Derks Sarah, Postma Cindy, Moerkerk Peter T M, van den Bosch Sandra M, Carvalho Beatriz, Hermsen Mario A J A, Giaretti Walter, Herman James G, Weijenberg Matty P, de Bruïne Adriaan P, Meijer Gerrit A, van Engeland Manon
Department of Pathology, Research Institute GROW, University Maastricht, The Netherlands.
Cell Oncol. 2006;28(5-6):247-57. doi: 10.1155/2006/846251.
Colorectal cancers are characterized by genetic and epigenetic alterations. This study aimed to explore the timing of promoter methylation and relationship with mutations and chromosomal alterations in colorectal carcinogenesis.
In a series of 47 nonprogressed adenomas, 41 progressed adenomas (malignant polyps), 38 colorectal carcinomas and 18 paired normal tissues, we evaluated promoter methylation status of hMLH1, O6MGMT, APC, p14ARF, p16INK4A, RASSF1A, GATA-4, GATA-5, and CHFR using methylation-specific PCR. Mutation status of TP53, APC and KRAS were studied by p53 immunohistochemistry and sequencing of the APC and KRAS mutation cluster regions. Chromosomal alterations were evaluated by comparative genomic hybridization.
Our data demonstrate that nonprogressed adenomas, progressed adenomas and carcinomas show similar frequencies of promoter methylation for the majority of the genes. Normal tissues showed significantly lower frequencies of promoter methylation of APC, p16INK4A, GATA-4, and GATA-5 (P-values: 0.02, 0.02, 1.1x10(-5) and 0.008 respectively). P53 immunopositivity and chromosomal abnormalities occur predominantly in carcinomas (P values: 1.1x10(-5) and 4.1x10(-10)).
Since promoter methylation was already present in nonprogressed adenomas without chromosomal alterations, we conclude that promoter methylation can be regarded as an early event preceding TP53 mutation and chromosomal abnormalities in colorectal cancer development.
结直肠癌具有基因和表观遗传学改变的特征。本研究旨在探讨启动子甲基化的时间及其与结直肠癌发生过程中突变和染色体改变的关系。
在47个未进展的腺瘤、41个进展期腺瘤（恶性息肉）、38例结直肠癌和18对配对的正常组织中，我们使用甲基化特异性PCR评估hMLH1、O6MGMT、APC、p14ARF、p16INK4A、RASSF1A、GATA-4、GATA-5和CHFR的启动子甲基化状态。通过p53免疫组织化学以及APC和KRAS突变簇区域的测序研究TP53、APC和KRAS的突变状态。通过比较基因组杂交评估染色体改变。
我们的数据表明，对于大多数基因，未进展的腺瘤、进展期腺瘤和癌显示出相似的启动子甲基化频率。正常组织中APC、p16INK4A、GATA-4和GATA-5的启动子甲基化频率显著较低（P值分别为：0.02、0.02、1.1×10⁻⁵和0.008）。p53免疫阳性和染色体异常主要发生在癌中（P值分别为：1.1×10⁻⁵和4.1×10⁻¹⁰）。
由于在没有染色体改变的未进展腺瘤中已经存在启动子甲基化，我们得出结论，在结直肠癌发展过程中，启动子甲基化可被视为先于TP53突变和染色体异常的早期事件。
