Department of Cancer Biology, Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
PLoS Pathog. 2013;9(4):e1003266. doi: 10.1371/journal.ppat.1003266. Epub 2013 Apr 4.
PKR-like endoplasmic reticulum (ER) kinase (PERK) is an ER-associated stress sensor protein which phosphorylates eukaryotic initiation factor 2α (eIF2α) to induce translation attenuation in response to ER stress. PERK is also a regulator of lipogenesis during adipocyte differentiation through activation of the cleavage of sterol regulatory element binding protein 1 (SREBP1), resulting in the upregulation of lipogenic enzymes. Our recent studies have shown that human cytomegalovirus (HCMV) infection in human fibroblasts (HF) induces adipocyte-like lipogenesis through the activation of SREBP1. Here, we report that PERK expression is highly increased in HCMV-infected cells and is necessary for HCMV growth. Depletion of PERK, using short hairpin RNA (shRNA), resulted in attenuation of HCMV growth, inhibition of lipid synthesis and reduction of lipogenic gene expression. Examination of the cleavage of SREBP proteins showed PERK depletion inhibited the cleavage of SREBP1, but not SREBP2, in HCMV-infected cells, suggesting different cleavage regulatory mechanisms for SREBP1 and 2. Further studies showed that the depletion of SREBP1, but not SREBP2, reduced lipid synthesis in HCMV infection, suggesting that activation of SREBP1 is sufficient to induce lipogenesis in HCMV infection. The reduction of lipid synthesis by PERK depletion can be partially restored by expressing a Flag-tagged nuclear form of SREBP1a. Our studies also suggest that the induction of PERK in HCMV-infected cells stimulates SREBP1 cleavage by reducing levels of Insig1 (Insulin inducible gene 1) protein; this occurs independent of the phosphorylation of eIF2α. Introduction of an exogenous Insig1-Myc into HCMV infected cells significantly reduced HCMV growth and lipid synthesis. Our data demonstrate that the induction of PERK during HCMV infection is necessary for full activation of lipogenesis; this effect appears to be mediated by limiting the levels of Insig1 thus freeing SREBP1-SCAP complexes for SREBP1 processing.
PKR 样内质网（ER）激酶（PERK）是一种 ER 相关应激传感器蛋白，可磷酸化真核起始因子 2α（eIF2α），以响应 ER 应激诱导翻译衰减。PERK 也是脂肪细胞分化过程中脂生成的调节剂，通过激活固醇调节元件结合蛋白 1（SREBP1）的切割，导致脂生成酶的上调。我们最近的研究表明，人巨细胞病毒（HCMV）感染人成纤维细胞（HF）通过激活 SREBP1 诱导脂肪细胞样脂生成。在这里，我们报告说 PERK 表达在 HCMV 感染的细胞中高度增加，并且是 HCMV 生长所必需的。使用短发夹 RNA（shRNA）耗尽 PERK 会导致 HCMV 生长减弱、脂质合成抑制和脂生成基因表达减少。检查 SREBP 蛋白的切割表明，PERK 耗尽抑制了 HCMV 感染细胞中 SREBP1 的切割，但不抑制 SREBP2 的切割，表明 SREBP1 和 2 的切割调节机制不同。进一步的研究表明，SREBP1 的耗尽，而不是 SREBP2 的耗尽，减少了 HCMV 感染中的脂质合成，表明 SREBP1 的激活足以诱导 HCMV 感染中的脂生成。PERK 耗尽导致的脂质合成减少可以通过表达 Flag 标记的 SREBP1a 核形式部分恢复。我们的研究还表明，HCMV 感染细胞中 PERK 的诱导通过降低胰岛素诱导基因 1（Insig1）蛋白的水平刺激 SREBP1 的切割；这发生在 eIF2α 磷酸化之外。将外源性 Insig1-Myc 引入 HCMV 感染细胞中可显著降低 HCMV 生长和脂质合成。我们的数据表明，HCMV 感染期间 PERK 的诱导对于完全激活脂生成是必需的；这种效应似乎是通过限制 Insig1 的水平来介导的，从而使 SREBP1-SCAP 复合物释放出来用于 SREBP1 加工。
Zotero 插件
