Tokinaga Kenji, Okuda Heiwa, Nomura Asuka, Ashida Shingo, Furihata Mutsuo, Shuin Taro
Department of Urology, Kochi Medical School, Kochi 783-8505, Japan.
Oncol Rep. 2004 Oct;12(4):805-10.
Hypermethylation associated inactivation of RASSF1A tumor suppressor gene at chromosome 3p21.3 has been observed in several human malignancies. Relatively high (91%) or low (23%) frequencies were reported in the methylation status of promoter region of the RASSF1A gene in clear cell renal carcinoma (RCC) depending on the country the report was from. To clarify exact contribution of the hypermethylation of RASSF1A gene in the development of RCC in Japan, we analyzed the methylation status of the RASSF1A promoter region in 50 Japanese clear cell RCC and RCC cell lines. Although relatively high frequency of hypermethylation in RASSF1A promoter (39 of 50 tumors, 78%) was observed, most of matched proximal normal tissue DNA also showed weak methylation. By comparison with methylation level of adapted normal kidney tissue DNA, tumor preferential hypermethylation in RASSF1A promoter was recognized as 40% (20/50 matched sets) of primary clear cell RCCs. Hypermethylation in RASSF1A promoter was observed in 36% (15/42) and 64% (5/8) of stage I-II or III-IV tumors, and also observed in 42% (11/26) and 38% (9/24) of our tumor samples with pathological grade I or II, respectively. In addition, 16 of 19 RCC cell lines (84%) showed complete or partial methylation of RASSF1A promoter region. There was no association between the frequency of RASSF1A methylation and inactivation of VHL tumor suppressor gene in either primary RCCs or RCC cell lines. Our results showed tumor specific RASSF1A promoter hypermethylation in up to 40% of low grade or low stage clear cell RCCs. It is essential to compare the methylation status of RASSF1A promoter in tumor with normal tissue to understand tumor specific hypermethylation. Since considerable cases of normal kidney are hypermethylated, contribution of the RASSF1A for the development and progression of kidney cancer may be more complex than expected.
在几种人类恶性肿瘤中均观察到3号染色体p21.3区域RASSF1A肿瘤抑制基因的高甲基化相关失活。根据报告来自的国家不同，透明细胞肾细胞癌（RCC）中RASSF1A基因启动子区域的甲基化状态报告的频率相对较高（91%）或较低（23%）。为了阐明RASSF1A基因高甲基化在日本RCC发生发展中的确切作用，我们分析了50例日本透明细胞RCC及RCC细胞系中RASSF1A启动子区域的甲基化状态。尽管观察到RASSF1A启动子中高甲基化频率相对较高（50个肿瘤中有39个，78%），但大多数匹配的近端正常组织DNA也显示出弱甲基化。与适配的正常肾组织DNA的甲基化水平相比，RASSF1A启动子中肿瘤优先高甲基化在原发性透明细胞RCC中占40%（20/50对匹配样本）。在I-II期或III-IV期肿瘤中，RASSF1A启动子的高甲基化分别在36%（15/42）和64%（5/8）中观察到，在我们病理分级为I级或II级的肿瘤样本中分别在42%（11/26）和38%（9/24）中观察到。此外，19个RCC细胞系中有16个（84%）显示RASSF1A启动子区域完全或部分甲基化。在原发性RCC或RCC细胞系中，RASSF1A甲基化频率与VHL肿瘤抑制基因失活之间均无关联。我们的结果显示，在高达40%的低级别或低分期透明细胞RCC中存在肿瘤特异性的RASSF1A启动子高甲基化。为了解肿瘤特异性高甲基化，将肿瘤中RASSF1A启动子的甲基化状态与正常组织进行比较至关重要。由于相当一部分正常肾组织存在高甲基化，RASSF1A在肾癌发生发展中的作用可能比预期更为复杂。
