Role Of Endoplasmic Reticulum Stress Response Research Articles

ROOT HAIR DEFECTIVE3 Is a Receptor for Selective Autophagy of the Endoplasmic Reticulum in Arabidopsis.

ROOT HAIR DEFECTIVE3 (RHD3) is a plant member of atlastin GTPases, which belong to an evolutionally conserved family of proteins that mediate the homotypic fusion of the endoplasmic reticulum (ER). An atlastin in mammalian cells has recently been shown to act as an ER-phagy receptor for selective autophagy of the ER (ER-phagy) during nutrient starvation. Although RHD3 has been indicated to play a role in ER stress response, it is not very clear how RHD3 is involved in the process. In this study, we showed that the rhd3 mutant is hyposensitive to ER as well as salt stress. We employed an YFP-tagged ER membrane marker YFP-TMC to monitor the efficiency of ER-phagy microscopically and biochemically. We found that rhd3 is defective in ER-phagy under ER stress. Furthermore, there is an increased association of YFP-RHD3 with ATG8e-marked autophagosomes. YFP-RHD3 is also visible with ATG8e in the vacuole, and there is a breakdown of YFP-RHD3 under ER stress. RHD3 has two putative ATG8 interaction motifs (AIM1-2). We revealed that RHD3 but not RHD3(ΔAIM1) physically interacts with ATG8, a core autophagosomal component that interacts with various receptor proteins to recruit cargos for degradation by selective autophagy. Furthermore, their interaction is enhanced under ER stress. We thus propose that RHD3 acts as an ER-phagy receptor under ER stress to promote ER-phagy in Arabidopsis.

20-O-(β-D-glucopyranosyl)-20(S)-protopanaxadiol induces apoptosis via induction of endoplasmic reticulum stress in human colon cancer cells

Previously, we reported that 20-O-(β-D-gluco-pyranosyl)-20(S)-protopanaxadiol (Compound K, a meta-bolite of ginseng saponin) induces mitochondria-dependent and caspase-dependent apoptosis in HT-29 human colon cancer cells via the generation of reactive oxygen species. The aim of the present study was to elucidate the mechanism underlying apoptosis induced by Compound K with respect to endoplasmic reticulum (ER) stress in HT-29 cells. In the present study, CompoundK induced apoptotic cell death as confirmed by DNA fragmentation and apoptotic sub-G1 cell population. Compound K also induced ER stress as indicated by staining with ER tracker, cytosolic and mitochondrial Ca2+ overloading, phosphorylation of protein-kinase-like endoplasmic reticulum kinase (PERK), phosphorylation of eukaryotic initiation factor-2α (eIF-2α), phosphorylation of IRE-1, splicing of ER stress-specific X-box transcription factor-1 (XBP-1), cleavage of activating transcription factor-6 (ATF-6), upregulation of glucose-regulated protein-78 (GRP-78/BiP) and CCAAT/enhancer-binding protein-homologous protein (CHOP), and cleavage of caspase-12. Furthermore, downregulation of CHOP expression using siCHOP RNA attenuated CompoundK-induced apoptosis. Taken together, these results support the important role of ER stress response in mediating CompoundK-induced apoptosis in human colon cancer cells.

Role of ER Stress Response in Photodynamic Therapy: ROS Generated in Different Subcellular Compartments Trigger Diverse Cell Death Pathways

We have analyzed the molecular mechanisms of photoinduced cell death using porphyrins with similar structure differing only in the position of the ethylene glycol (EG) chain on the phenyl ring. Meta- and para-positioned EG chains targeted porphyrins to different subcellular compartments. After photoactivation, both types of derivatives induced death of tumor cells via reactive oxygen species (ROS). Para derivatives pTPP(EG)4 and pTPPF(EG)4 primarily accumulated in lysosomes activated the p38 MAP kinase cascade, which in turn induced the mitochondrial apoptotic pathway. In contrast, meta porphyrin derivative mTPP(EG)4 localized in the endoplasmic reticulum (ER) induced dramatic changes in Ca2+ homeostasis manifested by Ca2+ rise in the cytoplasm, activation of calpains and stress caspase-12 or caspase-4. ER stress developed into unfolded protein response. Immediately after irradiation the PERK pathway was activated through phosphorylation of PERK, eIF2α and induction of transcription factors ATF4 and CHOP, which regulate stress response genes. PERK knockdown and PERK deficiency protected cells against mTPP(EG)4-mediated apoptosis, confirming the causative role of the PERK pathway.

Nonimmune mechanisms of muscle damage in myositis: role of the endoplasmic reticulum stress response and autophagy in the disease pathogenesis

Recent literature in inflammatory myopathies suggests that both immune (cell-mediated and humoral) and nonimmune [endoplasmic reticulum (ER) stress and autophagy] mechanisms play a role in muscle fiber damage and dysfunction. This review describes these findings and discusses their relevance to disease pathogenesis and therapy. Recent studies highlight the role of ER stress response, especially the roles of hexose-6-phosphate dehydrogenase and ER-anchored RING finger E3 ligase in the activation of unfolded protein response and the formation of vacuoles and inclusions in myopathies. Several studies investigated the link between inflammation and the beta-amyloid-associated muscle fiber degeneration and loss of muscle function. Likewise, the roles of ER stress and autophagy in skeletal muscle damage have been explored in multiple muscle diseases. Current data indicate that the ER stress, nuclear factor-kappaB pathway and autophagy are active in the skeletal muscle of myositis patients, and the proinflammatory nuclear factor-kappaB pathway connects the immune and nonimmune pathways of muscle damage. The relative contributions of each of these pathways to muscle fiber damage are currently unclear. Therefore, further defining the role of these pathways in disease pathogenesis should help to design effective therapeutic agents for these diseases.

The structure of the conserved neurotrophic factors MANF and CDNF explains why they are bifunctional

We have solved the structures of mammalian mesencephalic astrocyte-derived neurotrophic factor (MANF) and conserved dopamine neurotrophic factor (CDNF). CDNF protects and repairs midbrain dopaminergic neurons in vivo; MANF supports their survival in culture and is also cytoprotective against endoplasmic reticulum (ER) stress. Neither protein structure resembles any known growth factor but the N-terminal domain is a saposin-like lipid-binding domain. MANF and CDNF may thus bind lipids or membranes. Consistent with this, there are two patches of conserved lysines and arginines. The natively unfolded MANF C-terminus contains a CKGC disulphide bridge, such as reductases and disulphide isomerases, consistent with a role in ER stress response. The structure thus explains why MANF and CDNF are bifunctional; neurotrophic activity may reside in the N-terminal domain and ER stress response in the C-terminal domain. Finally, we identified three changes, (MANF)I10-->K(CDNF), (MANF)E79-->M(CDNF) and (MANF)K88-->L(CDNF), that may account for the biological differences between the proteins.

Endoplasmic Reticulum Stress Signal Mediators Are Targets of Selenium Action

A monomethylated selenium metabolite, called methylseleninic acid (MSA), has recently been shown to cause global thiol redox modification of proteins. These changes represent a form of cellular stress due to protein misfolding or unfolding. An accumulation of aberrantly folded proteins in the endoplasmic reticulum (ER) triggers a defined set of transducers to correct the defects or commit the cells to apoptosis if the rescue effort is exhausted. Treatment of PC-3 human prostate cancer cells with MSA was found to induce a number of signature ER stress markers: (a) the survival/rescue molecules such as phosphorylated protein kinase-like ER-resident kinase (phospho-PERK), phosphorylated eukaryotic initiation factor-2alpha (phospho-eIF2alpha), glucose-regulated protein (GRP)-78, and GRP94; and (b) the apoptotic molecules such as caspase-12, caspase-7, and CAAT/enhancer binding protein homologous protein or growth arrest DNA damage-inducible gene 153 (CHOP/GADD153). Additional evidence suggested that CHOP/GADD153 might be an important transcription factor in apoptosis induction by MSA. In general, a higher concentration of MSA was required to elicit the apoptotic markers compared with the rescue markers. The apoptotic markers increased proportionally with the dose of MSA, whereas the rescue markers failed to keep pace with the increasing challenge from MSA. GRP78 is the rheostat of the ER stress transducers. In GRP78-overexpressing cells, the ability of MSA to up-regulate phospho-PERK, phospho-eIF2alpha, GRP94, caspase-12, caspase-7, and CHOP/GADD153 was significantly muted. A generous supply of GRP78 would allow cells to cope better with ER stress, thereby improving the odds for survival and negating the commitment to apoptotic death. The present study thus provides strong evidence to support an important role of ER stress response in mediating the anticancer effect of selenium.