bims-unfpre 2021-09-19 papers

Issue of 2021–09–19
six papers selected by
Susan Logue, University of Manitoba

J Am Heart Assoc. 2021 Sep 17. e020441

Aging and Hypercholesterolemia Differentially Affect the Unfolded Protein Response in the Vasculature of ApoE-/- Mice.

Yuxiang Zhou, Xueping Wan, Kerstin Seidel, Mo Zhang, Jena B Goodman, Francesca Seta, Naomi Hamburg, Jingyan Han.

Background Persistent activation of endoplasmic reticulum stress and the unfolded protein response (UPR) induces vascular cell apoptosis, contributing to atherogenesis. Aging and hypercholesterolemia are 2 independent proatherogenic factors. How they affect vascular UPR signaling remains unclear. Methods and Results Transcriptome analysis of aortic tissues from high fat diet-fed and aged ApoE-/- mice revealed 50 overlapping genes enriched for endoplasmic reticulum stress- and UPR-related pathways. Aortae from control, Western diet (WD)-fed, and aged ApoE-/- mice were assayed for (1) 3 branches of UPR signaling (pancreatic ER eIF2-alpha kinase /alpha subunit of the eukaryotic translation initiation factor 1/activating transcription factor 4, inositol-requiring enzyme 1 alpha/XBP1s, activating transcription factor 6); (2) UPR-mediated protective adaptation (upregulation of immunoglobulin heavy chain-binding protein and protein disulfide isomerase); and (3) UPR-mediated apoptosis (induction of C/EBP homologous transcription factor, p-JNK, and cleaved caspase-3). Aortic UPR signaling was differentially regulated in the aged and WD-fed groups. Consumption of WD activated all 3 UPR branches; in the aged aorta, only the ATF6α arm was activated, but it was 10 times higher than that in the WD group. BiP and protein disulfide isomerase protein levels were significantly decreased only in the aged aorta despite a 5-fold increase in their mRNA levels. Importantly, the aortae of aged mice exhibited a substantially enhanced proapoptotic UPR compared with that of WD-fed mice. In lung tissues, UPR activation and the resultant adaptive/apoptotic responses were not significantly different between the 2 groups. Conclusions Using a mouse model of atherosclerosis, this study provides the first in vivo evidence that aging and an atherogenic diet activate differential aortic UPR pathways, leading to distinct vascular responses. Compared with dietary intervention, aging is associated with impaired endoplasmic reticulum protein folding and increased aortic apoptosis.

Keywords: aging; apoE deficient mice; hypercholesterolemia; unfolded protein response; vascular cells

DOI: https://doi.org/10.1161/JAHA.120.020441

J Exp Clin Cancer Res. 2021 Sep 14. 40(1): 289

The non-canonical mechanism of ER stress-mediated progression of prostate cancer.

BACKGROUND: The development of persistent endoplasmic reticulum (ER) stress is one of the cornerstones of prostate carcinogenesis; however, the mechanism is missing. Also, alcohol is a physiological ER stress inducer, and the link between alcoholism and progression of prostate cancer (PCa) is well documented but not well characterized. According to the canonical model, the mediator of ER stress, ATF6, is cleaved sequentially in the Golgi by S1P and S2P proteases; thereafter, the genes responsible for unfolded protein response (UPR) undergo transactivation.
METHODS: Cell lines used were non-malignant prostate epithelial RWPE-1 cells, androgen-responsive LNCaP, and 22RV1 cells, as well as androgen-refractory PC-3 cells. We also utilized PCa tissue sections from patients with different Gleason scores and alcohol consumption backgrounds. Several sophisticated approaches were employed, including Structured illumination superresolution microscopy, Proximity ligation assay, Atomic force microscopy, and Nuclear magnetic resonance spectroscopy.
RESULTS: Herein, we identified the trans-Golgi matrix dimeric protein GCC185 as a Golgi retention partner for both S1P and S2P, and in cells lacking GCC185, these enzymes lose intra-Golgi situation. Progression of prostate cancer (PCa) is associated with overproduction of S1P and S2P but monomerization of GCC185 and its downregulation. Utilizing different ER stress models, including ethanol administration, we found that PCa cells employ an elegant mechanism that auto-activates ER stress by fragmentation of Golgi, translocation of S1P and S2P from Golgi to ER, followed by intra-ER cleavage of ATF6, accelerated UPR, and cell proliferation. The segregation of S1P and S2P from Golgi and activation of ATF6 are positively correlated with androgen receptor signaling, different disease stages, and alcohol consumption. Finally, depletion of ATF6 significantly retarded the growth of xenograft prostate tumors and blocks production of pro-metastatic metabolites.
CONCLUSIONS: We found that progression of PCa associates with translocation of S1P and S2P proteases to the ER and subsequent ATF6 cleavage. This obviates the need for ATF6 transport to the Golgi and enhances UPR and cell proliferation. Thus, we provide the novel mechanistic model of ATF6 activation and ER stress implication in the progression of PCa, suggesting ATF6 is a novel promising target for prostate cancer therapy.

Keywords: Alcohol abuse; ER stress; Golgi fragmentation; Prostate cancer

DOI: https://doi.org/10.1186/s13046-021-02066-7

Front Endocrinol (Lausanne). 2021 ;12 734079

Endoplasmic Reticulum Stress Induced Proliferation Remains Intact in Aging Mouse β-Cells.

Jarin T Snyder, Christine Darko, Rohit B Sharma, Laura C Alonso.

Aging is associated with loss of proliferation of the insulin-secreting β-cell, a possible contributing factor to the increased prevalence of type 2 diabetes in the elderly. Our group previously discovered that moderate endoplasmic reticulum (ER) stress occurring during glucose exposure increases the adaptive β-cell proliferation response. Specifically, the ATF6α arm of the tripartite Unfolded Protein Response (UPR) promotes β-cell replication in glucose excess conditions. We hypothesized that β-cells from older mice have reduced proliferation due to aberrant UPR signaling or an impaired proliferative response to ER stress or ATF6α activation. To investigate, young and old mouse islet cells were exposed to high glucose with low-dose thapsigargin or activation of overexpressed ATF6α, and β-cell proliferation was quantified by BrdU incorporation. UPR pathway activation was compared by qPCR of target genes and semi-quantitative Xbp1 splicing assay. Intriguingly, although old β-cells had reduced proliferation in high glucose compared to young β-cells, UPR activation and induction of proliferation in response to low-dose thapsigargin or ATF6α activation in high glucose were largely similar between young and old. These results suggest that loss of UPR-led adaptive proliferation does not explain the reduced cell cycle entry in old β-cells, and raise the exciting possibility that future therapies that engage adaptive UPR could increase β-cell number through proliferation even in older individuals.

Keywords: ATF6 (activating transcription factor 6); aging/aging beta cells; endoplasm Reticulum Stress; pancreatic beta cells; proliferation; thapsigargin; unfolded protein response

DOI: https://doi.org/10.3389/fendo.2021.734079

Front Cell Infect Microbiol. 2021 ;11 707107

Sec62 Regulates Endoplasmic Reticulum Stress and Autophagy Balance to Affect Foot-and-Mouth Disease Virus Replication.

Jin'en Wu, Zhihui Zhang, Zhidong Teng, Sahibzada Waheed Abdullah, Shiqi Sun, Huichen Guo.

Endoplasmic reticulum (ER) stress-induced autophagy is closely associated with viral infection and propagation. However, the intrinsic link between ER stress, autophagy, and viral replication during foot-and-mouth disease virus (FMDV) infection is not fully elucidated. Our previous studies demonstrated that FMDV infection activated the ER stress-associated UPR of the PERK-eIF2a and ATF6 signaling pathway, whereas the IRE1a signaling was suppressed. We found that the activated-ATF6 pathway participated in FMDV-induced autophagy and FMDV replication, while the IRE1α pathway only affected FMDV replication. Further studies indicated that Sec62 was greatly reduced in the later stages of FMDV infection and blocked the activation of the autophagy-related IRE1α-JNK pathway. Moreover, it was also found that Sec62 promoted IRE1a phosphorylation and negatively regulated FMDV proliferation. Importantly, Sec62 may interact with LC3 to regulate ER stress and autophagy balance and eventually contribute to FMDV clearance via fusing with lysosomes. Altogether, these results suggest that Sec62 is a critical molecule in maintaining and recovering ER homeostasis by activating the IRE1α-JNK pathway and delivering autophagosome into the lysosome, thus providing new insights on FMDV-host interactions and novel antiviral therapies.

Keywords: ER stress; FMDV; Sec62; UPR; autophagy

DOI: https://doi.org/10.3389/fcimb.2021.707107

MicroPubl Biol. 2021 ;2021

Decreased Mitochondrial Membrane Potential Activates the Mitochondrial Unfolded Protein Response.

Brandon J Berry, Tyrone O Nieves, Andrew P Wojtovich.

Mitochondria are ATP-producing organelles that also signal throughout the cell. Mitochondrial protein homeostasis is regulated through membrane potential-dependent protein import and quality control signaling. The mitochondrial unfolded protein response (UPRmt) is a specific program that responds to imbalances in nuclear and mitochondrial gene expression. Mounting evidence suggests that the electrochemical gradient that powers mitochondrial function, the mitochondrial membrane potential (Δψm), is a core regulator of the UPRmt. Here we tested this notion directly by pharmacologically dissipating Δψm and monitoring UPRmt activation. We found that chemical dissipation of Δψm using FCCP indeed activated UPRmt dose-dependently in C. elegans assayed by the HSP-60::GFP reporter strain.

DOI: https://doi.org/10.17912/micropub.biology.000445

J Biol Chem. 2021 Sep 11. pii: S0021-9258(21)00993-5. [Epub ahead of print] 101191

The AKT modulator A-443654 reduces α-synuclein expression and normalizes ER stress and autophagy.

Mandi Gandelman, Warunee Dansithong, Stephen C Kales, Sharan Paul, Gentrie Maag, Erika Aoyama, Alexey Zakharov, Ganesha Rai, Thomas Dexheimer, Brooke M Whitehill, Hongmao Sun, Ajit Jadhav, Anton Simeonov, Mark J Henderson, Duong P Huynh, Stefan M Pulst, Daniel R Scoles.

Accumulation of α-synuclein is a main underlying pathological feature of Parkinson's disease (PD) and α-synucleinopathies, for which lowering expression of the α-synuclein gene (SNCA) is a potential therapeutic avenue. Using a cell-based luciferase reporter of SNCA expression we performed a quantitative high throughput screen (qHTS) of 155,885 compounds and identified A-443654, an inhibitor of the multiple functional kinase AKT, as a potent inhibitor of SNCA. HEK-293 cells with CAG repeat expanded ATXN2 (ATXN2-Q58 cells) have increased levels of α-synuclein. We found that A-443654 normalized levels of both SNCA mRNA and α-synuclein monomers and oligomers in ATXN2-Q58 cells. A-443654 also normalized levels of α-synuclein in fibroblasts and iPSC-derived dopaminergic neurons from a patient carrying a triplication of the SNCA gene. Analysis of autophagy and endoplasmic reticulum stress markers showed that A-443654 successfully prevented α-synuclein toxicity and restored cell function in ATXN2-Q58 cells, normalizing the levels of mTOR, LC3-II, p62, STAU1, BiP and CHOP. A-443654 also decreased the expression of DCLK1, an inhibitor of α-synuclein lysosomal degradation. Our study identifies A-443654 and AKT inhibition as a potential strategy for reducing SNCA expression and preventing PD pathology.

Keywords: A-443654; AKT; Parkinson disease; SNCA; STAU1; alpha‐synuclein (α‐synuclein); autophagy; endoplasmic reticulum stress (ER stress); high‐throughput screening (HTS); staufen1

DOI: https://doi.org/10.1016/j.jbc.2021.101191