Alternative Mechanisms of p53 Action During the Unfolded Protein Response

Short-chain chlorinated paraffins may induce thymic aging in mice by activating PERK-CHOP

Humans indirectly consume approximately 0.02 mg/kg/day of short-chained chlorinated paraffins (SCCPs) through the environment; however, the thymic senescence/damage induced by SCCPs has not been assessed. In this study, 16 female mice (4-week-old) per group were orally administered 0, 0.01, 0.1, and 1 mg/kg/day of SCCPs for 21 days, and the phenotypes and levels of superoxide dismutase (SOD), malondialdehyde (MDA), Tβ4, αβ TCR, SA-β-Gal, GRP78, PERK/CHOP, P53/P21, and CASPASE-1 of the thymus were assessed as indicators. Another group comprising 16 mice was killed at 4-week-old and these indicators were assessed. Thereafter, the thymuses cultured in vitro were exposed to 0, 14, 140, and 1400 μg/L SCCPs, respectively, and the above indicators were measured after 7-day. Based on the results, the oral administration of ≥0.01 mg/kg/day SCCPs to mice and ≥14 μg/L of SCCPs in medium caused thymic aging features, such as a decrease in the ratio of cortex to medulla, gradual blurring of the boundary between the cortex and medulla, dose-dependent oxidative stress (decreased SOD and increased MDA), and decreased levels of Tβ4 and αβ TCRs in the thymus. The oral administration of ≥1 mg/kg/day of SCCPs also impeded the growth and development of female mice and their thymuses. Exposure to the low levels of SCCPs activated PERK-CHOP in the mouse thymus, which modulated increases in SA-β-Gal, IL-1β, P53, and CASPASE-1 in vivo and in vitro. Overall, environmental levels and human blood concentrations (14.8-1400 μg/L) of SCCPs may induce mouse thymus senescence by activating PERK-CHOP in vivo and in vitro, respectively.

Emerging mechanisms of the unfolded protein response in therapeutic resistance: from chemotherapy to Immunotherapy

The accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and activates the unfolded protein response (UPR). As an adaptive cellular response to hostile microenvironments, such as hypoxia, nutrient deprivation, oxidative stress, and chemotherapeutic drugs, the UPR is activated in diverse cancer types and functions as a dynamic tumour promoter in cancer development; this role of the UPR indicates that regulation of the UPR can be utilized as a target for tumour treatment. T-cell exhaustion mainly refers to effector T cells losing their effector functions and expressing inhibitory receptors, leading to tumour immune evasion and the loss of tumour control. Emerging evidence suggests that the UPR plays a crucial role in T-cell exhaustion, immune evasion, and resistance to immunotherapy. In this review, we summarize the molecular basis of UPR activation, the effect of the UPR on immune evasion, the emerging mechanisms of the UPR in chemotherapy and immunotherapy resistance, and agents that target the UPR for tumour therapeutics. An understanding of the role of the UPR in immune evasion and therapeutic resistance will be helpful to identify new therapeutic modalities for cancer treatment. Video Abstract.

Omics-Based Investigations of Breast Cancer

Breast cancer (BC) is characterized by an extensive genotypic and phenotypic heterogeneity. In-depth investigations into the molecular bases of BC phenotypes, carcinogenesis, progression, and metastasis are necessary for accurate diagnoses, prognoses, and therapy assessments in predictive, precision, and personalized oncology. This review discusses both classic as well as several novel omics fields that are involved or should be used in modern BC investigations, which may be integrated as a holistic term, onco-breastomics. Rapid and recent advances in molecular profiling strategies and analytical techniques based on high-throughput sequencing and mass spectrometry (MS) development have generated large-scale multi-omics datasets, mainly emerging from the three "big omics", based on the central dogma of molecular biology: genomics, transcriptomics, and proteomics. Metabolomics-based approaches also reflect the dynamic response of BC cells to genetic modifications. Interactomics promotes a holistic view in BC research by constructing and characterizing protein-protein interaction (PPI) networks that provide a novel hypothesis for the pathophysiological processes involved in BC progression and subtyping. The emergence of new omics- and epiomics-based multidimensional approaches provide opportunities to gain insights into BC heterogeneity and its underlying mechanisms. The three main epiomics fields (epigenomics, epitranscriptomics, and epiproteomics) are focused on the epigenetic DNA changes, RNAs modifications, and posttranslational modifications (PTMs) affecting protein functions for an in-depth understanding of cancer cell proliferation, migration, and invasion. Novel omics fields, such as epichaperomics or epimetabolomics, could investigate the modifications in the interactome induced by stressors and provide PPI changes, as well as in metabolites, as drivers of BC-causing phenotypes. Over the last years, several proteomics-derived omics, such as matrisomics, exosomics, secretomics, kinomics, phosphoproteomics, or immunomics, provided valuable data for a deep understanding of dysregulated pathways in BC cells and their tumor microenvironment (TME) or tumor immune microenvironment (TIMW). Most of these omics datasets are still assessed individually using distinct approches and do not generate the desired and expected global-integrative knowledge with applications in clinical diagnostics. However, several hyphenated omics approaches, such as proteo-genomics, proteo-transcriptomics, and phosphoproteomics-exosomics are useful for the identification of putative BC biomarkers and therapeutic targets. To develop non-invasive diagnostic tests and to discover new biomarkers for BC, classic and novel omics-based strategies allow for significant advances in blood/plasma-based omics. Salivaomics, urinomics, and milkomics appear as integrative omics that may develop a high potential for early and non-invasive diagnoses in BC. Thus, the analysis of the tumor circulome is considered a novel frontier in liquid biopsy. Omics-based investigations have applications in BC modeling, as well as accurate BC classification and subtype characterization. The future in omics-based investigations of BC may be also focused on multi-omics single-cell analyses.

Role of NADPH Oxidase 4 in Corneal Endothelial Cells Is Mediated by Endoplasmic Reticulum Stress and Autophagy

Human corneal-endothelial cells (hCEnCs) are located on the inner layer of the cornea. Injury to CEnCs leads to permanent corneal edema, requiring corneal transplantation. NADPH oxidase 4 (NOX4) has been reported to be implicated in the pathogenesis of CEnCs diseases. Thus, we investigated the role of NOX4 in CEnCs in this study. In an animal study, siRNA for NOX4 (siNOX4) or plasmid for NOX4 (pNOX4) was introduced into the corneal endothelium of rats by electroporation, using a square-wave electroporator (ECM830, Havard apparatus) to decrease or increase the expression of NOX4, respectively, and the rat corneas were cryoinjured through contact with a metal rod of 3 mm diameter frozen in liquid nitrogen for 10 min. The immunofluorescence staining of NOX4 and 8-OHdG showed that the levels of NOX4 and 8-OHdG were decreased in the siNOX4 group compared to the siControl, and increased in the pNOX4 group compared to the pControl at one week after treatment. Without cryoinjury, corneal opacity was more severe, and the density of CEnCs was lower, in pNOX4-treated rats compared to pControl. After cryoinjury, the corneas were more transparent, and the CEnC density was higher, in siNOX4-treated rats. The hCEnCs were cultured and transfected with siNOX4 and pNOX4. The silencing of NOX4 in hCEnCs resulted in a normal cell shape, higher viability, and higher proliferation rate than those transfected with the siControl, while NOX4 overexpression had the opposite effect. NOX4 overexpression increased the number of senescent cells and intracellular oxidative stress levels. NOX4 overexpression increased ATF4 and ATF6 levels, and nuclear translocation of XBP-1, which is the endoplasmic reticulum (ER) stress marker, while the silencing of NOX4 had the opposite effect. Additionally, the mitochondrial membrane potential was hyperpolarized by the silencing of NOX4, and depolarized by NOX4 overexpression. The LC3II levels, a marker of autophagy, were decreased by the silencing of NOX4, and increased by NOX4 overexpression. In conclusion, NOX4 plays a pivotal role in the wound-healing and senescence of hCEnCs, by modulating oxidative stress, ER stress, and autophagy. The regulation of NOX4 may be a potential therapeutic strategy for regulating the homeostasis of CEnCs, and treating corneal-endothelial diseases.

Prion protein-dependent regulation of p53-MDM2 crosstalk during endoplasmic reticulum stress and doxorubicin treatments might be essential for cell fate in human breast cancer cell line, MCF-7

In this study, we investigated the effect of doxorubicin and tunicamycin treatment alone or in combination on MDM-, Cul9-and prion protein (PrP)-mediated subcellular regulation of p53 in the context of apoptosis and autophagy. MTT analysis was performed to determine the cytotoxic effect of the agents. Apoptosis was monitorized by ELISA, flow cytometry and JC-1 assay. Monodansylcadaverine assay was performed for autophagy. Western blotting and immunofluorescence were performed to determine p53, MDM2, CUL9 and PrP levels. Doxorubicin increased p53, MDM2 and CUL9 levels in a dose-dependent manner. Expression of p53 and MDM2 was higher at the 0.25 μM concentration of tunicamycin compared to the control, but it decreased at 0.5 μM and 1 μM concentrations. CUL9 expression was significantly decreased only after treatment of tunicamycin at 0.25 μM. According to its glycosylation status, the upper band of PrP increased only in combination treatment. In combination treatment, p53 expression was higher than control, whereas MDM2 and CUL9 expressions were decreased. Combination treatments may make MCF-7 cells more susceptible to apoptosis rather than autophagy. In conclusion, PrP may be important in determining the fate of cell death through crosstalk between proteins such as p53 and MDM2 under endoplasmic reticulum (ER) stress conditions. Further studies are needed to obtain in-depth information on these potential molecular networks.

The p53 endoplasmic reticulum stress-response pathway evolved in humans but not in mice via PERK-regulated p53 mRNA structures

Cellular stress conditions activate p53-dependent pathways to counteract the inflicted damage. To achieve the required functional diversity, p53 is subjected to numerous post-translational modifications and the expression of isoforms. Little is yet known how p53 has evolved to respond to different stress pathways. The p53 isoform p53/47 (p47 or ΔNp53) is linked to aging and neural degeneration and is expressed in human cells via an alternative cap-independent translation initiation from the 2nd in-frame AUG at codon 40 (+118) during endoplasmic reticulum (ER) stress. Despite an AUG codon in the same location, the mouse p53 mRNA does not express the corresponding isoform in either human or mouse-derived cells. High-throughput in-cell RNA structure probing shows that p47 expression is attributed to PERK kinase-dependent structural alterations in the human p53 mRNA, independently of eIF2α. These structural changes do not take place in murine p53 mRNA. Surprisingly, PERK response elements required for the p47 expression are located downstream of the 2nd AUG. The data show that the human p53 mRNA has evolved to respond to PERK-mediated regulation of mRNA structures in order to control p47 expression. The findings highlight how p53 mRNA co-evolved with the function of the encoded protein to specify p53-activities under different cellular conditions.

Apoptosis as a Barrier against CIN and Aneuploidy

Aneuploidy is the gain or loss of entire chromosomes, chromosome arms or fragments. Over 100 years ago, aneuploidy was described to be a feature of cancer and is now known to be present in 68-90% of malignancies. Aneuploidy promotes cancer growth, reduces therapy response and frequently worsens prognosis. Chromosomal instability (CIN) is recognized as the main cause of aneuploidy. CIN itself is a dynamic but stochastic process consisting of different DNA content-altering events. These can include impaired replication fidelity and insufficient clearance of DNA damage as well as chromosomal mis-segregation, micronuclei formation, chromothripsis or cytokinesis failure. All these events can disembogue in segmental, structural and numerical chromosome alterations. While low levels of CIN can foster malignant disease, high levels frequently trigger cell death, which supports the "aneuploidy paradox" that refers to the intrinsically negative impact of a highly aberrant karyotype on cellular fitness. Here, we review how the cellular response to CIN and aneuploidy can drive the clearance of karyotypically unstable cells through the induction of apoptosis. Furthermore, we discuss the different modes of p53 activation triggered in response to mitotic perturbations that can potentially trigger CIN and/or aneuploidy.

Drug Resistance and Endoplasmic Reticulum Stress in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and deadly cancers worldwide. It is usually diagnosed in an advanced stage and is characterized by a high intrinsic drug resistance, leading to limited chemotherapeutic efficacy and relapse after treatment. There is therefore a vast need for understanding underlying mechanisms that contribute to drug resistance and for developing therapeutic strategies that would overcome this. The rapid proliferation of tumor cells, in combination with a highly inflammatory microenvironment, causes a chronic increase of protein synthesis in different hepatic cell populations. This leads to an intensified demand of protein folding, which inevitably causes an accumulation of misfolded or unfolded proteins in the lumen of the endoplasmic reticulum (ER). This process is called ER stress and triggers the unfolded protein response (UPR) in order to restore protein synthesis or—in the case of severe or prolonged ER stress—to induce cell death. Interestingly, the three different arms of the ER stress signaling pathways have been shown to drive chemoresistance in several tumors and could therefore form a promising therapeutic target. This review provides an overview of how ER stress and activation of the UPR contributes to drug resistance in HCC.

Zinc Supplementation Enhances the Pro-Death Function of UPR in Lymphoma Cells Exposed to Radiation

Simple Summary

It is of fundamental importance to find strategies able to reduce the minimum doses of anticancer treatments, such as radiations, and concomitantly maintain efficient killing of cancer cells. The interconnection between ER stress and DNA repair may represent a promising approach to obtaining this goal. Here we found that pretreatment of lymphoma cells with Zinc chloride rendered these cells more sensitive to 2 Gy radiation. The exacerbation of ER stress and the activation pro-death function of UPR were among the underlying mechanisms leading to higher cytotoxicity of Zinc/radiation combination treatment. This evidence encourages the use of Zinc to reduce the doses of radiation in the treatment of lymphoma cells, allowing a high cytotoxicity to be obtained while minimizing the side effects.

Abstract

We have previously shown that Zinc supplementation triggered ER stress/UPR in cancer cells undergoing treatment by genotoxic agents, reactivated wtp53 in cancer cells harboring mutant p53 (mutp53) and potentiated the activity of wtp53 in those carrying wtp53. In this study, we used Zinc chloride alone or in combination with 2 Gy radiation to treat Primary Effusion Lymphoma (PEL) cells, an aggressive B-cell lymphoma associated with KSHV that harbors wt or partially functioning p53. We found that Zinc triggered a mild ER stress/UPR in these lymphoma cells and activated ERK1/2, molecule known to sustain cell survival in the course of UPR activation. In combination with radiations, Zinc triggered a stronger p53 activation that counteracted its mediated ERK1/2 phosphorylation, further upregulating the UPR molecule CHOP and promoting cell death. These data suggest that Zinc supplementation could be a promising strategy to reduce the doses of radiation and possibly of other DNA-damaging agents to obtain an efficient capacity to induce lymphoma cell death.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.

The Leloir Cycle in Glioblastoma: Galactose Scavenging and Metabolic Remodeling

BACKGROUND

Glioblastoma (GBM) can use metabolic fuels other than glucose (Glc). The ability of GBM to use galactose (Gal) as a fuel via the Leloir pathway is investigated.

METHODS

Gene transcript data were accessed to determine the association between expression of genes of the Leloir pathway and patient outcomes. Growth studies were performed on five primary patient-derived GBM cultures using Glc-free media supplemented with Gal. The role of Glut3/Glut14 in sugar import was investigated using antibody inhibition of hexose transport. A specific inhibitor of GALK1 (Cpd36) was used to inhibit Gal catabolism. Gal metabolism was examined using proton, carbon and phosphorous NMR spectroscopy, with ¹³C-labeled Glc and Gal as tracers.

RESULTS

Data analysis from published databases revealed that elevated levels of mRNA transcripts of SLC2A3 (Glut3), SLC2A14 (Glut14) and key Leloir pathway enzymes correlate with poor patient outcomes. GBM cultures proliferated when grown solely on Gal in Glc-free media and switching Glc-grown GBM cells into Gal-enriched/Glc-free media produced elevated levels of Glut3 and/or Glut14 enzymes. The ¹³C NMR-based metabolic flux analysis demonstrated a fully functional Leloir pathway and elevated pentose phosphate pathway activity for efficient Gal metabolism in GBM cells.

CONCLUSION

Expression of Glut3 and/or Glut14 together with the enzymes of the Leloir pathway allows GBM to transport and metabolize Gal at physiological glucose concentrations, providing GBM cells with an alternate energy source. The presence of this pathway in GBM and its selective targeting may provide new treatment strategies.

The regulatory roles of p53 in cardiovascular health and disease

Cardiovascular disease (CVD) remains the leading cause of mortality globally, so further investigation is required to identify its underlying mechanisms and potential targets for its prevention. The transcription factor p53 functions as a gatekeeper, regulating a myriad of genes to maintain normal cell functions. It has received a great deal of research attention as a tumor suppressor. In the past three decades, evidence has also shown a regulatory role for p53 in the heart. Basal p53 is essential for embryonic cardiac development; it is also necessary to maintain normal heart architecture and physiological function. In pathological cardiovascular circumstances, p53 expression is elevated in both patient samples and animal models. Elevated p53 plays a regulatory role via anti-angiogenesis, pro-programmed cell death, metabolism regulation, and cell cycle arrest regulation. This largely promotes the development of CVDs, particularly cardiac remodeling in the infarcted heart, hypertrophic cardiomyopathy, dilated cardiomyopathy, and diabetic cardiomyopathy. Roles for p53 have also been found in atherosclerosis and chemotherapy-induced cardiotoxicity. However, it has different roles in cardiomyocytes and non-myocytes, even in the same model. In this review, we describe the different effects of p53 in cardiovascular physiological and pathological conditions, in addition to potential CVD therapies targeting p53.

P53 in acute respiratory distress syndrome

P53 is a tumor suppressor protein, associated with strong anti-inflammatory activities. Recent evidence suggest that this transcription factor counteracts lung inflammatory diseases, including the lethal acute respiratory distress syndrome. Herein we provide a brief discussion on the relevant topic.

Simvastatin Induces Unfolded Protein Response and Enhances Temozolomide-Induced Cell Death in Glioblastoma Cells

Glioblastoma (GBM) is the most prevalent malignant primary brain tumor with a very poor survival rate. Temozolomide (TMZ) is the common chemotherapeutic agent used for GBM treatment. We recently demonstrated that simvastatin (Simva) increases TMZ-induced apoptosis via the inhibition of autophagic flux in GBM cells. Considering the role of the unfolded protein response (UPR) pathway in the regulation of autophagy, we investigated the involvement of UPR in Simva–TMZ-induced cell death by utilizing highly selective IRE1 RNase activity inhibitor MKC8866, PERK inhibitor GSK-2606414 (PERKi), and eIF2α inhibitor salubrinal. Simva–TMZ treatment decreased the viability of GBM cells and significantly increased apoptotic cell death when compared to TMZ or Simva alone. Simva–TMZ induced both UPR, as determined by an increase in GRP78, XBP splicing, eukaryote initiation factor 2α (eIF2α) phosphorylation, and inhibited autophagic flux (accumulation of LC3β-II and inhibition of p62 degradation). IRE1 RNase inhibition did not affect Simva–TMZ-induced cell death, but it significantly induced p62 degradation and increased the microtubule-associated proteins light chain 3 (LC3)β-II/LC3β-I ratio in U87 cells, while salubrinal did not affect the Simva–TMZ induced cytotoxicity of GBM cells. In contrast, protein kinase RNA-like endoplasmic reticulum kinase (PERK) inhibition significantly increased Simva–TMZ-induced cell death in U87 cells. Interestingly, whereas PERK inhibition induced p62 accumulation in both GBM cell lines, it differentially affected the LC3β-II/LC3β-I ratio in U87 (decrease) and U251 (increase) cells. Simvastatin sensitizes GBM cells to TMZ-induced cell death via a mechanism that involves autophagy and UPR pathways. More specifically, our results imply that the IRE1 and PERK signaling arms of the UPR regulate Simva–TMZ-mediated autophagy flux inhibition in U251 and U87 GBM cells.

When Endoplasmic Reticulum Proteostasis Meets the DNA Damage Response

Sustaining both proteome and genome integrity (GI) requires the integration of a wide range of mechanisms and signaling pathways. These comprise, in particular, the unfolded protein response (UPR) and the DNA damage response (DDR). These adaptive mechanisms take place respectively in the endoplasmic reticulum (ER) and in the nucleus. UPR and DDR alterations are associated with aging and with pathologies such as degenerative diseases, metabolic and inflammatory disorders, and cancer. We discuss the emerging signaling crosstalk between UPR stress sensors and the DDR, as well as their involvement in cancer biology.