Merhavi Efrat, Cohen Yoram, Avraham Bat Chen R, Frenkel Shahar, Chowers Itay, Pe'er Jacob, Goldenberg-Cohen Nitza
The Krieger Eye Research Laboratory, Felsenstein Medical Research Center, Tel Aviv University, Petach Tikva, Israel.
Invest Ophthalmol Vis Sci. 2007 Oct;48(10):4403-6. doi: 10.1167/iovs.07-0272.
Aberrant promoter hypermethylation of CpG islands is thought to play an important role in the inactivation of tumor-suppressor genes (TSGs) in cancer. Studies of cutaneous melanoma have reported a high methylation rate for MGMT, DAPK, RAR-b2, and RASSF1A. In colon cancer, SOCS-1, IGF-2, RUNX3, NEUROG1, and CACNA1G are commonly inactivated. The concomitant methylation of at least three of these genes may represent a distinct trait, the CpG island methylator phenotype (CIMP). The purpose of the present study was to investigate the role of epigenetic inactivation of multiple genes in uveal melanoma.
Twenty samples of uveal melanoma were analyzed for the methylation status of nine candidate cancer-related genes: MGMT, DAPK, RAR-b2, RASSF1A, SOCS-1, IGF-2, RUNX3, NEUROG1, and CACNA1G, using real-time quantitative methylation-specific polymerase chain reaction after sodium bisulfite modification.
Methylation rates of the genes commonly inactivated in cutaneous melanoma were 70% for RASSFIA, 5% for MGMT and DAPK, and 0 for RAR-b2. The rates for the CIMP-related genes were 25% for RUNX3, 5% for NEUROG1 and CACNA1G, and 0 for SOCS-1 and IGF-2. None of the samples was CIMP-positive.
In this study uveal melanoma was negative for CIMP, with hypermethylation of RASSF1A. The negative CIMP phenotype and frequent RASSF1A methylation in uveal melanoma is in accord with its known lack of BRAF mutations. Given that mutations in genes of the RAS pathway are rarely observed in uveal melanoma, epigenetic inactivation of RASSF1A may be an alternative mechanism of tumorigenesis. The low frequency of promoter methylation of TSGs commonly inactivated in cutaneous melanoma further stratifies the different tumorigenesis pathway in cutaneous and uveal melanoma.
CpG岛异常的启动子高甲基化被认为在癌症中肿瘤抑制基因（TSGs）的失活中起重要作用。皮肤黑色素瘤的研究报告了MGMT、DAPK、RAR-b2和RASSF1A的高甲基化率。在结肠癌中，SOCS-1、IGF-2、RUNX3、NEUROG1和CACNA1G通常失活。这些基因中至少三个基因的同时甲基化可能代表一种独特的特征，即CpG岛甲基化表型（CIMP）。本研究的目的是探讨多个基因的表观遗传失活在葡萄膜黑色素瘤中的作用。
使用亚硫酸氢钠修饰后的实时定量甲基化特异性聚合酶链反应，分析20例葡萄膜黑色素瘤样本中9个候选癌症相关基因（MGMT、DAPK、RAR-b2、RASSF1A、SOCS-1、IGF-2、RUNX3、NEUROG1和CACNA1G）的甲基化状态。
皮肤黑色素瘤中通常失活的基因的甲基化率为：RASSFIA为70%，MGMT和DAPK为5%，RAR-b2为0。与CIMP相关的基因的甲基化率为：RUNX3为25%，NEUROG1和CACNA1G为5%，SOCS-1和IGF-为0。没有样本为CIMP阳性。
在本研究中，葡萄膜黑色素瘤CIMP为阴性，RASSF1A存在高甲基化。葡萄膜黑色素瘤中CIMP阴性表型和频繁的RASSF1A甲基化与其已知缺乏BRAF突变一致。鉴于在葡萄膜黑色素瘤中很少观察到RAS途径基因的突变，RASSF1A的表观遗传失活可能是肿瘤发生的另一种机制。皮肤黑色素瘤中通常失活的TSGs启动子甲基化频率较低，进一步区分了皮肤和葡萄膜黑色素瘤不同的肿瘤发生途径。
