bims-ershed Biomed News
on ER Stress in Health and Diseases
Issue of 2021‒03‒21
27 papers selected by
Matías Eduardo González Quiroz
Worker’s Hospital

  1. Cell Mol Biol Lett. 2021 Mar 17. 26(1): 11
      Inositol requiring enzyme 1 alpha (IRE1α) is one of three signaling sensors in the unfolding protein response (UPR) that alleviates endoplasmic reticulum (ER) stress in cells and functions to promote cell survival. During conditions of irrevocable stress, proapoptotic gene expression is induced to promote cell death. One of the three signaling stressors, IRE1α is an serine/threonine-protein kinase/endoribonuclease (RNase) that promotes nonconventional splicing of XBP1 mRNA that is translated to spliced XBP1 (XBP1s), an active prosurvival transcription factor. Interestingly, elevated IRE1α and XBP1s are both associated with poor cancer survival and drug resistance. In this study, we used next-generation sequencing analyses to demonstrate that triazoloacridone C-1305, a microtubule stabilizing agent that also has topoisomerase II inhibitory activity, dramatically decreases XBP1s mRNA levels and protein production during ER stress conditions, suggesting that C-1305 does this by decreasing IRE1α's endonuclease activity.
    Keywords:  ER stress; IRE1α; UPR; XBP1s
  2. Plant Physiol. 2021 Mar 15. pii: kiab126. [Epub ahead of print]
      The unfolded protein response (UPR) is a conserved stress adaptive signaling pathway in eukaryotic organisms activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). UPR can be elicited in the course of plant defense, playing important roles in plant-microbe interactions. The major signaling pathways of plant UPR rely on the transcriptional activity of activated forms of ER membrane-associated stress sensors bZIP60 and bZIP28, which are transcription factors that modulate expression of UPR genes. In this study, we report the plant susceptibility factor RTP1 (Resistance to Phytophthora parasitica 1) is involved in ER stress sensing and rtp1-mediated resistance against P. parasitica is synergistically regulated with UPR, as demonstrated by the simultaneous strong induction of UPR and ER stress-associated immune genes in Arabidopsis thaliana rtp1 mutant plants during infection by P. parasitica. We further demonstrate RTP1 contributes to stabilization of the ER membrane-associated bZIP60 and bZIP28 through manipulating the bifunctional protein kinase/ribonuclease IRE1-mediated bZIP60 splicing activity and interacting with bZIP28. Consequently, we find rtp1bzip60 and rtp1bzip28 mutant plants exhibit compromised resistance accompanied with attenuated induction of ER stress-responsive immune genes and reduction of callose deposition in response to P. parasitica infection. Taken together, we demonstrate RTP1 may exert negative modulating roles in the activation of key UPR regulators bZIP60 and bZIP28, which are required for rtp1-mediated plant resistance to P. parasitica. This facilitates our understanding of the important roles of stress adaptive UPR and ER stress in plant immunity.
    Keywords:  ER stress; Phytophthora parasitica; RTP1; UPR; bZIP28; bZIP60; immunity; susceptibility
  3. Nature. 2021 Mar 17.
    Keywords:  Biochemistry; Molecular biology
  4. Adv Exp Med Biol. 2021 ;1316 191-211
      Immune checkpoints are essential for the regulation of immune cell functions. Although the abrogation of immunosurveillance of tumor cells is known, the regulators of immune checkpoints are not clear. Lipid metabolism is one of the important metabolic activities in organisms. In lipid metabolism, a large number of metabolites produced can regulate the gene expression and activation of immune checkpoints through various pathways. In addition, increasing evidence has shown that lipid metabolism leads to transient generation or accumulation of toxic lipids that result in endoplasmic reticulum (ER) stress and then regulate the transcriptional and posttranscriptional modifications of immune checkpoints, including transcription, protein folding, phosphorylation, palmitoylation, etc. More importantly, the lipid metabolism can also affect exosome transportation of checkpoints and the degradation of checkpoints by affecting ubiquitination and lysosomal trafficking. In this chapter, we mainly empathize on the roles of lipid metabolism in the regulation of immune checkpoints, such as gene expression, activation, and degradation.
    Keywords:  Immune checkpoints; Lipid metabolism; Lysosomal; Ubiquitination; Unfolded protein response
  5. Am J Physiol Gastrointest Liver Physiol. 2021 Mar 17.
      BACKGROUND/AIMS: Liver injury and the Unfolded Protein Response (UPR) are tightly linked, but their relationship differs with cell-type and injurious stimuli. UPR initiation promotes hepatic stellate cell (HSC) activation and fibrogenesis, but the underlying mechanisms are unclear. Despite the complexity and overlap downstream of UPR transducers IRE1α, ATF6α, and PERK, previous research in HSCs primarily focused on IRE1α. Here, we interrogated the fibrogenic role of ATF6α or PERK in vitro and HSC-specific UPR signaling in vivo.METHODS/RESULTS: Overexpression of ATF6α, but not the PERK effector ATF4, promoted HSC activation and fibrogenic gene transcription in immortalized HSCs. Furthermore, ATF6α inhibition through Ceapin-A7, or Atf6a deletion, disrupted TGFβ-mediated activation of primary hHSCs or mHSCs respectively. We interrogated the fibrogenic role of ATF6α in vivo through conditional HSC-specific Atf6a deletion. Atf6aHSCΔ/Δ mice displayed reduced fibrosis and HSC activation following bile-duct ligation (BDL) or CCl4-induced injury. The Atf6aHSCΔ/Δ phenotype differed from HSC-specific Ire1a deletion, as Ire1aHSCΔ/Δ mice showed reduced fibrogenic gene transcription no changes in fibrosis compared to Ire1afl/fl mice following BDL. Interestingly, ATF6α signaling increased in Ire1aΔ/Δ HSCs, while IRE1α signaling was upregulated in Atf6aΔ/Δ HSCs. Finally, we asked whether co-deletion of Arf6a and Ire1a additively limits fibrosis. Unexpectedly, fibrosis worsened in Atf6aHSCΔ/ΔIre1aHSCΔ/Δ mice following BDL, and Atf6aΔ/ΔIre1aΔ/Δ mHSCs showed increased fibrogenic gene transcription.
    CONCLUSIONS: ATF6α and IRE1α individually promote fibrogenic transcription in HSCs and ATF6α drives fibrogenesis in vivo. Unexpectedly, disruption of both pathways sensitizes the liver to fibrogenesis, suggesting that fine-tuned UPR signaling is critical for regulating HSC activation and fibrogenesis.
    Keywords:  ER Stress; Endoplasmic Reticulum; Hepatic Fibrosis; Unfolded Protein Response
  6. Commun Biol. 2021 Mar 19. 4(1): 378
      Protein-protein interactions (PPIs) are critical for cellular activity regulation. Visualization of PPIs using bimolecular fluorescence complementation (BiFC) techniques helps to understand how PPIs implement their functions. However, current BiFC is based on fluorescent proteins and the brightness and photostability are suboptimal for single molecule tracking experiments, resulting in either low spatiotemporal resolution or incapability of tracking for extended time course. Here, we developed the TagBiFC technique based on split HaloTag, a self-labeling tag that could conjugate an organic dye molecule and thus offered better brightness and photostability than fluorescent proteins for PPI visualization inside living cells. Through screening and optimization, we demonstrated that the reconstituted HaloTag exhibited higher localization precision and longer tracking length than previous methods. Using TagBiFC, we reveal that the dynamic interactions of transcription factor dimers with chromatin DNA are distinct and closely related to their dimeric states, indicating a general regulatory mechanism for these kinds of transcription factors. In addition, we also demonstrated the advantageous applications of TagBiFC in single nucleosome imaging, light-burden imaging of single mRNA, low background imaging of cellular structures. We believe these superior properties of our TagBiFC system will have broad applications in the studies of single molecule imaging inside living cells.
  7. Cancer Med. 2021 Mar 20.
      The protein disulphide isomerase (PDI) gene family is a large, diverse group of enzymes recognised for their roles in disulphide bond formation within the endoplasmic reticulum (ER). PDI therefore plays an important role in ER proteostasis, however, it also shows involvement in ER stress, a characteristic recognised in multiple disease states, including cancer. While the exact mechanisms by which PDI contributes to tumorigenesis are still not fully understood, PDI exhibits clear involvement in the unfolded protein response (UPR) pathway. The UPR acts to alleviate ER stress through the activation of ER chaperones, such as PDI, which act to refold misfolded proteins, promoting cell survival. PDI also acts as an upstream regulator of the UPR pathway, through redox regulation of UPR stress receptors. This demonstrates the pro-protective roles of PDI and highlights PDI as a potential therapeutic target for cancer treatment. Recent research has explored the use of PDI inhibitors with PACMA 31 in particular, demonstrating promising anti-cancer effects in ovarian cancer. This review discusses the properties and functions of PDI family members and focuses on their potential as a therapeutic target for cancer treatment.
    Keywords:  cancer; protein disulphide isomerase; protein disulphide isomerase inhibitors
  8. Mol Cell. 2021 Mar 04. pii: S1097-2765(21)00132-5. [Epub ahead of print]
      Eukaryotic cells integrate multiple quality control (QC) responses during protein synthesis in the cytoplasm. These QC responses are signaled by slow or stalled elongating ribosomes. Depending on the nature of the delay, the signal may lead to translational repression, messenger RNA decay, ribosome rescue, and/or nascent protein degradation. Here, we discuss how the structure and composition of an elongating ribosome in a troubled state determine the downstream quality control pathway(s) that ensue. We highlight the intersecting pathways involved in RNA decay and the crosstalk that occurs between RNA decay and ribosome rescue.
  9. Biochem Biophys Rep. 2021 Jul;26 100967
      Obesity-induced endoplasmic reticulum (ER) stress contributes to low-grade chronic inflammation in adipose tissue and may cause metabolic disorders such as diabetes mellitus and dyslipidemia. Identification of high serpina A1 (alpha-1 antitrypsin, A1AT) expression in mouse adipose tissue and adipocytes prompted us to explore the role of A1AT in the inflammatory response of adipocytes under ER stress. We aimed to determine the role of A1AT expression in adipocytes with ER stress during regulation of adipocyte homeostasis and inflammation. To this end, we chemically induced ER stress in A1AT small interfering RNA-transfected differentiating adipocytes using thapsigargin. Induction of CCAAT-enhancer-binding protein homologous protein (CHOP), an ER stress marker, by thapsigargin was lower in A1AT-deficient SW872 adipocytes. Thapsigargin or the proinflammatory cytokine tumor necrosis factor (TNF)α increased basal expression of cytokines such as interleukin (IL)-1β and IL-8 in both SW872 and primary omental adipocytes. This thapsigargin- or TNFα-induced expression of proinflammatory genes was increased by A1AT deficiency. These findings indicate that adipose A1AT may suppress the ER stress response to block excessive expression of proinflammatory factors, which suggests that A1AT protects against adipose tissue dysfunction associated with ER stress activation.
    Keywords:  Adipocyte; Alpha-1 antitrypsin; Endoplasmic reticulum stress; Proinflammatory factor
  10. Eur J Nutr. 2021 Mar 19.
      Obesity challenges lipid and carbohydrate metabolism. The resulting glucolipotoxicity  causes endoplasmic reticulum (ER) dysfunction, provoking the accumulation of immature proteins, which triggers the unfolded protein reaction (UPR) as an attempt to reestablish ER homeostasis. When the three branches of UPR fail to correct the unfolded/misfolded proteins, ER stress happens. Excessive dietary saturated fatty acids or fructose exhibit the same impact on the ER stress, induced by excessive ectopic fat accumulation or rising blood glucose levels, and meta-inflammation. These metabolic abnormalities can alleviate through dietary interventions. Many pathways are disrupted in adipose tissue, liver, and pancreas during ER stress, compromising browning and thermogenesis, favoring hepatic lipogenesis, and impairing glucose-stimulated insulin secretion within pancreatic beta cells. As a result, ER stress takes part in obesity, hepatic steatosis, and diabetes pathogenesis, arising as a potential target to treat or even prevent metabolic diseases. The scientific community seeks strategies to alleviate ER stress by avoiding inflammation, apoptosis, lipogenesis suppression, and insulin sensitivity augmentation through pharmacological and non-pharmacological interventions. This comprehensive review aimed to describe the contribution of excessive dietary fat or sugar to ER stress and the impact of this adverse cellular environment on adipose tissue, liver, and pancreas function.
    Keywords:  ER stress; Fructose; High-fat diet; Inflammation; Insulin resistance; Obesity
  11. Front Cell Dev Biol. 2021 ;9 613336
      In recent decades, compelling evidence has emerged showing that organelles are not static structures but rather form a highly dynamic cellular network and exchange information through membrane contact sites. Although high-throughput techniques facilitate identification of novel contact sites (e.g., organelle-organelle and organelle-vesicle interactions), little is known about their impact on cellular physiology. Moreover, even less is known about how the dysregulation of these structures impacts on cellular function and therefore, disease. Particularly, cancer cells display altered signaling pathways involving several cell organelles; however, the relevance of interorganelle communication in oncogenesis and/or cancer progression remains largely unknown. This review will focus on organelle contacts relevant to cancer pathogenesis. We will highlight specific proteins and protein families residing in these organelle-interfaces that are known to be involved in cancer-related processes. First, we will review the relevance of endoplasmic reticulum (ER)-mitochondria interactions. This section will focus on mitochondria-associated membranes (MAMs) and particularly the tethering proteins at the ER-mitochondria interphase, as well as their role in cancer disease progression. Subsequently, the role of Ca2+ at the ER-mitochondria interphase in cancer disease progression will be discussed. Members of the Bcl-2 protein family, key regulators of cell death, also modulate Ca2+ transport pathways at the ER-mitochondria interphase. Furthermore, we will review the role of ER-mitochondria communication in the regulation of proteostasis, focusing on the ER stress sensor PERK (PRKR-like ER kinase), which exerts dual roles in cancer. Second, we will review the relevance of ER and mitochondria interactions with other organelles. This section will focus on peroxisome and lysosome organelle interactions and their impact on cancer disease progression. In this context, the peroxisome biogenesis factor (PEX) gene family has been linked to cancer. Moreover, the autophagy-lysosome system is emerging as a driving force in the progression of numerous human cancers. Thus, we will summarize our current understanding of the role of each of these organelles and their communication, highlighting how alterations in organelle interfaces participate in cancer development and progression. A better understanding of specific organelle communication sites and their relevant proteins may help to identify potential pharmacological targets for novel therapies in cancer control.
    Keywords:  cancer; endoplasmic reticulum; interorganelle communication; lysosome; mitochondria; peroxisome
  12. Sci Prog. 2021 Jan-Mar;104(1):104(1): 36850421997273
      DDIT4 is a mitochondrial and tumor-related protein involved in anti-tumor therapy resistance, proliferation, and invasion, etc. Its expression level increases under the stress such as chemotherapy, hypoxia, and DNA damage. A number of clinical studies have confirmed that DDIT4 can change the behavior of tumor cells and the prognosis of patients with cancer. However, the role of DDIT4 in promoting or suppressing cancer is still inconclusive. This article summarized the four characteristics of DDIT4 including a mitochondria-related protein, interactions with various protein molecules, immune and metabolic cell related proteins and participator in the oxygen sensing pathway, which may be related to the progress of cancer.
    Keywords:  DNA damage-inducible transcript 4; Hypoxia; adipocytes; cancer; immune
  13. Cell Death Dis. 2021 Mar 17. 12(4): 286
      p97/VCP, an evolutionarily concerned ATPase, partakes in multiple cellular proteostatic processes, including the endoplasmic reticulum (ER)-associated protein degradation (ERAD). Elevated expression of p97 is common in many cancers and is often associated with poor survival. Here we report that the levels of p97 positively correlated with the histological grade, tumor size, and lymph node metastasis in breast cancers. We further examined p97 expression in the stem-like cancer cells or cancer stem cells (CSCs), a cell population that purportedly underscores cancer initiation, therapeutic resistance, and recurrence. We found that p97 was consistently at a higher level in the CD44+/CD24-, ALDH+, or PKH26+ CSC populations than the respective non-CSC populations in human breast cancer tissues and cancer cell lines and p97 expression also positively correlated with that of SOX2, another CSC marker. To assess the role of p97 in breast cancers, cancer proliferation, mammosphere, and orthotopic growth were analyzed. Similarly as p97 depletion, two pharmacological inhibitors, which targets the ER-associated p97 or globally inhibits p97's ATPase activity, markedly reduced cancer growth and the CSC population. Importantly, depletion or inhibition of p97 greatly suppressed the proliferation of the ALDH+ CSCs and the CSC-enriched mammospheres, while exhibiting much less or insignificant inhibitory effects on the non-CSC cancer cells. Comparable phenotypes produced by blocking ERAD suggest that ER proteostasis is essential for the CSC integrity. Loss of p97 gravely activated the unfolded protein response (UPR) and modulated the expression of multiple stemness and pluripotency regulators, including C/EBPδ, c-MYC, SOX2, and SKP2, which collectively contributed to the demise of CSCs. In summary, p97 controls the breast CSC integrity through multiple targets, many of which directly affect cancer stemness and are induced by UPR activation. Our findings highlight the importance of p97 and ER proteostasis in CSC biology and anticancer therapy.
  14. Mutagenesis. 2021 Mar 19. pii: geab011. [Epub ahead of print]
      Previous studies have indicated important roles for NIMA-related kinase 1 (NEK1) in modulating DNA damage checkpoints and DNA repair capacity. To broadly assess the contributions of NEK1 to genotoxic stress and mitochondrial functions, we characterized several relevant phenotypes of NEK1 CRISPR knockout (KO) and WT HAP1 cells. Our studies revealed that NEK1 KO cells resulted in increased apoptosis and hypersensitivity to the alkylator methyl methanesulfonate, the radiomimetic bleomycin, and UVC light, yet increased resistance to the crosslinker cisplatin. Mitochondrial functionalities were also altered in NEK1 KO cells, with phenotypes of reduced mitophagy, increased total mitochondria, elevated levels of reactive oxygen species, impaired complex I activity, and higher amounts of mitochondrial DNA damage. RNA-seq transcriptome analysis coupled with qRT-PCR studies comparing NEK1 KO cells with NEK1 overexpressing cells revealed that the expression of genes involved in DNA repair pathways, such as base excision repair, nucleotide excision repair, and double-strand break repair, are altered in a way that might influence genotoxin resistance. Together, our studies underline and further support that NEK1 serves as a hub signaling kinase in response to DNA damage, modulating DNA repair capacity, mitochondrial activity and cell fate determination.
    Keywords:  DNA Damage; DNA Repair; Mitochondria; NEK1
  15. Autophagy. 2021 Mar 17. 1-10
      TEX264 (testes expressed gene 264) is a single-pass transmembrane protein, consisting of an N-terminal hydrophobic region, a gyrase inhibitory (GyrI)-like domain, and a loosely structured C terminus. TEX264 was first identified as an endoplasmic reticulum (ER)-resident Atg8-family-binding protein that mediates the degradation of portions of the ER during starvation (i.e., reticulophagy). More recently, TEX264 was identified as a cofactor of VCP/p97 ATPase that promotes the repair of covalently trapped TOP1 (DNA topoisomerase 1)-DNA crosslinks. This review summarizes the current knowledge of TEX264 as a protein with roles in both autophagy and DNA repair and provides an evolutionary and structural analysis of GyrI proteins. Based on our phylogenetic analysis, we provide evidence that TEX264 is a member of a large superfamily of GyrI-like proteins that evolved in bacteria and are present in metazoans, including invertebrates and chordates.Abbreviations: Atg8: autophagy related 8; Atg39: autophagy related 39; Cdc48: cell division cycle 48; CGAS: cyclic GMP-AMP synthase; DPC: DNA-protein crosslinks; DSB: DNA double-strand break; ER: endoplasmic reticulum; GyrI: gyrase inhibitory domain; LRR: leucine-rich repeat; MAFFT: multiple alignment using fast Fourier transform; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; STUBL: SUMO targeted ubiquitin ligase; SUMO: small ubiquitin-like modifier; TEX264: testis expressed gene 264; TOP1cc: topoisomerase 1-cleavage complex; UBZ: ubiquitin binding Zn finger domain; VCP: valosin containing protein.
    Keywords:  Autophagy; DNA repair; TEX264; gyrase inhibitory-like proteins; nucleophagy; reticulophagy
  16. Cell Death Differ. 2021 Mar 15.
      Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in the US. Understanding the mechanisms of CRC progression is essential to improve treatment. Mitochondria is the powerhouse for healthy cells. However, in tumor cells, less energy is produced by the mitochondria and metabolic reprogramming is an early hallmark of cancer. The metabolic differences between normal and cancer cells are being interrogated to uncover new therapeutic approaches. Mitochondria targeting PTEN-induced kinase 1 (PINK1) is a key regulator of mitophagy, the selective elimination of damaged mitochondria by autophagy. Defective mitophagy is increasingly associated with various diseases including CRC. However, a significant gap exists in our understanding of how PINK1-dependent mitophagy participates in the metabolic regulation of CRC. By mining Oncomine, we found that PINK1 expression was downregulated in human CRC tissues compared to normal colons. Moreover, disruption of PINK1 increased colon tumorigenesis in two colitis-associated CRC mouse models, suggesting that PINK1 functions as a tumor suppressor in CRC. PINK1 overexpression in murine colon tumor cells promoted mitophagy, decreased glycolysis and increased mitochondrial respiration potentially via activation of p53 signaling pathways. In contrast, PINK1 deletion decreased apoptosis, increased glycolysis, and reduced mitochondrial respiration and p53 signaling. Interestingly, PINK1 overexpression in vivo increased apoptotic cell death and suppressed colon tumor xenograft growth. Metabolomic analysis revealed that acetyl-CoA was significantly reduced in tumors with PINK1 overexpression, which was partly due to activation of the HIF-1α-pyruvate dehydrogenase (PDH) kinase 1 (PDHK1)-PDHE1α axis. Strikingly, treating mice with acetate increased acetyl-CoA levels and rescued PINK1-suppressed tumor growth. Importantly, PINK1 disruption simultaneously increased xenografted tumor growth and acetyl-CoA production. In conclusion, mitophagy protein PINK1 suppresses colon tumor growth by metabolic reprogramming and reducing acetyl-CoA production.
  17. Front Cell Dev Biol. 2021 ;9 638559
      Meiosis is essential to the continuity of life in sexually-reproducing organisms through the formation of haploid gametes. Unlike somatic cells, the germ cells undergo two successive rounds of meiotic divisions after a single cycle of DNA replication, resulting in the decrease in ploidy. In humans, errors in meiotic progression can cause infertility and birth defects. Post-translational modifications, such as phosphorylation, ubiquitylation and sumoylation have emerged as important regulatory events in meiosis. There are dynamic equilibrium of protein phosphorylation and protein dephosphorylation in meiotic cell cycle process, regulated by a conservative series of protein kinases and protein phosphatases. Among these protein phosphatases, PP2A, PP4, and PP6 constitute the PP2A-like subfamily within the serine/threonine protein phosphatase family. Herein, we review recent discoveries and explore the role of PP2A-like protein phosphatases during meiotic progression.
    Keywords:  PP2A; PP4; PP6; meiosis; protein phosphorylation
  18. Sci Rep. 2021 Mar 18. 11(1): 6293
      The type 2A protein phosphatase regulatory protein alpha4 (α4) constitutes an anti-apoptotic protein in non-cardiac tissue, however it's anti-apoptotic properties in the heart are poorly defined. To this end, we knocked down α4 protein expression (α4 KD) using siRNA in cultured H9c2 cardiomyocytes and confirmed the lack of DNA damage/cell death by TUNEL staining and MTT assay. However, α4 KD did increase the phosphorylation of p53 and ATM/ATR substrates, decreased the expression of poly ADP-ribose polymerase and associated fragments. Expression of anti-apoptotic proteins Bcl-2 and Bcl-xL was reduced, whereas expression of pro-apoptotic BAX protein did not change. Alpha4 KD reduced basal H2AX Ser139 phosphorylation, whereas adenoviral-mediated re-expression of α4 protein following α4 KD, restored basal H2AX phosphorylation at Ser139. The sensitivity of H9c2 cardiomyocytes to doxorubicin-induced DNA damage and cytotoxicity was augmented by α4 KD. Adenoviral-mediated overexpression of α4 protein in ARVM increased PP2AC expression and augmented H2AX Ser139 phosphorylation in response to doxorubicin. Furthermore, pressure overload-induced heart failure was associated with reduced α4 protein expression, increased ATM/ATR protein kinase activity, increased H2AX expression and Ser139 phosphorylation. Hence, this study describes the significance of altered α4 protein expression in the regulation of DNA damage, cardiomyocyte cell death and heart failure.
  19. Nat Aging. 2021 Feb;1(2): 165-178
      Organisms respond to mitochondrial stress by activating multiple defense pathways including the mitochondrial unfolded protein response (UPRmt). However, how UPRmt regulators are orchestrated to transcriptionally activate stress responses remains largely unknown. Here we identified CBP-1, the worm ortholog of the mammalian acetyltransferases CBP/p300, as an essential regulator of the UPRmt, as well as mitochondrial stress-induced immune response, reduction of amyloid-β aggregation and lifespan extension in Caenorhabditis elegans. Mechanistically, CBP-1 acts downstream of histone demethylases, JMJD-1.2/JMJD-3.1, and upstream of UPRmt transcription factors including ATFS-1, to systematically induce a broad spectrum of UPRmt genes and execute multiple beneficial functions. In mouse and human populations, transcript levels of CBP/p300 positively correlate with UPRmt transcripts and longevity. Furthermore, CBP/p300 inhibition disrupts, while forced expression of p300 is sufficient to activate, the UPRmt in mammalian cells. These results highlight an evolutionarily conserved mechanism that determines mitochondrial stress response, and promotes health and longevity through CBP/p300.
  20. Neurooncol Adv. 2021 Jan-Dec;3(1):3(1): vdab015
      Glioblastoma (GBM), the most aggressive primary brain tumor, has a dismal prognosis. Despite our growing knowledge of genomic and epigenomic alterations in GBM, standard therapies and outcomes have not changed significantly in the past two decades. There is therefore an urgent unmet need to develop novel therapies for GBM. The inter- and intratumoral heterogeneity of GBM, inadequate drug concentrations in the tumor owing to the blood-brain barrier, redundant signaling pathways contributing to resistance to conventional therapies, and an immunosuppressive tumor microenvironment, have all hindered the development of novel therapies for GBM. Given the high frequency of DNA damage pathway alterations in GBM, researchers have focused their efforts on pharmacologically targeting key enzymes, including poly(ADP-ribose) polymerase (PARP), DNA-dependent protein kinase, ataxia telangiectasia-mutated, and ataxia telangiectasia and Rad3-related. The mainstays of GBM treatment, ionizing radiation and alkylating chemotherapy, generate DNA damage that is repaired through the upregulation and activation of DNA damage response (DDR) enzymes. Therefore, the use of PARP and other DDR inhibitors to render GBM cells more vulnerable to conventional treatments is an area of intense investigation. In this review, we highlight the growing body of data behind DDR inhibitors in GBM, with a focus on putative predictive biomarkers of response. We also discuss the challenges involved in the successful development of DDR inhibitors for GBM, including the intracranial location and predicted overlapping toxicities of DDR agents with current standards of care, and propose promising strategies to overcome these hurdles.
    Keywords:  DDR inhibitors; MGMT methylation; glioblastoma; radiation; temozolomide
  21. Cell Rep. 2021 Mar 16. pii: S2211-1247(21)00187-X. [Epub ahead of print]34(11): 108873
      Contacts between organelles create microdomains that play major roles in regulating key intracellular activities and signaling pathways, but whether they also regulate systemic functions remains unknown. Here, we report the ultrastructural organization and dynamics of the inter-organellar contact established by sheets of curved rough endoplasmic reticulum closely wrapped around the mitochondria (wrappER). To elucidate the in vivo function of this contact, mouse liver fractions enriched in wrappER-associated mitochondria are analyzed by transcriptomics, proteomics, and lipidomics. The biochemical signature of the wrappER points to a role in the biogenesis of very-low-density lipoproteins (VLDL). Altering wrappER-mitochondria contacts curtails VLDL secretion and increases hepatic fatty acids, lipid droplets, and neutral lipid content. Conversely, acute liver-specific ablation of Mttp, the most upstream regulator of VLDL biogenesis, recapitulates this hepatic dyslipidemia phenotype and promotes remodeling of the wrappER-mitochondria contact. The discovery that liver wrappER-mitochondria contacts participate in VLDL biology suggests an involvement of inter-organelle contacts in systemic lipid homeostasis.
    Keywords:  MAM; MUP; Rrbp1; VLDL; endoplasmic reticulum; inter-organelle contact; lipoprotein; liver metabolism; mitochondria; wrappER
  22. Front Oncol. 2020 ;10 612337
      m6A RNA methylation, which serves as a critical regulator of transcript expression, has gathered tremendous scientific interest in recent years. From RNA processing to nuclear export, RNA translation to decay, m6A modification has been studied to affect various aspects of RNA metabolism, and it is now considered as one of the most abundant epitranscriptomic modification. RNA methyltransferases (writer), m6A-binding proteins (readers), and demethylases (erasers) proteins are frequently upregulated in several neoplasms, thereby regulating oncoprotein expression, augmenting tumor initiation, enhancing cancer cell proliferation, progression, and metastasis. Though the potential role of m6A methylation in growth and proliferation of cancer cells has been well documented, its potential role in development of therapy resistance in cancer is not clear. In this review, we focus on m6A-associated regulation, mechanisms, and functions in acquired chemoresistance, radioresistance, and resistance to immunotherapy in cancer.
    Keywords:  ALKBH5; METTL3; PD-1; YTHDF1; cisplatin; m6A methylation
  23. Mol Cancer. 2021 Mar 15. 20(1): 52
      In vitro-transcribed messenger RNA-based therapeutics represent a relatively novel and highly efficient class of drugs. Several recently published studies emphasize the potential efficacy of mRNA vaccines in treating different types of malignant and infectious diseases where conventional vaccine strategies and platforms fail to elicit protective immune responses. mRNA vaccines have lately raised high interest as potent vaccines against SARS-CoV2. Direct application of mRNA or its electroporation into dendritic cells was shown to induce polyclonal CD4+ and CD8+ mediated antigen-specific T cell responses as well as the production of protective antibodies with the ability to eliminate transformed or infected cells. More importantly, the vaccine composition may include two or more mRNAs coding for different proteins or long peptides. This enables the induction of polyclonal immune responses against a broad variety of epitopes within the encoded antigens that are presented on various MHC complexes, thus avoiding the restriction to a certain HLA molecule or possible immune escape due to antigen-loss. The development and design of mRNA therapies was recently boosted by several critical innovations including the development of technologies for the production and delivery of high quality and stable mRNA. Several technical obstacles such as stability, delivery and immunogenicity were addressed in the past and gradually solved in the recent years.This review will summarize the most recent technological developments and application of mRNA vaccines in clinical trials and discusses the results, challenges and future directions with a special focus on the induced innate and adaptive immune responses.
    Keywords:  B cells; COVID19; Cancer; Immune response; T cells; Tumor-associated antigen; mRNA vaccine
  24. Mol Ther Nucleic Acids. 2021 Mar 05. 23 1243-1257
      Circular RNAs (circRNAs) are a type of endogenous non-coding RNA that were discovered to regulate gene expression through multiple pathways. Metastasis remains one of the biggest obstacles in cancer treatment. In this review, we focus on circRNAs involved in cancer tumorigenesis and metastasis. We present recently identified tumor-related circRNAs and discuss their functioning in tumor progression and metastasis. These circRNAs are categorized into different functional mechanisms, including microRNA (miRNA) sponging, protein binding, regulation of host genes, translation of circRNAs, and exosomal circRNAs. Additionally, the indirect functions of circRNAs that regulate epithelial-mesenchymal transition and autophagy are also discussed.
    Keywords:  cancer; circular RNA; gene regulation; metastasis
  25. Bio Protoc. 2021 Feb 20. 11(4): e3930
      The molecular mechanisms of P-glycoprotein (P-gp; also known as MDR1 or ABCB1) have been mainly investigated using artificial membranes such as lipid-detergent mixed micelles, artificial lipid bilayers, and membrane vesicles derived from cultured cells. Although these in vitro experiments help illustrate details about the molecular mechanisms of P-gp, they do not reflect physiological membrane environments in terms of lateral pressure, curvature, constituent lipid species, etc. The protocol presented here includes a detailed guide for analyzing the conformational change of human P-gp in living HEK293 cells by using intramolecular fluorescence resonance energy transfer (FRET), in which excitation of the donor fluorophore is transferred to the acceptor without emission of a photon when two fluorescent proteins are in close proximity. Combining FRET analysis with membrane permeabilization, the contribution of small molecules such as nucleotides to the conformational change can be evaluated in living cells.
    Keywords:  ABC transporter; Conformational change; Intramolecular FRET; Live cell analysis; Membrane protein; P-glycoprotein
  26. Proc Natl Acad Sci U S A. 2021 Mar 23. pii: e2025126118. [Epub ahead of print]118(12):
      Ubiquitin is a common posttranslational modification canonically associated with targeting proteins to the 26S proteasome for degradation and also plays a role in numerous other nondegradative cellular processes. Ubiquitination at certain sites destabilizes the substrate protein, with consequences for proteasomal processing, while ubiquitination at other sites has little energetic effect. How this site specificity-and, by extension, the myriad effects of ubiquitination on substrate proteins-arises remains unknown. Here, we systematically characterize the atomic-level effects of ubiquitination at various sites on a model protein, barstar, using a combination of NMR, hydrogen-deuterium exchange mass spectrometry, and molecular dynamics simulation. We find that, regardless of the site of modification, ubiquitination does not induce large structural rearrangements in the substrate. Destabilizing modifications, however, increase fluctuations from the native state resulting in exposure of the substrate's C terminus. Both of the sites occur in regions of barstar with relatively high conformational flexibility. Nevertheless, destabilization appears to occur through different thermodynamic mechanisms, involving a reduction in entropy in one case and a loss in enthalpy in another. By contrast, ubiquitination at a nondestabilizing site protects the substrate C terminus through intermittent formation of a structural motif with the last three residues of ubiquitin. Thus, the biophysical effects of ubiquitination at a given site depend greatly on local context. Taken together, our results reveal how a single posttranslational modification can generate a broad array of distinct effects, providing a framework to guide the design of proteins and therapeutics with desired degradation and quality control properties.
    Keywords:  energy landscape; hydrogen exchange; molecular dynamics; ubiquitin