Role of PERK/eIF2α/CHOP Endoplasmic Reticulum Stress Pathway in Oxidized Low-density Lipoprotein Mediated Induction of Endothelial Apoptosis

Objective PERK/eI F2α/CHOP is a major signaling pathway mediating endoplasmic reticulum(ER) stress related with atherosclerosis.Oxidized LDL(ox-LDL) also induces endothelial apoptosis and plays a vital role in the initiation and progression of atherosclerosis.The present study was conducted to explore the regulatory effect of ox-LDL on PERK/e IF2α/CHOP signaling pathway in vascular endothelial cells.Methods The effects of ox-LDL on PERK and p-e IF2α protein expression of primary human umbilical vein endothelial cells(HUVECs) were investigated by Western blot analysis.PERK gene silencing and selective eI F2α phosphatase inhibitor,salubrinal were used to inhibit the process of ox-LDL induced endothelial cell apoptosis,caspase-3 activity,and CHOP mR NA level.Results Ox-LDL treatment significantly increased the expression of PERK,PERK-mediated inactivation of e IF2α phosphorylation,and the expression of CHOP,as well as the caspase-3 activity and apoptosis.The effects of ox-LDL were markedly decreased by knocking down PERK with stable transduction of lentiviral sh RNA or by selective eI F2α phosphatase inhibitor,salubrinal.Conclusion This study provides the first evidence that ox-LDL induces apoptosis in vascular endothelial cells mediated largely via the PERK/eI F2α/CHOP ER-stress pathway.It adds new insights into the molecular mechanisms underlying the pathogenesis and progression of atherosclerosis.     

The unfolded protein response is activated in Alzheimer’s disease

Alzheimers disease (AD) is, at the neuropathological level, characterized by the accumulation and aggregation of misfolded proteins. The presence of misfolded proteins in the endoplasmic reticulum (ER) triggers a cellular stress response called the unfolded protein response (UPR) that may protect the cell against the toxic buildup of misfolded proteins. In this study we investigated the activation of the UPR in AD. Protein levels of BiP/GRP78, a molecular chaperone which is up-regulated during the UPR, was found to be increased in AD temporal cortex and hippocampus as determined by Western blot analysis. At the immunohistochemical level intensified staining of BiP/GRP78 was observed in AD, which did not co-localize with AT8-positive neurofibrillary tangles. In addition, we performed immunohistochemistry for phosphorylated (activated) pancreatic ER kinase (p-PERK), an ER kinase which is activated during the UPR. p-PERK was observed in neurons in AD patients, but not in non-demented control cases and did not co-localize with AT8-positive tangles. Overall, these data show that the UPR is activated in AD, and the increased occurrence of BiP/GRP78 and p-PERK in cytologically normal-appearing neurons suggest a role for the UPR early in AD neurodegeneration. Although the initial participation of the UPR in AD pathogenesis might be neuroprotective, sustained activation of the UPR in AD might initiate or mediate neurodegeneration.     

Endoplasmic reticulum stress is activated in light-induced retinal degeneration

Exposure to excessive levels of light induces photoreceptor apoptosis and has previously been used as a model for the study of retinal degeneration. During the light exposure, intracellular calcium levels increase, and reactive oxygen species (ROS) are generated, which have been shown to cause endoplasmic reticulum (ER) stress. In the present study, we investigated the role of ER stress in light-induced photoreceptor apoptosis. Our study demonstrated that, after light exposure, the ER stress sensors including glucose-regulated protein-78 (GRP78/BiP), caspase-12, phospho-eukaryotic initiation factor 2 alpha (eIF2 alpha), and phospho-pancreatic ER kinase (PERK) were significantly up-regulated in a time-dependent manner. The up-regulation of these proteins coincided with or preceded the photoreceptor apoptosis indicated by TUNEL. These data showed that ER stress played an important role in light-induced photoreceptor apoptosis. Therefore, ER stress modulators could be strong candidates as therapeutic agents in the treatment of retinal degenerative diseases.     

Sorafenib,a multikinase inhibitor,induces formation of stress granules in hepatocarcinoma cells

Stress granules (SGs) are cytoplasmic RNA multimeric bodies that form under stress conditions known to inhibit translation initiation. In most reported stress cases, the formation of SGs was associated with the cell recovery from stress and survival. In cells derived from cancer, SGs formation was shown to promote resistance to either proteasome inhibitors or 5-Fluorouracil used as chemotherapeutic agents. Despite these studies, the induction of SGs by chemotherapeutic drugs contributing to cancer cells resistance is still understudied. Here we identified sorafenib, a tyrosine kinase inhibitor used to treat hepatocarcinoma, as a potent chemotherapeutic inducer of SGs. The formation of SGs in sorafenib-treated hepatocarcionoma cells correlates with inhibition of translation initiation; both events requiring the phosphorylation of the translation initiation factor eIF2α. Further characterisation of the mechanism of sorafenib-induced SGs revealed PERK as the main eIF2α kinase responsible for SGs formation. Depletion experiments support the implication of PERK-eIF2α-SGs pathway in hepatocarcinoma cells resistance to sorafenib. This study also suggests the existence of an unexpected complex regulatory balance between SGs and phospho-eIF2α where SGs dampen the activation of the phospho-eIF2α-downstream ATF4 cell death pathway.