Frequent silencing of the candidate tumor suppressor PCDH20 by epigenetic mechanism in non-small-cell lung cancers
Frequent silencing of the candidate tumor suppressor PCDH20 by epigenetic mechanism in non-small-cell lung cancers
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DOI：
10.1158/0008-5472.can-05-4437
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发表时间：
2006-05-01
期刊：
影响因子：
11.2
通讯作者：
Inazawa, Johji
中科院分区：
文献类型：
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作者：
Imoto, Issei;Izumi, Hiroyuki;Inazawa, Johji
原钙粘附素是钙粘附素超家族的一个主要亚家族，但对其功能和细胞内信号转导知之甚少。在使用基于内部阵列的比较基因组杂交筛查一组非小细胞肺癌(NSCLC)细胞系(共20株)的基因组拷贝数异常的过程中，我们发现了Protocadherin 20(PCDH20，.13q21.2)的纯合缺失。PCDH20mRNA在正常肺组织中有表达，但在大多数非小细胞肺癌细胞系中不表达(10/19，52.6%)。基因沉默的NSCLC细胞经5-氮-2‘-脱氧胞苷处理后，PCDH20基因表达恢复。PCDH20 CpG富集区的DNA甲基化状态与基因的表达呈负相关，体外甲基化靶区显示出明显的启动子活性。PCDH20启动子甲基化在NSCLC组织中常见(59例肿瘤中32例，54.2%)。在我们的原发非小细胞肺癌病例中，PCDH20甲基化似乎与较短的总生存期有关(在ALL和I期肿瘤中，P分别为0.0140和0.0211；对数等级检验)，多因素分析显示PCDH20甲基化状态是一个独立的预后因素。此外，恢复PCDH20在NSCLC细胞中的表达减少了克隆形成和锚定非依赖性分析中的细胞数量。这些结果表明，PCDH20富含CpG启动子区域的表观遗传沉默导致PCDH20功能丧失，这可能是NSCLC发生的一个因素。
Protocadherins are a major subfamily of the cadherin superfamily, but little is known about their functions and intracellular signal transduction. We identified a homozygous loss of protocadherin 20 (PCDH20,.13q21.2) in the course of a program to screen a panel of non-small-cell lung cancer (NSCLC) cell lines (I of 20 lines) for genomic copy number aberrations using an in-house array-based comparative genomic hybridization. PCDH20 mRNA was expressed in normal lung tissue but was not expressed in the majority of NSCLC cell lines without a homozygous deletion of this gene (10 of 19 lines, 52.6%). Expression of PCDH20 mRNA was restored in gene-silenced NSCLC cells after treatment with 5-aza 2'-deoxycytidine. The DNA methylation status of the PCDH20 CpG-rich region correlated inversely with the expression of the gene and a putative target region for methylation showed clear promoter activity in vitro. Methylation of this PCDH20 promoter was frequently observed in primary NSCLC tissues (32 of 59 tumors, 54.2%). Among our primary NSCLC cases, the methylated PCDH20 seemed to be associated with a shorter overall survival (P = 0.0140 and 0.0211 in all and stage I tumors, respectively; log-rank test), and a multivariate analysis showed that the PCDH20 methylation status was an independent prognosticator. Moreover, restoration of PCDH20 expression in NSCLC cells reduced cell numbers in colony formation and anchorage-independent assays. These results suggest that epigenetic silencing by hypermethylation of the CpG-rich promoter region of PCDH20 leads to loss of PCDH20 function, which may be a factor in the carcinogenesis of NSCLC.