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Melanomas that result from mutations in the gene encoding BRAF often become resistant to BRAF inhibition (BRAFi), with multiple mechanisms contributing to resistance. While therapy-induced autophagy promotes resistance to a number of therapies, especially those that target PI3K/mTOR signaling, its role as an adaptive resistance mechanism to BRAFi is not well characterized. Using tumor biopsies from BRAF(V600E) melanoma patients treated either with BRAFi or with combined BRAF and MEK inhibition, we found that BRAFi-resistant tumors had increased levels of autophagy compared with baseline. Patients with higher levels of therapy-induced autophagy had drastically lower response rates to BRAFi and a shorter duration of progression-free survival. In BRAF(V600E) melanoma cell lines, BRAFi or BRAF/MEK inhibition induced cytoprotective autophagy, and autophagy inhibition enhanced BRAFi-induced cell death. Shortly after BRAF inhibitor treatment in melanoma cell lines, mutant BRAF bound the ER stress gatekeeper GRP78, which rapidly expanded the ER. Disassociation of GRP78 from the PKR-like ER-kinase (PERK) promoted a PERK-dependent ER stress response that subsequently activated cytoprotective autophagy. Combined BRAF and autophagy inhibition promoted tumor regression in BRAFi-resistant xenografts. These data identify a molecular pathway for drug resistance connecting BRAFi, the ER stress response, and autophagy and provide a rationale for combination approaches targeting this resistance pathway.

Purpose of Review: Hematopoietic stem cells (HSCs) possess the ability to regenerate over a lifetime in the face of extreme cellular proliferation and environmental stress. Yet, mechanisms that control the regenerative properties of HSCs remain elusive. ER stress has emerged as an important signaling event that supports HSC self-renewal and multipotency. The purpose of this review is to summarize the pathways implicating ER stress as cytoprotective in HSCs., Recent Findings: Recent studies have shown multiple signaling cascades of the unfolded protein response (UPR) are persistently activated in healthy HSCs, suggesting that low-dose ER stress is a feature HSCs. Stress adaptation is a feature ascribed to cytoprotection and longevity of cells as well as organisms, in what is known as hormesis. However, assembling this information into useful knowledge to improve the therapeutic application of HSCs remains challenging and the upstream activators and downstream transcriptional programs induced by ER stress that are required in HSCs remain to be discovered., Summary: The maintenance of HSCs requires a dose-dependent simulation of ER stress responses that involves persistent, low-dose UPR. Unraveling the complexity of this signaling node may elucidate mechanisms related to regeneration of HSCs that can be harnessed to expand HSCs for cellular therapeutics ex vivo and transplantation in vivo., (Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc.)

Endoplasmic reticulum (ER) stress and autophagy dysfunction contribute to the establishment and progression of diverse pathologies. Proteolytic activation of the transcription factor nSREBP1 is induced under ER stress; however, little is known about how SREBP1 and its nuclear active form nSREBP1 influence autophagy and unfolded protein response (UPR) activation in osteosarcoma cells. Our research focused on the effect of SREBP1/nSREBP1 upon apoptosis and autophagy during ER stress and the molecular mechanisms involved. Here, we showed that nSREBP1 binds to the promoter of protein kinase RNA-like endoplasmic reticulum kinase (PERK) and then regulates ER stress, cell growth, cell apoptosis, and autophagy through the PERK signaling pathway. nSREBP1 increased PERK gene expression and phosphorylation. nSREBP1 was further demonstrated to activate ER stress response through stimulatory effects on PERK signaling. Overexpression of SREBP1 increased its cleavage and release of nSREBP1; therefore, the effect of SREBP1 is achieved through the enhancement of the expression of nSREBP1. Overexpression of SREBP1/nSREBP1 amplifies PERK-associated cell cycle stagnation with G1 phase arresting, S phase reducing, and G2-M phase delaying. LV-SREBP1/nSREBP1 can also bolster PERK's ER stress-associated pro-apoptotic effects. LV-SREBP1/nSREBP1 and LV-PERK can activate autophagy in ER stress response, along with the overexpression of SREBP1/nSREBP1 and PERK. This resulted in amplification of PERK-related changes to cell proliferation and ER stress-mediated apoptosis and autophagy, with the biological effect of nSREBP1 relying on PERK, which makes up one of the three branches of the UPR signaling pathway. This study reveals important roles for SREBP1/nSREBP1 in PERK signaling under ER stress. Furthermore, nSREBP1, the nuclear active form of SREBP1, is able to robustly augment the effects of PERK. Description of the link between PERK and SREBP1/nSREBP1 function offers an improved understanding of the ER stress response and insight into the biological function of SREBP1/nSREBP1., (© 2019 Federation of European Biochemical Societies.)

Palmitic acid (PA) is the most common saturated long-chain fatty acid in food that causes cell apoptosis. However, little is known about the molecular mechanisms of PA toxicity. In this study, we explore the effects of PA on proliferation and apoptosis in human osteoblast-like Saos-2 cells and uncover the signaling pathways involved in the process. Our study showed that endoplasmic reticulum (ER) stress and autophagy are involved in PA-induced Saos-2 cell apoptosis. We found that PA inhibited the viability of Saos-2 cells in a dose- and time-dependent manner. At the same time, PA induced the expression of ER stress marker genes (glucose-regulated protein 78 (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP)), altered autophagy-related gene expression (microtubule-associated protein 1 light chain 3 (LC3), ATG5, p62, and Beclin), promoted apoptosis-related gene expression (Caspase 3 and BAX), and affected autophagic flux. Inhibiting ER stress with 4-PBA diminished the PA-induced cell apoptosis, activated autophagy, and increased the expression of Caspase 3 and BAX. Inhibiting autophagy with 3-MA attenuated the PA and ER stress-induced cell apoptosis and the apoptosis-related gene expression (Caspase 3 and BAX), but seemed to have no obvious effects on ER stress, although the CHOP expression was downregulated. Taken together, our results suggest that PA-induced Saos-2 cell apoptosis is activated via ER stress and autophagy, and the activation of autophagy depends on the ER stress during this process.

Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with high probability of recurrence and distant metastasis. Liver metastasis is the predominant metastatic mode developed in most pancreatic cancer cases, which seriously affects the overall survival rate of patients. Abnormally activated endoplasmic reticulum stress and lipid metabolism reprogramming are closely related to tumor growth and metastasis. This study aims to construct a prognostic model based on endoplasmic reticulum stress and lipid metabolism for pancreatic cancer, and further explore its correlation with tumor immunity and the possibility of immunotherapy. Methods: Transcriptomic and clinical data are acquired from TCGA, ICGC, and GEO databases. Potential prognostic genes were screened by consistent clustering and WGCNA methods, and the whole cohort was randomly divided into training and testing groups. The prognostic model was constructed by machine learning method in the training cohort and verified in the test, TCGA and ICGC cohorts. The clinical application of this model and its relationship with tumor immunity were analyzed, and the relationship between endoplasmic reticulum stress and intercellular communication was further explored. Results: A total of 92 characteristic genes related to endoplasmic reticulum stress, lipid metabolism and liver metastasis were identified in pancreatic cancer. We established and validated a prognostic model for pancreatic cancer with 7 signatures, including ADH1C, APOE, RAP1GAP, NPC1L1, P4HB, SOD2, and TNFSF10. This model is considered to be an independent prognosticator and is a more accurate predictor of overall survival than age, gender, and stage. TIDE score was increased in high-risk group, while the infiltration levels of CD8+ T cells and M1 macrophages were decreased. The number and intensity of intercellular communication were increased in the high ER stress group. Conclusions: We constructed and validated a novel prognostic model for pancreatic cancer, which can also be used as an instrumental variable to predict the prognosis and immune microenvironment. In addition, this study revealed the effect of ER stress on cell–cell communication in the tumor microenvironment. [ABSTRACT FROM AUTHOR]

Background: Colorectal cancer (CRC) is one of the most common malignant tumors globally, with high morbidity and mortality. Endoplasmic reticulum is a major organelle responsible for protein synthesis, processing, and transport. Endoplasmic reticulum stress (ERS) refers to the abnormal accumulation of unfolded and misfolded proteins in the endoplasmic reticulum, which are involved in tumorigenesis and cancer immunity. Nevertheless, the clinical significance of ERS remains largely unexplored in CRC. Methods: In present study, we performed an unsupervised clustering to identify two types of ERS-related subtypes [ERS clusters, and ERS-related genes (ERSGs) clusters] in multiple large-scale CRC cohorts. Through the utilization of machine learning techniques, we have successfully developed an uncomplicated yet robust gene scoring system (ERSGs signature). Furthermore, a series of analyses, including GO, KEGG, Tumor Immune Dysfunction and Exclusion (TIDE), the Consensus Molecular Subtypes (CMS), were used to explore the underlying biological differences and clinical significance between these groups. And immunohistochemical and bioinformatics analyses were performed to explore ZNF703, a gene of ERSGs scoring system. Results: We observed significant differences in prognosis and tumor immune status between the ERS clusters as well as ERSGs clusters. And the ERSGs scoring system was an independent risk factor for overall survival; and exhibited distinct tumor immune status in multicenter CRC cohorts. Besides, analyses of TNM stages, CMS groups demonstrated that patients in advanced stage and CMS4 had higher ERSGs scores. In addition, the ERSGs scores inversely correlated with positive ICB response predictors (such as, CD8A, CD274 (PD-L1), and TIS), and directly correlated with negative ICB response predictors (such as, TIDE, T cell Exclusion, COX-IS). Notably, immunohistochemical staining and bioinformatics analyses revealed that ZNF70 correlated with CD3 + and CD8 + T cells infiltration. Conclusion: Based on large-scale and multicenter transcriptomic data, our study comprehensively revealed the essential role of ERS in CRC; and constructed a novel ERSGs scoring system to predict the prognosis of patients and the efficacy of ICB treatment. Furthermore, we identified ZNF703 as a potentially promising target for ICB therapy in CRC. [ABSTRACT FROM AUTHOR]

Virilizer-like m6A methyltransferase-associated protein (VIRMA) maintains the stability of the m6A writer complex. Although VIRMA is critical for RNA m6A deposition, the impact of aberrant VIRMA expression in human diseases remains unclear. We show that VIRMA is amplified and overexpressed in 15–20% of breast cancers. Of the two known VIRMA isoforms, the nuclear-enriched full-length but not the cytoplasmic-localised N-terminal VIRMA promotes m6A-dependent breast tumourigenesis in vitro and in vivo. Mechanistically, we reveal that VIRMA overexpression upregulates the m6A-modified long non-coding RNA, NEAT1, which contributes to breast cancer cell growth. We also show that VIRMA overexpression enriches m6A on transcripts that regulate the unfolded protein response (UPR) pathway but does not promote their translation to activate the UPR under optimal growth conditions. Under stressful conditions that are often present in tumour microenvironments, VIRMA-overexpressing cells display enhanced UPR and increased susceptibility to death. Our study identifies oncogenic VIRMA overexpression as a vulnerability that may be exploited for cancer therapy. [ABSTRACT FROM AUTHOR]

Related studies have shown that chromium (Cr) is toxic to cells, and hydrogen can protect cells by regulating endoplasmic reticulum (ER) stress and autophagy. However, there are few reports on the protective effects of hydrogen on heavy metal-induced cell damage. The objective of this study was to investigate the protection of hydrogen-rich medium (HRM) on Cr(VI)-induced ER stress and autophagy in DF-1 cells. Therefore, HRM were pretreated for 30 min before Cr(VI) treatment, and detected the autophagy and ER stress-related indicators to determine the role of HRM. The results showed that HRM could reduce the cell damage caused by Cr(VI), and 3-methyladenine (3-MA) could protect cells by inhibiting over autophagy. HRM can reverse the changes of ER stress- and autophagy-related indexes caused by Cr(VI), and inhibit the excessive autophagy caused by Cr(VI). In conclusion, HRM can protect cells from damage induced by Cr(VI), and play a role by inhibiting ER stress-mediated autophagy. [ABSTRACT FROM AUTHOR]

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Outcomes of melanoma patient treatment remain unsatisfactory despite accessibility of oncoprotein-targeting drugs and immunotherapy. Here, we reported that 17-aminogeldanamycin more potently activated caspase-3/7 in BRAFV600E melanoma cells than geldanamycin, another inhibitor of heat shock protein 90 (HSP90). 17-aminogeldanamycin alleviated self-triggered compensatory increase in HSP70 mRNA level and induced endoplasmic reticulum (ER) stress, which was followed by selective diminution of cytoprotective IRE1α-XBP1s pathway activity of unfolded protein response (UPR), inhibition of ERK1/2 activity and induction of apoptosis. Concomitantly, ATF6/p50 level and expression of PERK-dependent genes, CHOP and BIM, remained unaltered. This might result from an inframe deletion in EIF2AK3 leading to a PERKL21del variant revealed by whole-exome sequencing in melanoma cell lines. 17-aminogeldanamycin exhibited similar activity in NRASQ61R melanoma cells that harbored a heterozygous inactivating variant of NAD(P)H:quinone oxidoreductase 1 (NQO1P187S). In addition, 17-aminogeldanamycin acted cooperatively with trametinib (an inhibitor of MEK1/2) and vemurafenib (an inhibitor of BRAFV600E) in induction of apoptosis in melanoma cell lines as evidenced by in-cell caspase-3/7 activation and PARP cleavage that occurred earlier compared with either drug used alone. As trametinib and vemurafenib did not significantly affect HSP70 and GRP78 transcript levels, cooperation of MEK/BRAFV600E inhibitors and 17-aminogeldanamycin might result from a concurrent inhibition of the RAS/RAF/MEK/ERK cascade and IRE1α-dependent signaling, and cell-intrinsic ER homeostasis can determine the extent of the drug cooperation. Our study indicates that 17-aminogeldanamycin takes several advantages compared with other HSP90-targeting compounds, and can complement activity of BRAF/MEK inhibitors in melanoma cells of different genetic subtypes. [ABSTRACT FROM AUTHOR]

Endoplasmic reticulum (ER) stress is a mechanism that allows the protection of normal cellular functions in response to both internal perturbations, such as accumulation of unfolded proteins, and external perturbations, for example redox stress, UVB irradiation, and infection. A hallmark of ER stress is the accumulation of misfolded and unfolded proteins. Physiological levels of ER stress trigger the unfolded protein response (UPR) that is required to restore normal ER functions. However, the UPR can also initiate a cell death program/apoptosis pathway in response to excessive or persistent ER stress. Recently, it has become evident that chronic ER stress occurs in several diseases, including skin diseases such as Darier's disease, rosacea, vitiligo and melanoma; furthermore, it is suggested that ER stress is directly involved in the pathogenesis of these disorders. Here, we review the role of ER stress in skin function, and discuss its significance in skin diseases. Physiological levels of endoplasmic reticulum (ER) stress are required for modulation of normal cellular functions in the skin, including keratinocyte differentiation, through the unfolded protein response (UPR). However, persistent or excessive levels of ER stress induce cell death and apoptosis signalling. Growing evidence describes chronic ER stress in several cutaneous diseases e.g., Darier's disease, rosacea, vitiligo, and melanoma. In this review, we discuss the role of ER stress in normal skin function and disease. [ABSTRACT FROM AUTHOR]

Cells under stressful microenvironmental conditions initiate integrated molecular circuitries that aim at reducing general protein translation rates while redirecting protein synthesis toward a selective set of stress-response proteins. The consequence of the activation of this dynamic system is a reduction of the energy expenditure of the cell, and a metabolic rewiring that shapes adaptation under stress, which will, in fine, promote cell survival. In general, the translation initiation step is the prime target of translation reduction, with 2 molcular modules inhibiting translation initiation: the mechanistic target of Rapamycin complex 1, and the stress related kinases eIF2 kinases, which are all involved in the cellular responses to kidney injuries. tRNA (tRNA) dynamics and fragmentation have recently gained a considerable weight in the field of the non-coding RNA biology, and emerge as an important system for protein translation modulation under cellular stress. More precisely, stress-induced tRNA (tiRNA), the cleavage products of the ribonuclease angiogenin, are generated under various stress conditions, including oxidative stress and endoplasmic reticulum stress, and contribute to protein translation reprogramming in mammal cells. Current clinical and experimental evidence indicates that the angiogenin-tRNA fragmentation system is initiated under renal insults, and is involved in the tissue adaptation upon kidney injury. In addition, this system represents a potential source for minimally-invasive or non invasive biomarkers of early kidney injury. Besides RNA interference, tRNA fragments are likely involved in other fundamental cellular functions, including inflammation, and a better understanding of the molecular basis of tRNA functions will drive discoveries on the fundamental role of non coding RNA biology, as exemplified by microRNA, in the regulation of kidney homeostasis. [ABSTRACT FROM AUTHOR]

Intestinal mucosal barrier, mainly consisting of the mucus layer and epithelium, functions in absorbing nutrition as well as prevention of the invasion of pathogenic microorganisms. Paneth cell, an important component of mucosal barrier, plays a vital role in maintaining the intestinal homeostasis by producing antimicrobial materials and controlling the host-commensal balance. Current evidence shows that the dysfunction of intestinal mucosal barrier, especially Paneth cell, participates in the onset and progression of inflammatory bowel disease (IBD). Autophagy, a cellular stress response, involves various physiological processes, such as secretion of proteins, production of antimicrobial peptides, and degradation of aberrant organelles or proteins. In the recent years, the roles of autophagy in the pathogenesis of IBD have been increasingly studied. Here in this review, we mainly focus on describing the roles of Paneth cell autophagy in IBD as well as several popular autophagy-related genetic variants in Penath cell and the related therapeutic strategies against IBD. [ABSTRACT FROM AUTHOR]

Leptin is an adipocyte-derived hormone and maintains adipose function under challenged conditions. Autophagy is also essential to maintain cellular homeostasis and regulate characteristics of adipose tissue. However, the effects of leptin on autophagy of adipocyte remain elusive. Here, we demonstrated endoplasmic reticulum (ER) stress and leptin were correlated with autophagy and inflammation by transcriptome sequencing of adipose tissue. Leptin-mediated inhibition of autophagy was involved in upstream reduction of ER stress proteins such as Chop, GRP78, and Atf4, since blockage of autophagy using pharmacological approach had no effect on tunicamycin-induced ER stress. Moreover, we determined KLF4, the potential transcriptional factor of Atf4, was required for the leptin-mediated autophagy in the regulation of adipocyte inflammation. Importantly, ATF4 physically interacted with ATG5 and subsequently formed a complex to promote adipocyte autophagy. Further analysis revealed that Atg5, a core component of autophagosome, was the target for leptin-mediate autophagy. In addition, leptin alleviated ER stress-induced inflammation by reducing autophagy-mediated degradation of IκB in adipocytes. Exogenous leptin treatment also ameliorated autophagy and inflammation of white adipose tissue in ob/ob mice. Taken together, our results indicated that leptin inhibited ER stress-mediated autophagy and inflammation through the negatively regulation of Atf4/Atg5 complex in adipocytes. These findings identify a new potential means for intervention of autophagy to prevent or treat obese caused metabolic syndrome of mammals. [ABSTRACT FROM AUTHOR]

The endoplasmic reticulum (ER) is the principal organelle responsible for several specific cellular functions including synthesis and folding of secretory or membrane proteins, lipid metabolism, and Ca storage. Different physiological as well as pathological stress conditions can, however, perturb ER homeostasis, giving rise to an accumulation of unfolded or misfolded proteins in the ER lumen, a condition termed ER stress. To deal with an increased folding demand, cells activate the unfolded protein response (UPR), which is initially protective but can become detrimental if ER stress is severe and prolonged. Accumulating evidence demonstrates a link between the UPR and ovarian development and function, including follicular growth and maturation, follicular atresia, and corpus luteum biogenesis. Additionally, ER stress and the UPR may also play an important role in the ovary under pathological conditions. Understanding the molecular mechanisms related to the dual role of unfolded protein response in the ovarian physiology and pathology may reveal the pathogenesis of some reproductive endocrine diseases and provide a new guidance to improve the assisted reproductive technology. Here we review the current literature and discuss concepts and progress in understanding the UPR, and we also analyze the role of ER stress and the UPR in the ovary. [ABSTRACT FROM AUTHOR]

When misfolded proteins accumulate in the endoplasmic reticulum (ER), the cell is said to experience ER stress. This triggers an unfolded protein response (UPR) to restore the balance between misfolded proteins and ER chaperones such as BiP. UPR signalling is required for the growth of many solid cancers. In chronic ER stress, factors including CHOP have been shown to mediate cell death. Colorectal adenocarcinoma arises due to progressive changes within pre-malignant lesions. Our aim was to test the hypothesis that the expression of BiP and CHOP correlates with the progression of those pre-malignant lesions.Eighty-one patients with colon neoplasms treated at Rouen University Hospital between January 1, 2003 and January 1, 2013 were randomly selected. The expression of BiP and CHOP was estimated by immunohistochemical staining of a tissue microarray generated from colon cores: normal tissue, low-grade and high-grade adenoma, invasive colon adenocarcinoma and lymph node metastasis of colon adenocarcinoma. In parallel, nine cases comprising areas from normal epithelium to dyplasia to invasive carcinoma and included in the TMA were analysed on whole sections.As colon epithelium shows increasing evidence of pre-malignant and then malignant changes, BiP expression significantly increases (p for trend < 0.001), whereas CHOP expression is attenuated (p for trend < 0.001).We identified a positive relationship between BiP expression and colon carcinogenesis, and a negative correlation for CHOP expression. These findings are consistent with a model in which ER stress accompanies oncogenesis and in which loss of proteins that mediate the toxicity of ER stress, such as CHOP, may facilitate tumorigenesis. This raises the exciting possibility that restoration of the negative feedback loop of UPR, if achievable, might antagonise the malignant process. [ABSTRACT FROM AUTHOR]

The endoplasmic reticulum is an organelle with multiple functions. The synthesis of transmembrane proteins and proteins that are to be secreted occurs in this organelle. Many conditions that impose stress on cells, including hypoxia, starvation, infections and changes in secretory needs, challenge the folding capacity of the cell and promote endoplasmic reticulum stress. The cellular response involves the activation of sensors that transduce signaling cascades with the aim of restoring homeostasis. This is known as the unfolded protein response, which also intersects with the integrated stress response that reduces protein synthesis through inactivation of the initiation factor eIF2α. Central to the unfolded protein response are the sensors PERK, IRE1 and ATF6, as well as other signaling nodes such as c-Jun N-terminal kinase 1 ( JNK) and the downstream transcription factors XBP1, ATF4 and CHOP. These proteins aim to restore homeostasis, but they can also induce cell death, which has been shown to occur by necroptosis and, more commonly, through the regulation of Bcl-2 family proteins (Bim, Noxa and Puma) that leads to mitochondrial apoptosis. In addition, endoplasmic reticulum stress and proteotoxic stress have been shown to induce TRAIL receptors and activation of caspase-8. Endoplasmic reticulum stress is a common feature in the pathology of numerous diseases because it plays a role in neurodegeneration, stroke, cancer, metabolic diseases and inflammation. Understanding how cells react to endoplasmic reticulum stress can accelerate discovery of drugs against these diseases. [ABSTRACT FROM AUTHOR]

During the last two decades, new insights into proteasome function and its role in several human diseases made it a potential therapeutic target. In this context, Amblyomin-X is a Kunitz-type FXa inhibitor similar to endogenous tissue factor pathway inhibitor (TFPI) and is a novel proteasome inhibitor. Herein, we have demonstrated Amblyomin-X cytotoxicity to different tumor cells lines such as pancreatic (Panc1, AsPC1BxPC3) and melanoma (SK-MEL-5 and SK-MEL-28). Of note, Amblyomin-X was not cytotoxic to normal human fibroblast cells. In addition, Amblyomin-X promoted accumulation of ER stress markers (GRP78 and GADD153) in sensitive (SK-MEL-28) and bortezomib-resistant (Mia-PaCa-2) tumor cells. The intracellular calcium concentration [Ca] was slightly modulated in human tumor cells (SK-MEL-28 and Mia-PaCa-2) after 24 h of Amblyomin-X treatment. Furthermore, Amblyomin-X induced mitochondrial dysfunction, cytochrome-c release, PARP cleavage, and activation of caspase cascade in both human tumor (SK-MEL-28 and Mia-PaCa-2) cells. These investigations might help in further understanding of the antitumor properties of Amblyomin-X. [ABSTRACT FROM AUTHOR]

Purpose: Perturbations in protein folding induce endoplasmic reticulum (ER) stress, which elicits coordinated response, namely the unfolded protein response (UPR), to cope with the accumulation of misfolded proteins in ER. In this study, we characterized mechanisms underlying ionizing radiation (IR)-induced UPR signaling pathways. Materials and methods: We analyzed alterations in UPR signaling pathways in human umbilical vein endothelial cells (HUVEC) and human coronary artery endothelial cells (HCAEC) irradiated with 15 Gy IR. Results: IR selectively activated the eIF2α/ATF4 branch of the UPR signaling pathway, with no alterations in the IRE1 and ATF6 branches in HUVEC and HCAEC. Phosphorylation of PERK was enhanced in response to IR, and the IR-induced activation of the eIF2α/ATF4 signaling pathway was completely inhibited by PERK knockdown with siRNA. Surprisingly, chemical chaperones, which inhibit the formation of misfolded proteins and sequential protein aggregates to reduce ER stress, failed to prevent the IR-induced phosphorylation of PERK and the subsequent activation of the eIF2α/ATF4 signaling pathway. Conclusions: PERK mediates the IR-induced selective activation of the eIF2α/ATF4 signaling pathway, and the IR-induced activation of PERK/eIF2α/ATF4 signaling in human vascular endothelial cells is independent of alterations in protein-folding homeostasis in the ER. [ABSTRACT FROM AUTHOR]

Background/aims: One of the most important metabolic hallmarks of breast cancer cells is enhanced lipogenesis. Increasing evidences suggest that fatty acid synthase (FAS) plays an important role in human breast cancer. Previously we discovered that alpha-mangostin showed apoptotic effect on human breast cancer cells via inhibiting FAS activity. The endoplasmic reticulum (ER) stress and autophagy are involved in cell apoptosis. However, the role of ER stress and autophagy in FAS inhibition induced apoptosis still remains unclear. Methods: We evaluated the effects of alpha-mangostin on ER stress and autophagy in human breast cancer cells. Intracellular FAS activity was measured by a spectrophotometer at 340 nm of NADPH absorption. Cell Counting Kit assay was used to test the cell viability. Immunoblot analysis was performed to detect protein expression levels. Apoptotic effects were detected by flow cytometry. Results: Alpha-mangostin induced endoplasmic reticulum stress and autophagy, both of which reduced the apoptotic effect of alpha-mangostin in MDA-MB-231 cells. Palmitic acid, the end product of FAS catalyzed reaction, rescued the ER stress and autophagy induced by alpha-mangostin. Cell apoptosis was markedly promoted by inhibiting ER stress and autophagy while treating cells with alpha-mangostin. Conclusion: We propose a hypothesis that a combination of FAS inhibition and ER stress and autophagy inhibition has an application potential in the chemoprevention and treatment of breast cancer. [ABSTRACT FROM AUTHOR]