Department of Emergency Medicine, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Neuroscience. 2010 Sep 1;169(3):1307-14. doi: 10.1016/j.neuroscience.2010.05.076. Epub 2010 Jun 9.
Transient global brain ischemia results in an immediate inhibition of protein translation upon reperfusion. During early brain reperfusion protein synthesis is inhibited by alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) phosphorylation by the PKR-like endoplasmic reticulum kinase (PERK). Normally, PERK is held in an inactive, monomeric state by the binding of the endoplasmic reticulum (ER) chaperone GRP78 to the lumenal end of PERK. The prevailing view is that ER stress leads to the accumulation of unfolded proteins in the ER lumen. GRP78 dissociates from PERK to bind these accumulated unfolded proteins, leading to PERK activation, phosphorylation of eIF2alpha, and inhibition of translation. To determine if an increase in unfolded nascent proteins following transient brain ischemia contributes to PERK activation, protein synthesis was blocked by intracerebral injection of anisomycin prior to induction of ischemia. Anisomycin inhibited protein synthesis by over 99% and reduced newly synthesized proteins in the ER to approximately 20% of controls. With an ER nearly devoid of newly synthesized proteins, PERK was still activated and was able to phosphorylate eIF2alpha in CA1 neurons during reperfusion. These data strongly argue that PERK activation is independent of the large increase in unfolded nascent proteins within the ER following transient global brain ischemia.
短暂全脑缺血再灌注后即刻会抑制蛋白质翻译。在早期脑再灌注期间，蛋白质合成受到真核起始因子 2（eIF2α）α亚单位的磷酸化的抑制，这种磷酸化由蛋白激酶 R 样内质网激酶（PERK）介导。通常情况下，PERK 通过内质网（ER）伴侣蛋白 GRP78 与 PERK 腔内腔的结合而处于非活性单体状态。普遍观点认为，内质网应激导致 ER 腔中未折叠蛋白的积累。GRP78 从 PERK 上解离以结合这些积累的未折叠蛋白，导致 PERK 激活、eIF2α 磷酸化和翻译抑制。为了确定短暂性脑缺血后未折叠新生蛋白的增加是否有助于 PERK 激活，在诱导缺血之前通过脑内注射放线菌酮来阻断蛋白质合成。放线菌酮使蛋白质合成抑制超过 99%，并使 ER 中的新合成蛋白减少到对照的约 20%。由于 ER 中几乎没有新合成的蛋白质，PERK 仍然被激活，并能够在再灌注期间使 CA1 神经元中的 eIF2α 磷酸化。这些数据强烈表明，PERK 的激活不依赖于短暂性全脑缺血后 ER 中未折叠新生蛋白的大量增加。
