Shim Yhong-Hee, Park Hye-Jung, Choi Mi Sun, Kim Jung Sun, Kim Hanseoung, Kim Jong Jae, Jang Ja-June, Yu Eunsil
Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Songpa-gu, Seoul, Korea.
Mod Pathol. 2003 May;16(5):430-6. doi: 10.1097/01.MP.0000066799.99032.A7.
Hepatoblastoma is the most frequent pediatric liver tumor that develops mostly in young children. Abnormal regulation of cell cycle regulatory genes including p16 has been described, displaying no p16 mRNA and p16 protein in hepatoblastomas. The inactivation of p16, leading to the disruption of cell cycle control is involved in many types of human malignancies. However, the mechanism of the p16 inactivation in hepatoblastomas has not yet been elucidated. In this present study, we examined the methylation status of the p16 gene promoter by using methylation-specific PCR in 24 cases of hepatoblastomas and in 20 cases of corresponding non-neoplastic liver tissue. Aberrant methylation of 5' CpG islands of p16 was present in 12 of 24 (50.0%) cases of hepatoblastoma. Clinicopathologic parameters were not associated with the methylation status of p16. To correlate the methylation status of p16 with the expression of p16, immunohistochemical staining was done in tumors and non-neoplastic liver tissue. All non-neoplastic liver tissues displayed moderate, but heterogeneous immunoreactivity for p16. Eight of 12 (66.6%) methylation-positive hepatoblastomas showed a complete lack of immunoreactivity for p16. The other 4 methylation-positive hepatoblastomas had heterogeneous immunoreactivity. Nine of 12 (75.0%) unmethylated cases of hepatoblastoma displayed diffuse immunoreactivity, whereas 3 cases of unmethylated hepatoblastoma were not immunostained for p16. Our data indicate that the hypermethylation of p16 is a major mechanism of the transcriptional repression of p16 in hepatoblastomas, and we suggest that the inactivation of p16, leading to the lack of p16, may play an important role in the tumorigenesis of hepatoblastomas.
肝母细胞瘤是最常见的儿童肝脏肿瘤，主要发生于幼儿。已有研究描述了包括p16在内的细胞周期调节基因的异常调控，肝母细胞瘤中未显示p16 mRNA和p16蛋白。p16的失活导致细胞周期控制的破坏，与多种人类恶性肿瘤有关。然而，肝母细胞瘤中p16失活的机制尚未阐明。在本研究中，我们使用甲基化特异性PCR检测了24例肝母细胞瘤及20例相应的非肿瘤性肝组织中p16基因启动子的甲基化状态。24例肝母细胞瘤中有12例（50.0%）存在p16基因5' CpG岛的异常甲基化。临床病理参数与p16的甲基化状态无关。为了将p16的甲基化状态与p16的表达相关联，我们对肿瘤和非肿瘤性肝组织进行了免疫组织化学染色。所有非肿瘤性肝组织对p16均显示中等强度但不均匀的免疫反应性。12例甲基化阳性的肝母细胞瘤中有8例（66.6%）对p16完全缺乏免疫反应性。另外4例甲基化阳性的肝母细胞瘤具有不均匀的免疫反应性。12例未甲基化的肝母细胞瘤中有9例（75.）显示弥漫性免疫反应性，而3例未甲基化的肝母细胞瘤未对p16进行免疫染色。我们的数据表明，p16基因的高甲基化是肝母细胞瘤中p16转录抑制的主要机制，并且我们认为p16的失活导致p16缺失，可能在肝母细胞瘤的肿瘤发生中起重要作用。
