Implication of BRG1 and cdk9 in the STAT3-mediated activation of the p21waf1 gene
Implication of BRG1 and cdk9 in the STAT3-mediated activation of the p21waf1 gene
复制标题
DOI：
10.1038/sj.onc.1207972
复制
发表时间：
2004-09-23
期刊：
影响因子：
8
通讯作者：
Coqueret, O
中科院分区：
文献类型：
--
作者：
Giraud, S;Hurlstone, A;Coqueret, O
STAT转录因子（信号转导和转录激活因子）是在细胞因子受体刺激下诱导基因激活的细胞质蛋白。酪氨酸磷酸化后，STAT蛋白转运到细胞核中并激活特定的靶基因。我们之前报道过STAT3通过与NcoA/SRC1a和CBP共激活因子的关联激活p21waf1基因的表达。在这项研究中，我们探讨了BRG1 （SWI/SNF染色质重塑复合体的一个组成部分）和cdk9（延伸因子P-TEFb的一个组成部分）在stat3介导的p21waf1表达中的作用。通过下拉实验和共免疫沉淀实验，我们发现这两种蛋白都与STAT3相关。染色质免疫沉淀（ChIP）实验表明STAT3 DNA结合导致组蛋白H3乙酰化和BRG1募集。通过Southern blot分析，我们发现BRG1的加载伴随着p21waf1近端启动子的可及性增加和RNA聚合酶II的关联。下一步，STAT3招募cdk9激酶磷酸化RNA聚合酶丝氨酸2的羧基末端结构域。因此，通过ChIP实验可以在基因的编码区检测到聚合酶的伸长形式，可能启动了mRNA的合成。因此，STAT3不仅促进转录起始，还通过与BRG1和cdk9的相互作用调控染色质重塑和转录延伸。
STAT transcription factors ( signal transducers and activators of transcription) are cytoplasmic proteins that induce gene activation in response to cytokine receptor stimulation. Following tyrosine phosphorylation, STAT proteins translocate into the nucleus and activate specific target genes. We have previously reported that STAT3 activates the expression of the p21waf1 gene through its association with the NcoA/SRC1a and CBP coactivators. In this study, we explore the role of BRG1, a component of the SWI/SNF chromatin-remodeling complex, and the role of cdk9, a component of the elongation factor P-TEFb, in the STAT3-mediated expression of p21waf1. We found using pull-down experiments and co-immunoprecipitation assays that both proteins associate with STAT3. Chromatin immunoprecipitation (ChIP) experiments indicate that STAT3 DNA binding results in histone H3 acetylation and BRG1 recruitment. Using Southern blot analysis, we found that the loading of BRG1 is followed by an increased accessibility of the proximal p21waf1 promoter and by the association of RNA polymerase II. As a next step, STAT3 then recruits the cdk9 kinase to phosphorylate the carboxy-terminal domain of the RNA polymerase at serine 2. Accordingly, the elongating form of the polymerase can be detected by ChIP experiments on the coding region of the gene, probably initiating mRNA synthesis. Therefore, STAT3 not only promotes the initiation of transcription but also regulates chromatin remodeling and transcription elongation through its interaction with BRG1 and cdk9.