bims-unfpre Biomed News
on Unfolded protein response
Issue of 2019‒12‒08
twelve papers selected by
Susan Logue
University of Manitoba

  1. J Biol Chem. 2019 Dec 02. pii: jbc.RA119.008336. [Epub ahead of print]
    Hiramatsu N, Chiang K, Aivati C, Rodvold JJ, Lee JM, Han J, Chea L, Zanetti M, Koo EH, Lin JH.
      Endoplasmic reticulum (ER) stress activates the unfolded protein response (UPR), which reduces levels of misfolded proteins.  However, if ER homeostasis is not restored and the UPR remains chronically activated, cells undergo apoptosis.  The UPR regulator, PKR-like endoplasmic reticulum kinase (PERK), plays an important role in promoting cell death when persistently activated; however, the underlying mechanisms are poorly understood.  Here, we profiled the microRNA (miRNA) transcriptome in human cells exposed to ER stress and identified miRNAs that are selectively induced by PERK signaling.  We found that expression of a PERK-induced miRNA, miR-483, promotes apoptosis in human cells.  miR-483 induction was mediated by a transcription factor downstream of PERK, activating transcription factor 4 (ATF4) but not by the CHOP transcription factor.  We identified the creatine kinase, brain-type (CKB) gene, encoding an enzyme that maintains cellular ATP reserves through phosphocreatine production, as being repressed during the UPR and targeted by miR-483.  We found that ER stress, selective PERK activation, and CKB knockdown all decrease cellular ATP levels, leading to increased vulnerability to ER stress-induced cell death.  Our findings identify miR-483 as a downstream target of the PERK branch of the UPR.  We propose that disruption of cellular ATP homeostasis through miR-483-mediated CKB silencing promotes ER stress-induced apoptosis.
    Keywords:  Activating Transcription Factor-4 (ATF-4); PKR-like endoplasmic reticulum kinase (PERK); endoplasmic reticulum (ER); endoplasmic reticulum stress (ER stress); microRNA (miRNA); stress response; translation; translation control; unfolded protein response (UPR)
  2. PLoS Pathog. 2019 Dec 02. 15(12): e1008185
    Johnston BP, Pringle ES, McCormick C.
      Herpesviruses usurp host cell protein synthesis machinery to convert viral mRNAs into proteins, and the endoplasmic reticulum (ER) to ensure proper folding, post-translational modification and trafficking of secreted and transmembrane viral proteins. Overloading ER folding capacity activates the unfolded protein response (UPR), whereby sensor proteins ATF6, PERK and IRE1 initiate a stress-mitigating transcription program that accelerates catabolism of misfolded proteins while increasing ER folding capacity. Kaposi's sarcoma-associated herpesvirus (KSHV) can be reactivated from latency by chemical induction of ER stress, which causes accumulation of the XBP1s transcription factor that transactivates the viral RTA lytic switch gene. The presence of XBP1s-responsive elements in the RTA promoter suggests that KSHV evolved a mechanism to respond to ER stress. Here, we report that ATF6, PERK and IRE1 were activated upon reactivation from latency and required for efficient KSHV lytic replication; genetic or pharmacologic inhibition of each UPR sensor diminished virion production. Despite UPR sensor activation during KSHV lytic replication, downstream UPR transcriptional responses were restricted; 1) ATF6 was cleaved to activate the ATF6(N) transcription factor but ATF6(N)-responsive genes were not transcribed; 2) PERK phosphorylated eIF2α but ATF4 did not accumulate; 3) IRE1 caused XBP1 mRNA splicing, but XBP1s protein did not accumulate and XBP1s-responsive genes were not transcribed. Ectopic expression of the KSHV host shutoff protein SOX did not affect UPR gene expression, suggesting that alternative viral mechanisms likely mediate UPR suppression during lytic replication. Complementation of XBP1s deficiency during KSHV lytic replication inhibited virion production in a dose-dependent manner in iSLK.219 cells but not in TREx-BCBL1-RTA cells. However, genetically distinct KSHV virions harvested from these two cell lines were equally susceptible to XBP1s restriction following infection of naïve iSLK cells. This suggests that cell-intrinsic properties of BCBL1 cells may circumvent the antiviral effect of ectopic XBP1s expression. Taken together, these findings indicate that while XBP1s plays an important role in reactivation from latency, it can inhibit virus replication at a later step, which the virus overcomes by preventing its synthesis. These findings suggest that KSHV hijacks UPR sensors to promote efficient viral replication while sustaining ER stress.
  3. J Biochem. 2019 Dec 02. pii: mvz101. [Epub ahead of print]
    Chamberlain N, Anathy V.
      Protein folding within the endoplasmic reticulum (ER) exists in a delicate balance; perturbations of this balance can overload the folding capacity of the ER and disruptions of ER homeostasis is implicated in numerous diseases. The unfolded protein response (UPR), a complex adaptive stress response, attempts to restore normal proteostasis, in part, through the up-regulation of various foldases and chaperone proteins including redox-active protein disulfide isomerases (PDIs). There are currently over 20 members of the PDI family each consisting of varying numbers of thioredoxin-like domains which, generally, assist in oxidative folding and disulfide bond rearrangement of peptides. While there is a large amount of redundancy in client proteins of the various PDIs, the size of the family would indicate more nuanced roles for the individual PDIs. However, the role of individual PDIs in disease pathogenesis remains uncertain. The following review briefly discusses recent findings of ER stress, the UPR, and the role of individual PDIs in various respiratory disease states.
    Keywords:  Disulfide Bond; ER stress; PDI; UPR; pulmonary disease
  4. Cancers (Basel). 2019 Dec 02. pii: E1921. [Epub ahead of print]11(12):
    Mansier O, Prouzet-Mauléon V, Jégou G, Barroso K, Raymundo DP, Chauveau A, Dumas PY, Lagarde V, Turcq B, Pasquet JM, Viallard JF, James C, Praloran V, Voutetakis K, Chatziioannou A, Mahon FX, Chevet E, Lippert E.
      BACKGROUND: Mutations in CALR observed in myeloproliferative neoplasms (MPN) were recently shown to be pathogenic via their interaction with MPL and the subsequent activation of the Janus Kinase - Signal Transducer and Activator of Transcription (JAK-STAT) pathway. However, little is known on the impact of those variant CALR proteins on endoplasmic reticulum (ER) homeostasis.METHODS: The impact of the expression of Wild Type (WT) or mutant CALR on ER homeostasis was assessed by quantifying the expression level of Unfolded Protein Response (UPR) target genes, splicing of X-box Binding Protein 1 (XBP1), and the expression level of endogenous lectins. Pharmacological and molecular (siRNA) screens were used to identify mechanisms involved in CALR mutant proteins degradation. Coimmunoprecipitations were performed to define more precisely actors involved in CALR proteins disposal.
    RESULTS: We showed that the expression of CALR mutants alters neither ER homeostasis nor the sensitivity of hematopoietic cells towards ER stress-induced apoptosis. In contrast, the expression of CALR variants is generally low because of a combination of secretion and protein degradation mechanisms mostly mediated through the ER-Associated Degradation (ERAD)-proteasome pathway. Moreover, we identified a specific ERAD network involved in the degradation of CALR variants.
    CONCLUSIONS: We propose that this ERAD network could be considered as a potential therapeutic target for selectively inhibiting CALR mutant-dependent proliferation associated with MPN, and therefore attenuate the associated pathogenic outcomes.
    Keywords:  ERAD; MPN; calreticulin; endoplasmic reticulum
  5. Cell Metab. 2019 Dec 03. pii: S1550-4131(19)30615-1. [Epub ahead of print]30(6): 999-1001
    Goncalves RLS, Hotamisligil GS.
      Cells utilize multiple mechanisms to support endoplasmic reticulum (ER) function. The unfolded protein response, UPRER, is engaged during proteotoxic challenges to either mitigate ER stress or promote apoptosis. In a CRISPR-based genetic screen, Schinzel et al. (2019) identified TMEM2 as a mediator of ER stress tolerance independent of the individual branches of the canonical UPRER and linked this path to nematode longevity.
  6. Cell Death Dis. 2019 Dec 02. 10(12): 903
    Jeong MH, Jeong HJ, Ahn BY, Pyun JH, Kwon I, Cho H, Kang JS.
      Endoplasmic reticulum (ER) stress signaling plays a critical role in the control of cell survival or death. Persistent ER stress activates proapoptotic pathway involving the ATF4/CHOP axis. Although accumulating evidences support its important contribution to cardiovascular diseases, but its mechanism is not well characterized. Here, we demonstrate a critical role for PRMT1 in the control of ER stress in cardiomyocytes. The inhibition of PRMT1 augments tunicamycin (TN)-triggered ER stress response in cardiomyocytes while PRMT1 overexpression attenuates it. Consistently, PRMT1 null hearts show exacerbated ER stress and cell death in response to TN treatment. Interestingly, ATF4 depletion attenuates the ER stress response induced by PRMT1 inhibition. The methylation-deficient mutant of ATF4 with the switch of arginine 239 to lysine exacerbates ER stress accompanied by enhanced levels of proapoptotic cleaved Caspase3 and phosphorylated-γH2AX in response to TN. The mechanistic study shows that PRMT1 modulates the protein stability of ATF4 through methylation. Taken together, our data suggest that ATF4 methylation on arginine 239 by PRMT1 is a novel regulatory mechanism for protection of cardiomyocytes from ER stress-induced cell death.
  7. Autophagy. 2019 Dec 03. 1-3
    Cui Y, Parashar S, Ferro-Novick S.
      Endoplasmic reticulum (ER) homeostasis is maintained by the removal of misfolded ER proteins via different quality control pathways. Aggregation-prone proteins, including certain disease-linked proteins, are resistant to conventional ER degradation pathways and require other disposal mechanisms. Reticulophagy is a disposal pathway that uses resident autophagy receptors. How these receptors, which are dispersed throughout the ER network, target a specific ER domain for degradation is unknown. We recently showed in budding yeast, that ER stress upregulates the reticulophagy receptor, triggering its association with the COPII cargo adaptor complex, Sfb3/Lst1-Sec23 (SEC24C-SEC23 in mammals), to discrete sites on the ER. These domains are packaged into phagophores for degradation to prevent the accumulation of protein aggregates in the ER. This unconventional role for Sfb3/Lst1 is conserved in mammals and is independent of its role as a cargo adaptor on the secretory pathway. Our findings may have important therapeutic implications in protein-aggregation linked neurodegenerative disorders.
    Keywords:  Aggregation-prone protein degradation; COPII cargo adaptor; SEC24C-SEC23; Sfb3/Lst1-Sec23; reticulophagy receptor
  8. J Cell Mol Med. 2019 Dec 07.
    Fan CL, Yao ZH, Ye MN, Fu LL, Zhu GN, Dai Y, Yao XS.
      Fuziline, an aminoalcohol-diterpenoid alkaloid derived from Aconiti lateralis radix preparata, has been reported to have a cardioprotective activity in vitro. However, the potential mechanism of fuziline on myocardial protection remains unknown. In this study, we aimed to explore the efficacy and mechanism of fuziline on isoproterenol (ISO)-induced myocardial injury in vitro and in vivo. As a result, fuziline effectively increased cell viability and alleviated ISO-induced apoptosis. Meanwhile, fuziline significantly decreased the production of ROS, maintained mitochondrial membrane potential (MMP) and blocked the release of cytochrome C, suggesting that fuziline could play the cardioprotective role through restoring the mitochondrial function. Fuziline also could suppress ISO-induced endoplasmic reticulum (ER) stress via the PERK/eIF2α/ATF4/Chop pathway. In addition, using ROS scavenger NAC could decrease ISO-induced apoptosis and block ISO-induced ER stress, while PERK inhibitor GSK2606414 did not reduce the production of ROS, indicating that excess production of ROS induced by ISO triggered ER stress. And fuziline protected against ISO-induced myocardial injury by inhibiting ROS-triggered ER stress. Furthermore, fuziline effectively improved cardiac function on ISO-induced myocardial injury in rats. Western blot analysis also showed that fuziline reduced ER stress-induced apoptosis in vivo. Above these results demonstrated that fuziline could reduce ISO-induced myocardial injury in vitro and in vivo by inhibiting ROS-triggered ER stress via the PERK/eIF2α/ATF4/Chop pathway.
    Keywords:  ER stress; ROS; apoptosis; fuziline; isoproterenol
  9. Cell Death Dis. 2019 Dec 04. 10(12): 921
    Li J, Li X, Liu D, Hamamura K, Wan Q, Na S, Yokota H, Zhang P.
      Bone loss in postmenopausal osteoporosis is induced chiefly by an imbalance of bone-forming osteoblasts and bone-resorbing osteoclasts. Salubrinal is a synthetic compound that inhibits de-phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α). Phosphorylation of eIF2α alleviates endoplasmic reticulum (ER) stress, which may activate autophagy. We hypothesized that eIF2α signaling regulates bone homeostasis by promoting autophagy in osteoblasts and inhibiting osteoclast development. To test the hypothesis, we employed salubrinal to elevate the phosphorylation of eIF2α in an ovariectomized (OVX) mouse model and cell cultures. In the OVX model, salubrinal prevented abnormal expansion of rough ER and decreased the number of acidic vesiculars. It regulated ER stress-associated signaling molecules such as Bip, p-eIF2α, ATF4 and CHOP, and promoted autophagy of osteoblasts via regulation of eIF2α, Atg7, LC3, and p62. Salubrinal markedly alleviated OVX-induced symptoms such as reduction of bone mineral density and bone volume fraction. In primary bone-marrow-derived cells, salubrinal increased the differentiation of osteoblasts, and decreased the formation of osteoclasts by inhibiting nuclear factor of activated T-cells cytoplasmic 1 (NFATc1). Live cell imaging and RNA interference demonstrated that suppression of osteoclastogenesis is in part mediated by Rac1 GTPase. Collectively, this study demonstrates that ER stress-autophagy axis plays an important role in OVX mice. Bone-forming osteoblasts are restored by maintaining phosphorylation of eIF2α, and bone-resorbing osteoclasts are regulated by inhibiting NFATc1 and Rac1 GTPase.
  10. Gut. 2019 Dec 02. pii: gutjnl-2019-318483. [Epub ahead of print]
    Powell N, Pantazi E, Pavlidis P, Tsakmaki A, Li K, Yang F, Parker A, Pin C, Cozzetto D, Minns D, Stolarczyk E, Saveljeva S, Mohamed R, Lavender P, Afzali B, Digby-Bell J, Tjir-Li T, Kaser A, Friedman J, MacDonald TT, Bewick GA, Lord GM.
      OBJECTIVE: The functional role of interleukin-22 (IL22) in chronic inflammation is controversial, and mechanistic insights into how it regulates target tissue are lacking. In this study, we evaluated the functional role of IL22 in chronic colitis and probed mechanisms of IL22-mediated regulation of colonic epithelial cells.DESIGN: To investigate the functional role of IL22 in chronic colitis and how it regulates colonic epithelial cells, we employed a three-dimentional mini-gut epithelial organoid system, in vivo disease models and transcriptomic datasets in human IBD.
    RESULTS: As well as inducing transcriptional modules implicated in antimicrobial responses, IL22 also coordinated an endoplasmic reticulum (ER) stress response transcriptional programme in colonic epithelial cells. In the colon of patients with active colonic Crohn's disease (CD), there was enrichment of IL22-responsive transcriptional modules and ER stress response modules. Strikingly, in an IL22-dependent model of chronic colitis, targeting IL22 alleviated colonic epithelial ER stress and attenuated colitis. Pharmacological modulation of the ER stress response similarly impacted the severity of colitis. In patients with colonic CD, antibody blockade of IL12p40, which simultaneously blocks IL12 and IL23, the key upstream regulator of IL22 production, alleviated the colonic epithelial ER stress response.
    CONCLUSIONS: Our data challenge perceptions of IL22 as a predominantly beneficial cytokine in IBD and provide novel insights into the molecular mechanisms of IL22-mediated pathogenicity in chronic colitis. Targeting IL22-regulated pathways and alleviating colonic epithelial ER stress may represent promising therapeutic strategies in patients with colitis.
    Keywords:  ER stress; Interleukin 22; inflammatory bowel disease
  11. J Cell Sci. 2019 Dec 02. pii: jcs232850. [Epub ahead of print]132(23):
    Bhattacharya A, Qi L.
      The recent literature has revolutionized our view on the vital importance of endoplasmic reticulum (ER)-associated degradation (ERAD) in health and disease. Suppressor/enhancer of Lin-12-like (Sel1L)-HMG-coA reductase degradation protein 1 (Hrd1)-mediated ERAD has emerged as a crucial determinant of normal physiology and as a sentinel against disease pathogenesis in the body, in a largely substrate- and cell type-specific manner. In this Review, we highlight three features of ERAD, constitutive versus inducible ERAD, quality versus quantity control of ERAD and ERAD-mediated regulation of nuclear gene transcription, through which ERAD exerts a profound impact on a number of physiological processes.
    Keywords:  Constitutive ERAD; Disease; ERAD substrate, Quality control; Health; Inducible ERAD; Nuclear gene transcription; Quantity control; Sel1L-Hrd1 ERAD
  12. Biol Proced Online. 2019 ;21 22
    Creedican S, Talty A, Fitzgerald SP, Samali A, Richardson C, Gorman AM, Martin K.
      Background: IRE1α-mediated unconventional splicing of XBP1 is emerging as a biomarker in several disease states and is indicative of activation of the unfolded protein response sensor IRE1. Splicing of XBP1 mRNA results in the translation of two distinct XBP1 protein isoforms (XBP1s and XBP1u) which, due to post-translational regulation, do not correlate with mRNA levels. As both XBP1 isoforms are implicated in pathogenic or disease progression mechanisms there is a need for a reliable, clinically applicable method to detect them.Methods: A multiplexed isoform-specific XBP1 array utilising Biochip array technology (BAT™) was assessed for specificity and suitability when using cell protein lysates. The array was applied to RIPA protein lysates from several relevant pre-clinical models with an aim to quantify XBP1 isoforms in comparison with RT-PCR or immunoblot reference methods.
    Results: A novel reliable, specific and sensitive XBP1 biochip was successfully utilised in pre-clinical research. Application of this biochip to detect XBP1 splicing at the protein level in relevant breast cancer models, under basal conditions as well as pharmacological inhibition and paclitaxel induction, confirmed the findings of previous studies. The biochip was also applied to non-adherent cells and used to quantify changes in the XBP1 isoforms upon activation of the NLRP3 inflammasome.
    Conclusions: The XBP1 biochip enables isoform specific quantification of protein level changes upon activation and inhibition of IRE1α RNase activity, using a routine clinical methodology. As such it provides a research tool and potential clinical tool with a quantified, simultaneous, rapid output that is not available from any other published method.
    Keywords:  Protein biochip; Quantitative XBP1 assessment; UPR; XBP1