Ying J, Li H, Seng T J, Langford C, Srivastava G, Tsao S W, Putti T, Murray P, Chan A T C, Tao Q
Cancer Epigenetics Laboratory, Sir YK Pao Cancer Center, Department of Clinical Oncology, The Chinese University of Hong Kong, Hong Kong, and Department of Pathology, National University Hospital, Singapore.
Oncogene. 2006 Feb 16;25(7):1070-80. doi: 10.1038/sj.onc.1209154.
Protocadherins constitute the largest subgroup in the cadherin superfamily of cell adhesion molecules. Their major functions are poorly understood, although some are implicated in nervous system development. As tumor-specific promoter methylation is a marker for tumor suppressor genes (TSG), we searched for epigenetically inactivated TSGs using methylation-subtraction combined with pharmacologic demethylation, and identified the PCDH10 CpG island as a methylated sequence in nasopharyngeal carcinoma (NPC). PCDH10 is broadly expressed in all normal adult and fetal tissues including the epithelia, though at different levels. It resides at 4q28.3--a region with hemizygous deletion detected by array-CGH in NPC cell lines; however, PCDH10 itself is not located within the deletion. In contrast, its transcriptional silencing and promoter methylation were frequently detected in multiple carcinoma cell lines in a biallelic way, including 12/12 nasopharyngeal, 13/16 esophageal, 3/4 breast, 5/5 colorectal, 3/4 cervical, 2/5 lung and 2/8 hepatocellular carcinoma cell lines, but not in any immortalized normal epithelial cell line. Aberrant methylation was further frequently detected in multiple primary carcinomas (82% in NPC, 42-51% for other carcinomas), but not normal tissues. The transcriptional silencing of PCDH10 could be reversed by pharmacologic demethylation with 5-aza-2'-deoxycytidine or genetic demethylation with double knockout of DNMT1 and DNMT3B, indicating a direct epigenetic mechanism. Ectopic expression of PCDH10 strongly suppressed tumor cell growth, migration, invasion and colony formation. Although the epigenetic and genetic disruptions of several classical cadherins as TSGs have been well documented in tumors, this is the first report that a widely expressed protocadherin can also function as a TSG that is frequently inactivated epigenetically in multiple carcinomas.
原钙黏蛋白构成了细胞黏附分子钙黏蛋白超家族中最大的亚群。尽管其中一些与神经系统发育有关，但其主要功能仍知之甚少。由于肿瘤特异性启动子甲基化是肿瘤抑制基因（TSG）的一个标志物，我们使用甲基化消减结合药物去甲基化方法寻找表观遗传失活的TSG，并确定PCDH10 CpG岛是鼻咽癌（NPC）中的一个甲基化序列。PCDH10在包括上皮细胞在内的所有正常成人和胎儿组织中广泛表达，不过表达水平有所不同。它位于4q28.3——在NPC细胞系中通过阵列比较基因组杂交检测到有半合子缺失的一个区域；然而，PCDH10本身并不位于缺失区域内。相反，在多个癌细胞系中经常以双等位基因方式检测到其转录沉默和启动子甲基化，包括12/12的鼻咽癌细胞系、13/16的食管癌细胞系、3/4的乳腺癌细胞系、5/5的结肠癌细胞系、3/4的宫颈癌细胞系、2/5的肺癌细胞系和2/8的肝癌细胞系，但在任何永生化正常上皮细胞系中均未检测到。在多个原发性癌中也经常检测到异常甲基化（NPC中为82%，其他癌为42 - 51%），但正常组织中未检测到。用5 - 氮杂 - 2'-脱氧胞苷进行药物去甲基化或通过DNMT1和DNMT3B双敲除进行基因去甲基化可逆转PCDH10的转录沉默，表明存在直接的表观遗传机制。PCDH10的异位表达强烈抑制肿瘤细胞的生长、迁移、侵袭和集落形成。尽管几种作为TSG的经典钙黏蛋白的表观遗传和基因破坏在肿瘤中已有充分记录，但这是首次报道一种广泛表达的原钙黏蛋白也可作为TSG，且在多种癌中经常发生表观遗传失活。
