人类抑癌基因beclin 1在胃癌和直结肠癌中表达下调的研究

人类抑癌基因beclin 1通过自噬作用调节细胞生长，但在胃癌和直结肠癌中其表达水平和调控机制仍不清楚．通过检测胃癌和直结肠肿瘤组织中beclin 1基因的表达水平，及DNA异常甲基化和杂合子缺失对其表达的影响，发现与癌旁组织相比，35％的胃癌标本和30％的直结肠癌标本中beclin 1基因表达显著下调．同时发现，beclin 1基因5’端存在一高密度CpG岛，在胃癌和直结肠癌中beclin 1的启动子区域和第二个内含子区域存在甲基化，而杂合子缺失仅在胃癌中发生．这些发现表明beclin 1基因的异常甲基化和杂合子缺失对其在胃癌和直结肠癌中的表达起调控作用．

The Expression of Human Tumor Suppressor Gene beclin 1 is Down-regulated in Gastric and Colorectal Cancer

Human tumor suppressor gene beclin 1 regulates cell growth through autophagy. The mRNA expression of beclin 1 was reported to be down-regulated in breast cancer with high frequency of loss of heterozygosity (LOH). However, there was no report about the expression levels or the regulatory mechanisms of beclin 1 in gastric and colorectal cancer. Both the mRNA and protein expression levels of beclin 1 was detected in the tissues of gastric and coiorectai cancers, as well as the aberrant DNA methylation and LOH related to the expression of beclin 1. By comparing with normal tissues adjacent to the tissue of these tumors, it was found that beclin 1 mRNA expression levels were significantly decreased in gastric tumor tissue. Furtherly by explorating the 5' region of beclin 1 gene sequence, a large and dense CpG island was discovered and meanwhile methylations in the promoter and the intron 2 regions of beclin 1 were found in both gastric and colorectal tumors. And LOH was found in gastric tumors. These findings suggested that aberrant DNA methylation, as well as LOH, were involved in the regulation of beclin 1 expression in gastric and colorectal cancer.