scholarly journals Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death

2011 ◽  
Vol 441 (2) ◽  
pp. 685-696 ◽  
Author(s):  
Deborah L. Duricka ◽  
R. Lane Brown ◽  
Michael D. Varnum
Keyword(s):  
Cell Death ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Apoptotic Cell ◽  
Cone Photoreceptor ◽  
Loss Of Function ◽  
Cellular Mechanisms ◽  
Unfolded Protein ◽  
Degradation Rates ◽  
Protein Response

Mutations that perturb the function of photoreceptor CNG (cyclic nucleotide-gated) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the ER (endoplasmic reticulum) is known to cause ER stress and trigger the UPR (unfolded protein response), an evolutionarily conserved cellular programme that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared with wild-type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones {TUDCA (tauroursodeoxycholate sodium salt), 4-PBA (sodium 4-phenylbutyrate) and the cGMP analogue CPT-cGMP [8-(4-chlorophenylthio)-cGMP]} differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER-stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization-defective CNG channels, and may represent a contributing factor for photoreceptor degeneration.

scholarly journals Opposing unfolded-protein-response signals converge on death receptor 5 to control apoptosis

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 98-101 ◽  
Author(s):  
Min Lu ◽  
David A. Lawrence ◽  
Scot Marsters ◽  
Diego Acosta-Alvear ◽  
Philipp Kimmig ◽  
...  
Keyword(s):  
Er Stress ◽  
Unfolded Protein Response ◽  
Cell Fate ◽  
Apoptotic Cell ◽  
Death Receptor ◽  
Caspase 8 ◽  
Death Receptor 5 ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response

Protein folding by the endoplasmic reticulum (ER) is physiologically critical; its disruption causes ER stress and augments disease. ER stress activates the unfolded protein response (UPR) to restore homeostasis. If stress persists, the UPR induces apoptotic cell death, but the mechanisms remain elusive. Here, we report that unmitigated ER stress promoted apoptosis through cell-autonomous, UPR-controlled activation of death receptor 5 (DR5). ER stressors induced DR5 transcription via the UPR mediator CHOP; however, the UPR sensor IRE1α transiently catalyzed DR5 mRNA decay, which allowed time for adaptation. Persistent ER stress built up intracellular DR5 protein, driving ligand-independent DR5 activation and apoptosis engagement via caspase-8. Thus, DR5 integrates opposing UPR signals to couple ER stress and apoptotic cell fate.

Modulation of ER Stress/Unfolded Protein Response (UPR) Pathways in Multiple Myeloma Cells by Inhibition of Hsp90 and Serine-Threonine Kinase CK2.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3840-3840
Author(s):  
Francesco Piazza ◽  
Sabrina Manni ◽  
Carmela Gurrieri ◽  
Anna Colpo ◽  
Laura Quotti Tubi ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Cell Death ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Hsp90 Inhibitors ◽  
Hsp90 Inhibition ◽  
Protein Levels ◽  
Unfolded Protein ◽  
Protein Response ◽  
Kinase Ck2

Abstract Abstract 3840 Poster Board III-776 Hsp90 is an essential chaperone molecule that helps in the maturation and folding of a number of cellular client proteins. Hsp90 function is essential for malignant plasma cell survival, since its inhibition in multiple myeloma (MM) cells results in cell death and activation of apoptosis. Clinical trials using Hsp90 inhibitors are currently ongoing in MM patients. Hsp90 inactivation in MM cells causes perturbation of the endoplasmic reticulum (ER) stress/unfolded protein response (UPR), eventually triggering the apoptotic cascades. Protein kinase CK2 critically regulates the activity of the chaperone complex formed by the Cdc37 and Hsp90 proteins. We already described that CK2 is over-expressed in a fraction of MM patients and is an essential MM pro-survival molecule. We have here investigated its role in the ER stress/UPR pathways and in Hsp90 inhibition-induced apoptosis in MM cells. Down-regulation of the catalytic CK2 alpha subunit with selective chemical inhibitors or RNA interference resulted in significant modifications of the main UPR regulating signaling cascades: 1) a marked reduction of IRE1alpha protein levels; 2) a reduction of BiP/GRP78 and Hsp70 chaperone protein levels; 3) an increase of PERK activity and phospho eIF2alpha levels. When UPR was triggered by thapsigargin in CK2-inactivated cells, we observed that the IRE1alpha-dependent axis of the UPR was greatly impaired, as XBP-1short isoform generation and the levels of some induced chaperones were reduced. Interestingly, thapsigargin was able to induce CK2 kinase activity. Remarkably, treatment of CK2-silenced MM cells with Hsp90 inhibitors geldanamycin or its derivative 17-AAG (17-(demethoxy)-17-allylamino geldanamycin) resulted in 1) an even more pronounced reduction of IRE1 alpha protein levels; 2) a marked inhibition of GA or 17-AAG-triggered BiP/GRP78 protein level raise; 3) a more evident increase of eIF2 alpha phosphorylation. Of note, CK2 plus Hsp90 inhibition was followed by apoptotic cell death to a much greater extent than that obtained with the single inhibition of the two molecules. Noteworthy, these effects were also reproduced upon modelling the MM bone marrow (BM) microenvironment by co-culturing MM cells with BM stromal cells. These data suggest that CK2-mediated signaling regulates the ER stress/UPR pathways and modulates the threshold to apoptosis of ER stressed MM cells. CK2 interacts with Hsp90, since its inhibition synergizes with GA or 17-AAG treatments in terms of induction of apoptosis and shift of the ER stress/UPR pathways towards the terminal phase. These results might be useful to set the groundwork in designing novel combination treatments for MM patients. Disclosures: No relevant conflicts of interest to declare.

scholarly journals ATR-101, a Selective and Potent Inhibitor of Acyl-CoA Acyltransferase 1, Induces Apoptosis in H295R Adrenocortical Cells and in the Adrenal Cortex of Dogs

Endocrinology ◽  
2016 ◽  
Vol 157 (5) ◽  
pp. 1775-1788 ◽  
Author(s):  
Christopher R. LaPensee ◽  
Jacqueline E. Mann ◽  
William E. Rainey ◽  
Valentina Crudo ◽  
Stephen W. Hunt ◽  
...  
Keyword(s):  
Cell Death ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Adrenal Cortex ◽  
Caspase 3 ◽  
Potent Inhibitor ◽  
Adrenocortical Cell ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response

Abstract ATR-101 is a novel, oral drug candidate currently in development for the treatment of adrenocortical cancer. ATR-101 is a selective and potent inhibitor of acyl-coenzyme A:cholesterol O-acyltransferase 1 (ACAT1), an enzyme located in the endoplasmic reticulum (ER) membrane that catalyzes esterification of intracellular free cholesterol (FC). We aimed to identify mechanisms by which ATR-101 induces adrenocortical cell death. In H295R human adrenocortical carcinoma cells, ATR-101 decreases the formation of cholesteryl esters and increases FC levels, demonstrating potent inhibition of ACAT1 activity. Caspase-3/7 levels and terminal deoxynucleotidyl transferase 2′-deoxyuridine 5′-triphosphate nick end labeled-positive cells are increased by ATR-101 treatment, indicating activation of apoptosis. Exogenous cholesterol markedly potentiates the activity of ATR-101, suggesting that excess FC that cannot be adequately esterified increases caspase-3/7 activation and subsequent cell death. Inhibition of calcium release from the ER or the subsequent uptake of calcium by mitochondria reverses apoptosis induced by ATR-101. ATR-101 also activates multiple components of the unfolded protein response, an indicator of ER stress. Targeted knockdown of ACAT1 in an adrenocortical cell line mimicked the effects of ATR-101, suggesting that ACAT1 mediates the cytotoxic effects of ATR-101. Finally, in vivo treatment of dogs with ATR-101 decreased adrenocortical steroid production and induced cellular apoptosis that was restricted to the adrenal cortex. Together, these studies demonstrate that inhibition of ACAT1 by ATR-101 increases FC, resulting in dysregulation of ER calcium stores that result in ER stress, the unfolded protein response, and ultimately apoptosis.

scholarly journals Characterization of Stanniocalcin 2, a Novel Target of the Mammalian Unfolded Protein Response with Cytoprotective Properties

2004 ◽  
Vol 24 (21) ◽  
pp. 9456-9469 ◽  
Author(s):  
Daisuke Ito ◽  
John R. Walker ◽  
Charlie S. Thompson ◽  
Isabella Moroz ◽  
William Lin ◽  
...  
Keyword(s):  
Cell Death ◽  
Unfolded Protein Response ◽  
Cortical Neurons ◽  
Apoptotic Cell ◽  
In Vivo Studies ◽  
Unfolded Protein ◽  
Stanniocalcin 2 ◽  
Novel Target ◽  
Protein Response

ABSTRACT Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces a highly conserved homeostatic response in all eukaryotic cells, termed the unfolded-protein response (UPR). Here we describe the characterization of stanniocalcin 2 (STC2), a mammalian homologue of a calcium- and phosphate-regulating hormone first identified in fish, as a novel target of the UPR. Expression of STC2 gene is rapidly upregulated in cultured cells after exposure to tunicamycin and thapsigargin, by ATF4 after activation of the ER-resident kinase PERK. In addition, STC2 expression is also activated in neuronal cells by oxidative stress and hypoxia but not by several cellular stresses unrelated to the UPR. In contrast, expression of another homologue, STC1, is only upregulated by hypoxia independent of PERK or ATF4 expression. In vivo studies revealed that rat cortical neurons rapidly upregulate STC2 after transient middle cerebral artery occlusion. Finally, siRNA-mediated inhibition of STC2 expression renders N2a neuroblastoma cells and HeLa cells significantly more vulnerable to apoptotic cell death after treatment with thapsigargin, and overexpression of STC2 attenuated thapsigargin-induced cell death. Consequently, induced STC2 expression is an essential feature of survival component of the UPR.

scholarly journals Translational and posttranslational regulation of XIAP by eIF2α and ATF4 promotes ER stress–induced cell death during the unfolded protein response

2014 ◽  
Vol 25 (9) ◽  
pp. 1411-1420 ◽  
Author(s):  
Nobuhiko Hiramatsu ◽  
Carissa Messah ◽  
Jaeseok Han ◽  
Matthew M. LaVail ◽  
Randal J. Kaufman ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Death ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Protein Misfolding ◽  
Down Regulation ◽  
Unfolded Protein ◽  
Activity Loss ◽  
The Unfolded Protein Response ◽  
Protein Response

Endoplasmic reticulum (ER) protein misfolding activates the unfolded protein response (UPR) to help cells cope with ER stress. If ER homeostasis is not restored, UPR promotes cell death. The mechanisms of UPR-mediated cell death are poorly understood. The PKR-like endoplasmic reticulum kinase (PERK) arm of the UPR is implicated in ER stress–induced cell death, in part through up-regulation of proapoptotic CCAAT/enhancer binding protein homologous protein (CHOP). Chop−/− cells are partially resistant to ER stress–induced cell death, and CHOP overexpression alone does not induce cell death. These findings suggest that additional mechanisms regulate cell death downstream of PERK. Here we find dramatic suppression of antiapoptosis XIAP proteins in response to chronic ER stress. We find that PERK down-regulates XIAP synthesis through eIF2α and promotes XIAP degradation through ATF4. Of interest, PERK's down-regulation of XIAP occurs independently of CHOP activity. Loss of XIAP leads to increased cell death, whereas XIAP overexpression significantly enhances resistance to ER stress–induced cell death, even in the absence of CHOP. Our findings define a novel signaling circuit between PERK and XIAP that operates in parallel with PERK to CHOP induction to influence cell survival during ER stress. We propose a “two-hit” model of ER stress–induced cell death involving concomitant CHOP up-regulation and XIAP down-regulation both induced by PERK.

Hsp90 Inhibitors Deliver a Death Signal Via the Endoplasmic Reticulum Stress Pathway in Myeloma.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 848-848
Author(s):  
Emma L. Davenport ◽  
Hannah Moore ◽  
Alan Dunlop ◽  
Paul Workman ◽  
Gareth J. Morgan ◽  
...  
Keyword(s):  
Cell Death ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Plasma Cells ◽  
Myeloma Cell ◽  
Misfolded Protein ◽  
Hsp90 Inhibitors ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response

Abstract Immunoglobulin production by plasma cells both defines them functionally and also provides a differential target for the therapy of their malignant counterparts. Plasma cells producing high levels of paraprotein are dependent upon the unfolded protein response (UPR) and chaperone proteins to ensure correct protein folding and cell survival. We have evaluated a strategy aimed at manipulating the UPR response to deliver a novel death signal in myeloma. In order to study the apoptotic effects of the disruption of the UPR, a panel of myeloma cell lines were treated with the ER stress inducers (thapsigargin (TG) a Ca2+-ATPase inhibitor and tunicamycin (TM) an N-linked glycosylation inhibitor); the HSP90 inhibitors, 17-AAG and radicicol; and the proteasome inhibitor bortezomib, which disrupts misfolded protein disposal. The presence of misfolded proteins in the ER is detected by a complex of proteins embedded within the membrane comprised of BiP, PERK, IRE-1 and ATF6, each of which has distinct downstream effects that are mediated by their release from the complex and activation of the UPR. Treatment with TG and TM led to the activation of all three branches of the UPR as demonstrated by early splicing of XBP1 to XBP1s indicative of IRE1 activation, PERK activation as measured by transcriptional upregulation of CHOP (7-22 fold) and ATF6 splicing. 17-AAG was also capable of inducing splicing of XBP1 and the induction of CHOP (30 fold) whereas bortezomib resulted in induction of CHOP (25 fold) and minimal, late onset splicing of XBP1. Following treatment with all the drugs expression levels of BiP mRNA were upregulated (3-10 fold), however due to high basal levels of BiP protein we were unable to detect any further rises in this protein. The ER-resident HSP90 analogue, Grp94, underwent minimal transcriptional upregulation (2–3 fold) in response to HSP90 inhibitors but larger responses were noted following treatment with TM and TG (3–5 fold). HSP90 protein expression remained constant following exposure to all drugs. In contrast a time-dependent upregulation of the anti-apoptotic HSP70 was noted in response to 17-AAG, radicicol and bortezomib treatment; TG and TM failed to affect levels of HSP70. Levels of the transcript of EDEM1, an ER stress inducible membrane protein that accelerates the degradation of misfolded protein in the ER by strengthening the ERAD machinery, were induced by all drugs with an increase in the transcript levels of between 2 and 4 fold after 24 hours. All drugs were capable of inhibiting proliferation as demonstrated by MTT assay. In addition TG, bortezomib, 17AAG and radicicol also induced myeloma cell death as demonstrated by trypan blue and Annexin V/PI staining. A distinct pattern of activation of caspases in response to the drugs was also established. Bortezomib activated both the intrinsic (caspases 9 and 3) and the extrinsic (caspases 8 and 3) caspase pathways, whilst 17-AAG appears to mediate cell death via the intrinsic pathway alone. In contrast, TM and TG failed to activate either the extrinsic or intrinsic pathways within 24 hours and within this time frame appeared to induce cell death by a caspase-independent mechanism. In conclusion as well as inducing apoptosis via the intrinsic caspase death pathway, HSP90 inhibitors also induce myeloma cell death via ER stress and the UPR death pathway. Our results confirm that the unfolded protein response is an exciting new pathway that can be therapeutically targeted in myeloma.

scholarly journals DJ-1 modulates the unfolded protein response and cell death via upregulation of ATF4 following ER stress

2019 ◽  
Vol 10 (2) ◽  
Author(s):  
Jungwoo Yang ◽  
Kwang Soo Kim ◽  
Grace O. Iyirhiaro ◽  
Paul C. Marcogliese ◽  
Steve M. Callaghan ◽  
...  
Keyword(s):  
Cell Death ◽  
Er Stress ◽  
Unfolded Protein Response ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response
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