Huang Jian, Zhang Xin, Zhang Min, Zhu Jing-De, Zhang Yun-Li, Lin Yun, Wang Ke-Sheng, Qi Xiao-Fei, Zhang Qin, Liu Guang-Zhen, Yu Jian, Cui Ying, Yang Peng-Yuan, Wang Zhi-Qin, Han Ze-Guang
Shanghai-Ministry Key Laboratory of Disease and Health Genomics, Chinese National Human Genome Center at Shanghai, 351 Guo Shou-Jing Road, Shanghai 201203, China.
Carcinogenesis. 2007 May;28(5):1094-103. doi: 10.1093/carcin/bgl215. Epub 2006 Nov 17.
Dysregulation of a genomic imprinting gene can contribute to carcinogenesis. Here, delta-like 1 homolog (Drosophila) (DLK1), a paternally expressed gene, was found to be significantly up-regulated in 60 (73.2%) of a total of 82 hepatocellular carcinoma (HCC) specimens using reverse transcription-polymerase chain reaction. In addition, immunohistochemistry staining was performed in another 88 HCC specimens, of which 50 (56.8%) cancerous tissues were considered as positive. The expression of DLK1 was obviously induced in HCC cells, Bel-7402 and MHCC-H, by a demethylation agent, 5-aza-2'-deoxycytidine. Furthermore, both demethylation of the DLK1 promoter (-565 to -362) and hypermethylation of the imprinting control domain in the region upstream of maternally expressed gene 3 were identified in a few HCC specimens. This implies that deregulation of genomic DNA methylation of the imprinted domain could be attributed to the up-regulation of DLK1 in HCC, although the undoubtedly complex mechanisms involved in the epigenetic event should be further investigated in HCC. Surprisingly, the expression of DLK1 in HCC was confirmed to be monoallelic specific, not biallelic, in three HCC specimens with a single nucleotide polymorphism as at T852C (rs2295660). Importantly, the exogenous DLK1 can significantly promote the cell proliferation of SMMC-7721 cells, a HCC cell line, whereas the suppression of endogenetic DLK1 through RNA interference can markedly inhibit cell growth, colony formation and tumorigenicity of HepG2, Hep3B and HuH-7 cells. These data suggest that DLK1 as an imprinted gene could be significantly up-regulated in HCC due to certain epigenetic events and contribute to the oncogenesis of this tumor.
基因组印记基因的失调可能导致癌症发生。在此，使用逆转录 - 聚合酶链反应发现，父系表达基因δ样1同源物（果蝇）（DLK1）在总共82例肝细胞癌（HCC）标本中的60例（73.2%）中显著上调。此外，对另外88例HCC标本进行免疫组织化学染色，其中50例（56.8%）癌组织被认为呈阳性。去甲基化剂5 - 氮杂 - 2'-脱氧胞苷可明显诱导HCC细胞Bel - 7402和MHCC - H中DLK1的表达。此外，在一些HCC标本中鉴定出DLK1启动子（-565至-362）的去甲基化以及母系表达基因3上游区域印记控制域的高甲基化。这意味着印记域基因组DNA甲基化的失调可能是HCC中DLK1上调的原因，尽管这种表观遗传事件所涉及的无疑复杂的机制在HCC中仍需进一步研究。令人惊讶的是，在三个具有T852C（rs2295660）单核苷酸多态性的HCC标本中，HCC中DLK1的表达被证实是单等位基因特异性的，而非双等位基因。重要的是，外源性DLK1可显著促进HCC细胞系SMMC - 7721细胞的增殖，而通过RNA干扰抑制内源性DLK1可明显抑制HepG2、Hep3B和HuH - 7细胞的生长、集落形成和致瘤性。这些数据表明，作为印记基因的DLK1可能由于某些表观遗传事件在HCC中显著上调，并促进该肿瘤的发生。
