PERK Activation Promotes Medulloblastoma Tumorigenesis by Attenuating Premalignant Granule Cell Precursor Apoptosis

Impact of proteostasis workload on sensitivity to proteasome inhibitors in multiple myeloma

Genomic alterations and enormous monoclonal immunoglobulin production cause multiple myeloma to heavily depend on proteostasis mechanisms, including protein folding and degradation. These findings support the use of proteasome inhibitors for treating multiple myeloma and mantle cell lymphoma. Myeloma treatment has evolved, especially with the availability of new drugs, such as proteasome inhibitors, into therapeutic strategies for both frontline and relapsed/refractory disease settings. However, proteasome inhibitors are generally not effective enough to cure most patients. Natural resistance and eventual acquired resistance led to relapsed/refractory disease and poor prognosis. Advances in the understanding of cellular proteostasis and the development of innovative drugs that also target other proteostasis network components offer opportunities to exploit the intrinsic vulnerability of myeloma cells. This review outlines recent findings on the molecular mechanisms regulating cellular proteostasis pathways, as well as resistance, sensitivity, and escape strategies developed against proteasome inhibitors and provides a rationale and examples for novel combinations of proteasome inhibitors with FDA-approved drugs and investigational drugs targeting the NRF1 (NFE2L1)-mediated proteasome bounce-back response, redox homeostasis, heat shock response, unfolding protein response, autophagy, and VCP/p97 to increase proteotoxic stress, which can improve the efficacy of antimyeloma therapy based on proteasome inhibitors.

CCT020312 exerts anti-prostate cancer effect by inducing G1 cell cycle arrest, apoptosis and autophagy through activation of PERK/eIF2α/ATF4/CHOP signaling

PERK/eIF2α/ATF4/CHOP signaling pathway is one of three major branches of unfolded protein response (UPR) and has been implicated in tumor progression. CCT020312 is a selective PERK activator and may have a potential anti-tumor effect. Here we investigated the anti-prostate cancer effect and its underlying mechanism of CCT020312. Our results showed that CCT020312 inhibited prostate cancer cell viability by inducing cell cycle arrest, apoptosis and autophagy through activation of PERK/eIF2α/ATF4/CHOP signaling. CCT020312 treatment caused cell cycle arrest at G1 phase and increased the levels of cleaved-Caspase3, cleaved-PARP and Bax in prostate cancer C4-2 and LNCaP cells. Moreover, CCT020312 increased LC3II/I, Atg12-Atg5 and Beclin1 levels and induced autophagosome formation. Furthermore, knockdown of CHOP reversed CCT020312-induced cell viability decrease, apoptosis and autophagy. Bafilomycin A1 reversed CCT020312-induced cell viability decrease but had no effect on CCT020312-induced CHOP activation in C4-2 and LNCaP cells. In vivo, CCT020312 suppressed tumor growth in C4-2 cells-derived xenograft mouse model, activated PERK pathway, and induced autophagy and apoptosis. Our study illustrates that CCT020312 exerts an anti-tumor effect in prostate cancer via activating the PERK pathway, thus indicating that CCT020312 may be a potential drug for prostate cancer.

Differential Signaling Pathways in Medulloblastoma: Nano-biomedicine Targeting Non-coding Epigenetics to Improve Current and Future Therapeutics

BACKGROUND

Medulloblastomas (MDB) are malignant, aggressive brain tumors that primarily affect children. The survival rate for children under 14 is approximately 72%, while for ages 15 to 39, it is around 78%. A growing body of evidence suggests that dysregulation of signaling mechanisms and noncoding RNA epigenetics play a pivotal role in this disease.

METHODOLOGY

This study conducted an electronic search of articles on websites like PubMed and Google. The current review also used an in silico databases search and bioinformatics analysis and an extensive comprehensive literature search for original research articles and review articles as well as retrieval of current and future medications in clinical trials.

RESULTS

This study indicates that several signaling pathways, such as sonic hedgehog, WNT/β-catenin, unfolded protein response mediated ER stress, notch, neurotrophins and TGF-β and ERK, MAPK, and ERK play a crucial role in the pathogenesis of MDB. Gene and ncRNA/protein are also involved as an axis long ncRNA to sponge micro-RNAs that affect downstream signal proteins expression and translation affection disease pathophysiology, prognosis and present potential target hit for drug repurposing. Current treatment options include surgery, radiation, and chemotherapy; unfortunately, the disease often relapses, and the survival rate is less than 5%. Therefore, there is a need to develop more effective treatments to combat recurrence and improve survival rates.

CONCLUSION

This review describes various MDB disease hallmarks, including the signaling mechanisms involved in pathophysiology, related-causal genes, epigenetics, downstream genes/epigenes, and possibly the causal disease genes/non-protein coding (nc)RNA/protein axis. Additionally, the challenges associated with MDB treatment are discussed, along with how they are being addressed using nano-technology and nano-biomedicine, with a listing of possible treatment options and future potential treatment modalities.

Unconventional Protein Secretion in Brain Tumors Biology: Enlightening the Mechanisms for Tumor Survival and Progression

Non-canonical secretion pathways, collectively known as unconventional protein secretion (UPS), are alternative secretory mechanisms usually associated with stress-inducing conditions. UPS allows proteins that lack a signal peptide to be secreted, avoiding the conventional endoplasmic reticulum-Golgi complex secretory pathway. Molecules that generally rely on the canonical pathway to be secreted may also use the Golgi bypass, one of the unconventional routes, to reach the extracellular space. UPS studies have been increasingly growing in the literature, including its implication in the biology of several diseases. Intercellular communication between brain tumor cells and the tumor microenvironment is orchestrated by various molecules, including canonical and non-canonical secreted proteins that modulate tumor growth, proliferation, and invasion. Adult brain tumors such as gliomas, which are aggressive and fatal cancers with a dismal prognosis, could exploit UPS mechanisms to communicate with their microenvironment. Herein, we provide functional insights into the UPS machinery in the context of tumor biology, with a particular focus on the secreted proteins by alternative routes as key regulators in the maintenance of brain tumors.

Detection of PERK Signaling in the Central Nervous System

In response to endoplasmic reticulum (ER) stress, activation of pancreatic ER kinase (PERK) signaling adapts cells to stressful conditions by phosphorylating eukaryotic translation initiation factor 2α (eIF2α). Phosphorylation of eIF2α inhibits global protein translation but stimulates the expression of numerous stress-responsive genes by inducing the transcription factor ATF4. A large number of studies have shown that activation of PERK signaling has beneficial or detrimental effects in various diseases of the central nervous system (CNS), including neurodegenerative diseases, myelin disorders, CNS injuries, among others. This chapter is devoted to describing the practical methods for the detection of PERK signaling in CNS diseases.

Sequential inverse dysregulation of the RNA helicases DDX3X and DDX3Y facilitates MYC-driven lymphomagenesis

DDX3X is a ubiquitously expressed RNA helicase involved in multiple stages of RNA biogenesis. DDX3X is frequently mutated in Burkitt lymphoma, but the functional basis for this is unknown. Here, we show that loss-of-function DDX3X mutations are also enriched in MYC-translocated diffuse large B cell lymphoma and reveal functional cooperation between mutant DDX3X and MYC. DDX3X promotes the translation of mRNA encoding components of the core translational machinery, thereby driving global protein synthesis. Loss-of-function DDX3X mutations moderate MYC-driven global protein synthesis, thereby buffering MYC-induced proteotoxic stress during early lymphomagenesis. Established lymphoma cells restore full protein synthetic capacity by aberrant expression of DDX3Y, a Y chromosome homolog, the expression of which is normally restricted to the testis. These findings show that DDX3X loss of function can buffer MYC-driven proteotoxic stress and highlight the capacity of male B cell lymphomas to then compensate for this loss by ectopic DDX3Y expression.

Characterization of a PERK Kinase Inhibitor with Anti-Myeloma Activity

Due to increased immunoglobulin production and uncontrolled proliferation, multiple myeloma (MM) plasma cells develop a phenotype of deregulated unfolded protein response (UPR). The eIF2-alpha kinase 3 [EIF2αK3, protein kinase R (PKR)-like ER kinase (PERK)], the third known sensor of endoplasmic reticulum (ER) stress, is a serine-threonine kinase and, like the other two UPR-related proteins, i.e., IRE1 and ATF6, it is bound to the ER membrane. MM, like other tumors showing uncontrolled protein secretion, is highly dependent to UPR for survival; thus, inhibition of PERK can be an effective strategy to suppress growth of malignant plasma cells. Here, we have used GSK2606414, an ATP-competitive potent PERK inhibitor, and found significant anti-proliferative and apoptotic effects in a panel of MM cell lines. These effects were accompanied by the downregulation of key components of the PERK pathway as well as of other UPR elements. Consistently, PERK gene expression silencing significantly increased cell death in MM cells, highlighting the importance of PERK signaling in MM biology. Moreover, GSK2606414, in combination with the proteasome inhibitor bortezomib, exerted an additive toxic effect in MM cells. Overall, our data suggest that PERK inhibition could represent a novel combinatorial therapeutic approach in MM.

Puncta intended: connecting the dots between autophagy and cell stress networks

Proteome profiling and global protein-interaction approaches have significantly improved our knowledge of the protein interactomes of autophagy and other cellular stress-response pathways. New discoveries regarding protein complexes, interaction partners, interaction domains, and biological roles of players that are part of these pathways are emerging. The fourth Vancouver Autophagy Symposium showcased research that expands our understanding of the protein interaction networks and molecular mechanisms underlying autophagy and other cellular stress responses in the context of distinct stressors. In the keynote presentation, Dr. Wade Harper described his team's recent discovery of a novel reticulophagy receptor for selective autophagic degradation of the endoplasmic reticulum, and discussed molecular mechanisms involved in ribophagy and non-autophagic ribosomal turnover. In other presentations, both omic and targeted approaches were used to reveal molecular players of other cellular stress responses including amyloid body and stress granule formation, anastasis, and extracellular vesicle biogenesis. Additional topics included the roles of autophagy in disease pathogenesis, autophagy regulatory mechanisms, and crosstalk between autophagy and cellular metabolism in anti-tumor immunity. The relationship between autophagy and other cell stress responses remains a relatively unexplored area in the field, with future investigations required to understand how the various processes are coordinated and connected in cells and tissues.Abbreviations: A-bodies: amyloid bodies; ACM: amyloid-converting motif; AMFR/gp78: autocrine motility factor receptor; ATG: autophagy-related; ATG4B: autophagy related 4B cysteine peptidase; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CAR T: chimeric antigen receptor T; CASP3: caspase 3; CCPG1: cell cycle progression 1; CAR: chimeric antigen receptor; CML: chronic myeloid leukemia; CCOCs: clear cell ovarian cancers; CVB3: coxsackievirus B3; CRISPR-Cas9: clustered regularly interspaced short palindromic repeats-CRISPR associated protein 9; DDXs: DEAD-box helicases; EIF2S1/EIF-2alpha: eukaryotic translation initiation factor 2 subunit alpha; EIF2AK3: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; EV: extracellular vesicle; FAO: fatty acid oxidation; GABARAP: GABA type A receptor-associated protein; ILK: integrin linked kinase; ISR: integrated stress response; MTOR: mechanistic target of rapamycin kinase; MPECs: memory precursory effector T cells; MAVS: mitochondrial antiviral signaling protein; NBR1: NBR1 autophagy cargo receptor; PI4KB/PI4KIIIβ: phosphatidylinositol 4-kinase beta; PLEKHM1: pleckstrin homology and RUN domain containing M1; RB1CC1: RB1 inducible coiled-coil 1; RTN3: reticulon 3; rIGSRNAs: ribosomal intergenic noncoding RNAs; RPL29: ribosomal protein L29; RPS3: ribosomal protein S3; S. cerevisiae: Saccharomyces cerevisiae; sEV: small extracellular vesicles; S. pombe: Schizosaccharomyces pombe; SQSTM1: sequestosome 1; SF3B1: splicing factor 3b subunit 1; SILAC-MS: stable isotope labeling with amino acids in cell culture-mass spectrometry; SNAP29: synaptosome associated protein 29; TEX264: testis expressed 264, ER-phagy receptor; TNBC: triple-negative breast cancer; ULK1: unc-51 like autophagy activating kinase 1; VAS: Vancouver Autophagy Symposium.

Profile of the unfolded protein response in rat cerebellar cortical development

The unfolded protein response (UPR) has been reported during normal development of cortical neurons and cerebellar white matter and may also contribute to the pathogenesis of neurological conditions, such as Marinesco-Sjogren syndrome and Borna virus infection, which result in cerebellar defects. The UPR is initiated when the processing capacity of the endoplasmic reticulum (ER) is overwhelmed. Misfolded proteins accumulate and can activate ER stress sensors; PKR-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1), activated transcription factor 6 (ATF6) and their downstream targets glucose-regulated protein 78 (GRP78), glucose-regulated protein 94 (GRP94) and protein disulfide isomerase (PDI). In order to provide a fuller appreciation of the possible importance of ER stress-associated proteins in the context of cerebellar disease, we have profiled the expression of ER stress sensors and their downstream targets in the developing cerebellar cortex in postnatal rat. Activation of PERK and IRE1 stress sensors was observed for the first time in normally developing granule cell precursors. A second proliferative pPERK-positive population was also detected in the internal granular layer (IGL). In general, the density of UPR protein-positive cells was found to decrease significantly when profiles in early and late postnatal ages were compared. These data may be relevant to studies of medulloblastoma and warrant further investigation.

Neuron-specific PERK inactivation exacerbates neurodegeneration during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), are chronic inflammatory demyelinating and neurodegenerative diseases of the CNS. Although neurodegeneration is the major contributor to chronic disability in MS, mechanisms governing the viability of axons and neurons in MS and EAE remain elusive. Data indicate that activation of pancreatic endoplasmic reticulum kinase (PERK) influences, positively or negatively, neuron and axon viability in various neurodegenerative diseases through induction of ATF4. In this study, we demonstrate that the PERK pathway was activated in neurons during EAE. We found that neuron-specific PERK inactivation impaired EAE resolution and exacerbated EAE-induced axon degeneration, neuron loss, and demyelination. Surprisingly, neuron-specific ATF4 inactivation did not alter EAE disease course or EAE-induced axon degeneration, neuron loss, and demyelination. These results suggest that PERK activation in neurons protects axons and neurons against inflammation in MS and EAE through ATF4-independent mechanisms.

Activation of PERK-eIF2α-ATF4-CHOP axis triggered by excessive ER stress contributes to lead-induced nephrotoxicity

Lead (Pb) is a known nephrotoxicant that causes damage to proximal tubular cells. PERK pathway plays an important role in the pathogenesis of renal diseases, but its role in Pb-induced nephrotoxicity remains largely unknown. In this study, data showed that Pb could induce ER stress as shown by increased phosphorylation of PERK with subsequent activation of the eIF2α-ATF4-CHOP axis in primary rat proximal tubular (rPT) cells, indicating the activation of PERK-eIF2α-ATF4-CHOP pathway due to excessive ER stress. Pb-activated PERK pathway can be effectively inhibited by 4-phenylbutyric acid and PERK gene silencing, respectively; whereas continuously up-regulated by tunicamycin (TM) treatment. Moreover, Pb-induced apoptosis and inhibition of autophagic flux in rPT cells were significantly augmented and aggravated by co-treatment with TM, respectively. Pharmacological or genetic inhibition of the PERK pathway results in alleviation of apoptosis and restoration of autophagy inhibition in Pb-exposed rPT cells. Mechanistically, activation of PERK-eIF2α-ATF4-CHOP axis triggered by excessive ER stress in rPT cells leads to Pb-induced apoptosis and blockage of autophagic flux, resulting in nephrotoxicity.

Activating transcription factor 6α deficiency exacerbates oligodendrocyte death and myelin damage in immune-mediated demyelinating diseases

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) play a critical role in immune-mediated demyelinating diseases, including multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE), by regulating the viability of oligodendrocytes. Our previous studies show that activation of the PERK branch of the UPR protects myelinating oligodendrocytes against ER stress in young, developing mice that express IFN-γ, a key pro-inflammatory cytokine in MS and EAE, in the CNS. Several studies also demonstrate that PERK activation preserves oligodendrocyte viability and function, protecting mice against EAE. While evidence suggests activation of the ATF6α branch of the UPR in oligodendrocytes under normal and disease conditions, the effects of ATF6α activation on oligodendrocytes in immune-mediated demyelinating diseases remain unknown. Herein, we showed that ATF6α deficiency had no effect on oligodendrocytes under normal conditions. Interestingly, we showed that ATF6α deficiency exacerbated ER stressed-induced myelinating oligodendrocyte death and subsequent myelin loss in the developing CNS of IFN-γ-expressing mice. Moreover, we found that ATF6α deficiency increased EAE severity and aggravated EAE-induced oligodendrocyte loss and demyelination, without affecting inflammation. Thus, these data suggest the protective effects of ATF6α activation on oligodendrocytes in immune-mediated demyelinating diseases.

Resistant starch prevents tumorigenesis of dimethylhydrazine-induced colon tumors via regulation of an ER stress-mediated mitochondrial apoptosis pathway

Resistant starch is as common soluble fiber that escapes digestion in the small intestine and can regulate intestinal function, metabolism of blood glucose and lipids, and may prevent tumorigenesis of gastrointestinal cancer. Epidemiology and other evidence have suggested that resistant starch may prevent colon cancer development. The aim of the current study was to explore the ameliorative effects and potential mechanisms of resistant starch in the tumorigenesis of colon tumors induced by dimethylhydrazine in C57BL/6 mice. Western blot analysis, ELISA, microscopy, immunofluorescence and immunohistochemistry were used to analyze the efficacy of resistant starch on the metabolic balance in the colon and tumorigenesis of colon tumors. The results demonstrated that a diet containing resistant starch decreased the animal body weight and reduced free ammonia, pH and short chain fatty acids in feces compared with mice that received a standard diet. Resistant starch reduced the incidence of colon tumors and suppressed the expression of carcinogenesis-associated proteins, including heat shock protein 25, protein kinase C-d and gastrointestinal glutathione peroxidase in colon epithelial cells compared with standard starch and control groups. Colon tumor cells proliferation and dedifferentiation were significantly decreased by a resistant starch diet. The results also demonstrated that resistant starch increased the apoptosis of colon tumor cells through regulation of apoptosis-associated gene expression levels in colon tumor cells. Oxidative stress and endoplasmic reticulum stress were upregulated, and elevation eukaryotic translation initiation factor 2α (eIF2α), activating transcription factor-4 and secretase-β expression levels were increased in the resistant starch diet group. Additionally, the activity of eIF2α and PERK were increased in colon tumor cells from mice that had received resistant starch. Increasing DNA damage-inducible transcript 3 protein (CHOP), binding immunoglobulin protein (BIP) and caspase-12 expression levels upregulated by resistant starch diet may contribute to the resistant starch-induced apoptosis of colon tumor cells induced by 1,2-dimethylhydrazine. In vitro assays demonstrated that knockdown of eIF2α inhibited apoptosis of colon tumor cells isolated from mice fed with resistant starch, which also downregulated CHOP, BIP and caspase-3 expression levels compared with controls. Furthermore, long-term survival of experimental mice was prolonged by the resistant starch diet compared with the standard diet group. In conclusion, the results indicate that resistant starch in the diet may prevent carcinogenesis of colon epithelial cells, mediated by enhancing apoptosis through an endoplasmic reticulum stress-mediated mitochondrial apoptosis pathway.

Dual role of the integrated stress response in medulloblastoma tumorigenesis

In response to endoplasmic reticulum (ER) stress, activation of pancreatic ER kinase (PERK) coordinates an adaptive program known as the integrated stress response (ISR) by phosphorylating translation initiation factor 2α (eIF2α). Phosphorylated eIF2α is quickly dephosphorylated by the protein phosphatase 1 and growth arrest and DNA damage 34 (GADD34) complex. Data indicate that the ISR can either promote or suppress tumor development. Our previous studies showed that the ISR is activated in medulloblastoma in both human patients and animal models, and that the decreased ISR via PERK heterozygous deficiency attenuates medulloblastoma formation in Patched1 heterozygous deficient (Ptch1+/-) mice by enhancing apoptosis of pre-malignant granule cell precursors (GCPs) during cell transformation. We showed here that GADD34 heterozygous mutation moderately enhanced the ISR and noticeably increased the incidence of medulloblastoma in adult Ptch1+/- mice. Surprisingly, GADD34 homozygous mutation strongly enhanced the ISR, but significantly decreased the incidence of medulloblastoma in adult Ptch1+/- mice. Intriguingly, GADD34 homozygous mutation significantly enhanced pre-malignant GCP apoptosis in cerebellar hyperplastic lesions and reduced the lesion numbers in young Ptch1+/- mice. Nevertheless, neither GADD34 heterozygous mutation nor GADD34 homozygous mutation had a significant effect on medulloblastoma cells in adult Ptch1+/- mice. Collectively, these data imply the dual role of the ISR, promoting and inhibiting, in medulloblastoma tumorigenesis by regulating apoptosis of pre-malignant GCPs during the course of malignant transformation.