Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.
J Biol Chem. 2011 Jan 21;286(3):1850-9. doi: 10.1074/jbc.M110.162107. Epub 2010 Nov 15.
Alpha actinins (ACTNs) are known for their ability to modulate cytoskeletal organization and cell motility by cross-linking actin filaments. We show here that ACTN4 harbors a functional LXXLL receptor interaction motif, interacts with nuclear receptors in vitro and in mammalian cells, and potently activates transcription mediated by nuclear receptors. Whereas overexpression of ACTN4 potentiates estrogen receptor α (ERα)-mediated transcription in transient transfection reporter assays, knockdown of ACTN4 decreases it. In contrast, histone deacetylase 7 (HDAC7) inhibits estrogen receptor α (ERα)-mediated transcription. Moreover, the ACTN4 mutant lacking the CaM (calmodulin)-like domain that is required for its interaction with HDAC7 fails to activate transcription by ERα. Chromatin immunoprecipitation (ChIP) assays demonstrate that maximal associations of ACTN4 and HDAC7 with the pS2 promoter are mutually exclusive. Knockdown of ACTN4 significantly decreases the expression of ERα target genes including pS2 and PR and also affects cell proliferation of MCF-7 breast cancer cells with or without hormone, whereas knockdown of HDAC7 exhibits opposite effects. Interestingly, overexpression of wild-type ACTN4, but not the mutants defective in interacting with ERα or HDAC7, results in an increase in pS2 and PR mRNA accumulation in a hormone-dependent manner. In summary, we have identified ACTN4 as a novel, atypical coactivator that regulates transcription networks to control cell growth.
α 辅肌动蛋白（ACTNs）以其交联肌动蛋白丝的能力而闻名，从而调节细胞骨架组织和细胞迁移。我们在这里表明，ACTN4 具有功能性 LXXLL 受体相互作用基序，在体外和哺乳动物细胞中与核受体相互作用，并能有效激活核受体介导的转录。虽然 ACTN4 的过表达增强了瞬时转染报告基因测定中雌激素受体 α（ERα）介导的转录，但 ACTN4 的敲低则降低了它。相比之下，组蛋白去乙酰化酶 7（HDAC7）抑制雌激素受体 α（ERα）介导的转录。此外，缺乏与 HDAC7 相互作用所需的 CaM（钙调蛋白）样结构域的 ACTN4 突变体无法激活 ERα 的转录。染色质免疫沉淀（ChIP）实验表明，ACTN4 和 HDAC7 与 pS2 启动子的最大结合是相互排斥的。ACTN4 的敲低显著降低了包括 pS2 和 PR 在内的 ERα 靶基因的表达，并且还影响有无激素的 MCF-7 乳腺癌细胞的增殖，而 HDAC7 的敲低则表现出相反的效果。有趣的是，野生型 ACTN4 的过表达，而不是与 ERα 或 HDAC7 相互作用有缺陷的突变体，导致 pS2 和 PR mRNA 积累以激素依赖的方式增加。总之，我们已经确定 ACTN4 是一种新的非典型共激活因子，它调节转录网络以控制细胞生长。
