DNA hypermethylation is a mechanism for loss of expression of the HLA class I genes in human esophageal squamous cell carcinomas
DNA hypermethylation is a mechanism for loss of expression of the HLA class I genes in human esophageal squamous cell carcinomas
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DOI：
10.1093/carcin/22.10.1615
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发表时间：
2001-10-01
期刊：
影响因子：
4.7
通讯作者：
Yang, CS
中科院分区：
文献类型：
--
作者：
Nie, Y;Yang, GY;Yang, CS
三种人类白细胞抗原（HLA） I类抗原，HLA- a， HLA- b和HLA- c，在细胞毒性T细胞消除转化细胞中起重要作用。这些抗原在细胞表面的频繁表达缺失已经在许多人类癌症中被观察到。各种转录后调控机制已被提出和测试，但转录调控的分子机制尚不清楚。我们通过免疫组化发现，29例人食管鳞状细胞癌（ESCC）样本中有26例（89%）缺乏HLA I类抗原。RT-PCR显示，26例ESCC样本中有11例至少丢失了一种HLA基因的mRNA表达。检测29对ESCC和邻近正常上皮细胞DNA的CpG岛高甲基化、纯合缺失、微卫星不稳定性（MSI）和杂合性缺失（LOH）。来自正常上皮组织的DNA没有检测到这些基因位点的CpG岛的甲基化。29份ESCC样本中有13份（45%）表现出3个HLA位点中的一个或多个甲基化，6份（21%）表现出所有3个位点的甲基化。HLA-B基因位点最常发生甲基化（38%）。在ESCC细胞系中，HLA-B高甲基化且不表达mRNA，经5-aza-2 ' -脱氧胞苷处理后，HLA-B mRNA表达被激活。未观察到这三个基因位点的纯合缺失。在靠近HLA-A、-B和-C位点的微卫星标记D6S306、D6S258、D6S273和D6S1666中，LOH和MSI的发生率相对较低，而在肿瘤抑制基因p21（Waf1）所在的附近位点（以标记D6S1051和D6S1560为代表）中LOH的发生率较高。在ESCC样本中观察到遗传改变与mRNA失活之间存在很强的相关性。我们的研究结果表明，在ESCC中，HLA- I类基因在蛋白和mRNA水平上的表达经常下调，HLA- a、-B和-C基因启动子区域的高甲基化是转录失活的主要机制。
The three human leukocyte antigen (HLA) class I antigens, HLA-A, HLA-B and HLA-C, play important roles in the elimination of transformed cells by cytotoxic T cells. Frequent loss of expression of these antigens at the cell surface has been observed in many human cancers. Various mechanisms for post-transcriptional regulation have been proposed and tested but the molecular mechanisms for transcriptional regulation are not clear. We show by immunohistochemistry that the HLA class I antigens are absent in 26 of 29 (89%) samples of human esophageal squamous cell carcinomas (ESCC). Eleven of the 26 ESCC samples lost mRNA expression for at least one of the HLA genes, as shown by RT-PCR. DNA from the 29 pairs of ESCC and neighboring normal epithelium were examined for CpG island hypermethylation, homozygous deletion, microsatellite instability (MSI) and loss of heterozygosity (LOH). DNA from normal epithelial tissues had no detectable methylation of the CpG islands of any of these gene loci. Thirteen of 29 ESCC samples (45%) exhibited methylation of one or more of the three HLA loci and six samples (21%) exhibited methylation of all three loci. The HLA-B gene locus was most frequently methylated (38%). HLA-B mRNA expression in an ESCC cell line, where HLA-B was hypermethylated and did not express mRNA, was activated after treatment with 5-aza-2 ' -deoxycytidine. Homozygous deletion of these three gene loci was not observed. Relatively low rates of LOH and MSI were observed for the microsatellite markers D6S306, D6S258, D6S273 and D6S1666, close to the HLA-A, -B and -C loci, although a high ratio of LOH was observed at a nearby locus (represented by the markers D6S1051 and D6S1560), where the tumor suppressor gene p21(Waf1) resides. A strong correlation between genetic alterations and mRNA inactivation was observed in the ESCC samples. Our results indicate that HLA class I gene expression was frequently down-regulated in ESCC at both the protein and mRNA levels and that hypermethylation of the promoter regions of the HLA-A, -B and -C genes is a major mechanism of transcriptional inactivation.