dramatically suppressed. Introduction of small hairpin (sh) RNA-BMI1 or -SUZ12 into BALB/c 3T3 cells resulted in suppression of arsenic-induced transformation. Histone H3K27 tri-methylation returned to normal in BMI1- or SUZ12-knockdown BALB/c 3T3 cells compared with BMI1- or SUZ12-wildtype cells after arsenic exposure. As a consequence, the expression of p16(INK4a) and p19(ARF) was recovered in arsenic-treated BMI1- or SUZ12-knockdown cells. Thus, arsenic-induced cell transformation was blocked by inhibition of PcG function. Taken together, these results strongly suggest that the polycomb proteins, BMI1 and SUZ12 are required for cell transformation induced by organic arsenic exposure.     

Histone Methylation Analysis and Pathway Predictions in Chickens after MDV Infection

Marek's disease (MD) is a lymphoproliferative disease in chicken induced by Marek's disease virus (MDV). Although studies have focused on the genetic differences between the resistant and susceptible chicken, less is known about the role of epigenetic factors in MD. In this study, genome-wide histone modifications in the non-MHC-associated resistant and susceptible chicken lines were examined. We found that tri-methylation at histone H3 Lys4 (H3K4me3) enrichment is positively correlated with the expression of protein coding genes as well as microRNA (miRNA) genes, whereas tri-methylation at histone H3 Lys27 (H3K27me3) exhibits a negative correlation. By identifying line-specific histone modifications in MDV infection, we found unique H3K4me3 islands in the resistant chicken activated genes, which are related to immune response and cell adhesion. Interestingly, we also found some miRNAs from unique H3K27me3 patterns in the susceptible chickens that targeted genes involved in 5-hydroxytryptamine (5-HT)-receptor and adrenergic receptor pathways. In conclusion, dynamic line-specific histone modifications in response to MDV infection suggested that intrinsic epigenetic mechanisms may play a role in MD-resistance and -susceptibility.     

Epigenetic regulation of cell type-specific expression patterns in the human mammary epithelium

Differentiation is an epigenetic program that involves the gradual loss of pluripotency and acquisition of cell type-specific features. Understanding these processes requires genome-wide analysis of epigenetic and gene expression profiles, which have been challenging in primary tissue samples due to limited numbers of cells available. Here we describe the application of high-throughput sequencing technology for profiling histone and DNA methylation, as well as gene expression patterns of normal human mammary progenitor-enriched and luminal lineage-committed cells. We observed significant differences in histone H3 lysine 27 tri-methylation (H3K27me3) enrichment and DNA methylation of genes expressed in a cell type-specific manner, suggesting their regulation by epigenetic mechanisms and a dynamic interplay between the two processes that together define developmental potential. The technologies we developed and the epigenetically regulated genes we identified will accelerate the characterization of primary cell epigenomes and the dissection of human mammary epithelial lineage-commitment and luminal differentiation.