树突状细胞分化发育及功能的表观遗传学调控机制的研究进展

树突状细胞（DCs）是体内功能最强的专职抗原提呈细胞,具有摄取、加工、处理和呈递抗原以及激活初始T淋巴细胞的功能。近年来研究发现,DNA甲基化、组蛋白修饰、染色质重塑、基因组印记以及非编码RNA等表观遗传学修饰能调控相关基因的表达,同时树突状细胞的分化发育及功能也受到表观遗传学调控。研究从DNA甲基化修饰、组蛋白修饰和非编码RNA,了解近年来很有必要树突状细胞的分化发育及功能的表观遗传学调控机制很有意义。     

HuD interacts with survival motor neuron protein and can rescue spinal muscular atrophy-like neuronal defects

Spinal muscular atrophy is an autosomal-recessive neuromuscular disease caused by disruption of the survival of motor neuron (SMN) gene, which promotes cytoplasmic assembly of the splicing core machinery. It remains unclear how a deficiency in SMN results in a disorder leading to selective degeneration of lower motor neurons. We report here that SMN interacts with RNA-binding protein HuD in neurites of motorneuron-derived MN-1 cells. This interaction is mediated through the Tudor domain of SMN and, importantly, naturally occurring Tudor mutations found in patients with severe spinal muscular atrophy (SMA) completely abrogate the interaction, underscoring its relevance to the disease process. We also characterized a regulatory pathway involving coactivator-associated arginine methyltransferase 1 (CARM1) and HuD. Specifically, we show that CARM1 expression is rapidly downregulated, at the protein level, following induction of differentiation through retinoid and neurotrophic signaling. Using purified proteins, we demonstrate that methylation of HuD by CARM1 reduces its interaction with the p21(cip1/waf1) mRNA, showing that CARM1 can directly influence RNA-binding activity. We further demonstrate that this CARM1-dependent regulatory switch mainly controls the activity of HuD in promoting cell-cycle exit, whereas the interaction between HuD and SMN is required for proper recruitment of HuD and its mRNA targets in neuronal RNA granules. Finally, we were able to rescue SMA-like defects in a hypomorphic Smn knockdown MN-1 cell line through overexpression of HuD. Together, these findings extend our understanding of specific role(s) of SMN in motor neurons and provide crucial insights into potential new avenues for SMA therapeutic strategies.     

Methylation of histones in myeloid leukemias as a potential marker of granulocyte abnormalities

We show that common heterochromatin antigenic protein markers [HP1alpha, -beta, -gamma and mono-, di-, and trimethylated histone H3 lysine 9 (H3K9)], although present in human blood progenitor CD34+ cells, differentiated lymphocytes, and monocytes, are absent in neutrophil granulocytes and to large extent, in eosinophils. Monomethylated and in particular, dimethylated H3K9 are present to variable degrees in the granulocytes of chronic myeloid leukemia (CML) patients, without being accompanied by HP1 proteins. In patients with an acute phase of CML and in acute myeloid leukemia patients, strong methylation of H3K9 and all isoforms of HP1 are detected. In chronic forms of CML, no strong correlations among the level of histone methylation, disease progression, and modality of treatment were observed. Histone methylation was found even in "cured" patients without Philadelphia chromosome (Ph) resulting from +(9;22)(q34;q11) BCR/ABL translocation, suggesting an incomplete process of developmentally regulated chromatin remodeling in the granulocytes of these patients. Similarly, reprogramming of leukemia HL-60 cells to terminal differentiation by retinoic acid does not eliminate H3K9 methylation and the presence of HP1 isoforms from differentiated granulocytes. Thus, our study shows for the first time that histone H3 methylation may be changed dramatically during normal cell differentiation. The residual histone H3 methylation in myeloid leukemia cells suggests an incomplete chromatin condensation that may be linked to the leukemia cell proliferation and may be important for the prognosis of disease treatment and relapse.     

Protein arginine methyltransferase 6 regulates embryonic stem cell identity

Histone arginine methylation has emerged as an important histone modification involved in gene regulation. Protein arginine methyltransferase (PRMT) 4 and 5 have been shown to play essential roles in early embryonic development and in embryonic stem (ES) cells. Recently, it has been reported that PRMT6-mediated di-methylation of histone H3 at arginine 2 (H3R2me2) can antagonize tri-methylation of histone H3 at lysine 4 (H3K4me3), which marks active genes. However, whether PRMT6 and PRMT6-mediated H3R2me2 play crucial roles in early embryonic development and ES cell identity remain unclear. Here, we have investigated their roles using gain and loss of function studies with mouse ES cells as a model system. We report that Prmt6 and histone H3R2 methylation levels increased when ES cells are induced to differentiate. Consistently, we find that differentiation of ES cells upon upregulation of Prmt6 is associated with decreased expression of pluripotency genes and increased expression of differentiation markers. We also observe that elevation of Prmt6 increases the methylation level of histone H3R2 and decreases H3K4me, Chd1, and Wdr5 levels at the promoter regions of Oct4 and Nanog. Surprisingly, knockdown of Prmt6 also leads to downregulation of pluripotency genes and induction of expression of differentiation markers suggesting that Prmt6 is important for ES cell pluripotency and self-renewal. Our results indicate that a critical level of Prmt6 and histone H3R2me must be maintained in mouse ES cells to sustain their pluripotency.     

CARM1维持羊水干细胞干性的机制

BACKGROUND:Studies have shown that methylation modification using CARM1-catalyzed histone H3R17/R26 can maintain the stemness of embryonic stem cells. However, mechanism underlying CARM1 effect on the stemness of amniotic fluid-derived stem cells is still unclear. OBJECTIVE:To investigate the function and underlying molecular mechanism of CARM1 to maintain stemness in the amniotic fluid-derived stem cells. METHODS:Amniotic fluid-derived stem cells from term pregnancy were isolated and cultured. RT-PCR was used to identify the stem cell mark and CARM1 gene expression. CARM1 expression in amniotic fluid-derived stem cells was knocked down by using two shRNA. RT-qPCR was used to detect the silencing efficiency, and western blot employed to examine the methylation level of Arginines 17 at N terminus of histone 3 (H3mR17). Moreover, the expression of embryonic stem cell markers, including OCT4, SOX2 and NANOG, were detected. RESULTS AND CONCLUSION:Amniotic fluid-derived stem cells from term pregnancy could express CARM1 and stem cell markers, including OCT4, SOX2, Nanog and KLF4. Both of the shRNAs could knock down the expression of CARM1 efficiently. When CARM1 was knocked down, the H3mR17 level was decreased and OCT4, SOX2 expression was also reduced, but NANOG expression had no change. All these indicate that CARM1 is required for amniotic fluid-derived stem cells to maintain stemness through regulating OCT4 and SOX2 expression.     

Chromatin remodeling at the Th2 cytokine gene loci in human type 2 helper T cells

The differentiation of mouse na?ve CD4 T cells into type 2 helper (Th2) cells is accompanied by chromatin remodeling at the nucleosomes associated with the IL-4, IL-13 and IL-5 genes. However, little is known about how chromatin remodeling of these Th2 cytokine gene loci occurs in human Th2 cells. We herein established an in vitro culture system in which both Th1 and Th2 cells are efficiently differentiated from human peripheral blood na?ve CD4 T cells. This system allowed us to investigate the chromatin status at the Th2 cytokine gene loci and the IFNgamma locus in human Th2 and Th1 cells, respectively. In typical individuals, the chromatin remodeling indicated by the induction of hyper-acetylation of histone H3 lysine 9 and hyper-methylation of histone H3 lysine 4 was induced at the whole Th2 cytokine gene loci in developing Th2 cells. We more precisely assessed the methylation status of histone H3 lysine 4 at the Th2 cytokine gene loci (IL-5 exon 3, IL-5 promoter, IL-5/RAD50 intergenic region, RAD50 promoter, CGRE, CNS1, IL-13 promoter, IL-4 promoter, and VA enhancer regions) and the IFNgamma locus in developing Th1 and Th2 cells prepared from 20 healthy volunteers. Th2-cell specific chromatin remodeling was induced at most of the Th2 cytokine gene loci. In parallel with the induction of chromatin remodeling, GATA3 mRNA was preferentially expressed in developing Th2 cells, whereas T-bet, HLX and ROG mRNA was selectively expressed in developing Th1 cells.     

Pharmacologic disruption of Polycomb-repressive complex 2-mediated gene repression selectively induces apoptosis in cancer cells

Polycomb-repressive complex 2 (PRC2)-mediated histone methylation plays an important role in aberrant cancer gene silencing and is a potential target for cancer therapy. Here we show that S-adenosylhomocysteine hydrolase inhibitor 3-Deazaneplanocin A (DZNep) induces efficient apoptotic cell death in cancer cells but not in normal cells. We found that DZNep effectively depleted cellular levels of PRC2 components EZH2, SUZ12, and EED and inhibited associated histone H3 Lys 27 methylation (but not H3 Lys 9 methylation). By integrating RNA interference (RNAi), genome-wide expression analysis, and chromatin immunoprecipitation (ChIP) studies, we have identified a prominent set of genes selectively repressed by PRC2 in breast cancer that can be reactivated by DZNep. We further demonstrate that the preferential reactivation of a set of these genes by DZNep, including a novel apoptosis affector, FBXO32, contributes to DZNep-induced apoptosis in breast cancer cells. Our results demonstrate the unique feature of DZNep as a novel chromatin remodeling compound and suggest that pharmacologic reversal of PRC2-mediated gene repression by DZNep may constitute a novel approach for cancer therapy.     

茶多酚的表遗传机制与肿瘤防治

茶多酚(tea polyphenols,TP)是绿茶中对人体有益的主要成分,其对多种不同类型的肿瘤发生可能具有防护作用,其中包括表遗传途径.表遗传指不改变DNA序列的情况下基因表达发生可遗传改变的机制,主要包括DNA甲基化、组蛋白修饰、染色质重塑、siRNA和miRNA调控等,在人类的大多数肿瘤中都观察到表修饰模式的异常.茶多酚具有抑制DNA甲基转移酶、改变组蛋白修饰和miRNA表达的生物学活性,对肿瘤的防护与治疗具有一定的价值.该文就茶多酚的表遗传机制的研究进展作一简要概述.     

茶多酚的表遗传机制与肿瘤防治

茶多酚(tea polyphenols,TP)是绿茶中对人体有益的主要成分,其对多种不同类型的肿瘤发生可能具有防护作用,其中包括表遗传途径.表遗传指不改变DNA序列的情况下基因表达发生可遗传改变的机制,主要包括DNA甲基化、组蛋白修饰、染色质重塑、siRNA和miRNA调控等,在人类的大多数肿瘤中都观察到表修饰模式的异常.茶多酚具有抑制DNA甲基转移酶、改变组蛋白修饰和miRNA表达的生物学活性,对肿瘤的防护与治疗具有一定的价值.该文就茶多酚的表遗传机制的研究进展作一简要概述.

Abstract：

Tea polyphenols (TP) is one of components from green teas, beneficial to human health. They may help prevent different types of tumors, and are involved in epigenetic pathway. Epigenetics is defined as reversible heritable changes in gene expression that occur without alteration in DNA sequence, including DNA methylation, histone modification, chromatin remodeling, and RNA interference.Most of tumors in humans have shown the abnormal patterns of epigenetics. Tea polyphenols demonstrated some effects of epigenetic agents, inducing epigenetic changes through modifying methylation, histone modifications and expression of some miRNAs. It has potential to be used as an agent for tunor prevention.     

HIV-1感染引起组蛋白乙酰化和增加p21WAF1表达

目的：DNA甲基化和组蛋白乙酰化是基因表达调控的主要形式。人类免疫缺陷病毒（HIV-1）可引起T淋巴细胞DNA甲基化酶上调。本文旨在明确HIV-1对细胞周期依赖刺激酶抑制剂p21^WAF1表达的影响。方法：建立HIV-1感染的Hut78细胞系；以RT-PCR和Westem blotting 分析p21^WAF1表达情况；以亚硫酸氢钠修饰DNA和基因测序，研究p21^WAF1基因启动子甲基化，以Western blot-ting 和染色体免疫测定探究总组蛋白和与p21^WAF1基因启动子相关的组蛋白乙酰化水平。并以GST pull-down和免疫沉淀分析HIV-1导致乙酰化及乙酰化引起p21^WAF1过表达的可能机理。结果：HIV-1感染后，其反式激活蛋白Tat与辅助转录因子P/CAF、hGCN5结合，共同刺激组蛋白H3乙酰化。尽管p21^WAF1启动子部分区域有甲基化发生，但p21^WAF1表达仍上调。这可能与E2A对p21^WAF1的作用有关。结论：HIV-1感染可引起T淋巴细胞p21^WAF1基因的甲基化和乙酰化紊乱，导致p21^WAF1表达增强。