Syk基因甲基化在肝癌中的研究进展及展望

脾酪氨酸激酶（spleen tyrosine kinase,Syk）是一种造血细胞特异性的信号分子,被认为是一种候选抑癌基因。DNA甲基化是肿瘤发生发展过程中较常见的表观遗传学改变,它与肿瘤的关系己成为肿瘤发病机制研究中的热点。本文综述了Syk基因甲基化的研究现状和它在肝癌中的表达情况及其与肿瘤发生、发展、转移的关系。     

脾酪氨酸激酶与肿瘤

脾酪氨酸激酶(spleen tyosine kinase,Syk)在较长时间里被认为是造血细胞特有的信号分子,在淋巴细胞的成熟和免疫细胞的激活中起重要作用.近年来发现Syk在多种非造血细胞也有表达.最初观察到Syk在乳腺癌的演进中显著降低,后来发现Syk异常表达也见于其它许多肿瘤.研究表明,Syk有抑制肿瘤发生和转移的功能,但Syk抑癌的分子机制仍大部分未明.Syk基因启动子超甲基化是其沉默的机制之一.日益增多的临床研究显示,Syk的低表达与肿瘤转移形成呈正相关,表明Syk可能是一个潜在的肿瘤抑制因子.     

微小RNA的DNA甲基化与肿瘤发生发展相关性的研究进展

目的:总结国内外关于微小RNA DNA甲基化在肿瘤发生发展过程的作用及其进行靶向调控的研究现状.方法:应用Medline及CNKI期刊全文数据库检索系统,以"肿瘤、微小RNA、DNA甲基化"为关键词,检索1993-01-2010-01的相关文献,共检索到英文文献62篇和中文文献2篇.纳入标准:1)微小RNA的起源和特点;2)微小RNA与DNA甲基化的关系;3)微小RNA DNA甲基化与肿瘤发生发展的关系;4)微小RNA DNA甲基化与肿瘤预后的关系.根据纳入标准符合分析文献23篇.结果:DNA甲基化可能是一种导致miRNA在肿瘤中表达沉默并影响其靶基因的表达和功能,进而影响肿瘤生物学行为的重要方式.结论:微小RNA DNA甲基化是肿瘤发生发展的重要机制之一,为肿瘤的诊断及治疗提供了新的方法.     

肿瘤与microRNA的DNA甲基化相关性研究进展

目的:总结国内外关于microRNA (miRNA)的DNA甲基化在各肿瘤中的研究进展.方法:应用PubMed及CNKI全文数据库检索系统,以“miRNA、DNA甲基化和肿瘤”为检索词,检索2004-04-2012-05的相关文献,共检索到英文文献401篇,中文文献40篇.文献纳入标准:1)miRNA的生物学特性;2)DNA甲基化的作用机制及与肿瘤的关系;3)miRNA的DNA甲基化与肿瘤发生发展的关系.根据纳入标准符合分析的文献27篇.结果:miRNA在肿瘤发生发展中可发挥癌基因和抑癌基因的作用,DNA甲基化是肿瘤发生的一个重要因素.20％受甲基化调控的miRNA在上游5 kb范围内有CpG岛,miRNA的DNA甲基化与CpG岛有密切关系.miR-34、miR-124、miR-9和miR-127的DNA甲基化在各种肿瘤中频繁发生,多数通过靶向调节癌基因或抑癌基因而在肿瘤发生发展中发挥作用.结论:miRNA的DNA甲基化在人类肿瘤中广泛存在,甲基化miRNA可能作为肿瘤早期诊断、治疗、转移和预后的分子标志.     

Syk基因甲基化和肝癌术后复发转移关系的研究

目的 探讨肝癌组织Syk基因启动子甲基化改变的特点,及其与肝癌术后复发转移的关系.方法 采用甲基化特异性PCR方法检测Syk基因启动子甲基化情况,结合随访结果,探讨Syk基因启动子甲基化和肝癌术后复发转移的关系.结果 在64例肝癌组织标本中,有19例检测到Syk基因启动子甲基化,发生率为29.7%;在对应癌周正常肝组织中,只有2例检测到Syk基因启动子甲基化,发生率为3.1%.癌组织Syk基因启动子甲基化发生率显著增高（P〈0.005）.在19例癌组织检测到Syk基因启动子甲基化的肝癌患者中,有14例术后发生癌复发转移,发生率为73.7%;在45例癌组织未检测到Syk基因启动子甲基化的肝癌患者中,只有19例术后发生癌复发转移,发生率为42.2%.癌组织检测到Syk基因启动子甲基化的肝癌患者术后复发转移发生率显著增高（P〈0.05）.结论 Syk基因启动子甲基化可能是肝癌发生发展过程中重要的机制之一.肝癌组织Syk基因启动子甲基化可能是预测患者术后复发转移潜在的生物标记物.     

DNA甲基化与肿瘤发生发展机制研究进展

表观遗传学在肿瘤发生发展中具有重要的作用,其中DNA甲基化被认为是肿瘤形成的重要机制之一.在肿瘤形成过程中,DNA甲基化的模式发生了巨大变化,包括整个基因组的去甲基化和部分区域高度甲基化两种现象.抑癌基因通常因高度甲基化而失活,这种基因沉默调控与体细胞突变共同促进了肿瘤的发展.目前对基因表达调控的研究加深了对基因沉默机制的理解,也为肿瘤发生机制研究及其早期诊断和潜在的治疗开辟新的方向.     

信息动态

叶酸是一种水溶性维生素,作为甲基供体在基因调控所需的甲基化过程中起重要的作用.一旦叶酸缺乏将会导致DNA甲基化的模式转变,DNA链乃至染色体断裂,所以普遍认为叶酸缺乏与人类肿瘤的发生密切相关.叶酸在肿瘤治疗中的应用也愈加广泛,在化疗和靶向治疗中均有使用.本文简要综述叶酸与肿瘤发生的关系及其在肿瘤治疗中应用的研究进展.     

5-羟甲基胞嘧啶与肿瘤

肿瘤的发生发展和侵袭与表观遗传学变化紧密相关。胞嘧啶甲基化产物5-甲基胞嘧啶(5-methylcytosine,5-mC)是重要的表观遗传学调控因子。羟甲基化是5-mC去甲基化的重要过程之一,其产物5-羟甲基胞嘧啶(5-hydroxymethylcytosine,5-hmC)也参与基因的表观遗传学调控。国内外研究提示,5-hmC表达水平及分布的改变与胚胎发育、肿瘤发生发展等密切相关。本文对5-hmC及其在肿瘤中的异常与肿瘤关系的研究进展进行综述。     

LAMA3基因在肿瘤中研究新进展

肿瘤的发生发展是一个受多因素影响的逐步发展的过程,其中全基因组低甲基化和局部性高甲基化是肿瘤产生的重要原因.LAMA3基因作为层黏连蛋白的编码基因,被证实参与肿瘤的发生发展.基因启动子区的高甲基化往往使得LA-MA3低表达甚至沉默,miRNA与RNA可变剪接等表观遗传修饰也调控肿瘤细胞中LAMA3的表达.LAMA3的异常表达还与黏着斑和细胞外基质-受体两条信号通路密切相关,从而影响肿瘤细胞的侵袭和转移.本文就LAMA3在肿瘤发生发展过程中的作用及其在肿瘤中异常表达与表观遗传学的关系作一综述.     

DNA甲基化与肿瘤发生发展机制研究进展

表观遗传学在肿瘤发生发展中具有重要的作用，其中DNA甲基化被认为是肿瘤形成的重要机制之一。在肿瘤形成过程中，DNA甲基化的模式发生了巨大变化，包括整个基因组的去甲基化和部分区域高度甲基化两种现象。抑癌基因通常因高度甲基化而失活，这种基因沉默调控与体细胞突变共同促进了肿瘤的发展。目前对基因表达调控的研究加深了对基因沉默机制的理解，也为肿瘤发生机制研究及其早期诊断和潜在的治疗开辟新的方向。     

Reactivation of Syk gene by AZA suppresses metastasis but not proliferation of breast cancer cells

Spleen tyrosine kinase (Syk) is reported to be involved in the suppression of proliferation and invasion of breast cancer. Methylation-mediated Syk gene silencing is found in a subset of breast cancer. In this study, we used a DNA methyltransferase inhibitor, 5-aza-2-deoxycytidine (AZA), to restore Syk expression of breast cancer cells. Surprisingly, we found that AZA treatment could reestablish the expression of Syk, but not affect the proliferation of breast cancer cells. Moreover, tumor formation in situ by MDA-MB-435s treated with (+) or without (−) AZA in a nude mice MFP (Mammary fat pad) model did not show significant difference, too. Interestingly, pulmonary metastasis was still significantly suppressed in MDA-MB-435s(+) group (1/9 vs. 7/9). Our findings suggested Syk may be more correlated to metastasis rather than proliferation. This study implied a potential use of Syk methylation as a valuable biomarker to detect high metastatic potential cancerous lesions and the prospect of AZA to join the arsenal of drug candidates to be developed as a new reagent for management of advanced breast cancer.     

B淋巴瘤细胞Syk基因启动子区甲基化及5-aza-CDR对细胞增殖和凋亡影响的研究

目的:探讨B淋巴瘤细胞Syk基因启动子区5′CpG甲基化情况及甲基化抑制剂5-氮杂脱氧胞苷(5-aza-2′-deoxycytidine,5-az-a-CDR)对淋巴瘤细胞的作用机制。方法:采用RT-PCR方法检测人B淋巴瘤细胞株Raji和Ramos中Syk mRNA的表达,用甲基化特异性PCR(MSP)方法检测Syk基因启动子区甲基化情况;采用MTT法检测5-aza-CDR对细胞增殖作用的影响,应用DNA凝胶电泳、流式细胞技术和电镜分析5-aza-CDR对B淋巴瘤细胞增殖、细胞周期和超微结构的影响。结果:Raji细胞Syk基因呈阳性表达,Ramos细胞未检测出Syk mRNA表达。Raji和Ramos细胞中均未检测到Syk基因启动子区的甲基化状态。5-aza-CDR可明显抑制Raji和Ramos细胞增殖,P<0.05;并存在明显的量效和时效依赖关系。5-aza-CDR可诱导Raji和Ramos细胞凋亡,P<0.05。DNA凝胶电泳检测结果显示明显的"DNAladder",并且有明显的细胞凋亡超微结构变化。然而,5-aza-CDR对Raji和Ramos细胞周期未见明显影响。结论:在Raji和Ramos细胞中,Syk基因沉默可能与甲基化无关;5-aza-CDR能明显抑制B淋巴瘤细胞增殖,诱导细胞凋亡,但对细胞周期无明显影响。     

B淋巴瘤细胞Syk基因启动子区甲基化及5-aza-ODR对细胞增殖和凋亡影响的研究

目的：探讨B淋巴瘤细胞Syk基因启动子区5′CpG甲基化情况及甲基化抑制剂5-氮杂脱氧胞苷（5-aza-2′-deoxycytidine,5-az-a-CDR）对淋巴瘤细胞的作用机制。方法：采用RT-PCR方法检测人B淋巴瘤细胞株Raji和Ramos中Syk mRNA的表达,用甲基化特异性PCR（MSP）方法检测Syk基因启动子区甲基化情况;采用MTT法检测5-aza-CDR对细胞增殖作用的影响,应用DNA凝胶电泳、流式细胞技术和电镜分析5-aza-CDR对B淋巴瘤细胞增殖、细胞周期和超微结构的影响。结果：Raji细胞Syk基因呈阳性表达,Ramos细胞未检测出Syk mRNA表达。Raji和Ramos细胞中均未检测到Syk基因启动子区的甲基化状态。5-aza-CDR可明显抑制Raji和Ramos细胞增殖,P〈0.05;并存在明显的量效和时效依赖关系。5-aza-CDR可诱导Raji和Ramos细胞凋亡,P〈0.05。DNA凝胶电泳检测结果显示明显的“DNAladder”,并且有明显的细胞凋亡超微结构变化。然而,5-aza-CDR对Raji和Ramos细胞周期未见明显影响。结论：在Raji和Ramos细胞中,Syk基因沉默可能与甲基化无关;5-aza-CDR能明显抑制B淋巴瘤细胞增殖,诱导细胞凋亡,但对细胞周期无明显影响。     

Frequent epigenetic inactivation of spleen tyrosine kinase gene in human hepatocellular carcinoma.

PURPOSE: The aim of present study was to investigate the methylation and expression status of spleen tyrosine kinase (SYK) in human hepatocellular carcinoma (HCC) and to evaluate this information for its ability to predict disease prognosis. E-cadherin and TIMP-3 methylation was also analyzed here as control because both were associated with poor prognosis in some types of tumors. EXPERIMENTAL DESIGN: We analyzed the methylation status of SYK, E-cadherin, and TIMP-3 in 124 cases of HCC and assessed the correlation of such methylations with clinicopathologic variables and prognosis after tumor resection. RESULTS: We found that SYK, E-cadherin, and TIMP-3 genes were methylated in 27%, 27%, and 42% of HCC neoplastic tissues, respectively. The loss of SYK mRNA or Syk protein expression was highly correlated with SYK gene methylation. The patients with methylated SYK in neoplastic tissues had a significantly lower overall survival rate after hepatectomy than those with unmethylated SYK. No significant difference in overall survival rates, however, was found between groups of patients with methylated and unmethylated E-cadherin or TIMP-3. Patients with negative Syk protein expression had a significantly lower overall survival rate than those with positive Syk protein expression. Multivariate analyses indicated that factors affecting overall survival were tumor-node-metastasis stage, Child-Pugh classification, SYK methylation, or Syk protein status. CONCLUSIONS: Our results indicate that SYK methylation and loss of Syk expression in HCC neoplastic tissues are independent biomarkers of poor patient outcome and that determination of SYK methylation or Syk expression status may offer guidance for selecting appropriate treatments.     

Progressive loss of Syk and abnormal proliferation in breast cancer cells

The tumor suppressor gene Syk tyrosine kinase is absent or reduced in invasive breast cancer tissues and cell lines; its loss in breast tissues is linked to poor prognosis and metastasis. Also, evidence shows that in vitro Syk is involved in regulating proliferation. Here, we show by in situ hybridization on breast tissue sections that the loss of Syk expression is progressive during tumor development. Strikingly, Syk is already partially lost in normal epithelial tissue adjacent to the cancer lesion. In vivo, cell proliferation (as measured by the proliferative index Ki67) increased from normal to ductal carcinoma in situ to invasive, whereas Syk in situ staining in the same tissues decreased. In vitro, the presence of Syk was associated with reduced cell proliferation in an epidermal growth factor receptor-overexpressing breast cancer cell line, BT549, whereas changes in apoptosis were undetected. Concomitantly, the kinase activity of the proto-oncogene Src was reduced by approximately 30%. A 5-fold increase in abnormal mitoses was observed in the Syk-transfected cells compared with vector control. We propose that Syk is involved in the regulation of cell proliferation, possibly by controlling mechanisms of mitosis and cytokinesis via Src signal transduction pathway(s). Because of its progressive and early loss during tumor onset and development, monitoring of Syk loss in breast epithelial cells by noninvasive techniques such as ductal lavage may be a powerful tool for screening purposes.     

乳腺癌细胞中Syk(L)调节基因转录的生物学机制

背景与目的:全长型脾脏酪氨酸激酶[full-length form of spleen tyrosine kinase,Syk(L)]在乳腺癌中具有抑癌功能,可移位到细胞核内,作为转录抑制因子调节基因的转录.本研究拟探讨Syk(L)行使转录抑制功能的具体分子生物学机制.方法:将pFLAG-CMV-Syk(L)转染人人胚肾细胞HEK293中,采用免疫沉淀方法检测组蛋白去乙酰化酶(histone deacetylases,HDACs)与外源性Syk(L)的结合.采用免疫沉淀方法检测乳腺癌细胞MB468中内源性Syk(L)与HDACl的结合.构建带有FLAG标志的Syk(L)各个功能域质粒,并将其转染人HEK293细胞中,采用免疫沉淀方法检测HDACl与Syk(L)各个功能域之间的结合.采用HDAC活力检测系统检测Syk(L)免疫沉淀复合物中的HDAC活性.结果:HEK293细胞中外源性Syk(L)可与HDAC1、3、6、7结合,Syk(L)通过SH2功能域和KD功能域与HDAC1相互结合.乳腺癌细胞MB468中内源性Syk(L)与HDACl可相互结合.Syk(L)免疫沉淀复合物有明显的HDAC活性.结论:在乳腺癌中,抑癌基因Syk(L)可能通过与HDAC形成复合物调节基因的转录.     

Hypermethylation of the spleen tyrosine kinase promoter in T-lineage acute lymphoblastic leukemia

Sequence analysis of the noncoding first exon (exon 1) of the Syk gene demonstrated the presence of a previously cloned CpG island (GenBank #Z 65706). Transient transfection analysis in Daudi cells demonstrated promoter activity (18-fold increase over parental luciferase plasmid) for a 348 bp BstXI-BsrBI fragment containing this island. This region exhibits a high GC content (approximately 75%), contains several SP1 binding sites and a potential initiator sequence, but lacks a strong TATA consensus. Bisulfite sequencing and methylation-specific PCR (MSP) of this region demonstrated that the Syk promoter CpG island was largely unmethylated in B-lineage leukemia cell lines, control peripheral blood cells, human thymocytes and CD3(+) T lymphocytes. However, dense methylation was seen in four T-lineage leukemia cell lines, Jurkat, H9, Molt 3 and HUT 78. MSP screening of leukemia cells from six T-lineage acute lymphoblastic leukemia (ALL) patients demonstrated methylation of the Syk promoter CpG island in one T-lineage ALL patient. Promoter methylation was correlated with reduced to absent expression of Syk mRNA and SYK protein in the T-lineage leukemia cell lines. Treatment of the leukemia lines Ha and Molt 3, with the methylation inhibitor, 5-aza-2'-deoxycytidine (5-aza-CdR) resulted in increased Syk mRNA expression. The presence of a methylated promoter sequence in these T-lineage leukemia cell lines and in one T-lineage patient suggests a potential role for SYK as a tumor suppressor in T-ALL.     

DNA甲基化在肿瘤中的研究进展

DNA甲基化是调节真核生物基因表达的重要方式之一.DNA甲基化在正常细胞癌变过程中发挥重要的作用.在多种肿瘤类型中,控制细胞周期、增殖、凋亡、转移、耐药性以及细胞内信号传导的相关基因存在异常甲基化.