Susceptibility of nonpromoter CpG islands to de novo methylation in normal and neoplastic cells
Susceptibility of nonpromoter CpG islands to de novo methylation in normal and neoplastic cells
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DOI：
10.1093/jnci/93.19.1465
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发表时间：
2001-10-03
期刊：
影响因子：
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通讯作者：
Jones, PA
中科院分区：
文献类型：
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作者：
Nguyen, C;Liang, GM;Jones, PA
背景：许多癌症显示CpG岛甲基化模式的改变，CpG岛是富含CpG二核苷酸的DNA片段，通常与基因启动子相关，参与基因转录的起始。这种甲基化可能会干扰对细胞增殖调控至关重要的基因的表达。异常甲基化并不局限于少数基因或启动子区域，而是在全基因组范围内发现的各种肿瘤，包括结直肠癌和急性髓性白血病。我们的目标是以定量的方式来描述可能针对不同癌症的异常甲基化基因的特征。方法:利用甲基化敏感单核苷酸引物延伸（MS-SNuPE）的定量分析，我们分析了两种周期蛋白依赖性激酶抑制剂[p15（INK4B）和p16(INK4A)]和PAX6基因的启动子和外显子（编码区）CpG岛的甲基化水平，PAX6基因编码一种参与神经元增殖的转录因子，这些DNA样本来自慢性髓性白血病、急性髓性白血病、骨髓增生异常综合征和结直肠癌患者。结果：肿瘤中所有三个外显子位点的从头甲基化-相对于在非肿瘤组织或血液中发现的基线水平-在血液学肿瘤、实体肿瘤以及正常结肠组织中观察到。然而，启动子区域的甲基化更为有限。此外，两种不同的启动子甲基化模式将白血病与结直肠癌区分开来：仅在白血病中发现了ply启动子超甲基化，而p16启动子超甲基化仅发生在结肠肿瘤中。然而，我们没有前瞻性地解决这个问题；因此，这样的观察只是假设生成。结论：我们观察到的甲基化模式表明，外显子CpG岛比启动子岛更容易发生从头甲基化，甲基化可能在外显子区域播种，并可从其传播到其他岛屿，包括启动子区域。随后选择具有生长优势的细胞，通过甲基化扩散到特定启动子并使其失活，可能导致特定类型癌症的发生。
Background: Many cancers display alterations in methylation patterns of CpG islands-stretches of DNA rich in CpG dinucleotides often associated with gene promoters that are involved in initiation of gene transcription. This methylation may perturb expression of genes critical to the regulation of cell proliferation. Aberrant methylation is not limited to a few genes or to promoter regions but has been found on a genome-wide scale in a variety of neoplasias, including colorectal cancer and acute myelogenous leukemia. Our goal was to characterize, in a quantitative manner, the profiles of abnormally methylated genes that may be specific for different cancers. Methods: Using a quantitative assay, methylation-sensitive single nucleotide primer extension (MS-SNuPE), we have analyzed the methylation levels of promoter and exonic (coding region) CpG islands of two cyclin-dependent kinase inhibitors [p15(INK4B) and p16(INK4A)] and the PAX6 gene, which encodes a transcriptional factor involved in neuronal proliferation, in DNA samples taken from patients with chronic myelogenous leukemia, acute myelogenous leukemia, myelodysplastic syndrome, and colorectal cancer. Results: De novo methylation of all three exonic loci in tumors-relative to baseline levels found in nontumor tissue or blood-was observed in hematologic neoplasias and in solid tumors as well as in normal colonic tissue. However, methylation of promoter regions was more limited. Moreover, two different patterns of promoter methylation distinguished the leukemias from colorectal cancer: ply promoter hypermethylation was found only in the leukemias, and p16 promoter hypermethylation occurred only in colon tumors. However, we did not address this issue prospectively; therefore, such an observation is only hypothesis generating. Conclusions: The methylation patterns that we observed suggest that exonic CpG islands are more susceptible to de novo methylation than promoter islands and that methylation may be seeded in exonic regions, from which it can spread to other islands, including promoter regions. Subsequent selection of cells with a growth advantage conferred by spread of methylation into and inactivation of a particular promoter might then contribute to the genesis of a specific type of cancer.