bims-unfpre Biomed News
on Unfolded protein response
Issue of 2020‒11‒15
nine papers selected by
Susan Logue
University of Manitoba


  1. Front Genet. 2020 ;11 570355
    Oommen D, Kizhakkedath P, Jawabri AA, Varghese DS, Ali BR.
      Familial hypercholesterolemia (FH) is an autosomal genetic disease characterized by high serum low-density lipoprotein (LDL) content leading to premature coronary artery disease. The main genetic and molecular causes of FH are mutations in low-density lipoprotein receptor gene (LDLR) resulting in the non-clearance of LDL from the blood by hepatocytes and consequently the formation of plaques. LDLR is synthesized and glycosylated in the endoplasmic reticulum (ER) and then transported to the plasma membrane via Golgi. It is estimated that more than 50% of reported FH-causing mutations in LDLR result in misfolded proteins that are transport-defective and hence retained in ER. ER accumulation of misfolded proteins causes ER-stress and activates unfolded protein response (UPR). UPR aids protein folding, blocks further protein synthesis, and eliminates misfolded proteins via ER-associated degradation (ERAD) to alleviate ER stress. Various studies demonstrated that ER-retained LDLR mutants are subjected to ERAD. Interestingly, chemical chaperones and genetic or pharmacological inhibition of ERAD have been reported to rescue the transport defective mutant LDLR alleles from ERAD and restore their ER-Golgi transport resulting in the expression of functional plasma membrane LDLR. This suggests the possibility of pharmacological modulation of proteostasis in the ER as a therapeutic strategy for FH. In this review, we picture a detailed analysis of UPR and the ERAD processes activated by ER-retained LDLR mutants associated with FH. In addition, we discuss and critically evaluate the potential role of chemical chaperones and ERAD modulators in the therapeutic management of FH.
    Keywords:  Class II mutations; ER stress; ERAD pathway; LDLR; cholesterol; familial hypercholesterolemia; lipid metabolism; unfolded protein response
    DOI:  https://doi.org/10.3389/fgene.2020.570355
  2. Sci Rep. 2020 Nov 12. 10(1): 19730
    Kawaguchi Y, Hagiwara D, Miyata T, Hodai Y, Kurimoto J, Takagi H, Suga H, Kobayashi T, Sugiyama M, Onoue T, Ito Y, Iwama S, Banno R, Grinevich V, Arima H.
      The immunoglobulin heavy chain binding protein (BiP), also referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress. Our previous studies showed that BiP is expressed in arginine vasopressin (AVP) neurons under non-stress conditions and that BiP expression is upregulated in proportion to the increased AVP expression under dehydration. To clarify the role of BiP in AVP neurons, we used a viral approach in combination with shRNA interference for BiP knockdown in mouse AVP neurons. Injection of a recombinant adeno-associated virus equipped with a mouse AVP promoter and BiP shRNA cassette provided specific BiP knockdown in AVP neurons of the supraoptic (SON) and paraventricular nuclei (PVN) in mice. AVP neuron-specific BiP knockdown led to ER stress and AVP neuronal loss in the SON and PVN, resulting in increased urine volume due to lack of AVP secretion. Immunoelectron microscopy of AVP neurons revealed that autophagy was activated through the process of AVP neuronal loss, whereas no obvious features characteristic of apoptosis were observed. Pharmacological inhibition of autophagy by chloroquine exacerbated the AVP neuronal loss due to BiP knockdown, indicating a protective role of autophagy in AVP neurons under ER stress. In summary, our results demonstrate that BiP is essential for the AVP neuron system.
    DOI:  https://doi.org/10.1038/s41598-020-76839-z
  3. Sci Rep. 2020 Nov 12. 10(1): 19669
    Matsuki Y, Matsuo Y, Nakano Y, Iwasaki S, Yoko H, Udagawa T, Li S, Saeki Y, Yoshihisa T, Tanaka K, Ingolia NT, Inada T.
      eIF2α phosphorylation-mediated translational regulation is crucial for global translation repression by various stresses, including the unfolded protein response (UPR). However, translational control during UPR has not been demonstrated in yeast. This study investigated ribosome ubiquitination-mediated translational controls during UPR. Tunicamycin-induced ER stress enhanced the levels of ubiquitination of the ribosomal proteins uS10, uS3 and eS7. Not4-mediated monoubiquitination of eS7A was required for resistance to tunicamycin, whereas E3 ligase Hel2-mediated ubiquitination of uS10 was not. Ribosome profiling showed that the monoubiquitination of eS7A was crucial for translational regulation, including the upregulation of the spliced form of HAC1 (HAC1i) mRNA and the downregulation of Histidine triad NucleoTide-binding 1 (HNT1) mRNA. Downregulation of the deubiquitinating enzyme complex Upb3-Bre5 increased the levels of ubiquitinated eS7A during UPR in an Ire1-independent manner. These findings suggest that the monoubiquitination of ribosomal protein eS7A plays a crucial role in translational controls during the ER stress response in yeast.
    DOI:  https://doi.org/10.1038/s41598-020-76239-3
  4. Autophagy. 2020 Nov 08.
    Stephani M, Picchianti L, Dagdas Y.
      Reticulophagy, the autophagic degradation of the endoplasmic reticulum, is crucial to maintain ER homeostasis during stress. Although several reticulophagy receptors have been discovered recently, most of them have been studied using nutrient starvation. How macroautophagy/autophagy cross-talks with other ER-quality control mechanisms is largely unknown. Using ATG8-based affinity proteomics in the model plant Arabidopsis thaliana, we identified AT5G06830/C53, a soluble protein that directly interacts with ATG8. Biochemical and biophysical characterization of C53-ATG8 interaction using both human (CDK5RAP3) and Arabidopsis proteins revealed that C53 binds ATG8 via shuffled Atg8-family interacting motifs (sAIMs) located at its intrinsically disordered region (IDR). C53 is recruited to phagophores, precursors to autophagosomes, during ER stress in an autophagy-dependent manner. Consistently, c53 mutants are highly sensitive to ER stress treatments. C53 senses ER stress by forming a tripartite receptor complex that involves UFL1, the E3 ligase that mediates ufmylation, and its ER-resident adaptor protein DDRGK1. C53 activity is regulated by another ubiquitin-like protein, UFM1, which is transferred from C53 to the ribosomes upon ribosome collision/stalling at the ER, thereby activating the C53 pathway to recycle stalled nascent chains. Altogether our findings suggest C53 forms an ancient quality control pathway that links ribosome-associated quality control with selective autophagy at the ER.
    Keywords:   Arabidopsis thaliana CDK5RAP3; ER-phagy; ER-quality control; UFMylation; ribosome stalling; selective autophagy; selective autophagy receptor
    DOI:  https://doi.org/10.1080/15548627.2020.1846304
  5. J Clin Invest. 2020 Nov 09. pii: 141455. [Epub ahead of print]
    De Franco E, Lytrivi M, Ibrahim H, Montaser H, Wakeling MN, Fantuzzi F, Patel K, Demarez C, Cai Y, Igoillo-Esteve M, Cosentino C, Lithovius V, Vihinen H, Jokitalo E, Laver TW, Johnson MB, Sawatani T, Shakeri H, Pachera N, Haliloglu B, Ozbek MN, Unal E, Yıldırım R, Godbole T, Yildiz M, Aydin B, Bilheu A, Suzuki I, Flanagan SE, Vanderhaeghen P, Senée V, Julier C, Marchetti P, Eizirik DL, Ellard S, Saarimäki-Vire J, Otonkoski T, Cnop M, Hattersley AT.
      Neonatal diabetes is caused by single gene mutations reducing pancreatic β cell number or impairing β cell function. Understanding the genetic basis of rare diabetes subtypes highlights fundamental biological processes in β cells. We identified 6 patients from 5 families with homozygous mutations in the YIPF5 gene, which is involved in trafficking between the endoplasmic reticulum (ER) and the Golgi. All patients had neonatal/early-onset diabetes, severe microcephaly, and epilepsy. YIPF5 is expressed during human brain development, in adult brain and pancreatic islets. We used 3 human β cell models (YIPF5 silencing in EndoC-βH1 cells, YIPF5 knockout and mutation knockin in embryonic stem cells, and patient-derived induced pluripotent stem cells) to investigate the mechanism through which YIPF5 loss of function affects β cells. Loss of YIPF5 function in stem cell-derived islet cells resulted in proinsulin retention in the ER, marked ER stress, and β cell failure. Partial YIPF5 silencing in EndoC-βH1 cells and a patient mutation in stem cells increased the β cell sensitivity to ER stress-induced apoptosis. We report recessive YIPF5 mutations as the genetic cause of a congenital syndrome of microcephaly, epilepsy, and neonatal/early-onset diabetes, highlighting a critical role of YIPF5 in β cells and neurons. We believe this is the first report of mutations disrupting the ER-to-Golgi trafficking, resulting in diabetes.
    Keywords:  Cell Biology; Cell stress; Diabetes; Genetics; Human stem cells
    DOI:  https://doi.org/10.1172/JCI141455
  6. J Clin Invest. 2020 Nov 09. pii: 142364. [Epub ahead of print]
    Pollin TI, Taylor SI.
      Identifying genes that result in monogenic diabetes can provide insights that can build a scientific foundation for precision medicine. At present, nearly 20% of neonatal diabetes cases have unknown causes. In this issue of the JCI, De Franco and Lytrivi et al. sequenced the genome of two probands with a rare neonatal diabetes subtype that also associated with microcephaly and epilepsy. The authors revealed mutations in the YIPF5 gene. YIPF5 resides in the Golgi apparatus and is thought to play a critical role in vesicular trafficking. Notably, disrupting YIPF5 in β cell-based models induced ER stress signaling and resulted in the accumulation of intracellular proinsulin. We believe that utilizing registries and biobanks to reveal other monogenic atypical forms of diabetes is an important approach to gaining insight and suggest that an insulin sensitizer may alleviate ER stress associated with YIPF5 disruption by decreasing the demand for insulin secretion.
    DOI:  https://doi.org/10.1172/JCI142364
  7. Nat Commun. 2020 11 09. 11(1): 5661
    Lee SM, Lee SH, Jung Y, Lee Y, Yoon JH, Choi JY, Hwang CY, Son YH, Park SS, Hwang GS, Lee KP, Kwon KS.
      Sarcopenia is characterized by decreased skeletal muscle mass and function with age. Aged muscles have altered lipid compositions; however, the role and regulation of lipids are unknown. Here we report that FABP3 is upregulated in aged skeletal muscles, disrupting homeostasis via lipid remodeling. Lipidomic analyses reveal that FABP3 overexpression in young muscles alters the membrane lipid composition to that of aged muscle by decreasing polyunsaturated phospholipid acyl chains, while increasing sphingomyelin and lysophosphatidylcholine. FABP3-dependent membrane lipid remodeling causes ER stress via the PERK-eIF2α pathway and inhibits protein synthesis, limiting muscle recovery after immobilization. FABP3 knockdown induces a young-like lipid composition in aged muscles, reduces ER stress, and improves protein synthesis and muscle recovery. Further, FABP3 reduces membrane fluidity and knockdown increases fluidity in vitro, potentially causing ER stress. Therefore, FABP3 drives membrane lipid composition-mediated ER stress to regulate muscle homeostasis during aging and is a valuable target for sarcopenia.
    DOI:  https://doi.org/10.1038/s41467-020-19501-6
  8. Biol Rev Camb Philos Soc. 2020 Nov 08.
    Yap KN, Yamada K, Zikeli S, Kiaris H, Hood WR.
      Considerable progress has been made in understanding the physiological basis for variation in the life-history patterns of animals, particularly with regard to the roles of oxidative stress and hormonal regulation. However, an underappreciated and understudied area that could play a role in mediating inter- and intraspecific variation of life history is endoplasmic reticulum (ER) stress, and the resulting unfolded protein response (UPRER ). ER stress response and the UPRER maintain proteostasis in cells by reducing the intracellular load of secretory proteins and enhancing protein folding capacity or initiating apoptosis in cells that cannot recover. Proper modulation of the ER stress response and execution of the UPRER allow animals to respond to intracellular and extracellular stressors and adapt to constantly changing environments. ER stress responses are heritable and there is considerable individual variation in UPRER phenotype in animals, suggesting that ER stress and UPRER phenotype can be subjected to natural selection. The variation in UPRER phenotype presumably reflects the way animals respond to ER stress and environmental challenges. Most of what we know about ER stress and the UPRER in animals has either come from biomedical studies using cell culture or from experiments involving conventional laboratory or agriculturally important models that exhibit limited genetic diversity. Furthermore, these studies involve the assessment of experimentally induced qualitative changes in gene expression as opposed to the quantitative variations that occur in naturally existing populations. Almost all of these studies were conducted in controlled settings that are often quite different from the conditions animals experience in nature. Herein, we review studies that investigated ER stress and the UPRER in relation to key life-history traits including growth and development, reproduction, bioenergetics and physical performance, and ageing and senescence. We then ask if these studies can inform us about the role of ER stress and the UPRER in mediating the aforementioned life-history traits in free-living animals. We propose that there is a need to conduct experiments pertaining to ER stress and the UPRER in ecologically relevant settings, to characterize variation in ER stress and the UPRER in free-living animals, and to relate the observed variation to key life-history traits. We urge others to integrate multiple physiological systems and investigate how interactions between ER stress and oxidative stress shape life-history trade-offs in free-living animals.
    Keywords:  ageing; development; endoplasmic reticulum stress; life history; oxidative stress; performance; protein folding; reproduction; unfolded protein response
    DOI:  https://doi.org/10.1111/brv.12667
  9. J Biol Chem. 2020 Nov 09. pii: jbc.RA120.014415. [Epub ahead of print]
    Mukherjee T, Ramaglia V, Abdel-Nour M, Bianchi AA, Tsalikis J, Chau HN, Kalia SK, Kalia LV, Chen JJ, Arnoult D, Gommerman JL, Philpott DJ, Girardin SE.
      Large cytosolic protein aggregates are removed by two main cellular processes, autophagy and the ubiquitin-proteasome system (UPS), and defective clearance of these protein aggregates results in proteotoxicity and cell death. Recently, we found that the eIF2α kinase heme-regulated inhibitory (HRI) induced a cytosolic unfolded protein response (cUPR) to prevent aggregation of innate immune signalosomes, but whether HRI acts as a general sensor of proteotoxicity in the cytosol remains unclear. Here we show that HRI controls autophagy to clear cytosolic protein aggregates when the UPS is inhibited. We further report that silencing HRI expression resulted in decreased levels of BAG3 and HSPB8, two proteins involved in chaperone-assisted selective autophagy (CASA), suggesting that HRI controls proteostasis in the cytosol at least in part through CASA. Moreover, knocking down the expression of HRI resulted in cytotoxic accumulation of over-expressed α-synuclein, a protein known to aggregate in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. In agreement with these data, protein aggregate accumulation and microglia activation were observed in the spinal cord white matter of 7-month old Hri-/- mice as compared to Hri+/+ littermates. Moreover, aged Hri-/- mice showed accumulation of misfolded α-synuclein, indicative of misfolded proteins, in the lateral collateral pathway, a region of the sacral spinal cord horn that receives visceral sensory afferents from the bladder and distal colon, a pathological feature common to α-synucleinopathies in humans. Together, these results suggest that HRI contributes to a general cUPR that could be leveraged to bolster the clearance of cytotoxic protein aggregates.
    Keywords:  Integrated Stress Response; Parkinson disease; autophagy; eIF2alpha; synuclein; ubiquitin-dependent protease; unfolded protein response (UPR)
    DOI:  https://doi.org/10.1074/jbc.RA120.014415