Division of Hematology/Oncology, Department of Medicine, University of Florida, Gainesville, FL, USA.
Department of Pathology, University of Florida, Gainesville, FL, USA.
Oncogene. 2014 Jan 30;33(5):653-64. doi: 10.1038/onc.2012.613. Epub 2013 Mar 25.
Brahma (BRM) is a novel anticancer gene, which is frequently inactivated in a variety of tumor types. Unlike many anticancer genes, BRM is not mutated, but rather epigenetically silenced. In addition, histone deacetylase complex (HDAC) inhibitors are known to reverse BRM silencing, but they also inactivate it via acetylation of its C-terminus. High-throughput screening has uncovered many compounds that are effective at pharmacologically restoring BRM and thereby inhibit cancer cell growth. As we do not know which specific proteins, if any, regulate BRM, we sought to identify the proteins, which underlie the epigenetic suppression of BRM. By selectively knocking down each HDAC, we found that HDAC3 and HDAC9 regulate BRM expression, whereas HDAC2 controls its acetylation. Similarly, we ectopically overexpressed 21 different histone acetyltransferases and found that KAT6A, KAT6B and KAT7 induce BRM expression, whereas KAT2B and KAT8 induce its acetylation. We also investigated the role of two transcription factors (TFs) linked to either BRM (GATA3) or HDAC9 (MEF2D) expression. Knockdown of either GATA3 and/or MEF2D downregulated HDAC9 and induced BRM. As targets for molecular biotherapy are typically uniquely, or simply differentially expressed in cancer cells, we also determined if any of these proteins are dysregulated. However, by sequencing, no mutations were found in any of these BRM-regulating HDACs, HATs or TFs. We selectively knocked down GATA3, MEF2D, HDAC3 and HDAC9, and found that each gene-specific knockdown induced growth inhibition. We observed that both GATA3 and HDAC9 were greatly overexpressed only in BRM-negative cell lines indicating that HDAC9 may be a good target for therapy. We also found that the mitogen-activated protein (MAP) kinase pathway regulates both BRM acetylation and BRM silencing as MAP kinase pathway inhibitors both induced BRM as well as caused BRM deacetylation. Together, these data identify a cadre of key proteins, which underlie the epigenetic regulation of BRM.
Brahma (BRM) 是一种新型的抗癌基因，它在多种肿瘤类型中经常失活。与许多抗癌基因不同，BRM 不是突变的，而是被表观遗传沉默。此外，组蛋白去乙酰化酶复合物（HDAC）抑制剂已知可以逆转 BRM 的沉默，但它们也通过乙酰化其 C 末端使其失活。高通量筛选发现了许多有效的化合物，可以在药理学上恢复 BRM 的功能，从而抑制癌细胞的生长。由于我们不知道哪些特定的蛋白质（如果有的话）调节 BRM，我们试图确定哪些蛋白质是 BRM 表观遗传抑制的基础。通过选择性敲低每种 HDAC，我们发现 HDAC3 和 HDAC9 调节 BRM 的表达，而 HDAC2 控制其乙酰化。同样，我们异位过表达了 21 种不同的组蛋白乙酰转移酶，发现 KAT6A、KAT6B 和 KAT7 诱导 BRM 的表达，而 KAT2B 和 KAT8 诱导其乙酰化。我们还研究了与 BRM（GATA3）或 HDAC9（MEF2D）表达相关的两个转录因子（TFs）的作用。敲低 GATA3 和/或 MEF2D 下调了 HDAC9 并诱导了 BRM 的表达。由于分子治疗的靶点通常在癌细胞中是独特的，或者只是差异表达的，我们还确定了这些蛋白质是否失调。然而，通过测序，在这些调节 BRM 的 HDAC、HAT 或 TF 中没有发现任何突变。我们选择性地敲低了 GATA3、MEF2D、HDAC3 和 HDAC9，发现每种基因特异性敲低都诱导了生长抑制。我们观察到，只有在 BRM 阴性细胞系中，GATA3 和 HDAC9 的表达量都大大上调，这表明 HDAC9 可能是一个很好的治疗靶点。我们还发现，有丝分裂原激活的蛋白（MAP）激酶通路调节 BRM 的乙酰化和沉默，因为 MAP 激酶通路抑制剂既能诱导 BRM 的表达，又能引起 BRM 的去乙酰化。总的来说，这些数据确定了一组关键的蛋白质，它们是 BRM 表观遗传调控的基础。
