Kang Sokbom, Lee Jae Myun, Jeon Eun-Sook, Lee Sun, Kim Hogeun, Kim Hy-Sook, Seo Sang-Soo, Park Sang-Yoon, Sidransky David, Dong Seung Myung
Research Institute and Hospital, National Cancer Center, Goyang, Gyeonggi, Korea.
Int J Cancer. 2006 Sep 15;119(6):1316-21. doi: 10.1002/ijc.21991.
Both hypermethylation of the tumor suppressor gene RASSF1A and activating mutations of the KRAS and/or BRAF gene have been reported in a variety of human cancers. To investigate these epigenetic and genetic alterations in endometrial carcinoma (EC), we examined their frequency in 4 uterine EC cell lines and in 75 sporadic primary ECs. Using methylation specific PCR, we found RASSF1A methylation in 25 of 75 (33.3%) ECs. RASSF1A methylation was significantly associated with microsatellite instability (MSI, p < 0.001) and also with hMLH1 methylation (p < 0.001). KRAS mutations were detected in 14 of 75 (18.7%) ECs. BRAF mutations were identified in only 3 of 75 (4.0%) ECs and were not found in ECs with KRAS mutations or RASSF1A methylation. RASSF1A methylation was more frequent in KRAS mutation-negative ECs than in KRAS mutation-positive ECs (37.7% vs 14.3%), but this inverse correlation is not statistically significant (p = 0.122). However, we observed that RASSF1A methylation was inversely correlated with KRAS and/or BRAF mutations (p = 0.028) in MSI-negative ECs, while this inverse correlation disappeared in MSI-positive ECs. Furthermore, in MSI-positive ECs, 2 cases of concomitant RASSF1A methylation and KRAS mutation were found. Taken together, these results provide strong evidence that, in EC tumorigenesis, RASSF1A promoter hypermethylation is as important as KRAS mutations in activating the RAS pathway.
肿瘤抑制基因RASSF1A的高甲基化以及KRAS和/或BRAF基因的激活突变在多种人类癌症中均有报道。为了研究子宫内膜癌（EC）中的这些表观遗传和基因改变，我们检测了4种子宫EC细胞系和75例散发性原发性EC中它们的发生频率。使用甲基化特异性PCR，我们在75例EC中的25例（33.3%）中发现了RASSF1A甲基化。RASSF1A甲基化与微卫星不稳定性（MSI，p < 0.001）以及hMLH1甲基化均显著相关（p < 0.001）。在75例EC中的14例（18.7%）中检测到KRAS突变。仅在75例EC中的3例（4.0%）中鉴定出BRAF突变，且在具有KRAS突变或RASSF1A甲基化的EC中未发现BRAF突变。RASSF1A甲基化在KRAS突变阴性的EC中比在KRAS突变阳性的EC中更常见（37.7%对14.3%），但这种负相关无统计学意义（p = 0.122）。然而，我们观察到在MSI阴性的EC中，RASSF1A甲基化与KRAS和/或BRAF突变呈负相关（p = 0.028），而在MSI阳性的EC中这种负相关消失。此外，在MSI阳性的EC中，发现了2例同时存在RASSF1A甲基化和KRAS突变的病例。综上所述，这些结果提供了有力证据，即在EC肿瘤发生过程中，RASSF1A启动子高甲基化在激活RAS途径方面与KRAS突变同样重要。
