Chen Hong, Tu Szu-wei, Hsieh Jer-Tsong
Department of Urology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9110, USA.
J Biol Chem. 2005 Jun 10;280(23):22437-44. doi: 10.1074/jbc.M501379200. Epub 2005 Apr 6.
Human DAB2IP (hDAB2IP), a novel GTPase-activating protein modulating the Ras-mediated signaling and tumor necrosis factor-mediated apoptosis, is a potent growth inhibitor in human prostate cancer (PCa). Loss of hDAB2IP expression in PCa is due to altered epigenetic regulation (i.e. DNA methylation and histone modification) of its promoter region. The elevated polycomb Ezh2, a histone methyltransferase, has been associated with PCa progression. In this study, we have demonstrated that an increased Ezh2 expression in normal prostatic epithelial cells can suppress hDAB2IP gene expression. In contrast, knocking down the endogenous Ezh2 levels in PCa by a specific small interfering RNA can increase hDAB2IP expression. The association of Ezh2 complex (including Eed and Suz12) with hDAB2IP gene promoter is also detected in PCa cells but not in normal prostatic epithelial cells. Increased Ezh2 expression in normal prostatic epithelial cells by cDNA transfection facilitates the recruitment of other components of Ezh2 complex to the hDAB2IP promoter region accompanied with the increased levels of methyl histone H3 (H3) and histone deacetylase (HDAC1). Consistently, data from PCa cells transfected with Ezh2 small interfering RNA demonstrated that reduced Ezh2 levels resulted in the dissociation of Ezh2 complex accompanied with decreased levels of both methyl H3 and HDAC1 from hDAB2IP gene promoter. We further unveiled that the methylation status of Lys-27 but not Lys-9 of H3 in hDAB2IP promoter region is consistent with the hDAB2IP levels in both normal prostatic epithelial cells and PCa cells. Together, we conclude that hDAB2IP gene is a target gene of Ezh2 in prostatic epithelium, which provides an underlying mechanism of the down-regulation of hDAB2IP gene in PCa.
人DAB2IP（hDAB2IP）是一种新型的GTP酶激活蛋白，可调节Ras介导的信号传导和肿瘤坏死因子介导的细胞凋亡，是人类前列腺癌（PCa）中一种有效的生长抑制剂。PCa中hDAB2IP表达的缺失是由于其启动子区域表观遗传调控（即DNA甲基化和组蛋白修饰）的改变。组蛋白甲基转移酶多梳蛋白Ezh2水平升高与PCa进展相关。在本研究中，我们证明正常前列腺上皮细胞中Ezh2表达增加可抑制hDAB2IP基因表达。相反，通过特异性小干扰RNA敲低PCa中内源性Ezh2水平可增加hDAB2IP表达。在PCa细胞中也检测到Ezh2复合物（包括Eed和Suz12）与hDAB2IP基因启动子的结合，但在正常前列腺上皮细胞中未检测到。通过cDNA转染增加正常前列腺上皮细胞中Ezh2的表达，促进Ezh2复合物的其他成分募集到hDAB2IP启动子区域，同时甲基化组蛋白H3（H3）和组蛋白去乙酰化酶（HDAC1）水平增加。一致地，用Ezh2小干扰RNA转染的PCa细胞的数据表明，Ezh2水平降低导致Ezh2复合物解离，同时hDAB2IP基因启动子上甲基化H3和HDAC1水平降低。我们进一步揭示，hDAB2IP启动子区域H3的赖氨酸-27而非赖氨酸-9的甲基化状态与正常前列腺上皮细胞和PCa细胞中的hDAB2IP水平一致。总之，我们得出结论，hDAB2IP基因是前列腺上皮中Ezh2的靶基因，这为PCa中hDAB2IP基因下调提供了潜在机制。
