HEXIM1 forms a transcriptionally abortive complex with glucocorticoid receptor without involving 7SK RNA and positive transcription elongation factor b
HEXIM1 forms a transcriptionally abortive complex with glucocorticoid receptor without involving 7SK RNA and positive transcription elongation factor b
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DOI：
10.1073/pnas.0409863102
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发表时间：
2005-06-14
影响因子：
11.1
通讯作者：
Tanaka, H
中科院分区：
文献类型：
--
作者：
Shimizu, N;Ouchida, R;Tanaka, H
HEXIM1蛋白已被证明可形成由7SK小核RNA和正转录延伸因子b（P-TEFb）组成的蛋白-RNA复合物，该因子b由细胞周期蛋白依赖性激酶9（CDK9）和细胞周期蛋白T1组成，并抑制CDK9的激酶活性，从而抑制RNA聚合酶II依赖性转录延伸。在这里，我们通过生化方法证明 HEXIM1 与糖皮质激素受体 (GR) 形成独特的复合物，而无需 RNA、CDK9 或细胞周期蛋白 T1。 HEXIM1 通过其富含精氨酸的核定位信号，直接与 GR 的配体结合域结合。引入 HEXIM1 短干扰 RNA 和腺病毒介导的 HEXIM1 外源表达分别正向和负向调节糖皮质激素反应基因的激活。在细胞核中，HEXIM1 与 p160 共激活因子转录中间因子 2 定位在不同的区室中。HEXIM1 的过度表达减少了 GR 和转录中间因子 2 之间的配体依赖性关联。反义介导的 7SK 破坏减弱了 HEXIM1 对芳基烃受体依赖性转录的负面影响，但对 GR 介导的转录没有影响。 一个，表明一类转录因子是 HEXIM1 的直接靶标。这些结果表明 HEXIM1 在转录调控中具有双重作用：抑制依赖于 7SK RNA 和正转录延伸因子 b 的转录延伸，以及通过直接的蛋白质-蛋白质相互作用干扰序列特异性转录因子 GR。此外，HEXIM1 的中央核定位信号对于这两种作用至关重要，这一事实可能会争论这些功能的串扰。
The HEXIM1 protein has been shown to form a protein-RNA complex composed of 7SK small nuclear RNA and positive transcription elongation factor b (P-TEFb), which is composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1, and to inhibit the kinase activity of CDK9, thereby suppressing RNA polymerase II-dependent transcriptional elongation. Here, we biochemically demonstrate that HEXIM1 forms a distinct complex with glucocorticoid receptor (GR) without RNA, CDK9, or cyclin T1. HEXIM1, through its arginine-rich nuclear localization signal, directly associates with the ligand-binding domain of GR. Introduction of HEXIM1 short interfering RNA and adenovirus-mediated exogenous expression of HEXIM1 positively and negatively modulated glucocorticoid-responsive gene activation, respectively. In the nucleus, HEXIM1 was shown to localize in a distinct compartment from that of the p160 coactivator transcriptional intermediary factor 2. Overexpression of HEXIM1 decreased ligand-dependent association between GR and transcriptional intermediary factor 2. Antisense-mediated disruption of 7SK blunted the negative effect of HEXIM1 on arylhydrocarbon receptor-dependent transcription but not on GR-mediated one, indicating that a class of transcription factors are direct targets of HEXIM1. These results indicate that HEXIM1 has dual roles in transcriptional regulation: inhibition of transcriptional elongation dependent on 7SK RNA and positive transcription elongation factor b and interference with the sequence-specific transcription factor GR via a direct protein-protein interaction. Moreover, the fact that the central nuclear localization signal of HEXIM1 is essential for both of these actions may argue the crosstalk of these functions.