Division of Metabolic Disease, Department of Biomedical Science, National Institutes of Health, #194 Tongillo, Eunpyung-gu, Seoul 122-701, South Korea.
Biochem Biophys Res Commun. 2011 Nov 4;414(4):681-7. doi: 10.1016/j.bbrc.2011.09.132. Epub 2011 Oct 2.
Chronic endoplasmic reticulum (ER) stress leads to β-cell failure via reduction of pancreatic and duodenal homeobox-1 (PDX-1) activity, which contributes to the pathogenesis of type 2 diabetes. However, the exact mechanisms by which ER stress reduces PDX-1 activity in pancreatic β-cells are unclear. Previously, we showed that ATF3 downregulates PDX-1 gene expression in MIN6N8 pancreatic β-cells. Here, we investigated another role of ATF3 on the regulation of PDX-1 activity. ATF3 significantly inhibited PDX-1-stimulated transactivation of reporter plasmid containing promoters for PDX-1 binding element and the PDX-1 target gene glucokinase, which is dependent on C-terminal domain of ATF3. ATF3 interacted with PDX-1, and effectively inhibited p300-mediated transcriptional coactivation of the PBE-containing promoter, whereas C-terminal domain-deleted ATF3 did not inhibit the transcoactivation of p300. ATF3 decreased the interaction of p300 with PDX-1 in MIN6N8 cells coexpressing PDX-1 and ATF3. In addition, chromatin immunoprecipitation analysis demonstrated that both tunicamycin treatment and ATF3 overexpression inhibited the recruitment of p300 to PDX-1 on the insulin promoter in MIN6N8 cells. Taken together, these results suggest that ATF3 inhibits PDX-1-mediated transactivation through the inhibition of p300-stimulated coactivation, which may lead to β-cell dysfunction by ER stress.
慢性内质网（ER）应激通过降低胰腺十二指肠同源盒-1（PDX-1）活性导致β细胞衰竭，这有助于 2 型糖尿病的发病机制。然而，内质网应激如何降低胰腺β细胞中 PDX-1 活性的确切机制尚不清楚。先前，我们表明 ATF3 下调 MIN6N8 胰腺β细胞中 PDX-1 的基因表达。在这里，我们研究了 ATF3 对 PDX-1 活性调节的另一个作用。ATF3 显著抑制 PDX-1 刺激的报告质粒的转录激活，该报告质粒包含 PDX-1 结合元件和 PDX-1 靶基因葡萄糖激酶的启动子，这依赖于 ATF3 的 C 端结构域。ATF3 与 PDX-1 相互作用，并有效抑制包含 PBE 的启动子的 p300 介导的转录共激活，而缺失 C 端结构域的 ATF3 则不抑制 p300 的转激活。ATF3 降低了 MIN6N8 细胞中共表达 PDX-1 和 ATF3 时 p300 与 PDX-1 的相互作用。此外，染色质免疫沉淀分析表明，无论是衣霉素处理还是 ATF3 过表达，都抑制了 MIN6N8 细胞中 p300 在内源胰岛素启动子上与 PDX-1 的募集。总之，这些结果表明 ATF3 通过抑制 p300 刺激的共激活来抑制 PDX-1 介导的转录激活，这可能导致 ER 应激引起的β细胞功能障碍。
