McGivern A, Wynter C V A, Whitehall V L J, Kambara T, Spring K J, Walsh M D, Barker M A, Arnold S, Simms L A, Leggett B A, Young J, Jass J R
Conjoint Gastroenterology Laboratory, Bancroft Centre, Herston, Brisbane, Queensland, Australia.
Fam Cancer. 2004;3(2):101-7. doi: 10.1023/B:FAME.0000039861.30651.c8.
Colorectal cancers resulting from defective DNA mismatch repair can occur in both hereditary non-polyposis colon cancer (HNPCC) and in the sporadic setting. They are characterised by a high level of microsatellite instability (MSI-H) and superficially resemble each other in that they are frequently located in the proximal colon and share features such as circumscribed tumour margins and tumour-infiltrating lymphocytes. However, significant differences can be demonstrated at the molecular level including widespread promoter hypermethylation and BRAF -activating mutations which occur significantly less often in HNPCC.
In this study, we sought to determine whether the presence of widespread promoter hypermethylation and BRAF mutations would exclude HNPCC.
We investigated the methylation status of four methylated in tumour markers (MINTs 1,2,12 and 31), and the promoter regions of 5 genes hMLH1, HPP1, MGMT, p16INK4A and p14ARF, in 21 sporadic MSI-H colorectal cancers and compared these with 18 cancers from HNPCC patients. The methylation status of CpG islands were determined by either methylation specific PCR (MSP) or combined bisulfite restricton analysis (COBRA). In addition we considered the BRAF mutation status of 18 HNPCC tumours and 19 sporadic MSI-H cancers which had been previously determined by RFLP analysis and confirmatory sequencing.
Methylation of the promoter regions in target genes occurred less frequently within the HNPCC tumours (27% of analyses), compared with the sporadic MSI-H tumours (59% of analyses) (P < 0.001). Methylation of MINTs 1, 2, 12 and 31 occurred in 4% of analyses for HNPCC tumours contrasted with 73% for sporadic MSI-H tumours (P < 0.001). BRAF mutations were detected in 74% of sporadic tumours but none of the HNPCC cancers tested.
The total number of genes and MINTs methylated in HNPCC was lower than in MSI-H colorectal tumours. No HNPCC tumour showed evidence of widespread promoter hypermethylation or BRAF mutation suggesting this feature could be used as a discriminator between familial and sporadic cases.
由DNA错配修复缺陷导致的结直肠癌可发生于遗传性非息肉病性结直肠癌（HNPCC）及散发性病例中。它们的特征是微卫星高度不稳定（MSI-H），并且在表面上彼此相似，因为它们常位于近端结肠，且具有一些共同特征，如肿瘤边界清晰和肿瘤浸润淋巴细胞。然而，在分子水平上可发现显著差异，包括广泛的启动子高甲基化和BRAF激活突变，这些在HNPCC中发生的频率明显较低。
在本研究中，我们试图确定广泛的启动子高甲基化和BRAF突变的存在是否可排除HNPCC。
我们调查了21例散发性MSI-H结直肠癌中4种肿瘤标志物（MINTs 1、2、12和31）以及5个基因（hMLH1、HPP1、MGMT、p16INK4A和p14ARF）启动子区域的甲基化状态，并将其与18例HNPCC患者的癌症进行比较。通过甲基化特异性PCR（MSP）或联合亚硫酸氢盐限制性分析（COBRA）确定CpG岛的甲基化状态。此外，我们还考虑了18例HNPCC肿瘤和19例散发性MSI-H癌症的BRAF突变状态，这些状态先前已通过限制性片段长度多态性分析（RFLP）和验证性测序确定。
与散发性MSI-H肿瘤（59%的分析）相比，HNPCC肿瘤中靶基因启动子区域的甲基化发生频率较低（27%的分析）（P < 0.001）。HNPCC肿瘤中MINTs 1、2、12和31的甲基化在4%的分析中出现，而散发性MSI-H肿瘤中为73%（P < 0.001）。在74%的散发性肿瘤中检测到BRAF突变，但在检测的HNPCC癌症中均未发现。
HNPCC中甲基化的基因和MINTs总数低于MSI-H结直肠癌肿瘤。没有HNPCC肿瘤显示出广泛的启动子高甲基化或BRAF突变的证据，这表明该特征可用于区分家族性和散发性病例。
