Schagdarsurengin Undraga, Gimm Oliver, Hoang-Vu Cuong, Dralle Henning, Pfeifer Gerd P, Dammann Reinhard
AG Tumorgenetik der Medizinischen Fakultät, Martin-Luther-Universität Halle-Wittenberg, Halle/Saale, Germany.
Cancer Res. 2002 Jul 1;62(13):3698-701.
Loss of heterozygosity of chromosome 3p21 is one of the most frequent alterations in solid tumors, including thyroid carcinomas. Recently, we have characterized the novel tumor suppressor gene RASSF1 located in this locus. The RASSF1A isoform is epigenetically inactivated in a variety of human primary tumors. In this study, we investigated the expression and methylation status of the RASSF1 gene in thyroid carcinoma. In nine thyroid cancer cell lines, the RASSF1A promoter CpG island was methylated completely, and expression was absent. Treatment of these cell lines with the DNA methylation inhibitor 5-aza-2'-deoxycytidine reactivated the transcription of RASSF1A. The methylation status of the RASSF1A promoter was analyzed in 38 primary thyroid tumors, including 1 poorly differentiated thyroid carcinoma, 5 medullary thyroid carcinoma (MTC), 10 follicular thyroid carcinoma (FTC), 9 undifferentiated thyroid carcinoma (UTC), and 13 papillary thyroid carcinoma (PTC). In 71% of thyroid carcinomas, the RASSF1A CpG island was hypermethylated. Methylation frequency was higher in the aggressive forms of thyroid carcinoma and was found in 80% of MTC, in 78% of UTC, and in 70% of FTC, compared with 62% in the more benign PTC. RASSF1A inactivation was detected in all stages of thyroid carcinoma scored by Tumor-Node-Metastasis classification. Additionally, we analyzed the methylation frequency of the CpG island of cell cycle inhibitor p16(INK4a) in the same thyroid tumors. The p16 gene was inactivated in 56 and 25% of cell lines and primary tumors, respectively. p16 methylation was detected in 56% of UTC, 10% of FTC, and 25% of PTC but not in MTC. In UTC, which belongs to the most aggressive carcinomas in humans, the most common combined inactivation of RASSF1A and p16 was detected. In general, 90% of tumors with p16 inactivation were also silenced for RASSF1A expression. However, RASSF1A hypermethylation was detected three times more frequently in thyroid cancers. Thus, RASSF1A inactivation may play a crucial role in the malignancy of thyroid carcinoma.
3p21染色体杂合性缺失是实体瘤（包括甲状腺癌）中最常见的改变之一。最近，我们鉴定了位于该位点的新型肿瘤抑制基因RASSF1。RASSF1A亚型在多种人类原发性肿瘤中发生表观遗传失活。在本研究中，我们调查了RASSF1基因在甲状腺癌中的表达和甲基化状态。在9种甲状腺癌细胞系中，RASSF1A启动子CpG岛完全甲基化，且无表达。用DNA甲基化抑制剂5-氮杂-2'-脱氧胞苷处理这些细胞系可重新激活RASSF1A的转录。分析了38例原发性甲状腺肿瘤中RASSF1A启动子的甲基化状态，包括1例低分化甲状腺癌、5例髓样甲状腺癌（MTC）、10例滤泡状甲状腺癌（FTC）、9例未分化甲状腺癌（UTC）和13例乳头状甲状腺癌（PTC）。在71%的甲状腺癌中，RASSF1A CpG岛发生高甲基化。在侵袭性甲状腺癌中甲基化频率更高，在80%的MTC、78%的UTC和70%的FTC中发现甲基化，而在较良性的PTC中为62%。在根据肿瘤-淋巴结-转移分类评分的甲状腺癌各阶段均检测到RASSF1A失活。此外，我们分析了同一甲状腺肿瘤中细胞周期抑制剂p16（INK4a）的CpG岛甲基化频率。p16基因在56%的细胞系和25%的原发性肿瘤中失活。在56%的UTC、10%的FTC和25%的PTC中检测到p16甲基化，但在MTC中未检测到。在人类最具侵袭性的癌症UTC中，检测到RASSF1A和p16最常见的联合失活。一般来说，90%的p16失活肿瘤RASSF1A表达也沉默。然而，在甲状腺癌中检测到RASSF1A高甲基化的频率是其三倍。因此，RASSF1A失活可能在甲状腺癌的恶性发展中起关键作用。
