Sato Hironobu, Suzuki Hiromu, Toyota Minoru, Nojima Masanori, Maruyama Reo, Sasaki Shigeru, Takagi Hideyasu, Sogabe Yohei, Sasaki Yasushi, Idogawa Masashi, Sonoda Tomoko, Mori Mitsuru, Imai Kohzoh, Tokino Takashi, Shinomura Yasuhisa
First Department of Internal Medicine, Sapporo Medical University, Sapporo 060-8543, Japan.
Carcinogenesis. 2007 Dec;28(12):2459-66. doi: 10.1093/carcin/bgm178. Epub 2007 Aug 3.
Activation of Wnt signaling has been implicated in tumorigenesis, and epigenetic silencing of Wnt antagonist genes has been detected in various cancers. In the present study, we examined the expression and methylation of DICKKOPF (DKK) family genes in gastrointestinal cancer cell lines. We found that all known DKK genes were frequently silenced in colorectal cancer (CRC) cells (DKK1, 3/9, 33%; DKK2, 8/9, 89%; DKK3, 5/9, 56% and DKK4, 5/9, 56%), but not in normal colon mucosa. DKK1, -2 and -3 have 5' CpG islands, and show an inverse relation between expression and methylation. DKK methylation also was frequently observed in gastric cancer (GC) cell lines (DKK1, 6/16, 38%; DKK2, 15/16, 94% and DKK3, 10/16, 63%), but was seen less frequently in hepatocellular carcinoma and pancreatic cancer cell lines. DKKs also were frequently methylated in primary CRCs (DKK1, 7/58, 12%; DKK2, 45/58, 78% and DKK3, 12/58, 21%) and GCs (DKK1, 15/31, 48%; DKK2, 26/31, 84% and DKK3, 12/31, 39%). Against a background of CTNNB1 or APC mutations, Dickkopfs (Dkks) were less effective inhibitors of Wnt signaling than secreted frizzled-related proteins, though over-expression of Dkks suppressed colony formation of CRC cells with such mutations. Our results demonstrate that DKKs are frequent targets of epigenetic silencing in gastrointestinal tumors, and that loss of DKKs may facilitate tumorigenesis through beta-catenin/T-cell factor-independent mechanisms.
Wnt信号通路的激活与肿瘤发生有关，并且在多种癌症中均检测到Wnt拮抗剂基因的表观遗传沉默。在本研究中，我们检测了胃肠道癌细胞系中DICKKOPF（DKK）家族基因的表达和甲基化情况。我们发现，所有已知的DKK基因在结肠直肠癌（CRC）细胞中经常发生沉默（DKK1，3/9，33%；DKK2，8/9，89%；DKK3，5/9，56%；DKK4，5/9，56%），但在正常结肠黏膜中未出现这种情况。DKK1、-2和-3具有5' CpG岛，并且在表达与甲基化之间呈现负相关关系。在胃癌（GC）细胞系中也经常观察到DKK甲基化（DKK1，6/16，38%；DKK2，15/16，94%；DKK3，10/16，63%），但在肝癌和胰腺癌细胞系中较少见。在原发性CRC（DKK1，7/58，12%；DKK2，45/58，78%；DKK3，12/58，21%）和GC（DKK1，15/31，48%；DKK2，26/31，84%；DKK3，12/31，39%）中，DKK也经常发生甲基化。在CTNNB1或APC突变的背景下，Dickkopfs（Dkks）作为Wnt信号通路的抑制剂，其效果不如分泌型卷曲相关蛋白，不过Dkks的过表达抑制了具有此类突变的CRC细胞的集落形成。我们的结果表明，DKK是胃肠道肿瘤中表观遗传沉默的常见靶点，并且DKK的缺失可能通过β-连环蛋白/T细胞因子非依赖机制促进肿瘤发生。
