Pdx-1 links histone H3-Lys-4 methylation to RNA polymerase II elongation during activation of insulin transcription
Pdx-1 links histone H3-Lys-4 methylation to RNA polymerase II elongation during activation of insulin transcription
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DOI：
10.1074/jbc.m505741200
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发表时间：
2005-10-28
影响因子：
4.8
通讯作者：
Mirmira, RG
中科院分区：
文献类型：
--
作者：
Francis, J;Chakrabarti, SK;Mirmira, RG
胰岛素基因的表达几乎只存在于胰岛的β细胞中。虽然调控胰岛素表达的序列特异性转录因子已经得到了很好的研究，但这些因子、染色质结构和RNA聚合酶II （pol II）转录延伸之间的相互关系仍然不明确。在这方面，最近的研究已经开始确定组蛋白H3的甲基化在pol II转录的起始或延伸中的作用。为了确定转录激活因子Pdx-1在维持胰岛素基因染色质结构和pol II募集中的作用，我们在β TC3细胞中进行了小干扰rna介导的Pdx-1敲低，随后通过染色质免疫沉淀研究了组蛋白修饰和pol II募集。我们在这里证明，在敲除Pdx-1后，胰岛素转录下降50%，同时胰岛素启动子处的二甲基化组蛋白H3-Lys-4下降60%。胰岛素启动子的H3-Lys-4甲基化至少部分由甲基转移酶Set9介导。免疫组织化学分析显示，Set9在胰腺中以胰岛富集模式表达，类似于Pdx-1的表达模式。Set9向胰岛素基因募集似乎是其与Pdx-1直接相互作用的结果，而小干扰rna介导的Set9的敲低会减弱胰岛素转录。Pdx-1基因敲低还与胰岛素基因募集pol II亚型的整体转变有关，从延伸亚型（Ser(P)-2）到起始亚型（Ser(P)-5）。因此，我们的研究结果提出了一个模型，其中Pdx-1在将H3-Lys-4二甲基化和pol II延伸与胰岛素转录联系起来方面发挥了新的作用。
Expression of the insulin gene is nearly exclusive to the beta cells of the pancreatic islets. Although the sequence-specific transcription factors that regulate insulin expression have been well studied, the interrelationship between these factors, chromatin structure, and transcriptional elongation by RNA polymerase II (pol II) has remained undefined. In this regard, recent studies have begun to establish a role for the methylation of histone H3 in the initiation or elongation of transcription by pol II. To determine a role for the transcriptional activator Pdx-1 in the maintenance of chromatin structure and pol II recruitment at the insulin gene, we performed small interfering RNA-mediated knockdown of Pdx-1 in beta TC3 cells and subsequently studied histone modifications and pol II recruitment by chromatin immunoprecipitation. We demonstrated here that the 50% fall in insulin transcription following knockdown of Pdx-1 is accompanied by a 60% fall in dimethylated histone H3-Lys-4 at the insulin promoter. H3-Lys-4 methylation at the insulin promoter may bemediated, at least partially, by the methyltransferase Set9. Immunohistochemical analysis revealed that Set9 is expressed in an islet-enriched pattern in the pancreas, similar to the pattern of Pdx-1 expression. The recruitment of Set9 to the insulin gene appears to be a consequence of its direct interaction with Pdx-1, and small interfering RNA-mediated knockdown of Set9 attenuates insulin transcription. Pdx-1 knockdown was also associated with an overall shift in the recruitment of pol II isoforms to the insulin gene, from an elongation isoform (Ser( P)-2) to an initiation isoform ( Ser( P)-5). Our findings therefore suggest a model whereby Pdx-1 plays a novel role in linking H3-Lys-4 dimethylation and pol II elongation to insulin transcription.