Protein Tyrosine Phosphatase 1B Deficiency Potentiates PERK/eIF2α Signaling in Brown Adipocytes

BackgroundProtein-tyrosine phosphatase 1B (PTP1B) is a physiological regulator of glucose homeostasis and body mass, and has been implicated in endoplasmic reticulum (ER) stress. Herein, we assess the role of PTP1B in ER stress in brown adipocytes, which are key regulators of thermogenesis and metabolic response. Methodology/Principal FindingsTo determine the role of PTP1B in ER stress, we utilized brown adipose tissue (BAT) from mice with adipose-specific PTP1B deletion, and brown adipocytes deficient in PTP1B and reconstituted with PTP1B wild type (WT) or the substrate-trapping PTP1B D181A (D/A) mutant. PTP1B deficiency led to upregulation of PERK-eIF2α phosphorylation and IRE1α-XBP1 sub-arms of the unfolded protein response. In addition, PTP1B deficiency sensitized differentiated brown adipocytes to chemical-induced ER stress. Moreover, PERK activation and tyrosine phosphorylation were increased in BAT and adipocytes lacking PTP1B. Increased PERK activity resulted in the induction of eIF2α phosphorylation at Ser51 and better translatability of ATF4 mRNA in response to ER stress. At the molecular level, we demonstrate direct interaction between PTP1B and PERK and identify PERK Tyr615 as a mediator of this association. ConclusionsCollectively, the data demonstrate that PTP1B is a physiologically-relevant modulator of ER stress in brown adipocytes and that PTP1B deficiency modulates PERK-eIF2α phosphorylation and protein synthesis.

背景：蛋白质酪氨酸磷酸酶1B（Protein-tyrosine phosphatase 1B, PTP1B）是葡萄糖稳态与体质量的生理性调节因子，且与内质网（endoplasmic reticulum, ER）应激密切相关。本研究旨在探讨PTP1B在棕色脂肪细胞内质网应激中的作用——棕色脂肪细胞是产热与代谢应答的关键调节因子。
材料与方法/主要研究结果：为明确PTP1B在内质网应激中的功能，我们使用了脂肪组织特异性PTP1B敲除小鼠的棕色脂肪组织（brown adipose tissue, BAT），以及PTP1B缺陷并分别重组野生型（wild type, WT）PTP1B或底物捕获型PTP1B D181A（D/A）突变体的棕色脂肪细胞。研究发现，PTP1B缺陷会导致未折叠蛋白反应的PERK-eIF2α磷酸化通路与IRE1α-XBP1信号分支上调。此外，PTP1B缺陷会使已分化的棕色脂肪细胞对化学诱导的内质网应激敏感性升高。进一步检测发现，在缺乏PTP1B的棕色脂肪组织与脂肪细胞中，PERK的激活与酪氨酸磷酸化水平均升高。PERK活性增强可促使eIF2α在Ser51位点发生磷酸化，并提升ATF4 mRNA在面对内质网应激时的翻译效率。在分子层面，我们证实PTP1B与PERK存在直接相互作用，并确定PERK Tyr615是二者结合的介导位点。
结论：综上，本研究数据表明，PTP1B是棕色脂肪细胞内质网应激的生理性调控因子，PTP1B缺陷可调控PERK-eIF2α磷酸化水平与蛋白质合成过程。