Endoplasmic reticulum stress, the unfolded protein response, autophagy, and the integrated regulation of breast cancer cell fate

Anticipatory UPR Activation: A Protective Pathway and Target in Cancer

The endoplasmic reticulum (EnR) stress sensor, the unfolded protein response (UPR), plays a key role in regulating intracellular protein homeostasis. The extensively studied reactive mode of UPR activation is characterized by unfolded protein, or other EnR stress, triggering UPR activation. Here we focus on the emerging anticipatory mode of UPR activation in which mitogenic steroid and peptide hormones and other effectors preactivate the UPR and anticipate a future need for increased protein folding capacity. Mild UPR activation in breast cancer can be protective and contributes to antiestrogen resistance. Hyperactivation of the anticipatory UPR pathway in cancer cells with a small molecule converts it from cytoprotective to cytotoxic, highlighting its potential as a therapeutic target in estrogen receptor-positive breast cancer.

Endoplasmic Reticulum Stress Protein GRP78 Modulates Lipid Metabolism to Control Drug Sensitivity and Antitumor Immunity in Breast Cancer

The unfolded protein response is an endoplasmic reticulum stress pathway mediated by the protein chaperone glucose regulated-protein 78 (GRP78). Metabolic analysis of breast cancer cells shows that GRP78 silencing increases the intracellular concentrations of essential polyunsaturated fats, including linoleic acid. Accumulation of fatty acids is due to an inhibition of mitochondrial fatty acid transport, resulting in a reduction of fatty acid oxidation. These data suggest a novel role of GRP78-mediating cellular metabolism. We validated the effect of GRP78-regulated metabolite changes by treating tumor-bearing mice with tamoxifen and/or linoleic acid. Tumors treated with linoleic acid plus tamoxifen exhibited reduced tumor area and tumor weight. Inhibition of either GRP78 or linoleic acid treatment increased MCP-1 serum levels, decreased CD47 expression, and increased macrophage infiltration, suggesting a novel role for GRP78 in regulating innate immunity. GRP78 control of fatty acid oxidation may represent a new homeostatic function for GRP78. Cancer Res; 76(19); 5657-70. ©2016 AACR.

A novel chemical, STF-083010, reverses tamoxifen-related drug resistance in breast cancer by inhibiting IRE1/XBP1

Recent studies show that the unfolded protein response (UPR) within the endoplasmic reticulum is correlated with breast cancer drug resistance. In particular, human X-box binding protein-1(XBP1), a transcription factor which participates in UPR stress signaling, is reported to correlate with poor clinical responsiveness to tamoxifen. In this study, we develop a tamoxifen-resistant MCF-7 cell line by treating the cell line with low concentration of tamoxifen, and we find that XBP1 is indeed up-regulated at both the mRNA and protein levels compared to normal MCF-7 cells. STF-083010, a novel inhibitor which specifically blocks the XBP1 splicing, reestablishes tamoxifen sensitivity to resistant MCF-7 cells. Moreover, co-treatment with STF-083010 and tamoxifen can significantly delay breast cancer progression in a xenograft mammary tumor model. We next investigate the expression of XBP1s in over 170 breast cancer patients' samples and the results demonstrate that XBP1s expression level is highly correlated with overall survival in the ER⁺ subgroup, but not in the ER⁻ subgroup, suggesting a potential therapeutic application of XBP1 inhibitors in ER⁺breast cancer treatment.

SERPINB3 and B4: From biochemistry to biology

Human SERPINB3 and SERPINB4 are evolutionary duplicated serine/cysteine protease inhibitors. Genomic analysis indicates that these paralogous genes were encoded from independent loci arising from tandem gene duplication. Although the two molecules share 92% identity of their amino acid sequences, they are distinct in the Reactive Center Loop (RCL) including a hinge region and catalytic sequences which accounts for altered substrate specificity. Elevated expression of the two molecules has been reported to contribute to numerous pathological conditions such as inflammatory diseases and cancer. In this review, we focus on summarizing the biochemical features of SERPINB3/B4 and discussing the mechanistic basis for their biological functions and implications in human diseases.

Tunicamycin-induced endoplasmic reticulum stress reduces in vitro subpopulation and invasion of CD44+/CD24- phenotype breast cancer stem cells

Tunicamycin is an inhibitor of glycosylation that disturbs protein folding machinery in eukaryotic cells. Tunicamycin causes accumulation of unfolded proteins in cell endoplasmic reticulum (ER) and induces ER stress. ER stress is an essential mechanism for cellular homeostasis has role in cell death via reprogramming of protein processing, regulation of autophagy and apoptosis. In this study we show effect of tunicamycin on subpopulation and invasion of CD44+/CD24- MCF7 breast cancer stem cells. CD44+/CD24- cells were isolated from MCF7 cell line by fluorescence activated cell sorting (FACS) and treated with tunicamycin. ER stress was monitored by evaluation of X-box binding protein 1(XBP-1) mRNA splicing, cleaved activating transcription factor 6 (ATF6) nuclear translocation and CCAAT/enhancer-binding protein homologous protein (CHOP) expression. CD44+/CD24- subpopulation was analyzed using flow cytometry. Invasion was investigated by scratch assay, trypan blue staining, 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) proliferation and in vitro migration assays. Increased level of spliced XBP-1, ATF6 nuclear translocation and CHOP protein expression were detected in CD44+/CD24- and original MCF7 cells treated with tunicamycin. Also, a significant decline in CD44+/CD24- cell subpopulation was determined in the cells treated with tunicamycin. The results also showed inhibited invasion, increased cell death, suppressed proliferation and reduced migration in the CD44+/CD24- and CD44+/CD24- rich MCF7 cell culture, under effect of tunicamycin. Our results indicate that CD44+/CD24- phenotype MCF7 cells are susceptible to tunicamycin. The results showed that tunicamycin-induced ER stress suppresses CD44+/CD24- phenotype cell subpopulation and in vitro invasion and accelerates tumorosphore formation. These results suggest that tunicamycin-induced ER stress inhibits CD44+/CD24- phenotype MCF7 breast cancer stem cells. We conclude that using ER-targeting chemicals like tunicamycin is an interesting approach to target breast cancer stem cells inside tumor.

Induction of C/EBP homologous protein-mediated apoptosis and autophagy by licochalcone A in non-small cell lung cancer cells

Licochalcone A (LCA), a flavonoid isolated from the famous Chinese medicinal herb Glycyrrhiza uralensis Fisch, presents obvious anti-cancer effects. In this study, the anti-cancer effects and potential mechanisms of LCA in non-small cell lung cancer (NSCLC) cells were studied. LCA decreased cell viability, increased lactate dehydrogenase release, and induced apoptosis in a concentration-dependent manner in NSCLC cells while not in human embryonic lung fibroblast cells. The expression of phosphatidylethanolamine-modified microtubule-associated protein light-chain 3 (LC3-II) and formation of GFP-LC3 punta, two autophagic markers, were increased after treatment with LCA. LCA-induced LC3-II expression was increased when combined with chloroquine (CQ), while knock-down of autophagy related protein (ATG) 7 or ATG5 reversed LCA-induced LC3-II expression and GFP-LC3 punta formation, suggesting that LCA induced autophagy in NSCLC cells. Inhibition of autophagy could not reverse the LCA-induced cell viability decrease and apoptosis. In addition, LCA increased the expression of endoplasmic reticulum stress related proteins, such as binding immunoglobulin protein and C/EBP homologous protein (CHOP). Knock-down of CHOP reversed LCA-induced cell viability decrease, apoptosis, and autophagy. Taken together, LCA-induced autophagic effect is an accompanied phenomenon in NSCLC cells, and CHOP is critical for LCA-induced cell viability decrease, apoptosis, and autophagy.

Protein disulfide isomerases in the endoplasmic reticulum promote anchorage-independent growth of breast cancer cells

Metastatic breast cancer cells are exposed to stress of detachment from the extracellular matrix (ECM). Cultured breast cancer cells that survive this stress and are capable of anchorage-independent proliferation form mammospheres. The purpose of this study was to explore a link between mammosphere growth, ECM gene expression, and the protein quality control system in the endoplasmic reticulum (ER). We compared the mRNA and protein levels of ER folding factors in SUM159PT and MCF10DCIS.com breast cancer cells grown as mammospheres versus adherent conditions. Publicly available gene expression data for mammospheres formed by primary breast cancer cells and for circulating tumor cells (CTCs) were analyzed to assess the status of ECM/ER folding factor genes in clinically relevant samples. Knock-down of selected protein disulfide isomerase (PDI) family members was performed to examine their roles in SUM159PT mammosphere growth. We found that cells grown as mammospheres had elevated expression of ECM genes and ER folding quality control genes. CTC gene expression data for an index patient indicated that upregulation of ECM and ER folding factor genes occurred at the time of acquired therapy resistance and disease progression. Knock-down of PDI, ERp44, or ERp57, three members of the PDI family with elevated protein levels in mammospheres, in SUM159PT cells partially inhibited the mammosphere growth. Thus, breast cancer cell survival and growth under detachment conditions require enhanced assistance of the ER protein folding machinery. Targeting ER folding factors, in particular members of the PDI family, may improve the therapeutic outcomes in metastatic breast cancer.

Innate immunity and hepatocarcinoma: Can toll-like receptors open the door to oncogenesis?

Hepatocarcinoma (HCC) is a highly prevalent cancer worldwide and its inflammatory background was established long ago. Recent studies have shown that innate immunity is closely related to the HCC carcinogenesis. An effective innate immunity response relies on the toll-like receptors (TLR) found in several different liver cells which, through different ligands and many signaling pathways can elicit, not only a pro-inflammatory but also an oncogenic or anti-oncogenic response. Our aim was to study the role of TLRs in the liver oncogenesis and as a consequence their value as potential therapeutic targets. We performed a systematic review of PubMed searching for original articles studying the relationship between HCC and TLRs until March 2015. TLR2 appears to be a fundamental stress-sensor as its absence reveals an augmented tendency to accumulate DNA-damages and to cell survival. However, pathways are still not fully understood as TLR2 up-regulation was also associated to enhanced tumorigenesis. TLR3 has a well-known protective role influencing crucial processes like angiogenesis, cell growth or proliferation. TLR4 works as an interesting epithelial-mesenchymal transition’s inducer and a promoter of cell survival probably inducing HCC carcinogenesis even though an anti-cancer role has already been observed. TLR9’s influence on carcinogenesis is also controversial and despite a potential anti-cancer capacity, a pro-tumorigenic role is more likely. Genetic polymorphisms in some TLRs have been found and its influence on the risk of HCC has been reported. As therapeutic targets, TLRs are already in use and have a great potential. In conclusion, TLRs have been shown to be an interesting influence on the HCC’s microenvironment, with TLR3 clearly determining an anti-tumour influence. TLR4 and TLR9 are considered to have a positive relationship with tumour development even though, in each of them anti-tumorigenic signals have been described. TLR2 presents a more ambiguous role, possibly depending on the stage of the inflammation-HCC axis.

Involvement of autophagy in the procedure of endoplasmic reticulum stress introduced apoptosis in bone marrow mesenchymal stem cells from nonobese diabetic mice

Recent studies showed that bone marrow mesenchymal stem cells (BM-MSCs) from nonobese diabetic (NOD) mice exhibited the phenomenon of apoptosis. However, the mechanisms of apoptosis remained largely unknown. In this study, endoplasmic reticulum (ER) stress and autophagy were evidenced in BM-MSCs from NOD mice for the first time. We found the ER stress-mediated apoptosis was supported by the up-regulation of ER stress markers including augmented phosphorylation of phosphorylated protein kinase RNA-like ER kinase and eukaryotic translation initiator factor 2α as well as cleavage of caspase-3. Evidence of autophagy included the formation of the acidic vesicular organelles and increase of LC3 accumulation. Intriguingly, blockage of ER stress could reduce the apoptosis of BM-MSCs from NOD mice and alleviated accumulation of LC3, which indicated that ER stress induced apoptosis and autophagy. Furthermore, our results showed that the mechanism of ER stress-induced autophagy was associated with the decrease of p-S6 (a marker of mTOR activity). Here, we demonstrated that ER stress-induced cell death was mediated by autophagy that was partly attributed to the inactivation of the mammalian target of rapamycin.

SIGNIFICANCE PARAGRAPH

We report for the first time that endoplasmic reticulum (ER) stress mediated apoptosis of bone marrow mesenchymal stem cells (BM-MSCs) from nonobese diabetic (NOD) mice. The evidence of autophagy was also found in BM-MSCs from NOD mice, included the formation of the acidic vesicular organelles and increase of LC3 accumulation. Furthermore, we demonstrated that ER stress-induced cell death was mediated by autophagy that was partly attributed to the inactivation of the mammalian target of rapamycin. Deciphering the mechanisms of ER stress signalling involved in the apoptosis of BM-MSCs from NOD mice will help improve transplantation efficacy of BM-MSCs in type 1 diabetes patients.

Requirement of clusterin expression for prosurvival autophagy in hypoxic kidney tubular epithelial cells

Cellular autophagy is a prosurvival mechanism in the kidney against ischemia-reperfusion injury (IRI), but the molecular pathways that activate the autophagy in ischemic kidneys are not fully understood. Clusterin (CLU) is a chaperone-like protein, and its expression is associated with kidney resistance to IRI. The present study investigated the role of CLU in prosurvival autophagy in the kidney. Renal IRI was induced in mice by clamping renal pedicles at 32°C for 45 min. Hypoxia in renal tubular epithelial cell (TEC) cultures was induced by exposure to a 1% O2 atmosphere. Autophagy was determined by either light chain 3-BII expression with Western blot analysis or light chain 3-green fluorescent protein aggregation with confocal microscopy. Cell apoptosis was determined by flow cytometric analysis. The unfolded protein response was determined by PCR array. Here, we showed that autophagy was significantly activated by IRI in wild-type (WT) but not CLU-deficient kidneys. Similarly, autophagy was activated by hypoxia in human proximal TECs (HKC-8) and WT mouse primary TECs but was impaired in CLU-null TECs. Hypoxia-activated autophagy was CLU dependent and positively correlated with cell survival, and inhibition of autophagy significantly promoted cell death in both HKC-8 and mouse WT/CLU-expressing TECs but not in CLU-null TECs. Further experiments showed that CLU-dependent prosurvival autophagy was associated with activation of the unfolded protein response in hypoxic kidney cells. In conclusion, these data suggest that activation of prosurvival autophagy by hypoxia in kidney cells requires CLU expression and may be a key cytoprotective mechanism of CLU in the protection of the kidney from hypoxia/ischemia-mediated injury.

Network Analysis Shows Novel Molecular Mechanisms of Action for Copper-Based Chemotherapy

The understanding of the mechanisms associated with the action of chemotherapeutic agents is fundamental to assess and account for possible side-effects of such treatments. Casiopeínas have demonstrated a cytotoxic effect by activation of pro-apoptotic processes in malignant cells. Such processes have been proved to activate the apoptotic intrinsic route, as well as cell cycle arrest. Despite this knowledge, the whole mechanism of action of Casiopeínas is yet to be completely understood. In this work we implement a systems biology approach based on two pathway analysis tools (Over-Representation Analysis and Causal Network Analysis) to observe changes in some hallmarks of cancer, induced by this copper-based chemotherapeutic agent in HeLa cell lines. We find that the metabolism of metal ions is exacerbated, as well as cell division processes being globally diminished. We also show that cellular migration and proliferation events are decreased. Moreover, the molecular mechanisms of liver protection are increased in the cell cultures under the actions of Casiopeínas, unlike the case in many other cytotoxic drugs. We argue that this chemotherapeutic agent may be promising, given its protective hepatic function, concomitant with its cytotoxic participation in the onset of apoptotic processes in malignant cells.

Lysozyme Mutants Accumulate in Cells while Associated at their N-terminal Alpha-domain with the Endoplasmic Reticulum Chaperone GRP78/BiP

Amyloidogenic human lysozyme variants deposit in cells and cause systemic amyloidosis. We recently observed that such lysozymes accumulate in the endoplasmic reticulum (ER) with the ER chaperone GRP78/BiP, accompanying the ER stress response. Here we investigated the region of lysozyme that is critical to its association with GRP78/BiP. In addition to the above-mentioned variants of lysozyme, we constructed lysozyme truncation or substitution mutants. These were co-expressed with GRP78/BiP (tagged with FLAG) in cultured human embryonic kidney cells, which were analyzed by western blotting and immunocytochemistry using anti-lysozyme and anti-FLAG antibodies. The amyloidogenic variants were confirmed to be strongly associated with GRP78/BiP as revealed by the co-immunoprecipitation assay, whereas N-terminal mutants pruned of 1-41 or 1-51 residues were found not to be associated with the chaperone. Single amino acid substitutions for the leucine array along the α-helices in the N-terminal region resulted in wild-type lysozyme remaining attached to GRP78/BiP. These mutations also tended to show lowered secretion ability. We conclude that the N-terminal α-helices region of the lysozyme is pivotal for its strong adhesion to GRP78/BiP. We suspect that wild-type lysozyme interacts with the GRP at this region as a step in the proper folding monitored by the ER chaperone.

Endocrine resistance in breast cancer--An overview and update

Tumors that express detectable levels of the product of the ESR1 gene (estrogen receptor-α; ERα) represent the single largest molecular subtype of breast cancer. More women eventually die from ERα+ breast cancer than from either HER2+ disease (almost half of which also express ERα) and/or from triple negative breast cancer (ERα-negative, progesterone receptor-negative, and HER2-negative). Antiestrogens and aromatase inhibitors are largely indistinguishable from each other in their abilities to improve overall survival and almost 50% of ERα+ breast cancers will eventually fail one or more of these endocrine interventions. The precise reasons why these therapies fail in ERα+ breast cancer remain largely unknown. Pharmacogenetic explanations for Tamoxifen resistance are controversial. The role of ERα mutations in endocrine resistance remains unclear. Targeting the growth factors and oncogenes most strongly correlated with endocrine resistance has proven mostly disappointing in their abilities to improve overall survival substantially, particularly in the metastatic setting. Nonetheless, there are new concepts in endocrine resistance that integrate molecular signaling, cellular metabolism, and stress responses including endoplasmic reticulum stress and the unfolded protein response (UPR) that provide novel insights and suggest innovative therapeutic targets. Encouraging evidence that drug combinations with CDK4/CDK6 inhibitors can extend recurrence free survival may yet translate to improvements in overall survival. Whether the improvements seen with immunotherapy in other cancers can be achieved in breast cancer remains to be determined, particularly for ERα+ breast cancers. This review explores the basic mechanisms of resistance to endocrine therapies, concluding with some new insights from systems biology approaches further implicating autophagy and the UPR in detail, and a brief discussion of exciting new avenues and future prospects.

Fluoxetine induces cytotoxic endoplasmic reticulum stress and autophagy in triple negative breast cancer

AIM: To investigate the mechanism of action of lipophilic antidepressant fluoxetine (FLX) in representative molecular subtypes of breast cancer.

METHODS: The anti-proliferative effects and mechanistic action of FLX in triple-negative (SUM149PT) and luminal (T47D and Au565) cancer cells and non-transformed MCF10A were investigated. Reverse phase protein microarray (RPPM) was performed with and without 10 μmol/L FLX for 24 and 48 h to determine which proteins are significantly changed. Viability and cell cycle analysis were also performed to determine drug effects on cell growth. Western blotting was used to confirm the change in protein expression examined by RPPM or pursue other signaling proteins.

RESULTS: The FLX-induced cell growth inhibition in all cell lines was concentration- and time-dependent but less pronounced in early passage MCF10A. In comparison to the other lines, cell growth reduction in SUM149PT coincided with significant induction of endoplasmic reticulum (ER) stress and autophagy after 24 and 48 h of 10 μmol/L FLX, resulting in decreased translation of proteins along the receptor tyrosine kinase/Akt/mammalian target of rapamycin pathways. The increase in autophagy marker, cleaved microtubule-associated protein 1 light chain 3, in SUM149PT after 24 h of FLX was likely due to increased metabolic demands of rapidly dividing cells and ER stress. Consequently, the unfolded protein response mediated by double-stranded RNA-dependent protein kinase-like ER kinase resulted in inhibition of protein synthesis, growth arrest at the G1 phase, autophagy, and caspase-7-mediated cell death.

CONCLUSION: Our study suggests a new role for FLX as an inducer of ER stress and autophagy, resulting in death of aggressive triple negative breast cancer SUM149PT.

A new class of small molecule estrogen receptor-alpha antagonists that overcome anti-estrogen resistance

Previous studies indicate that BRCA1 protein binds to estrogen receptor-alpha (ER) and inhibits its activity. Here, we found that BRCA1 over-expression not only inhibits ER activity in anti-estrogen-resistant LCC9 cells but also partially restores their sensitivity to Tamoxifen. To simulate the mechanism of BRCA1 inhibition of ER in the setting of Tamoxifen resistance, we created a three-dimensional model of a BRCA1-binding cavity within the ER/Tamoxifen complex; and we screened a pharmacophore database to identify small molecules that could fit into this cavity. Among the top 40 “hits”, six exhibited potent ER inhibitory activity in anti-estrogen-sensitive MCF-7 cells and four of the six exhibited similar activity (IC₅₀ ≤ 1.0 μM) in LCC9 cells. We validated the model by mutation analysis. Two representative compounds (4631-P/1 and 35466-L/1) inhibited ER-dependent cell proliferation in Tamoxifen-resistant cells (LCC9 and LCC2) and partially restored sensitivity to Tamoxifen. The compounds also disrupted the association of BRCA1 with ER. In electrophoretic mobility shift assays, the compounds caused dissociation of ER from a model estrogen response element. Finally, a modified form of compound 35446 (hydrochloride salt) inhibited growth of LCC9 tumor xenografts at non-toxic concentrations. These results identify a novel group of small molecules that can overcome Tamoxifen resistance.

Morphological and ultrasound characteristics of endometrium in patients with breast cancer and the risk of secondary tumors

The analysis of features of endometrial hyperplasia in patients with breast cancer (BC) receiving adjuvant tamoxifen therapy in the period from 2011 to 2014 inclusive. 196 patients with breast cancer with ultrasound criteria of endometrial hyperplasia were examined. A postoperative histopathologic examination revealed that the lesions were endometrial hyperplasias and with 4,1% malignant findings. Hyperplasia, polyps and endometrial cancer were diagnosed in patients receiving tamoxifen, which allowed a comparison clinicoanamnestic, ultrasound, morphological and genetic characteristics of the endometrium to recover a high risk of developing a second cancer, as well as offer a pathogenic variant of its prevention. The article can be interesting as for obstetrician-gynecologist, watching women after breast cancer treatment, and oncologists, choosing a drug for adjuvant therapy.

Neuroprotective effects of atorvastatin against cerebral ischemia/reperfusion injury through the inhibition of endoplasmic reticulum stress

Cerebral ischemia triggers secondary ischemia/reperfusion injury and endoplasmic reticulum stress initiates cell apoptosis. However, the regulatory mechanism of the signaling pathway remains unclear. We hypothesize that the regulatory mechanisms are mediated by the protein kinase-like endoplasmic reticulum kinase/eukaryotic initiation factor 2α in the endoplasmic reticulum stress signaling pathway. To verify this hypothesis, we occluded the middle cerebral artery in rats to establish focal cerebral ischemia/reperfusion model. Results showed that the expression levels of protein kinase-like endoplasmic reticulum kinase and caspase-3, as well as the phosphorylation of eukaryotic initiation factor 2α, were increased after ischemia/reperfusion. Administration of atorvastatin decreased the expression of protein kinase-like endoplasmic reticulum kinase, caspase-3 and phosphorylated eukaryotic initiation factor 2α, reduced the infarct volume and improved ultrastructure in the rat brain. After salubrinal, the specific inhibitor of phosphorylated eukaryotic initiation factor 2α was given into the rats intragastrically, the expression levels of caspase-3 and phosphorylated eukaryotic initiation factor 2α in the were decreased, a reduction of the infarct volume and less ultrastructural damage were observed than the untreated, ischemic brain. However, salubrinal had no impact on the expression of protein kinase-like endoplasmic reticulum kinase. Experimental findings indicate that atorvastatin inhibits endoplasmic reticulum stress and exerts neuroprotective effects. The underlying mechanisms of attenuating ischemia/reperfusion injury are associated with the protein kinase-like endoplasmic reticulum kinase/eukaryotic initiation factor 2α/caspase-3 pathway.

Hydroxychloroquine inhibits autophagy to potentiate antiestrogen responsiveness in ER+ breast cancer

PURPOSE

Estrogen receptor-α (ERα)-targeted therapies including tamoxifen (TAM) or Faslodex (ICI) are used to treat ER(+) breast cancers. Up to 50% of tumors will acquire resistance to these interventions. Autophagy has been implicated as a major driver of antiestrogen resistance. We have explored the ability of hydroxychloroquine (HCQ), which inhibits autophagy, to affect antiestrogen responsiveness.

EXPERIMENTAL DESIGN

TAM-resistant MCF7-RR and ICI-resistant/TAM cross-resistant LCC9 ER(+) breast cancer cells were injected into mammary fat pads of female athymic mice and treated with TAM and/or ICI in combination with oral low-dose HCQ.

RESULTS

We show that HCQ can increase antiestrogen responsiveness in MCF7-RR and LCC9 cells and tumors, likely through the inhibition of autophagy. However, the combination of ICI+HCQ was less effective than HCQ alone in vivo, unlike the TAM+HCQ combination. Antiestrogen treatment stimulated angiogenesis in tumors but did not prevent HCQ effectiveness. The lower efficacy of ICI+HCQ was associated with ICI effects on cell-mediated immunity within the tumor microenvironment. The mouse chemokine KC (CXCL1) and IFNγ were differentially regulated by both TAM and ICI treatments, suggesting a possible effect on macrophage development/activity. Consistent with these observations, TAM+HCQ treatment increased tumor CD68(+) cells infiltration, whereas ICI and ICI+HCQ reduced peripheral tumor macrophage content. Moreover, macrophage elimination of breast cancer target cells in vitro was reduced following exposure to ICI.

CONCLUSION

HCQ restores antiestrogen sensitivity to resistant tumors. Moreover, the beneficial combination of TAM+HCQ suggests a positive outcome for ongoing neoadjuvant clinical trials using this combination for the treatment of ER(+) ductal carcinoma in situ lesions.

Role of GRP78 in promoting therapeutic-resistant breast cancer

Over 230,000 new cases of invasive breast cancer are diagnosed annually within the USA. Recurrent breast cancer remains a mostly incurable disease with drug resistance, tumor latency and distant metastases driving breast tumor recurrence and morbidity. Understanding drug resistance is a critical component of combating breast cancer. Recently, the protein chaperone GRP78 and the unfolded protein response were implicated as drivers of drug resistance. Preclinical studies show inhibiting GRP78 can reverse drug resistance. Furthermore, drugs developed to target GRP78 show clinical promise in several ongoing clinical trials.

Hydrogen sulfide in cancer: Friend or foe?

Hydrogen sulfide (H₂S) is the third gaseous signaling molecule that plays important roles in cancer biological processes. Recent studies indicate that H₂S has both pro-cancer and anti-cancer effects. Endogenous H₂S can exert pro-cancer functions through induction of angiogenesis regulation of mitochondrial bioenergetics, acceleration of cell cycle progression, and anti-apoptosis mechanisms. Thus, the inhibition of the production of H₂S in cancer cells may be a new cancer treatment strategy. In contrast to the pro-cancer effect of H₂S, relatively high concentrations of exogenous H₂S could suppress the growth of cancer cells by inducing uncontrolled intracellular acidification, inducing cell cycle arrest, and promoting apoptosis. Therefore, H₂S donors and H₂S-releasing hybrids could be designed and developed as novel anti-cancer drugs. In this review, the production and metabolism of H₂S in cancer cells are summarized and the role and mechanism of H₂S in cancer development and progression are further discussed.

Crosstalk events in the estrogen signaling pathway may affect tamoxifen efficacy in breast cancer molecular subtypes

Steroid hormones are involved on cell growth, development and differentiation. Such effects are often mediated by steroid receptors. One paradigmatic example of this coupling is the estrogen signaling pathway. Its dysregulation is involved in most tumors of the mammary gland. It is thus an important pharmacological target in breast cancer. This pathway, however, crosstalks with several other molecular pathways, a fact that may have consequences for the effectiveness of hormone modulating drug therapies, such as tamoxifen. For this work, we performed a systematic analysis of the major routes involved in crosstalk phenomena with the estrogen pathway - based on gene expression experiments (819 samples) and pathway analysis (493 samples) - for biopsy-captured tissue and contrasted in two independent datasets with in vivo and in vitro pharmacological stimulation. Our results confirm the presence of a number of crosstalk events across the estrogen signaling pathway with others that are dysregulated in different molecular subtypes of breast cancer. These may be involved in proliferation, invasiveness and apoptosis-evasion in patients. The results presented may open the way to new designs of adjuvant and neoadjuvant therapies for breast cancer treatment.

TMEM33: a new stress-inducible endoplasmic reticulum transmembrane protein and modulator of the unfolded protein response signaling

Endoplasmic reticulum (ER) stress leads to activation of the unfolded protein response (UPR) signaling cascade and induction of an apoptotic cell death, autophagy, oncogenesis, metastasis, and/or resistance to cancer therapies. Mechanisms underlying regulation of ER transmembrane proteins PERK, IRE1α, and ATF6α/β, and how the balance of these activities determines outcome of the activated UPR, remain largely unclear. Here, we report a novel molecule transmembrane protein 33 (TMEM33) and its actions in UPR signaling. Immunoblotting and northern blot hybridization assays were used to determine the effects of ER stress on TMEM33 expression levels in various cell lines. Transient transfections, immunofluorescence, subcellular fractionation, immunoprecipitation, and immunoblotting were used to study the subcellular localization of TMEM33, the binding partners of TMEM33, and the expression of downstream effectors of PERK and IRE1α. Our data demonstrate that TMEM33 is a unique ER stress-inducible and ER transmembrane molecule, and a new binding partner of PERK. Exogenous expression of TMEM33 led to increased expression of p-eIF2α and p-IRE1α and their known downstream effectors, ATF4-CHOP and XBP1-S, respectively, in breast cancer cells. TMEM33 overexpression also correlated with increased expression of apoptotic signals including cleaved caspase-7 and cleaved PARP, and an autophagosome protein LC3II, and reduced expression of the autophagy marker p62. TMEM33 is a novel regulator of the PERK-eIE2α-ATF4 and IRE1-XBP1 axes of the UPR signaling. Therefore, TMEM33 may function as a determinant of the ER stress-responsive events in cancer cells.

Ca(2+) homeostasis and endoplasmic reticulum (ER) stress: An integrated view of calcium signaling

Cellular Ca(2+) homeostasis is maintained through the integrated and coordinated function of Ca(2+) transport molecules, Ca(2+) buffers and sensors. These molecules are associated with the plasma membrane and different cellular compartments, such as the cytoplasm, nucleus, mitochondria, and cellular reticular network, including the endoplasmic reticulum (ER) to control free and bound Ca(2+) levels in all parts of the cell. Loss of nutrients/energy leads to the loss of cellular homeostasis and disruption of Ca(2+) signaling in both the reticular network and cytoplasmic compartments. As an integral part of cellular physiology and pathology, this leads to activation of ER stress coping responses, such as the unfolded protein response (UPR), and mobilization of pathways to regain ER homeostasis.

Anticancer drugs for the modulation of endoplasmic reticulum stress and oxidative stress

Prior research has demonstrated how the endoplasmic reticulum (ER) functions as a multifunctional organelle and as a well-orchestrated protein-folding unit. It consists of sensors which detect stress-induced unfolded/misfolded proteins and it is the place where protein folding is catalyzed with chaperones. During this folding process, an immaculate disulfide bond formation requires an oxidized environment provided by the ER. Protein folding and the generation of reactive oxygen species (ROS) as a protein oxidative byproduct in ER are crosslinked. An ER stress-induced response also mediates the expression of the apoptosis-associated gene C/EBP-homologous protein (CHOP) and death receptor 5 (DR5). ER stress induces the upregulation of tumor necrosis factor-related apoptosis inducing ligand (TRAIL) receptor and opening new horizons for therapeutic research. These findings can be used to maximize TRAIL-induced apoptosis in xenografted mice. This review summarizes the current understanding of the interplay between ER stress and ROS. We also discuss how damage-associated molecular patterns (DAMPs) function as modulators of immunogenic cell death and how natural products and drugs have shown potential in regulating ER stress and ROS in different cancer cell lines. Drugs as inducers and inhibitors of ROS modulation may respectively exert inducible and inhibitory effects on ER stress and unfolded protein response (UPR). Reconceptualization of the molecular crosstalk among ROS modulating effectors, ER stress, and DAMPs will lead to advances in anticancer therapy.

Polymorphisms in a Putative Enhancer at the 10q21.2 Breast Cancer Risk Locus Regulate NRBF2 Expression

Genome-wide association studies have identified SNPs near ZNF365 at 10q21.2 that are associated with both breast cancer risk and mammographic density. To identify the most likely causal SNPs, we fine mapped the association signal by genotyping 428 SNPs across the region in 89,050 European and 12,893 Asian case and control subjects from the Breast Cancer Association Consortium. We identified four independent sets of correlated, highly trait-associated variants (iCHAVs), three of which were located within ZNF365. The most strongly risk-associated SNP, rs10995201 in iCHAV1, showed clear evidence of association with both estrogen receptor (ER)-positive (OR = 0.85 [0.82-0.88]) and ER-negative (OR = 0.87 [0.82-0.91]) disease, and was also the SNP most strongly associated with percent mammographic density. iCHAV2 (lead SNP, chr10: 64,258,684:D) and iCHAV3 (lead SNP, rs7922449) were also associated with ER-positive (OR = 0.93 [0.91-0.95] and OR = 1.06 [1.03-1.09]) and ER-negative (OR = 0.95 [0.91-0.98] and OR = 1.08 [1.04-1.13]) disease. There was weaker evidence for iCHAV4, located 5' of ADO, associated only with ER-positive breast cancer (OR = 0.93 [0.90-0.96]). We found 12, 17, 18, and 2 candidate causal SNPs for breast cancer in iCHAVs 1-4, respectively. Chromosome conformation capture analysis showed that iCHAV2 interacts with the ZNF365 and NRBF2 (more than 600 kb away) promoters in normal and cancerous breast epithelial cells. Luciferase assays did not identify SNPs that affect transactivation of ZNF365, but identified a protective haplotype in iCHAV2, associated with silencing of the NRBF2 promoter, implicating this gene in the etiology of breast cancer.

Unfolding the Role of Stress Response Signaling in Endocrine Resistant Breast Cancers

The unfolded protein response (UPR) is an ancient stress response that enables a cell to manage the energetic stress that accompanies protein folding. There has been a significant recent increase in our understanding of the UPR, how it integrates physiological processes within cells, and how this integration can affect cancer cells and cell fate decisions. Recent publications have highlighted the role of UPR signaling components on mediating various cell survival pathways, cellular metabolism and bioenergenics, and autophagy. We address the role of UPR on mediating endocrine therapy resistance and estrogen receptor-positive breast cancer cell survival.

Expression of ribosome-binding protein 1 correlates with shorter survival in Her-2 positive breast cancer

The aim of this study is to investigate the expression of ribosome-binding protein 1 (RRBP1) in invasive breast cancer and to analyze its relationship to clinical features and prognosis. RRBP1 expression was studied using real-time quantitative PCR and western blotting using pair-matched breast samples and immunohistochemical staining using a tissue microarray. Then the correlation between RRBP1 expression and clinicopathologic features was analyzed. RRBP1 mRNA and protein expression were significantly increased in breast cancer tissues compared with normal tissues. The protein level of RRBP1 is proved to be positively related to histological grade (P = 0.02), molecular subtype (P = 0.048) and status of Her-2 (P = 0.026) and P53 (P = 0.015). We performed a grade-stratified analysis of all patients according to the level of RRBP1 expression and found that RRBP1 overexpression highly affected overall survival in patients with early-stage (I and II) tumors (P = 0.042). Furthermore, Her-2 positive patients with negative RRBP1 expression had longer overall survival rates than those with positive RRBP1 expression (P = 0.031). Using multivariate analysis, it was determined that lymph node metastasis (LNM, P = 0.002) and RRBP1 expression (P = 0.005) were independent prognosis factors for overall survival. RRBP1 is a valuable prognostic factor in Her-2-positive breast cancer patients, indicating that RRBP1 is a potentially important target for the prediction of prognosis.

Dynamic Modeling of the Interaction Between Autophagy and Apoptosis in Mammalian Cells

Autophagy is a conserved biological stress response in mammalian cells that is responsible for clearing damaged proteins and organelles from the cytoplasm and recycling their contents via the lysosomal pathway. In cases of mild stress, autophagy acts as a survival mechanism, while in cases of severe stress cells may switch to programmed cell death. Understanding the decision process that moves a cell from autophagy to apoptosis is important since abnormal regulation of autophagy occurs in many diseases, including cancer. To integrate existing knowledge about this decision process into a rigorous, analytical framework, we built a mathematical model of cell fate decisions mediated by autophagy. Our dynamical model is consistent with existing quantitative measurements of autophagy and apoptosis in rat kidney proximal tubular cells responding to cisplatin-induced stress.

Linking autophagy with inflammation through IRF1 signaling in ER+ breast cancer

Resistance to antiestrogen therapy remains a critical determinant of mortality in patients affected by ER+ breast cancer. Our previous work identified autophagy and interferon regulatory factor 1 (IRF1) signaling as key regulators of this process. We have recently demonstrated a novel reciprocal interaction between IRF1 and ATG7, linking inflammation and autophagy.

Unfolding the promise of translational targeting in neurodegenerative disease

With the rise of aging populations, new challenges for health care systems are emerging. Degenerative conditions of the central nervous system share a strikingly great deal of similarities, particularly the production and buildup of malfolded proteins. As a result, stress pathways within the endoplasmic reticulum become activated, triggering widespread neuronal apoptosis. New pharmacological compounds targeting this response are emerging as promising treatment strategies. This review examines the current evidence for protein aggregation in neurodegenerative disease states and discusses future mechanisms of therapeutically targeting the endoplasmic reticulum.

Application of metabolomics in drug resistant breast cancer research

The metabolic profiles of breast cancer cells are different from normal mammary epithelial cells. Breast cancer cells that gain resistance to therapeutic interventions can reprogram their endogenous metabolism in order to adapt and proliferate despite high oxidative stress and hypoxic conditions. Drug resistance in breast cancer, regardless of subgroups, is a major clinical setback. Although recent advances in genomics and proteomics research has given us a glimpse into the heterogeneity that exists even within subgroups, the ability to precisely predict a tumor’s response to therapy remains elusive. Metabolomics as a quantitative, high through put technology offers promise towards devising new strategies to establish predictive, diagnostic and prognostic markers of breast cancer. Along with other “omics” technologies that include genomics, transcriptomics, and proteomics, metabolomics fits into the puzzle of a comprehensive systems biology approach to understand drug resistance in breast cancer. In this review, we highlight the challenges facing successful therapeutic treatment of breast cancer and the innovative approaches that metabolomics offers to better understand drug resistance in cancer.

Molecular mechanisms of tamoxifen-associated endometrial cancer (Review)

Tamoxifen has been prescribed to millions of females for breast cancer prevention or treatment. However, tamoxifen is known to significantly enhance the risk of developing endometrial lesions, including hyperplasia, polyps, carcinomas, and sarcoma. Notably, tamoxifen-associated endometrial cancer often has a poor clinical outcome. Understanding the molecular mechanism of tamoxifen-induced endometrial cancer is essential for developing strategies that minimize tamoxifen’s effects on the endometrium without jeopardizing its breast cancer treatment effects. However, this understanding remains limited. Tamoxifen appears to mediate its effect on endometrial cells through estrogenic and non-genomic pathways, rather than introducing a genomic alteration as a carcinogen. Although tamoxifen functions as an agonist and promotes cell proliferation in endometrial cancer, it also displays antagonist activity towards some estrogen targets. Alterations in estrogen receptor-α and its isoforms, as well as the membrane associated estrogen receptor G protein-coupled receptor 30, have been observed with tamoxifen-exposed endometrial cells, and likely mediate the effects of tamoxifen on endometrial cancer cell proliferation and invasion. In addition, gene profile studies of short-term exposure to tamoxifen indicate that the majority of tamoxifen targets are tamoxifen-specific. However, the tamoxifen regulated gene targets that are involved in mediating the effects of long-term exposure to tamoxifen are not yet fully understood. Recent progress has indicated a potential role of unfolded protein response and mammalian target of rapamycin signaling in tamoxifen-associated endometrial cancer. In the future, studies focusing on long-term effects of tamoxifen exposure are required to understand the molecular mechanisms of tamoxifen-associated endometrial cancer.

The E3 ubiquitin ligase ARIH1 protects against genotoxic stress by initiating a 4EHP-mediated mRNA translation arrest

DNA damage response signaling is crucial for genome maintenance in all organisms and is corrupted in cancer. In an RNA interference (RNAi) screen for (de)ubiquitinases and sumoylases modulating the apoptotic response of embryonic stem (ES) cells to DNA damage, we identified the E3 ubiquitin ligase/ISGylase, ariadne homologue 1 (ARIH1). Silencing ARIH1 sensitized ES and cancer cells to genotoxic compounds and ionizing radiation, irrespective of their p53 or caspase-3 status. Expression of wild-type but not ubiquitinase-defective ARIH1 constructs prevented sensitization caused by ARIH1 knockdown. ARIH1 protein abundance increased after DNA damage through attenuation of proteasomal degradation that required ATM signaling. Accumulated ARIH1 associated with 4EHP, and in turn, this competitive inhibitor of the eukaryotic translation initiation factor 4E (eIF4E) underwent increased nondegradative ubiquitination upon DNA damage. Genotoxic stress led to an enrichment of ARIH1 in perinuclear, ribosome-containing regions and triggered 4EHP association with the mRNA 5' cap as well as mRNA translation arrest in an ARIH1-dependent manner. Finally, restoration of DNA damage-induced translation arrest in ARIH1-depleted cells by means of an eIF2 inhibitor was sufficient to reinstate resistance to genotoxic stress. These findings identify ARIH1 as a potent mediator of DNA damage-induced translation arrest that protects stem and cancer cells against genotoxic stress.

NF-κB signaling is required for XBP1 (unspliced and spliced)-mediated effects on antiestrogen responsiveness and cell fate decisions in breast cancer

Antiestrogen therapy induces the unfolded protein response (UPR) in estrogen receptor-positive (ER(+)) breast cancer. X-box binding protein 1 (XBP1), which exists in the transcriptionally inactive unspliced form [XBP1(U)] and the spliced active form [XBP1(S)], is a key UPR component mediating antiestrogen resistance. We now show a direct link between the XBP1 and NF-κB survival pathways in driving the cell fate decisions in response to antiestrogens in ER(+) breast cancer cells, both in vitro and in a xenograft mouse model. Using novel spliced and nonspliceable forms of XBP1, we show that XBP1(U) functions beyond being a dominant negative of XBP1(S). Both isoforms regulate NF-κB activity via ERα; XBP1(S) is more potent because it also directly regulates p65/RelA expression. These findings provide new insights into the fundamental signaling activities of spliced and unspliced XBP1 in breast cancer, establish NF-κB to be a mediator of these activities, and identify XBP1 and its splicing to be novel therapeutic targets.

ERβ decreases breast cancer cell survival by regulating the IRE1/XBP-1 pathway

Unfolded protein response (UPR) is an adaptive reaction that allows cancer cells to survive endoplasmic reticulum (EnR) stress that is often induced in the tumor microenvironment because of inadequate vascularization. Previous studies report an association between activation of the UPR and reduced sensitivity to antiestrogens and chemotherapeutics in estrogen receptor α (ERα)-positive and triple-negative breast cancers, respectively. ERα has been shown to regulate the expression of a key mediator of the EnR stress response, the X-box-binding protein-1 (XBP-1). Although network prediction models have associated ERβ with the EnR stress response, its role as regulator of the UPR has not been experimentally tested. Here, upregulation of wild-type ERβ (ERβ1) or treatment with ERβ agonists enhanced apoptosis in breast cancer cells in the presence of pharmacological inducers of EnR stress. Targeting the BCL-2 to the EnR of the ERβ1-expressing cells prevented the apoptosis induced by EnR stress but not by non-EnR stress apoptotic stimuli indicating that ERβ1 promotes EnR stress-regulated apoptosis. Downregulation of inositol-requiring kinase 1α (IRE1α) and decreased splicing of XBP-1 were associated with the decreased survival of the EnR-stressed ERβ1-expressing cells. ERβ1 was found to repress the IRE1 pathway of the UPR by inducing degradation of IRE1α. These results suggest that the ability of ERβ1 to target the UPR may offer alternative treatment strategies for breast cancer.

MYC regulates the unfolded protein response and glucose and glutamine uptake in endocrine resistant breast cancer

Background

About 70% of all breast cancers are estrogen receptor alpha positive (ER+) and are treated with antiestrogens. However, 50% of ER + tumors develop resistance to these drugs (endocrine resistance). In endocrine resistant cells, an adaptive pathway called the unfolded protein response (UPR) is elevated that allows cells to tolerate stress more efficiently than in sensitive cells. While the precise mechanism remains unclear, the UPR can trigger both pro-survival and pro-death outcomes that depend on the nature and magnitude of the stress. In this study, we identified MYC, an oncoprotein that is upregulated in endocrine resistant breast cancer, as a regulator of the UPR in glucose-deprived conditions.

Methods

ER+ human breast cancer cell lines (LCC1, LCC1, LY2 and LCC9) and rat mammary tumors were used to confirm upregulation of MYC in endocrine resistance. To evaluate functional relevance of proteins, siRNA-mediated inhibition or small molecule inhibitors were used. Cell density/number was evaluated with crystal violet assay; cell cycle and apoptosis were measured by flow cytometry. Relative quantification of glutamine metabolites were determined by mass spectrometry. Signaling molecules of the UPR, apoptosis or autophagy pathways were investigated by western blotting.

Results

Increased MYC function in resistant cells correlated with increased dependency on glutamine and glucose for survival. Inhibition of MYC reduced cell growth and uptake of both glucose and glutamine in resistant cells. Interestingly, in glucose-deprived conditions, glutamine induced apoptosis and necrosis, arrested autophagy, and triggered the unfolded protein response (UPR) though GRP78-IRE1α with two possible outcomes: (i) inhibition of cell growth by JNK activation in most cells and, (ii) promotion of cell growth by spliced XBP1 in the minority of cells. These disparate effects are regulated, at different signaling junctions, by MYC more robustly in resistant cells.

Conclusions

Endocrine resistant cells overexpress MYC and are better adapted to withstand periods of glucose deprivation and can use glutamine in the short term to maintain adequate metabolism to support cell survival. Our findings reveal a unique role for MYC in regulating cell fate through the UPR, and suggest that targeting glutamine metabolism may be a novel strategy in endocrine resistant breast cancer.

Estrogen receptor-α signaling and localization regulates autophagy and unfolded protein response activation in ER+ breast cancer

Antiestrogen therapy is commonly used to treat estrogen receptor (ER)+ breast cancers but acquired and de novo resistance limits their overall curative potential. An endoplasmic reticulum stress pathway, the unfolded protein response, and autophagy are both implicated in the development of antiestrogen therapy resistance in estrogen receptor-α (ER) positive breast cancer. Thus, we recently investigated how ERα can regulate autophagy and the unfolded protein response (Cook et al., FASEBJ, 2014). We showed that inhibiting ERα signaling stimulates autophagosome formation and flux. Moreover, we showed that ERα knockdown inhibited the unfolded protein response (UPR) signaling components. Here we support and extend this recent report showing additional data on ERα localization and provide a schematic of the overall signaling implicated by our results. Differential activation of UPR and autophagy highlight the pivotal role of ERα in regulating pro-survival signaling in breast cancer through UPR and autophagy. Furthermore, these data suggest new approaches to successful targeting ERα and preventing the regulation of key pro-survival signaling that confers resistance to endocrine therapies.

SCCA1/SERPINB3 promotes oncogenesis and epithelial-mesenchymal transition via the unfolded protein response and IL6 signaling

The serine/cysteine protease inhibitor SCCA1 (SERPINB3) is upregulated in many advanced cancers with poor prognosis, but there is limited information about whether it makes functional contributions to malignancy. Here, we show that SCCA1 expression promoted oncogenic transformation and epithelial-mesenchymal transition (EMT) in mammary epithelial cells, and that SCCA1 silencing in breast cancer cells halted their proliferation. SCCA1 overexpression in neu(+) mammary tumors increased the unfolded protein response (UPR), IL6 expression, and inflammatory phenotypes. Mechanistically, SCCA1 induced a prolonged nonlethal increase in the UPR that was sufficient to activate NF-κB and expression of the protumorigenic cytokine IL6. Overall, our findings established that SCCA1 contributes to tumorigenesis by promoting EMT and a UPR-dependent induction of NF-κB and IL6 autocrine signaling that promotes a protumorigenic inflammation.

Mpl traffics to the cell surface through conventional and unconventional routes

Myeloproliferative neoplasms (MPNs) are often characterized by JAK2 or calreticulin (CALR) mutations, indicating aberrant trafficking in pathogenesis. This study focuses on Mpl trafficking and Jak2 association using two model systems: human erythroleukemia cells (HEL; JAK2V617F) and K562 myeloid leukemia cells (JAK2WT). Consistent with a putative chaperone role for Jak2, Mpl and Jak2 associate on both intracellular and plasma membranes (shown by proximity ligation assay) and siRNA-mediated knockdown of Jak2 led to Mpl trapping in the endoplasmic reticulum (ER). Even in Jak2 sufficient cells, Mpl accumulates in punctate structures that partially colocalize with ER-tracker, the ER exit site marker (ERES) Sec31a, the autophagy marker LC3 and LAMP1. Mpl was fused to miniSOG, a genetically encoded tag for correlated light and electron microscopy. Results suggest that a fraction of Mpl is taken up into autophagic structures from the ER and routed to autolyososomes. Surface biotinylation shows that both immature and mature Mpl reach the cell surface; in K562 cells Mpl is also released in exosomes. Both forms rapidly internalize upon ligand addition, while recovery is primarily attributed to immature Mpl. Mpl appears to reach the plasma membrane via both conventional ER-Golgi and autolysosome secretory pathways, as well as recycling.

Knockdown of estrogen receptor-α induces autophagy and inhibits antiestrogen-mediated unfolded protein response activation, promoting ROS-induced breast cancer cell death

Approximately 70% of all newly diagnosed breast cancers express estrogen receptor (ER)-α. Although inhibiting ER action using targeted therapies such as fulvestrant (ICI) is often effective, later emergence of antiestrogen resistance limits clinical use. We used antiestrogen-sensitive and -resistant cells to determine the effect of antiestrogens/ERα on regulating autophagy and unfolded protein response (UPR) signaling. Knockdown of ERα significantly increased the sensitivity of LCC1 cells (sensitive) and also resensitized LCC9 cells (resistant) to antiestrogen drugs. Interestingly, ERα knockdown, but not ICI, reduced nuclear factor (erythroid-derived 2)-like (NRF)-2 (UPR-induced antioxidant protein) and increased cytosolic kelch-like ECH-associated protein (KEAP)-1 (NRF2 inhibitor), consistent with the observed increase in ROS production. Furthermore, autophagy induction by antiestrogens was prosurvival but did not prevent ERα knockdown-mediated death. We built a novel mathematical model to elucidate the interactions among UPR, autophagy, ER signaling, and ROS regulation of breast cancer cell survival. The experimentally validated mathematical model explains the counterintuitive result that knocking down the main target of ICI (ERα) increased the effectiveness of ICI. Specifically, the model indicated that ERα is no longer present in excess and that the effect on proliferation from further reductions in its level by ICI cannot be compensated for by increased autophagy. The stimulation of signaling that can confer resistance suggests that combining autophagy or UPR inhibitors with antiestrogens would reduce the development of resistance in some breast cancers.

The prosurvival role of autophagy in resveratrol-induced cytotoxicity in GH3 cells

In a previous study, we reported that resveratrol exerts antitumor effects through the estrogen receptor in prolactinoma. The autophagy/lysosomal degradation pathway plays an important role in damage control and energy efficiency. In this study, we investigated the involvement of autophagy and the related signaling pathways in resveratrol-induced apoptosis of GH3 cells. We demonstrate that resveratrol inhibits cell proliferation and induces apoptosis in a dose-dependent manner in GH3 cells. The cleavage of PARP was also observed, and the activation of caspase-3 and caspase-8 was detected. Consistent with this finding, the inhibition of caspase activation effectively attenuated resveratrol-induced cell apoptosis. In addition, the decreased level of Bcl-2 was also observed. The induction of autophagy was confirmed by the detection of the formation of autophagic vacuoles, and the increase in microtubule-associated protein 1 light chain 3 (LC3)-II and beclin-1 levels, two hallmarks of autophagy. Pre-treatment with bafilomycin A1 or 3-methyladenine, inhibitors of autophagy, enhanced the resveratrol-mediated caspase activation and cell death. Moreover, resveratrol induced the activation of ERK1/2, as well as the downregulation of Akt and mTOR phosphorylation. Taken together, these findings indicate that resveratrol induces caspase-dependent apoptosis and decreases Bcl-2 levels. In addition, resveratrol-induced autophagy is regulated by the PI3K/Akt/mTOR and ERK1/2 pathways. Furthermore, the inhibition of autophagy increases the cytotoxicity of resveratrol to GH3 cells.

QSOX1 inhibits autophagic flux in breast cancer cells

The QSOX1 protein (Quiescin Sulfhydryl oxidase 1) catalyzes the formation of disulfide bonds and is involved in the folding and stability of proteins. More recently, QSOX1 has been associated with tumorigenesis and protection against cellular stress. It has been demonstrated in our laboratory that QSOX1 reduces proliferation, migration and invasion of breast cancer cells in vitro and reduces tumor growth in vivo. In addition, QSOX1 expression has been shown to be induced by oxidative or ER stress and to prevent cell death linked to these stressors. Given the function of QSOX1 in these two processes, which have been previously linked to autophagy, we wondered whether QSOX1 might be regulated by autophagy inducers and play a role in this catabolic process. To answer this question, we used in vitro models of breast cancer cells in which QSOX1 was overexpressed (MCF-7) or extinguished (MDA-MB-231). We first showed that QSOX1 expression is induced following amino acid starvation and maintains cellular homeostasis. Our results also indicated that QSOX1 inhibits autophagy through the inhibition of autophagosome/lysosome fusion. Moreover, we demonstrated that inhibitors of autophagy mimic the effect of QSOX1 on cell invasion, suggesting that its role in this process is linked to the autophagy pathway. Previously published data demonstrated that extinction of QSOX1 promotes tumor growth in NOG mice. In this study, we further demonstrated that QSOX1 null tumors present lower levels of the p62 protein. Altogether, our results demonstrate for the first time a role of QSOX1 in autophagy in breast cancer cells and tumors.

Polyphenon E(R), a standardized green tea extract, induces endoplasmic reticulum stress, leading to death of immortalized PNT1a cells by anoikis and tumorigenic PC3 by necroptosis

Increasing doses of Polyphenon E®, a standardized green tea extract, were given to PNT1a and PC3 prostate epithelial cells mimicking initial and advanced stages of prostate cancer (PCa), respectively. Cell death occurred in both cell lines, with PNT1a being more sensitive [half-maximal inhibitory concentration (IC50) = 35 μg/ml] than PC3 (IC50 = 145 μg/ml) to Polyphenon E®. Cell cycle arrest occurred at G0/G1 checkpoint for PNT1a, and G2/M for PC3 cells. Endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) occurred in both cell lines, with each exhibiting different timing in response to Polyphenon E®. Autophagy was transiently activated in PNT1a cells within 12 h after treatment as a survival response to overcome ERS; then activation of caspases and cleavage of poly (ADP ribose) polymerase 1 occurred, committing cells to anoikis death. Polyphenon E® induced severe ERS in PC3 cells, causing a dramatic enlargement of the ER; persistent activation of UPR produced strong upregulation of GADD153/CHOP, a key protein of ERS-mediated cell death. Thereafter, GADD153/CHOP activated Puma, a BH3-only protein, committing cells to necroptosis, a programmed caspase-independent mechanism of cell death. Our results provide a foundation for the identification of novel targets and strategies aimed at sensitizing apoptosis-resistant cells to alternative death pathways.

Cytochrome P450 2E1 (CYP2E1) regulates the response to oxidative stress and migration of breast cancer cells

Introduction

The cytochrome P450 (CYP) enzymes are a class of heme-containing enzymes involved in phase I metabolism of a large number of xenobiotics. The CYP family member CYP2E1 metabolises many xenobiotics and pro-carcinogens, it is not just expressed in the liver but also in many other tissues such as the kidney, the lung, the brain, the gastrointestinal tract and the breast tissue. It is induced in several pathological conditions including cancer, obesity, and type II diabetes implying that this enzyme is implicated in other biological processes beyond its role in phase I metabolism. Despite the detailed description of the role of CYP2E1 in the liver, its functions in other tissues have not been extensively studied. In this study, we investigated the functional significance of CYP2E1 in breast carcinogenesis.

Methods

Cellular levels of reactive oxygen species (ROS) were measured by H₂DCFDA (2 2.9.2 2′,7′-dichlorodihydrofluorescein diacetate) staining and autophagy was assessed by tracing the cellular levels of autophagy markers using western blot assays. The endoplasmic reticulum stress and the unfolded protein response (UPR) were detected by luciferase assays reflecting the splicing of mRNA encoding the X-box binding protein 1 (XBP1) transcription factor and cell migration was evaluated using the scratch wound assay. Gene expression was recorded with standard transcription assays including luciferase reporter and chromatin immunoprecipitation.

Results

Ectopic expression of CYP2E1 induced ROS generation, affected autophagy, stimulated endoplasmic reticulum stress and inhibited migration in breast cancer cells with different metastatic potential and p53 status. Furthermore, evidence is presented indicating that CYP2E1 gene expression is under the transcriptional control of the p53 tumor suppressor.

Conclusions

These results support the notion that CYP2E1 exerts an important role in mammary carcinogenesis, provide a potential link between ethanol metabolism and breast cancer and suggest that progression, and metastasis, of advanced stages of breast cancer can be modulated by induction of CYP2E1 activity.

Antioxidant N-acetylcysteine attenuates hepatocarcinogenesis by inhibiting ROS/ER stress in TLR2 deficient mouse

Hepatocellular carcinoma (HCC) remains one of the most deadly solid tumor malignancies worldwide. We recently find that the loss of toll-like receptor 2 (TLR2) activities promotes the diethylnitrosamine (DEN) induced hepatocellular carcinogenesis and tumor progression, which associates with an abundant accumulation of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. This finding suggests that the ROS/ER stress plays a role in TLR2 modulated carcinogenesis of HCC. To investigate the mechanism of TLR2 activity defending against hepatocarcinogenesis, the TLR2-deficient mice were treated with or without antioxidant N-acetylcysteine (NAC) before DEN administration. We found that pretreatment of these animals with NAC attenuated carcinogenesis and progression of HCC in the TLR2-deficient mice, declined ROS/ER stress, and alleviated the unfold protein response and inflammatory response in TLR2-deficient liver tissue. Moreover, the NAC treatment significantly reduced the enhanced aggregation of p62 and Mallory-Denk bodies in the DEN-induced HCC liver tissue, suggesting that NAC treatment improves the suppressive autophagic flux in the TLR2-deficient liver. These findings indicate that TLR2 activity defends against hepatocarcinogenesis through diminishing the accumulation of ROS and alleviating ER stress and unfold protein response mediated inflammatory response in the liver.

Retigeric acid B-induced mitophagy by oxidative stress attenuates cell death against prostate cancer cells in vitro

AIM

Retigeric acid B (RAB), a pentacyclic triterpenic acid from Lobaria kurokawae Yoshim, has been found to induce apoptosis in prostate cancer cells. The aim of this study was to investigate the roles of mitochondrial damage-caused mitophagy in RAB-induced prostate cancer cell death in vitro.

METHODS

Human prostate cancer PC3 and LNCaP cells were tested. Cell viability was analyzed with MTT assay. Cell apoptosis, ROS level and mitochondrial transmembrane potential (mtΔψ) were measured with flow cytometry. Autophagy- and apoptosis-related proteins were studied using Western blotting. GFP-LC3B puncta, mitochondrial swelling and mitophagy were examined morphologically. Quantitative RT-PCR was used to measure LC3B mRNA level, and siRNA was used to knock down LC3BII.

RESULTS

In both PC3 and LNCaP cells, RAB (15 μmol/L) increased ROS accumulation and decreased mtΔψ in a time-dependent manner. Furthermore, RAB induced mitochondrial swelling and mitophagy, significantly increased LC3B expression and conversion of LC3BI to LC3BII, and the elimination of mitochondria by LC3BII-containing autophagolysosomes. In addition, RAB suppressed the PI3K/Akt/mTOR pathway activation. Pretreatment of PC3 cells with autophagy inhibitor 3-MA (5 mmol/L) or the lysosomal protease inhibitor CQ (10 μmol/L) significantly increased RAB-induced apoptosis. Similar results were obtained in RAB-treated PC3 cells with LC3B knocked down.

CONCLUSION

RAB induces mitochondrial damage and mitophagy that attenuates RAB-induced prostate cancer cell death. Thus, suppression of mitophagy might be a potential strategy for improving the chemotherapeutic effects of RAB.

B19, a novel monocarbonyl analogue of curcumin, induces human ovarian cancer cell apoptosis via activation of endoplasmic reticulum stress and the autophagy signaling pathway

BACKGROUND

The unfolded protein response, autophagy and endoplasmic reticulum (ER) stress-induced apoptosis regulate tumor cell fate and have become novel signaling targets for the development of cancer therapeutic drugs. Curcumin has been used to treat several different cancers, including ovarian cancer, in clinical trials and research; however, the role of ER stress and autophagy in the therapeutic effects of curcumin and new curcumin analogues remains unclear.

METHODS

Cell viability was determined using the MTT assay. Apoptosis was detected using flow cytometry with PI/Annexin V-FITC staining. The expression levels of ER stress- and autophagy-related proteins were analyzed by western blotting. The activation of autophagy was detected using immunofluorescence staining.

RESULTS

We demonstrated that B19 induced HO8910 cell apoptosis in a dose-responsive manner. We also determined and that this effect was associated with corresponding increases in a series of key components in the UPR and ER stress-mediated apoptosis pathways, followed by caspase 3 cleavage and activation. We also observed that B19 treatment induced autophagy in HO8910 cells. The inhibition of autophagy using 3-methyladenine (3-MA) increased levels of intracellular misfolded proteins, which enhanced ovarian cancer apoptosis.

CONCLUSIONS

Our data indicate that ER stress and autophagy may play a role in the apoptosis that is induced by the curcumin analogue B19 in an epithelial ovarian cancer cell line and that autophagy inhibition can increase curcumin analogue-induced apoptosis by inducing severe ER stress.