Guo MingZhou, House Michael G, Suzuki Hiromu, Ye Ying, Brock Malcolm V, Lu Fengmin, Liu Zhihua, Rustgi Anil K, Herman James G
Department of Oncology, Cancer Biology Program, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD 21231-1000, USA.
Int J Cancer. 2007 Sep 15;121(6):1219-26. doi: 10.1002/ijc.22828.
CDX2, a mammalian homologue of the homeobox gene 'caudal,' is expressed in gut epithelia and plays an important role in establishing the intestinal phenotype during development. Mice heterozygously disrupted for CDX2 develop disorganized polypoid hamartomas with glandular epithelium and stratified squamous metaplasia resembling foregut mucosa. Since no genetic disruptions of CDX2 have been reported to explain loss of gene function, we examined whether epigenetic mechanisms altered CDX2 expression. Eleven of 17 squamous esophageal cancer cell lines lacked expression of CDX2 that was restored following treatment with 5-aza-2'-deoxycytidine, while all colorectal cancer cell lines expressed CDX2. Loss of expression was associated with DNA methylation in the 5' region of CDX2 determined by methylation specific PCR and bisulfite sequencing. Methylation of CDX2 was rare in primary colorectal (1 of 44 tumors, 2%) and esophageal adenocarcinoma neoplasms (2 of 43 tumors, 5%), but was common in esophageal squamous carcinoma (24 of 45 tumors, 49%). No CDX2 methylation was found in normal tissues. Using semi-quantitative RT-PCR, expression of CDX2 was found in low level in normal esophagus, at higher levels in primary adenocarcinoma of the esophagus, but not in primary squamous cancers of the esophagus. Restoration of CDX2 in silenced cell lines resulted in expression of the CDX2 target gene MUC2, a gene important in glandular differentiation. Our results suggest that the inactivation of CDX2 in esophageal cancer associated with DNA methylation may be an important determinant of the squamous or non-adenomatous phenotype.
CDX2是同源异型盒基因“尾型”的哺乳动物同源物，在肠道上皮中表达，在发育过程中建立肠道表型方面发挥重要作用。CDX2基因杂合缺失的小鼠会形成结构紊乱的息肉样错构瘤，伴有腺上皮和类似于前肠黏膜的复层鳞状化生。由于尚未报道有CDX2的基因破坏可解释基因功能丧失，我们研究了表观遗传机制是否改变了CDX2的表达。17种食管鳞癌细胞系中有11种缺乏CDX2表达，用5-氮杂-2'-脱氧胞苷处理后表达得以恢复，而所有结肠癌细胞系均表达CDX2。通过甲基化特异性PCR和亚硫酸氢盐测序确定，CDX2表达缺失与CDX2 5'区域的DNA甲基化有关。CDX2甲基化在原发性结肠癌（44个肿瘤中有1个，2%）和食管腺癌肿瘤（43个肿瘤中有2个，5%）中很少见，但在食管鳞癌中很常见（45个肿瘤中有24个，49%）。在正常组织中未发现CDX2甲基化。使用半定量RT-PCR发现，CDX2在正常食管中低水平表达，在原发性食管腺癌中表达水平较高，但在原发性食管鳞癌中不表达。在沉默的细胞系中恢复CDX2表达会导致CDX2靶基因MUC2表达，MUC2是腺分化中的一个重要基因。我们的结果表明，与DNA甲基化相关的食管癌中CDX2失活可能是鳞状或非腺瘤表型的重要决定因素。
