肿瘤候选抑制基因RASSF1A

新克隆的RASSF1A基因位于3p21．3，是新的肿瘤候选抑制基因，能明显抑制肿瘤细胞生长。RASSF1A失表达见于多种实性肿瘤组织，与RASSF1A启动子甲基化密切相关。RASSF1A启动子甲基化检测可能是很有用的临床指标。     

肿瘤候选抑制基因RASSF1A

新克隆的RASSF1A基因位于3p21.3,是新的肿瘤候选抑制基因,能明显抑制肿瘤细胞生长.RASSF1A失表达见于多种实性肿瘤组织,与RASSF1A启动子甲基化密切相关.RASSF1A启动子甲基化检测可能是很有用的临床指标.     

上皮性卵巢癌组织中RASSF1A和BRCA1及p16基因异常甲基化检测及其临床意义的研究

目的：探讨RASSF1A、BRCA1和p16基因异常甲基化在上皮性卵巢癌发生及发展中的作用。方法：采用甲基化特异性PCR法检测63例上皮性卵巢癌组织和相应的41例盆腹腔转移灶及10例癌旁卵巢组织中RASSF1A、BRCA1和p16基因启动子区甲基化状态。结果：上皮性卵巢癌组织原发灶及转移灶中RASSF1A、BRCA1和p16基因启动子区甲基化发生率分别为49．2％、25．4％、20．6％及58．5％、26．8％、22．0％,均显著高于正常卵巢组织中的发生率,P值均〈0．05。RASSF1A基因启动子区异常甲基化的发生率在临床Ⅰ、Ⅱ期显著低于Ⅲ、Ⅳ期,Х^2=13．018,P〈0．0001;在高、中分化癌的发生率均显著低于低分化癌,Х^2=8．481,P=0．004;Х^2=8．195,P=0．004。结论：RASSF1A、BRCA1和p16基因异常甲基化与上皮性卵巢癌的发生及发展相关,RASSF1A基因异常甲基化与上皮性卵巢癌临床分期及分化程度相关。     

白血病p16基因失活及其临床意义

目的：探讨ｐ１６基因失活对白血病发病及预后的关系。方法：应用聚合酶链反应（ＰＣＲ）与ＤＮＡ单链构象多态性分析（ＳＳＣＰ）及ＤＮＡ测序技术,甲基化检测技术。结果：ｐ１６基因的失活形式主要以缺失和甲基化为主。ｐ１６基因缺失与急性淋巴细胞白血病的发生密切相关,甲基化则主要发生在髓系白血病。结论：ｐ１６基因结构发生变化在高危白血病患者中比较多,ｐ１６基因的检测对于疾病的治疗及判断预后有着重要的意义。     

宫颈鳞癌组织中RASSF1A基因甲基化状态及其临床意义

背景与目的:Ras相关区域家族1A(ras associated domain family 1A,RASSF1A)基因是一种肿瘤候选抑痛基因,其启动子区高甲基化与多种人类上皮性肿瘤的发生有关.本研究通过检测宫颈鳞癌(cervical squamous cell carcinoma,CSCC)组织中RASSF1A基因启动子区甲基化状态及其蛋白表达情况,旨在分析RASSF1A基因甲基化与基因失活的相关性,并探讨RASSF1A基因甲基化与CSCC发生的关系.方法:分别采用甲基化特异性PCR(methylation-specific PCR,MSP)及免疫组织化学方法检测15例正常宫颈组织和46例CSCC组织中RASSF1A基因的甲基化程度及RASSF1A蛋白的表达情况,并分析RASSF1A基因甲基化与RASSF1A蛋白表达及其与CSCC临床病理特征之间的关系.结果:正常宫颈组织中未见RASSF1A基因甲基化,而CSCC组织中RASSF1A基因甲基化率为43.5%(20/46),两者比较差异具有统计学意义(P＜0.05).CSCC中临床Ⅰ期、Ⅱ期、Ⅲ～Ⅳ期的甲基化阳性率呈逐渐增高趋势(19.0%→58.8%→75.0%,P＜0.05),不同组织学分级、有无淋巴结转移与RASSF1A基因甲基化间未见明显相关性(P＞0.05).RASSF1A基因甲基化与RASSF1A蛋白的表达呈负相关(r=-0.469,P＜0.05).结论:RASSF1A基因启动子区甲基化是导致RASSF1A蛋白低表达的机制之一,可能与CSCC的发生发展有关.     

卵巢肿瘤组织和血清中RASSF1A基因甲基化检测及临床意义的研究

目的：检测卵巢肿瘤组织和血清中RASSF1A基因启动子区异常甲基化,探讨卵巢肿瘤组织和血清中RASSF1A基因甲基化与卵巢癌的关系。方法：收集新鲜的卵巢肿瘤组织及其对应的血清标本65例,10名健康志愿者血清标本。采用半巢式甲基化特异性PCR技术分别检测肿瘤组织DNA和血清游离DNA中RASSF1A基因启动子异常甲基化情况。结果：卵巢癌患者血清和癌组织中,RASSF1A基因甲基化的检出率分别为20．0％和31．4％。卵巢良性肿瘤组织和血清以及健康志愿者血清中,均未发生RASSF1A基因异常甲基化。肿瘤组织中,RASSF1A基因的甲基化状况与血清中出现RASSF1A基因甲基化关系密切,P〈0．01;卵巢癌患者血清和癌组织中,RASSF1A基因的甲基化异常改变与肿瘤的临床分期、细胞分化程度以及组织学类型无明显相关性,P〉0．05;与淋巴结转移密切相关,P〈0．05。结论：分析血清DNA的RASSF1A基因异常甲基化有可能成为辅助卵巢癌诊断的有效方法之一。     

甲基化结合蛋白与抑癌基因失活

通常认为肿瘤的发生与体细胞基因突变有关,但近年的研究发现它与基因表观遗传学改变也密切相关.DNA甲基化是基因表观遗传学改变最常见的类型.甲基化的DNA通过与多种甲基化结合蛋白结合使基因转录失活,这在许多肿瘤抑癌基因失活中起重要作用.     

RASSF1A基因在肿瘤发生发展中的作用

肿瘤的发生发展与癌基因的激活和抑癌基因的失活密切相关。大量研究发现,抑癌基因的失活与其启动子高甲基化有密切关联。Ras相关区域家族1A（Ras association domain family 1A,RASSF1A）是2000年发现的新型候选肿瘤抑制基因（tumor suppressor gene,TSG）。Ras基因是人类肿瘤研究中1种重要的癌基因,目前已成为研究得最为深入的癌基因之一。研究发现,Ras基因具有促进细胞生长、增殖的作用,而RASSF1A基因可能是Ras激活信号传导通路中1个负向调节基因,对肿瘤的发生、发展、预后等方面具有重要意义。近年来,国内外学者对其在多种肿瘤中的表达情况、抑癌机制、失活原因及临床应用前景等方面进行了广泛研究,现综述如下。     

食管癌组织与外周血RASSF 1A甲基化的检测及其临床意义

目的:通过对食管癌组织及同一患者对应的术前外周血中RASSF1A基因甲基化的检测,加深食管癌变分子机制的了解并为食管癌早期诊断和高危人群预警提供候选指标.方法:采用甲基化特异性PCR方法,分别检测来自食管癌高发区的30例食管癌患者血浆、肿瘤组织及癌旁正常组织中RASSF1A基因启动子甲基化状况.结果:食管癌组织RASSF1A甲基化阳性率为40%(12/30),而这12例癌组织甲基化阳性的患者其外周血甲基化阳性共7例,癌组织和外周血RASSF1A甲基化阳性一致率为58%(7/12),18例癌组织甲基化阴性的患者其外周血也均为阴性,阴性一致率为100%(18/18).癌旁正常食管组织甲基化率为13%(4/30),明显低于癌组织(40%,12/30),P<0.05.7例外周血甲基化阳性的患者中,淋巴结转移阳性5例(55%,5/9),阴性2例(10%,2/21),两者差异有统计学意义,P<0.05.低分化鳞癌的RASSF1A甲基化阳性率(83%,5/6)明显高于中分化鳞癌(24%,5/21),P<0.05.结论:外周血RASSF1A甲基化可以反映同一个体食管鳞癌组织中RASSF1A基因甲基化的状态,可能是高危人群筛查重要候选分子标志之一.     

胃癌组织ING1抑癌基因表达及其生物学意义探讨

目的:探讨生长抑制因子1(ING1)基因表达及其与胃癌临床病理特征的关系。方法:荧光定量PCR技术和免疫印迹技术检测70例胃腺癌组织及癌旁对照胃黏膜组织中ING1基因的表达水平,并分析其与胃癌患者临床特征的关系。结果:70例癌组织中有57例(81.43%)ING1基因mRNA表达明显下调,其中4例组织为ING1表达缺失,与癌旁正常胃黏膜比较差异有统计学意义,P<0.01。ING1基因表达与胃癌患者的性别无明显相关性,与胃癌的分化程度、肿瘤累及深度以及淋巴结转移有关。结论:ING1在人胃癌细胞中表达下调,其表达水平与分化程度、肿瘤累及深度以及淋巴结转移有关。     

Epigenetic inactivation of RASSF1A candidate tumor suppressor gene at 3p21.3 in brain tumors

The human Ras association domain family 1A (RASSF1A) gene, recently isolated from the lung and breast tumor suppressor locus 3p21.3, is highly methylated in primary lung, breast, nasopharyngeal and other tumors, and re-expression of RASSF1A suppresses the growth of several types of cancer cells. Epigenetic inactivation of RASSF1A by promoter hypermethylation is also important in the development of several human cancers. The methylation status of the promoter region of RASSF1A was analysed in primary brain tumors and glioma cell lines by methylation-specific polymerase chain reaction. In primary brain tumors, 25 of 46 (54.3%) gliomas and five of five (100%) medulloblastomas showed RASSF1A methylation. In benign tumors, only one of 10 (10%) schwannomas and two of 12 (16.7%) meningiomas showed RASSF1A methylation. The RASSF1A promoter region was methylated in all four glioma cell lines. RASSF1A was re-expressed in all methylated cell lines after treatment with the demethylating agent 5-aza-2'-deoxycytidine. Methylation of the promoter CpG islands of the RASSF1A may play an important role in the pathogenesis of glioma and medulloblastoma.     

Epigenetic inactivation of the RASSF1A 3p21.3 tumor suppressor gene in both clear cell and papillary renal cell carcinoma

Renal cell carcinoma (RCC), the most common adult kidney neoplasm, is histopathologically heterogeneous, with most sporadic RCCs ( approximately 80%) classified as clear cell (CC) tumors. Chromosome 3p allele loss is the most frequent genetic alteration in RCC but is associated specifically with sporadic and hereditary forms of clear cell RCC (CC-RCC) and is not a feature of non-CC-RCC, such as papillary (chromophilic) RCC. The VHL tumor suppressor gene (TSG) maps to chromosome 3p25, and somatic inactivation of the VHL gene occurs in up to 70% of CC-RCC tumors and cell lines. However, VHL inactivation is not sufficient for CC-RCC tumorigenesis, and inactivation of 3p12-p21 TSG(s) appears to be necessary in CC-RCC irrespective of VHL gene inactivation status. Recently, we demonstrated that the candidate 3p21 TSG, RASSF1A, is hypermethylated in most small cell lung cancers. We have now investigated the role of RASSF1A inactivation in primary RCC tumors. RASSF1A promoter methylation was detected in 23% (32 of 138) of primary CC-RCC tumors. In CC-RCC cell lines, RASSF1A methylation was associated with silencing of RASSF1A expression and restoration of expression after treatment with 5'-azacytidine. The frequency of RASSF1A methylation was similar in CC-RCC with and without VHL gene inactivation (24% versus 21%), and there was no association between epigenetic silencing of the RASSF1A and VHL TSGs, because 0 of 6 tumors with VHL hypermethylation had RASSF1A methylation, and VHL was not methylated in 26 CC-RCCs with RASSF1A methylation. Although 3p allele loss has been reported rarely in papillary RCC, we identified RASSF1A methylation in 44% (12 of 27) of papillary RCCs analyzed. Thus: (a) inactivation of RASSF1A is a frequent event in both CC-RCC and papillary RCC tumors; (b) there is no relationship between epigenetic silencing of RASSF1A and VHL inactivation status in CC-RCC. Fifty-four CC-RCCs analyzed for RASSF1A methylation were informative for 3p21 allele loss, and 20% (7 of 35) with 3p21 allele loss demonstrated RASSF1A methylation. All informative CC-RCCs with 3p21 allele loss and no RASSF1A methylation also demonstrated allele losses at other regions of 3p so that tumorigenesis in these cases may result from: (a) haploinsufficiency of RASSF1A; (b) inactivation of other 3p21 TSGs; or (c) inactivation of 3p TSGs from outside of 3p21. RASSF1A is the first TSG to be inactivated frequently in both papillary and CC-RCCs. The finding of frequent epigenetic inactivation of RASSF1A in papillary RCCs despite previous studies reporting infrequent 3p21 allele loss in this tumor type illustrates how the systematic identification of all major human cancer genes will require detailed analysis of the cancer genome and epigenome.     

Epigenetic inactivation of TSLC1 gene in nasopharyngeal carcinoma

Deletion of 11q23 is a common genetic aberration in nasopharyngeal carcinoma (NPC). Multiple candidate tumor suppressor genes (TSG) were mapped to this region but few of them were investigated in NPC. TSLC1 (tumor suppressor in lung cancer) is recently reported to be a putative TSG on 11q23. This gene was found to be inactivated by promoter hypermethylation in non-small cell lung carcinoma (NSCLC), liver cancer, and breast cancer. To study the role of TSLC1 gene in NPC tumorigenesis, we screened for mutations and aberrant methylation of TSLC1 gene in 5 NPC cell lines, 3 NPC xenografts, and 38 primary NPC cases. No somatic mutations of TSLC1 were detected in the NPC samples, but a 9-bp (CCACCACCA) deletion in exon 8 was found in a primary NPC and its corresponding blood sample. Bisulfite sequencing revealed aberrant methylation of TSLC1 promoter in four NPC cell lines. Loss of TSLC1 gene expression was found in two cell lines (HK-1 and CNE-2) with dense methylation. Expression of this gene was restored in these cell lines after treatment with demethylating agent 5-aza-2'-deoxycytidine. Our results showed that silencing of TSLC1 gene expression in NPC was associated with promoter hypermethylation. Promoter hypermethylation of TSLC1 gene was further illustrated in 34.2% (13/38) of primary NPCs. No aberrant promoter methylation was found in any of the four investigated normal nasopharyngeal epithelia. Frequent epigenetic inactivation of TSLC1 gene in NPC suggested that this gene is one of the target tumor suppressor genes of this endemic cancer.     

Epigenetic inactivation of RASSF2 in oral squamous cell carcinoma

Genetic and epigenetic alterations in tumor-suppressor genes play important roles in human neoplasia. Ras signaling is often activated in oral squamous cell carcinoma (OSCC), although Ras mutations are rarely detected in Japanese OSCC patients, and the mechanisms underlying the gene's activation remain unclear. Here, we examined the expression of Ras association family (RASSF) genes in a panel of OSCC cell lines and found that RASSF2 is often downregulated by DNA methylation in OSCC cells. In addition, aberrant methylation of RASSF2 was detected in 12 of 46 (26%) primary OSCC, and 18 (39%) of those OSCC showed methylation of at least one RASSF gene. Ectopic expression of RASSF2 in OSCC cells suppressed cell growth and induced apoptosis. A RASSF2 deletion mutant lacking the Ras-association domain, which was therefore unable to interact with Ras, exhibited less pro-apoptotic activity than the full-length protein, indicating that the pro-apoptotic activity of RASSF2 is related to its association with Ras. Genomic screening of genes regulated by RASSF2 showed that genes involved in immune responses, angiogenesis, and metastasis are suppressed by RASSF2. Our results suggest that epigenetic inactivation of RASSF2 plays an important role in OSCC tumorigenesis, and that RASSF2 may be a useful molecular target for the diagnosis and treatment of OSCC. ( Cancer Sci 2008; 99: 958–966)     

食管鳞状细胞癌组织PTEN基因表达及临床意义的探讨

目的:研究抑癌基因PTEN在原发性食管鳞状细胞癌(ESCC)组织中的表达及临床意义.方法:应用免疫组化SP法检测68例ESCC标本及相应癌旁组织中PTEN蛋白的表达情况,并分析与各临床病理因素和患者生存率的关系.结果:PTEN蛋白在ESCC组织中的阳性表达率为58.8%,显著低于癌旁组织95.0%;PTEN在组织学分级为Ⅱ/Ⅲ级的ESCC组织中表达率(51.0%)显著低于Ⅰ级(78.9%);在临床TNM分期为Ⅱ/Ⅲ期病例中的表达率(28.6%)显著低于Ⅰ期患者(80.0%);有淋巴结转移组的表达率(33.3%)显著低于无淋巴结转移组(75.6%);3年随访生存组患者的PTEN表达率(82.1%)显著高于死亡组患者(42.5%),各组差异均有统计学意义,P＜0.05.结论:抑癌基因PTEN在ESCC的发生发展过程中表达下调,可做为评价ESCC患者预后的有用参考指标.     

抑癌基因FASSF1在胃癌组织中表达及其临床意义的研究

目的:探讨Ras相关区域家族1基因(RASSF1)两种不同转录本RASSF1A和RASSF1B在胃癌组织中的表达情况及与临床病理特征的关系。方法:采用RT-PCR方法,检测32例胃癌组织及相应的32例远隔病灶部位胃组织和51例胃良性病变中RASSF1A和RASSF1B mRNA的表达情况,并探讨RASSF1与临床病理因素之间的关系。结果:RASSF1A和RASSF1B在癌旁组织中表达缺失率均为6.25%(2/32),在胃癌组织中的表达缺失率分别为59.3%(19/32)和28.1%(9/32),两者表达RASSF1A的缺失率比较差异有统计学意义,P=0.008;RASSF1B的差异无统计学意义,P=0.078。RASSF1A和RASSF1B在浅表性胃炎组织中表达缺失率分别是10.0%(3/30)和6.7%(2/30);在萎缩性胃炎组织中分别为28.6%(6/21)和14.3%(3/21),两组之间比较差异无统计学意义,P=0.060。RASSF1A和RASSF1B表达与胃癌高、中、低分化程度及肿瘤大小等均无相关性,P均>0.05。结论:RASSF1A在胃癌组织中的表达缺失更明显。RASSF1A在癌旁正常组织到胃良性病变到胃癌中表达缺失率逐渐增加,表明RASSF1A是一种抑癌基因。检测RASSF1A在胃癌组织中的缺失率对临床判断肿瘤发生发展有指导意义。