Division of Medicinal Chemistry, College of Pharmacy, Ohio State University, Columbus, Ohio 43210, USA.
J Biol Chem. 2011 Mar 25;286(12):9968-76. doi: 10.1074/jbc.M110.203240. Epub 2011 Jan 31.
Although energy restriction has been recognized as an important target for cancer prevention, the mechanism by which energy restriction-mimetic agents (ERMAs) mediate apoptosis remains unclear. By using a novel thiazolidinedione-derived ERMA, CG-12 (Wei, S., Kulp, S. K., and Chen, C. S. (2010) J. Biol. Chem. 285, 9780-9791), vis-à-vis 2-deoxyglucose and glucose deprivation, we obtain evidence that epigenetic activation of the tumor suppressor gene Kruppel-like factor 6 (KLF6) plays a role in ERMA-induced apoptosis in LNCaP prostate cancer cells. KLF6 regulates the expression of many proapoptotic genes, and shRNA-mediated KLF6 knockdown abrogated the ability of ERMAs to induce apoptosis. Chromatin immunoprecipitation analysis indicates that this KLF6 transcriptional activation was associated with increased histone H3 acetylation and histone H3 lysine 4 trimethylation occupancy at the promoter region. Several lines of evidence demonstrate that the enhancing effect of ERMAs on these active histone marks was mediated through transcriptional repression of histone deacetylases and H3 lysine 4 demethylases by down-regulating Sp1 expression. First, putative Sp1-binding elements are present in the promoters of the affected histone-modifying enzymes, and luciferase reporter assays indicate that site-directed mutagenesis of these Sp1 binding sites significantly diminished the promoter activities. Second, shRNA-mediated knockdown of Sp1 mimicked the repressive effect of energy restriction on these histone-modifying enzymes. Third, ectopic Sp1 expression protected cells from the repressive effect of CG-12 on these histone-modifying enzymes, thereby abolishing the activation of KLF6 expression. Together, these findings underscore the intricate relationship between energy restriction and epigenetic regulation of tumor suppressor gene expression, which has therapeutic relevance to foster novel strategies for prostate cancer therapy.
虽然能量限制已被认为是预防癌症的一个重要目标，但能量限制模拟剂（ERMAs）介导细胞凋亡的机制尚不清楚。通过使用一种新型噻唑烷二酮衍生的 ERMA，CG-12（Wei，S.，Kulp，S. K.和 Chen，C. S.（2010）J. Biol. Chem. 285，9780-9791），与 2-脱氧葡萄糖和葡萄糖剥夺相比，我们获得的证据表明，肿瘤抑制基因 Kruppel 样因子 6（KLF6）的表观遗传激活在 ERMA 诱导 LNCaP 前列腺癌细胞凋亡中发挥作用。KLF6 调节许多促凋亡基因的表达，shRNA 介导的 KLF6 敲低消除了 ERMA 诱导凋亡的能力。染色质免疫沉淀分析表明，这种 KLF6 转录激活与组蛋白 H3 乙酰化和组蛋白 H3 赖氨酸 4 三甲基化在启动子区域的占有率增加有关。有几条证据表明，ERMAs 对这些活性组蛋白标记的增强作用是通过下调 Sp1 表达来介导组蛋白去乙酰化酶和 H3 赖氨酸 4 去甲基酶的转录抑制。首先，受影响的组蛋白修饰酶的启动子中存在假定的 Sp1 结合元件，荧光素酶报告基因测定表明，这些 Sp1 结合位点的定点突变显著降低了启动子活性。其次，shRNA 介导的 Sp1 敲低模拟了能量限制对这些组蛋白修饰酶的抑制作用。第三，外源性 Sp1 表达保护细胞免受 CG-12 对这些组蛋白修饰酶的抑制作用，从而消除了 KLF6 表达的激活。总之，这些发现强调了能量限制与肿瘤抑制基因表达的表观遗传调控之间的复杂关系，这对促进前列腺癌治疗的新策略具有治疗意义。
