Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan.
J Mol Cell Cardiol. 2010 Jun;48(6):1280-9. doi: 10.1016/j.yjmcc.2010.02.004. Epub 2010 Feb 17.
The unfolded protein response (UPR) is triggered to assist protein folding when endoplasmic reticulum (ER) function is impaired. Recent studies demonstrated that ER stress can also induce cell-specific genes. In this study, we examined whether X-box binding protein 1 (XBP1), a major UPR-linked transcriptional factor, regulates the expression of brain natriuretic peptide (BNP) in cardiomyocytes. In samples from failing human hearts, extensive splicing of XBP1 was observed along with increased expression of glucose-regulated protein of 78 kDa (GRP78), a target of spliced XBP1 (sXBP1), suggesting that the UPR was induced in heart failure in humans. Interestingly, quantitative real-time PCR revealed a positive correlation between cardiac expression of GRP78 and BNP, leading us to test the hypothesis that sXBP1 regulates BNP as well as GRP78 in cardiomyocytes. A pharmacological ER stressor caused a dose-dependent increase in the expression of sXBP1 and BNP by cultured cardiomyocytes. Short interfering RNA targeting XBP1 suppressed the induction of BNP expression by a pharmacological ER stressor or norepinephrine, which was rescued by the adenovirus-mediated overexpression of sXBP1. The promoter assay with overexpression of sXBP1 or norepinephrine showed that the proximal AP1/CRE-like element in the promoter region of BNP was critical for transcriptional regulation of BNP by sXBP1. Direct binding of sXBP1 to this element was confirmed by the chromatin immunoprecipitation assay. These findings suggest that ER stress observed in failing hearts regulates cardiac BNP expression through a novel promoter region of the AP1/CRE-like element.
未折叠蛋白反应（UPR）是在内质网（ER）功能受损时触发的，以协助蛋白折叠。最近的研究表明，ER 应激也可以诱导细胞特异性基因。在这项研究中，我们研究了 X 盒结合蛋白 1（XBP1），一种主要的 UPR 相关转录因子，是否调节心肌细胞中脑钠肽（BNP）的表达。在衰竭的人类心脏样本中，观察到 XBP1 的广泛剪接，同时葡萄糖调节蛋白 78 kDa（GRP78）的表达增加，GRP78 是剪接 XBP1（sXBP1）的靶点，这表明 UPR 在人类心力衰竭中被诱导。有趣的是，定量实时 PCR 显示心脏 GRP78 和 BNP 的表达之间存在正相关，这使我们假设 sXBP1 调节心肌细胞中的 BNP 以及 GRP78。药理学 ER 应激剂引起培养的心肌细胞中 sXBP1 和 BNP 的表达呈剂量依赖性增加。靶向 XBP1 的短发夹 RNA 抑制药理学 ER 应激剂或去甲肾上腺素诱导的 BNP 表达，而 sXBP1 的腺病毒过表达可挽救这种抑制作用。用 sXBP1 或去甲肾上腺素过表达进行的启动子分析表明，BNP 启动子区域的近端 AP1/CRE 样元件对于 sXBP1 对 BNP 的转录调控至关重要。染色质免疫沉淀分析证实了 sXBP1 与该元件的直接结合。这些发现表明，衰竭心脏中观察到的 ER 应激通过 AP1/CRE 样元件的新启动子区域调节心脏 BNP 的表达。
