TBX2 interacts with heterochromatin protein 1 to recruit a novel repression complex to EGR1-targeted promoters to drive the proliferation of breast cancer cells
TBX2 interacts with heterochromatin protein 1 to recruit a novel repression complex to EGR1-targeted promoters to drive the proliferation of breast cancer cells
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DOI：
10.1038/s41388-019-0853-z
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发表时间：
2019-08-01
期刊：
影响因子：
8
通讯作者：
Mullan, P. B.
中科院分区：
文献类型：
--
作者：
Crawford, N. T.;McIntyre, A. J.;Mullan, P. B.
早期生长反应1 （EGR1）是一种应激反应转录因子，在乳腺组织中具有多种肿瘤抑制作用，其表达在乳腺癌中经常丢失。我们之前的研究表明，乳腺癌致癌基因TBX2 （T-BOX2）与EGR1相互作用，共同抑制EGR1靶基因，包括乳腺肿瘤抑制因子NDRG1。在这里，我们展示了这种TBX2抑制复合体的机制基础。我们发现，TBX2、EGR1、异染色质蛋白1 （HP1）亚型和HP1相关的协抑制蛋白KAP1的siRNA敲低均可抑制表达TBX2的乳腺癌细胞的生长。我们发现TBX2通过其n端保守的HP1结合基序与HP1相互作用，进而导致KAP1和其他相关蛋白的募集。TBX2-HP1结合域的突变使TBX2-HP1相互作用失效，靶基因如NDRG1的抑制丧失。染色质免疫沉淀（ChIP）实验表明，TBX2在NDRG1近端启动子周围建立了一个抑制染色质标记，特别是H3K9me3，与DNA甲基转移酶DNMT3B和组蛋白甲基转移酶（HMT）复合物组分（G9A， Zeste 2的增强子（EZH2）和Zeste 12的抑制子（SUZ12））的募集一致。G9A、EZH2或SUZ12的下调导致TBX2/EGR1共调控靶点上调，同时显著抑制细胞增殖。我们发现HMT活性的一种通用抑制剂DzNep可以诱导显性阴性TBX2的表型表达。TBX2、KAP1或HP1的敲低特异性抑制了NDRG1启动子的H3K9me3抑制标记的修饰。相应的，用G9A抑制剂治疗可以有效逆转TBX2对NDRG1的抑制，并协同下调TBX2功能抑制后的细胞增殖。这些数据表明TBX2通过向egr1响应启动子募集一个大的抑制复合体来促进正常生长控制机制的抑制，从而导致乳腺癌细胞不受控制的增殖。
Early Growth Response 1 (EGR1) is a stress response transcription factor with multiple tumour suppressor roles in breast tissue, whose expression is often lost in breast cancers. We have previously shown that the breast cancer oncogene TBX2 (T-BOX2) interacts with EGR1 to co-repress EGR1-target genes including the breast tumour suppressor NDRG1. Here, we show the mechanistic basis of this TBX2 repression complex. We show that siRNA knockdown of TBX2, EGR1, Heterochromatin Protein 1 (HP1) isoforms and the generic HP1-associated corepressor protein KAP1 all resulted in growth inhibition of TBX2-expressing breast cancer cells. We show that TBX2 interacts with HP1 through a conserved HP1-binding motif in its N-terminus, which in turn leads to the recruitment of KAP1 and other associated proteins. Mutation of the TBX2 HP1 binding domain abrogates the TBX2-HP1 interaction and loss of repression of target genes such as NDRG1. Chromatin-immunoprecipitation (ChIP) assays showed that TBX2 establishes a repressive chromatin mark, specifically H3K9me3, around the NDRG1 proximal promoter coincident with the recruitment of the DNA methyltransferase DNMT3B and histone methyltransferase (HMT) complex components (G9A, Enhancer of Zeste 2 (EZH2) and Suppressor of Zeste 12 (SUZ12)). Knockdown of G9A, EZH2 or SUZ12 resulted in upregulation of TBX2/EGR1 co-regulated targets accompanied by a dramatic inhibition of cell proliferation. We show that a generic inhibitor of HMT activity, DzNep, phenocopies expression of an inducible dominant negative TBX2. Knockdown of TBX2, KAP1 or HP1 inhibited NDRG1 promoter decoration specifically with the H3K9me3 repression mark. Correspondingly, treatment with a G9A inhibitor effectively reversed TBX2 repression of NDRG1 and synergistically downregulated cell proliferation following TBX2 functional inhibition. These data demonstrate that TBX2 promotes suppression of normal growth control mechanisms through recruitment of a large repression complex to EGR1-responsive promoters leading to the uncontrolled proliferation of breast cancer cells.