Institute of Pathology, University Hospital Jena, Ziegelmühlenweg 1, 07743 Jena, Germany.
Lung Cancer. 2011 Jul;73(1):38-44. doi: 10.1016/j.lungcan.2010.10.015. Epub 2010 Nov 20.
Insulin-like growth factor binding protein 7 (IGFBP7) was considered a tumor suppressor gene in lung cancer. However, the mechanism responsible for the downregulation of this gene has not yet been fully understood. In this study, we analyzed the epigenetic inactivation of IGFBP7 expression in human lung cancer. We found that 14 out of 16 lung cancer cell lines showed decreased expression of IGFBP7 compared to control cells by real-time RT-PCR, and 42 out of 90 patients (46.7%) with primary lung tumor exhibited negative staining of IGFBP7 by immunohistochemistry analysis. The IGFBP7 expression could be restored by demethylation agent 5-aza-2'-deoxycytidine (DAC) in 7 cancer cell lines. Methylation status of IGFBP7 was further evaluated by bisulfite sequencing (BS) and methylation-specific-PCR (MSP). It turned out that low expression of IGFBP7 was associated with DNA methylation in lung cancer cell lines and in primary lung tumors (P=0.019). To explore the regulatory role of p53 on IGFBP7, we transfected a wild type p53 expression vector into lung cancer cell lines H1299, H2228, and H82. Forced expression of p53 increased IGFBP7 expression only in H82 harboring no IGFBP7 methylation, while transfection in combination with DAC induced the expression of IGFBP7 in H1299 and H2228, in which IGFBP7 was methylated. Additionally, treatment with p53 inducer adriamycin (ADR) alone or in combination with DAC increased the expression of IGFBP7 in the 3 cell lines. Our data suggest that IGFBP7 is inactivated in lung cancer by DNA hypermethylation in both lung cancer cell lines and primary lung tumors, and IGFBP7 might be regulated by p53 in lung cancer cells.
胰岛素样生长因子结合蛋白 7（IGFBP7）在肺癌中被认为是一种肿瘤抑制基因。然而，导致该基因下调的机制尚未完全阐明。在本研究中，我们分析了人肺癌中 IGFBP7 表达的表观遗传失活。我们发现，16 个人肺癌细胞系中的 14 个通过实时 RT-PCR 显示 IGFBP7 的表达较对照细胞降低，90 例原发性肺癌患者中有 42 例（46.7%）通过免疫组织化学分析显示 IGFBP7 阴性染色。在 7 个癌细胞系中，去甲基化剂 5-氮杂-2'-脱氧胞苷（DAC）可以恢复 IGFBP7 的表达。通过亚硫酸氢盐测序（BS）和甲基化特异性-PCR（MSP）进一步评估 IGFBP7 的甲基化状态。结果表明，肺癌细胞系和原发性肺癌中 IGFBP7 的低表达与 DNA 甲基化有关（P=0.019）。为了探讨 p53 对 IGFBP7 的调节作用，我们将野生型 p53 表达载体转染到肺癌细胞系 H1299、H2228 和 H82 中。p53 的强制表达仅在 H82 中增加 IGFBP7 的表达，而在没有 IGFBP7 甲基化的 H82 中，转染与 DAC 联合诱导 H1299 和 H2228 中 IGFBP7 的表达。此外，单独或联合 DAC 用 p53 诱导剂阿霉素（ADR）处理这 3 个细胞系，均可增加 IGFBP7 的表达。我们的数据表明，IGFBP7 在肺癌细胞系和原发性肺癌中通过 DNA 超甲基化失活，并且 IGFBP7 可能在肺癌细胞中受 p53 调节。
