van Huizen Rika, Martindale Jennifer L, Gorospe Myriam, Holbrook Nikki J
Laboratory of Cellular and Molecular Biology, National Institute on Aging/NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA.
J Biol Chem. 2003 May 2;278(18):15558-64. doi: 10.1074/jbc.M212074200. Epub 2003 Feb 24.
The unfolded protein response, which is activated in response to the loss of endoplasmic reticulum (ER) Ca(2+) homeostasis and/or the accumulation of misfolded, unassembled, or aggregated proteins in the ER lumen, involves both transcriptional and translational regulation. In the current studies we sought to identify novel ER stress-induced genes by conducting microarray analysis on tunicamycin-treated cells. We identified P58(IPK), an inhibitor of the interferon-induced double-stranded RNA-activated protein kinase, as induced during ER stress. Additional studies suggested that p58(IPK) induction was mediated via ATF6 and that P58(IPK) played a role in down-regulating the activity of the pancreatic eIF2 kinase/eukaryotic initiation factor 2alpha (eIF2alpha)-like ER kinase/activation transcription factor (ATF) 4 pathway. Modulation of P58(IPK) levels altered the phosphorylation status of eIF2alpha, and thereby affected expression of its downstream targets, ATF4 and Gadd153. Overexpression of P58(IPK) inhibited eIF2alpha phosphorylation and reduced ATF4 and Gadd153 protein accumulation, whereas silencing of P58(IPK) expression enhanced pancreatic eIF2alpha-like ER kinase and eIF2alpha phosphorylation and increased ATF4 and Gadd153 accumulation. These findings implicate P58(IPK) as an important component of a negative feedback loop used by the cell to inhibit eIF2alpha signaling, and thus attenuate the unfolded protein response.
未折叠蛋白反应是在内质网（ER）钙（Ca2+）稳态丧失和/或ER腔内错误折叠、未组装或聚集蛋白积累时被激活的，它涉及转录和翻译调控。在当前的研究中，我们试图通过对衣霉素处理的细胞进行微阵列分析来鉴定新的内质网应激诱导基因。我们鉴定出P58（IPK），一种干扰素诱导的双链RNA激活蛋白激酶的抑制剂，在内质网应激期间被诱导。进一步的研究表明，p58（IPK）的诱导是通过ATF6介导的，并且P58（IPK）在下调胰腺eIF2激酶/真核起始因子2α（eIF2α）样内质网激酶/激活转录因子（ATF）4途径的活性中发挥作用。P58（IPK）水平的调节改变了eIF2α的磷酸化状态，从而影响其下游靶点ATF4和Gadd153的表达。P58（IPK）的过表达抑制了eIF2α的磷酸化并减少了ATF4和Gadd153蛋白的积累，而P58（IPK）表达的沉默增强了胰腺eIF2α样内质网激酶和eIF2α的磷酸化并增加了ATF4和Gadd153的积累。这些发现表明P58（IPK）是细胞用于抑制eIF2α信号传导从而减弱未折叠蛋白反应所使用的负反馈环的重要组成部分。
