The Actin-binding Protein, Actinin Alpha 4 (ACTN4), Is a Nuclear Receptor Coactivator that Promotes Proliferation of MCF-7 Breast Cancer Cells
The Actin-binding Protein, Actinin Alpha 4 (ACTN4), Is a Nuclear Receptor Coactivator that Promotes Proliferation of MCF-7 Breast Cancer Cells
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DOI：
10.1074/jbc.m110.162107
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发表时间：
2011-01-21
影响因子：
4.8
通讯作者：
Kao, Hung-Ying
中科院分区：
文献类型：
--
作者：
Khurana, Simran;Chakraborty, Sharmistha;Kao, Hung-Ying
α -肌动蛋白（actn）以其通过交联肌动蛋白丝调节细胞骨架组织和细胞运动的能力而闻名。我们在这里表明，ACTN4包含一个功能性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，并有效激活核受体介导的转录。在瞬时转染报告基因试验中，ACTN4过表达能增强雌激素受体α (ER α)介导的转录，而敲低ACTN4则能降低这种转录。相反，组蛋白去乙酰化酶7 （HDAC7）抑制雌激素受体α (ER α)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突变体不能通过ER α激活转录。染色质免疫沉淀（ChIP）分析表明，ACTN4和HDAC7与pS2启动子的最大关联是相互排斥的。敲低ACTN4可显著降低ER α靶基因pS2和PR的表达，并影响MCF-7乳腺癌细胞在有或无激素作用下的细胞增殖，而敲低HDAC7则相反。有趣的是，野生型ACTN4的过表达，而不是与ER α或HDAC7相互作用缺陷的突变体，以激素依赖的方式导致pS2和PR mRNA积累增加。总之，我们已经确定ACTN4是一种新型的非典型共激活因子，可以调节转录网络来控制细胞生长。
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 alpha (ER alpha)-mediated transcription in transient transfection reporter assays, knockdown of ACTN4 decreases it. In contrast, histone deacetylase 7 (HDAC7) inhibits estrogen receptor alpha (ER alpha)-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 ER alpha. 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 ER alpha 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 ER alpha 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.