The mutualistic fungus Piriformospora indica colonizes Arabidopsis roots by inducing an endoplasmic reticulum stress-triggered caspase-dependent cell death

In Arabidopsis thaliana roots, the mutualistic fungus Piriformospora indica initially colonizes living cells, which die as the colonization proceeds. We aimed to clarify the molecular basis of this colonization-associated cell death. Our cytological analyses revealed endoplasmic reticulum (ER) swelling and vacuolar collapse in invaded cells, indicative of ER stress and cell death during root colonization. Consistent with this, P. indica–colonized plants were hypersensitive to the ER stress inducer tunicamycin. By clear contrast, ER stress sensors bZIP60 and bZIP28 as well as canonical markers for the ER stress response pathway, termed the unfolded protein response (UPR), were suppressed at the same time. Arabidopsis mutants compromised in caspase 1–like activity, mediated by cell death–regulating vacuolar processing enzymes (VPEs), showed reduced colonization and decreased cell death incidence. We propose a previously unreported microbial invasion strategy during which P. indica induces ER stress but inhibits the adaptive UPR. This disturbance results in a VPE/caspase 1–like-mediated cell death, which is required for the establishment of the symbiosis. Our results suggest the presence of an at least partially conserved ER stress–induced caspase-dependent cell death pathway in plants as has been reported for metazoans

The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote ER stress resistance

Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (U PR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress

The adaptor protein CRK is a pro-apoptotic transducer of endoplasmic reticulum stress.

Excessive demands on the protein-folding capacity of the endoplasmic reticulum (ER) cause irremediable ER stress and contribute to cell loss in a number of cell degenerative diseases, including type 2 diabetes and neurodegeneration. The signals communicating catastrophic ER damage to the mitochondrial apoptotic machinery remain poorly understood. We used a biochemical approach to purify a cytosolic activity induced by ER stress that causes release of cytochrome c from isolated mitochondria. We discovered that the principal component of the purified pro-apoptotic activity is the proto-oncoprotein CRK (CT10-regulated kinase), an adaptor protein with no known catalytic activity. Crk(-/-) cells are strongly resistant to ER-stress-induced apoptosis. Moreover, CRK is cleaved in response to ER stress to generate an amino-terminal M(r)~14K fragment with greatly enhanced cytotoxic potential. We identified a putative BH3 (BCL2 homology 3) domain within this N-terminal CRK fragment, which sensitizes isolated mitochondria to cytochrome c release and when mutated significantly reduces the apoptotic activity of CRK in vivo. Together these results identify CRK as a pro-apoptotic protein that signals irremediable ER stress to the mitochondrial execution machinery

Novel elucidation and treatment of pancreatic chronic graft-versus-host disease in mice

Chronic graft-versus-host disease (cGVHD) is a severe complication of allogeneic haematopoietic stem cell transplantation. There is a growing understanding of cGVHD, and several effective therapies for cGVHD have been reported. However, pancreatic cGVHD is a potentially untapped study field. Our thought-provoking study using a mouse model of cGVHD suggested that the pancreas could be impaired by cGVHD-induced inflammation and fibrosis and that endoplasmic reticulum (ER) stress was augmented in the pancreas affected by cGVHD. These findings urged us to treat pancreatic cGVHD through reduction of ER stress, and we used 4-phenylbutyric acid (PBA) as an ER stress reducer. A series of experiments have indicated that PBA can suppress cGVHD-elicited ER stress in the pancreas and accordingly alleviate pancreatic cGVHD. Furthermore, we focused on a correlation between epithelial to mesenchymal transition (EMT) and fibrosis in the cGVHD-affected pancreas, because EMT was conceivably implicated in various fibrosis-associated diseases. Our investigation has suggested that the expression of EMT markers was increased in the cGVHD-disordered pancreas and that it could be reduced by PBA. Taken together, we have provided a clue to elucidate the pathogenic process of pancreatic cGVHD and created a potentially effective treatment of this disease using the ER stress alleviator PBA

Sirtuin1 protects endothelial Caveolin-1 expression and preserves endothelial function via suppressing miR-204 and endoplasmic reticulum stress.

Sirtuin1 (Sirt1) is a class III histone deacetylase that regulates a variety of physiological processes, including endothelial function. Caveolin1 (Cav1) is also an important determinant of endothelial function. We asked if Sirt1 governs endothelial Cav1 and endothelial function by regulating miR-204 expression and endoplasmic reticulum (ER) stress. Knockdown of Sirt1 in endothelial cells, and in vivo deletion of endothelial Sirt1, induced endothelial ER stress and miR-204 expression, reduced Cav1, and impaired endothelium-dependent vasorelaxation. All of these effects were reversed by a miR-204 inhibitor (miR-204 I) or with overexpression of Cav1. A miR-204 mimic (miR-204 M) decreased Cav1 in endothelial cells. In addition, high-fat diet (HFD) feeding induced vascular miR-204 and reduced endothelial Cav1. MiR-204-I protected against HFD-induced downregulation of endothelial Cav1. Moreover, pharmacologic induction of ER stress with tunicamycin downregulated endothelial Cav1 and impaired endothelium-dependent vasorelaxation that was rescued by overexpressing Cav1. In conclusion, Sirt1 preserves Cav1-dependent endothelial function by mitigating miR-204-mediated vascular ER stress

Targeting ER stress/ER stress response in myopathies

none1no: There is more skeletal muscle tissue in the body than any other tissue and, as it is the organ of the majority of metabolic activity, muscle defect can affect the health of the entire body. Endoplasmic reticulum (ER) stress due to defects in protein folding/degradation balance, altered calcium and lipid levels and alterations in ER-mitochondria contacts has recently been recognised as the pathogenic cause of many different myopathies. In addition, a maladaptive ER stress response triggered by ER stress and mediated by three ER stress sensors (PERK, IRE1 and ATF6) is involved in a failure to relieve muscle tissue from this stress. Targeting ER stress and the ER stress response pathway offers a broad range of opportunities for treating myopathies but, as the inhibition of the three ER stress sensors may not be safe because it could lead to unexpected effects; it therefore calls for careful analysis of the changes in downstream signal transduction in the different myopathies so these sub-pathways can be pharmacologically targeted. This review summarises the known inhibitors of the ER stress response and the successful results obtained using some of them in mouse models of muscle diseases caused by ER stress/ER stress response.openZito, EsterZito, Este

The Induction of Dendritic Cell Endoplasmic Reticulum Stress by Irradiated-Tumor Derived Extracellular Vesicles Supports the Adoption of a Pro-Tumor Phenotype

The Induction of Macrophage Endoplasmic Reticulum Stress by Irradiated-Tumor Derived Extracellular Vesicles Supports the Adoption of a Pro-Tumor Phenotype Sitara Mahmoodi, Depts. of Biology and Chemistry, with Dr. Sarah Golding, Dept. of Biology Recent studies have shown that long term exposure of tumor cells to sub-lethal levels of endoplasmic reticulum (ER) stress leads to the suppression of anti-tumor immunity through the manipulation of myeloid cells in the tumor microenvironment.1 While this effect seems to be dependent upon the ability of cancer cells to “transfer” the state of ER stress to myeloid cells, i.e. to initiate ER stress signaling in myeloid cells independent of the original stimulus, exactly how stressed cancer cells accomplish this is still not well understood1. Our focus is on exosomes which are extracellular vesicles and how they play a significant role in this mechanism. In recent studies, we demonstrated how extracellular vesicles secreted by irradiated melanoma cancer cells (IR-EVs) induce ER stress in Bone Marrow Dendritic Cells (BMDCs). In addition, BMDCs treated with IR-EVs demonstrated enhanced STAT3 and p38 signaling, two related pathways that have been demonstrated to induce tolerogenic DC phenotypes, in an ER stress dependent manner2. We have also found that IR- EVs stimulate the production of IL-10, a major negative regulator of antitumor immunity, from BMDCs and that this expression can be eliminated by STAT3 inhibition2. However, using a T-Cell Receptor/ tumor- associated antigen (TCR/TAA) system to model the interaction between BMDCs and cytotoxic T cells from a tumor rejection antigen (Pmel/gp100), we have observed that pharmaceutical ER stress or STAT3 inhibition dramatically inhibits T cell proliferation and IFN-gamma expression in response to antigen pulsed BMDCs. This suggests that ER stress and STAT3 signaling are both necessary for the presentation of tumor antigens to cytotoxic T cells, indicating that inhibition of these pathways would not be a desirable approach to enhance antitumor immunity in vivo. Thus, our current focus is on finding a way to inhibit the production or activity of these IR-EVs directly, inhibiting their effects on DCs in the body while leaving STAT3 signaling in proliferating T cells unaltered.https://scholarscompass.vcu.edu/uresposters/1346/thumbnail.jp

Endoplasmic reticulum stress, degeneration of pancreatic islet β-cells, and therapeutic modulation of the unfolded protein response in diabetes.

BackgroundMyriad challenges to the proper folding and structural maturation of secretory pathway client proteins in the endoplasmic reticulum (ER) - a condition referred to as "ER stress" - activate intracellular signaling pathways termed the unfolded protein response (UPR).Scope of reviewThrough executing transcriptional and translational programs the UPR restores homeostasis in those cells experiencing manageable levels of ER stress. But the UPR also actively triggers cell degeneration and apoptosis in those cells that are encountering ER stress levels that exceed irremediable thresholds. Thus, UPR outputs are "double-edged". In pancreatic islet β-cells, numerous genetic mutations affecting the balance between these opposing UPR functions cause diabetes mellitus in both rodents and humans, amply demonstrating the principle that the UPR is critical for the proper functioning and survival of the cell.Major conclusionsSpecifically, we have found that the UPR master regulator IRE1α kinase/endoribonuclease (RNase) triggers apoptosis, β-cell degeneration, and diabetes, when ER stress reaches critical levels. Based on these mechanistic findings, we find that novel small molecule compounds that inhibit IRE1α during such "terminal" UPR signaling can spare ER stressed β-cells from death, perhaps affording future opportunities to test new drug candidates for disease modification in patients suffering from diabetes