Department of Chemistry and Biochemistry, The University of Texas at Arlington, 700 Planetarium Place, Arlington, TX 76019, USA.
J Mol Biol. 2011 Aug 12;411(2):334-49. doi: 10.1016/j.jmb.2011.05.050. Epub 2011 Jun 12.
Homeobox (HOX)-containing gene HOXC6 is a critical player in mammary gland development and milk production, and is overexpressed in breast and prostate cancers. We demonstrated that HOXC6 is transcriptionally regulated by estrogen (E2). HOXC6 promoter contains two putative estrogen response elements (EREs), termed as ERE1(1/2) and ERE2(1/2). Promoter analysis using luciferase-based reporter assay demonstrated that both EREs are responsive to E2, with ERE1(1/2) being more responsive than ERE2(1/2). Estrogen receptors (ERs) ERα and ERβ bind to these EREs in an E2-dependent manner, and antisense-mediated knockdown of ERs suppressed the E2-dependent activation of HOXC6 expression. Similarly, knockdown of histone methylases MLL2 and MLL3 decreased the E2-mediated activation of HOXC6. However, depletion of MLL1 or MLL4 showed no significant effect. MLL2 and MLL3 were bound to the HOXC6 EREs in an E2-dependent manner. In contrast, MLL1 and MLL4 that were bound to the HOXC6 promoter in the absence of E2 decreased upon exposure to E2. MLL2 and MLL3 play key roles in histone H3 lysine-4 trimethylation and in the recruitment of general transcription factors and RNA polymerase II in the HOXC6 promoter during E2-dependent transactivation. Nuclear receptor corepressors N-CoR and SAFB1 were bound in the HOXC6 promoter in the absence of E2, and that binding was decreased upon E2 treatment, indicating their critical roles in suppressing HOXC6 gene expression under nonactivated conditions. Knockdown of either ERα or ERβ abolished E2-dependent recruitment of MLL2 and MLL3 into the HOXC6 promoter, demonstrating key roles of ERs in the recruitment of these mixed lineage leukemias into the HOXC6 promoter. Overall, our studies demonstrated that HOXC6 is an E2-responsive gene, and that histone methylases MLL2 and MLL3, in coordination with ERα and ERβ, transcriptionally regulate HOXC6 in an E2-dependent manner.
含有同源盒（HOX）基因 HOXC6 是乳腺发育和乳汁生产的关键因子，在乳腺癌和前列腺癌中过度表达。我们证明 HOXC6 受雌激素（E2）转录调控。HOXC6 启动子包含两个假定的雌激素反应元件（EREs），称为 ERE1（1/2）和 ERE2（1/2）。使用基于荧光素酶的报告基因分析进行的启动子分析表明，这两个 ERE 都对 E2 有反应，其中 ERE1（1/2）的反应性更强。雌激素受体（ERs）ERα 和 ERβ 以 E2 依赖的方式与这些 ERE 结合，并且 ERs 的反义介导敲低抑制了 HOXC6 表达的 E2 依赖性激活。同样，组蛋白甲基转移酶 MLL2 和 MLL3 的敲低降低了 E2 介导的 HOXC6 激活。然而，MLL1 或 MLL4 的耗竭没有显示出显著的效果。MLL2 和 MLL3 以 E2 依赖的方式与 HOXC6 ERE 结合。相比之下，在没有 E2 的情况下与 HOXC6 启动子结合的 MLL1 和 MLL4 在暴露于 E2 后减少。MLL2 和 MLL3 在 E2 依赖性反式激活过程中在 HOXC6 启动子中发挥关键作用，用于组蛋白 H3 赖氨酸-4 三甲基化以及一般转录因子和 RNA 聚合酶 II 的募集。核受体共抑制因子 N-CoR 和 SAFB1 在没有 E2 的情况下与 HOXC6 启动子结合，并且在 E2 处理后结合减少，表明它们在非激活条件下抑制 HOXC6 基因表达中起关键作用。ERα 或 ERβ 的敲低消除了 E2 依赖性 MLL2 和 MLL3 进入 HOXC6 启动子的募集，表明 ERs 在募集这些混合谱系白血病进入 HOXC6 启动子中的关键作用。总的来说，我们的研究表明 HOXC6 是一个 E2 反应性基因，组蛋白甲基转移酶 MLL2 和 MLL3 与 ERα 和 ERβ 协调，以 E2 依赖的方式转录调节 HOXC6。
