UPR: An Upstream Signal to EMT Induction in Cancer

The unfolded protein response machinery in glioblastoma genesis, chemoresistance and as a druggable target

BACKGROUND

The role of the unfolded protein response (UPR) has been progressively unveiled over the last decade and several studies have investigated its implication in glioblastoma (GB) development. The UPR restores cellular homeostasis by triggering the folding and clearance of accumulated misfolded proteins in the ER consecutive to endoplasmic reticulum stress. In case it is overwhelmed, it induces apoptotic cell death. Thus, holding a critical role in cell fate decisions.

METHODS

This article, reviews how the UPR is implicated in cell homeostasis maintenance, then surveils the evidence supporting the UPR involvement in GB genesis, progression, angiogenesis, GB stem cell biology, tumor microenvironment modulation, extracellular matrix remodeling, cell fate decision, invasiveness, and grading. Next, it concurs the evidence showing how the UPR mediates GB chemoresistance-related mechanisms.

RESULTS

The UPR stress sensors IRE1, PERK, and ATF6 with their regulator GRP78 are upregulated in GB compared to lower grade gliomas and normal brain tissue. They are activated in response to oncogenes and are implicated at different stages of GB progression, from its genesis to chemoresistance and relapse. The UPR arms can be effectors of apoptosis as mediators or targets.

CONCLUSION

Recent research has established the role of the UPR in GB pathophysiology and chemoresistance. Targeting its different sensors have shown promising in overcoming GB chomo- and radioresistance and inducing apoptosis.

Eleven metabolism‑related genes composed of Stard5 predict prognosis and contribute to EMT phenotype in HCC

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, with a high mortality and poor survival rate. Abnormal tumor metabolism is considered a hallmark of HCC and is a potential therapeutic target. This study aimed to identify metabolism-related biomarkers to evaluate the prognosis of patients with HCC.

METHOD

The Cancer Genome Atlas (TCGA) database was used to explore differential metabolic pathways based on high and low epithelial-mesenchymal transition (EMT) groupings. Genes in differential metabolic pathways were obtained for HCC metabolism-related molecular subtype analysis. Differentially expressed genes (DEGs) from the three subtypes were subjected to Lasso Cox regression analysis to construct prognostic risk models. Stard5 expression in HCC patients was detected by western blot and immunohistochemistry (IHC), and the role of Stard5 in the metastasis of HCC was investigated by cytological experiments.

RESULTS

Unsupervised clustering analysis based on metabolism-related genes revealed three subtypes in HCC with differential prognosis. A risk prognostic model was constructed based on 11 genes (STARD5, FTCD, SCN4A, ADH4, CFHR3, CYP2C9, CCL14, GADD45G, SOX11, SCIN, and SLC2A1) obtained by LASSO Cox regression analysis of the three subtypes of DEGs. We validated that the model had a good predictive power. In addition, we found that the high-risk group had a poor prognosis, higher proportion of Tregs, and responded poorly to chemotherapy. We also found that Stard5 expression was markedly decreased in HCC tissues, which was associated with poor prognosis and EMT. Knockdown of Stard5 contributed to the invasion and migration of HCC cells. Overexpression of Stard5 inhibited EMT in HCC cells.

CONCLUSION

We developed a new model based on 11 metabolism-related genes, which predicted the prognosis and response to chemotherapy or immunotherapy for HCC. Notably, we demonstrated for the first time that Stard5 acted as a tumor suppressor by inhibiting metastasis in HCC.

A computational peptide model induces cancer cells' apoptosis by docking Kringle 5 to GRP78

BACKGROUND

Cells can die through a process called apoptosis in both pathological and healthy conditions. Cancer development and progression may result from abnormal apoptosis. The 78-kDa glucose-regulated protein (GRP78) is increased on the surface of cancer cells. Kringle 5, a cell apoptosis agent, is bound to GRP78 to induce cancer cell apoptosis. Kringle 5 was docked to GRP78 using ClusPro 2.0. The interaction between Kringle 5 and GRP78 was investigated.

RESULTS

The interacting amino acids were found to be localized in three areas of Kringle 5. The proposed peptide is made up of secondary structure amino acids that contain Kringle 5 interaction residues. The 3D structure of the peptide model amino acids was created using the PEP-FOLD3 web tool.

CONCLUSIONS

The proposed peptide completely binds to the GRP78 binding site on the Kringle 5, signaling that it might be effective in the apoptosis of cancer cells.

Cycloartane triterpenoid from Euphorbia macrostegia modulates ER stress signaling pathways to induce apoptosis in MDA-MB231 and MCF-7 breast cancer cell lines

Unfolded protein response (UPR) is involved in breast cancer (BC) progression and drug resistance. Many natural products (NPs) could modulate UPR and used for therapeutic purposes. Herein, we aimed to investigate the molecular mechanism of Cycloart-23E-ene-3β, 25-diol (Cycloart-E25), cytotoxicity, as a NP extracted from Euphorbia macrostegia and focused on endoplasmic-reticulum stress (ERS) and UPR signaling pathways. Reactive oxygen species (ROS) were probed by DCFDA fluorescence dye. Apoptosis was assayed by annexin V/propidium iodide (PI), immunoblotting of anti- and proapoptotic, Bcl-2 and Bax proteins, and mitochondrial transmembrane potential (ΔΨm) changes. Thioflavin T (ThT) staining and immunoblotting of UPR signaling components (CHOP, PERK, ATF6, BiP, and XBP1) were recruited for the assessment of ERS. Our results indicated that Cycloart-E25 noticeably increases ROS levels in both MB-231 MDA-MB-231 and MCF-7 cell lines, p>0.05. Flow cytometry assessments revealed an increase in the cell population undergoing apoptosis. Also, the Bax/Bcl-2 ratio increased in a dose-dependent manner following Cycloart-E25 treatment, significantly, p>0.05. Mitochondrial involvement could be deduced by significant decreases in ΔΨm, p>0.05. Cycloart-E25 potently induces protein aggregation and upregulated CHOP, PERK, ATF6, BiP, and XBP1 factors in both MDA-MB-231 MB-231 and MCF-7 cell lines, indicating the involvement of ERS in Cycloart-E25-mediated apoptosis. In conclusion, Cycloart-E25 increased the accumulation of misfolded proteins and upregulated UPR components. Therefore, induction of ERS may be involved in the trigger of apoptosis in BC cell lines. Cycloart-E25 induced apoptosis in breast cancer cell lines through ERS. More assessments are needed to confirm its in vivo anti-tumoral effects.

Identification of heat shock protein family A member 5 (HSPA5) targets involved in nonalcoholic fatty liver disease

Heat shock protein family A (Hsp70) member 5 (HSPA5) is an endoplasmic reticulum chaperone, which regulates cell metabolism, particularly lipid metabolism. While HSPA5's role in regulating cell function is well described, HSPA5 binding to RNA and its biological function in nonalcoholic fatty liver disease (NAFLD) is still lacking. In the present study, the ability of HSPA5 to modulate alternative splicing (AS) of cellular genes was assessed using Real-Time PCR on 89 NAFLD-associated genes. RNA immunoprecipitation coupled to RNA sequencing (RIP-Seq) assays were also performed to identify cellular mRNAs bound by HSPA5. We obtained the HSPA5-bound RNA profile in HeLa cells and peak calling analysis revealed that HSPA5 binds to coding genes and lncRNAs. Moreover, RIP-Seq assays demonstrated that HSPA5 immunoprecipitates specific cellular mRNAs such as EGFR, NEAT1, LRP1 and TGFß1, which are important in the pathology of NAFLD. Finally, HSPA5 binding sites may be associated with splicing sites. We used the HOMER algorithm to search for motifs enriched in coding sequence (CDs) peaks, which identified over-representation of the AGAG motif in both sets of immunoprecipitated peaks. HSPA5 regulated genes at the 5'UTR alternative splicing and introns and in an AG-rich sequence-dependent manner. We propose that the HSPA5-AGAG interaction might play an important role in regulating alternative splicing of NAFLD-related genes. This report is the first to demonstrate that HSPA5 regulated pre-RNA alternative splicing, stability, or translation and affected target protein(s) via binding to lncRNA and mRNA linked to NAFLD.

Potent carotenoid astaxanthin expands the anti-cancer activity of cisplatin in human prostate cancer cells

Prostate cancer (PCa) is the second most common type of cancer and the sixth cause of death in men worldwide. Radiotherapy and immunotherapy are commonly used in treating PCa, but understanding the crosstalk mechanisms of carcinogenesis and new therapeutic approaches is essential for supporting poor diagnosis and existing therapies. Astaxanthin (ASX) is a member of the xanthophyll family that is an oxygenated derivative of carotenoids whose synthesis is in plant extracts from lycopene. ASX has protective effects on various diseases, such as Parkinson's disease and cancer by showing potent antioxidant and anti-inflammatory properties. However, there is an ongoing need for a detailed investigation of the molecular mechanism of action to expand its therapeutic use. In the present study, we showed the new regulatory role of ASX in PCa cells by affecting the unfolded protein response (UPR) signaling, autophagic activity, epithelial-mesenchymal transition (EMT) and regulating the expression level of angiogenesis-related protein vascular endothelial growth factor A (VEGF-A), proto-oncogene c-Myc and prostate-specific antigen (PSA). Additionally, we determined that it exhibited synergistic action with cisplatin and significantly enhanced apoptotic cell death in PCa cells. Present findings suggest that ASX may be a potent adjuvant therapeutic option in PCa treatment when used alone or combined with chemotherapeutics. Schematic illustration of the biochemical activity of astaxanthin and its combination with cisplatin.

Investigating the Function of Human Jumping Translocation Breakpoint Protein (hJTB) and Its Interacting Partners through In-Solution Proteomics of MCF7 Cells

Human jumping translocation breakpoint (hJTB) gene is located on chromosome 1q21 and is involved in unbalanced translocation in many types of cancer. JTB protein is ubiquitously present in normal cells but it is found to be overexpressed or downregulated in various types of cancer cells, where this protein and its isoforms promote mitochondrial dysfunction, resistance to apoptosis, genomic instability, proliferation, invasion and metastasis. Hence, JTB could be a tumor biomarker for different types of cancer, such as breast cancer (BC), and could be used as a drug target for therapy. However, the functions of the protein or the pathways through which it increases cell proliferation and invasiveness of cancer cells are not well-known. Therefore, we aim to investigate the functions of JTB by using in-solution digestion-based cellular proteomics of control and upregulated and downregulated JTB protein in MCF7 breast cancer cell line, taking account that in-solution digestion-based proteomics experiments are complementary to the initial in-gel based ones. Proteomics analysis allows investigation of protein dysregulation patterns that indicate the function of the protein and its interacting partners, as well as the pathways and biological processes through which it functions. We concluded that JTB dysregulation increases the epithelial-mesenchymal transition (EMT) potential and cell proliferation, harnessing cytoskeleton organization, apical junctional complex, metabolic reprogramming, and cellular proteostasis. Deregulated JTB expression was found to be associated with several proteins involved in mitochondrial organization and function, oxidative stress (OS), apoptosis, and interferon alpha and gamma signaling. Consistent and complementary to our previous results emerged by using in-gel based proteomics of transfected MCF7 cells, JTB-related proteins that are overexpressed in this experiment suggest the development of a more aggressive phenotype and behavior for this luminal type A non-invasive/poor-invasive human BC cell line that does not usually migrate or invade compared with the highly metastatic MDA-MB-231 cells. This more aggressive phenotype of MCF7 cells related to JTB dysregulation and detected by both in-gel and in-solution proteomics could be promoted by synergistic upregulation of EMT, Mitotic spindle and Fatty acid metabolism pathways. However, in both JTB dysregulated conditions, several downregulated JTB-interacting proteins predominantly sustain antitumor activities, attenuating some of the aggressive phenotypical and behavioral traits promoted by the overexpressed JTB-related partners.

The "Yin and Yang" of Unfolded Protein Response in Cancer and Immunogenic Cell Death

Physiological and pathological burdens that perturb endoplasmic reticulum homeostasis activate the unfolded protein response (UPR), a conserved cytosol-to-nucleus signaling pathway that aims to reinstate the vital biosynthetic and secretory capacity of the ER. Disrupted ER homeostasis, causing maladaptive UPR signaling, is an emerging trait of cancer cells. Maladaptive UPR sustains oncogene-driven reprogramming of proteostasis and metabolism and fosters proinflammatory pathways promoting tissue repair and protumorigenic immune responses. However, when cancer cells are exposed to conditions causing irreparable ER homeostasis, such as those elicited by anticancer therapies, the UPR switches from a survival to a cell death program. This lethal ER stress response can elicit immunogenic cell death (ICD), a form of cell death with proinflammatory traits favoring antitumor immune responses. How UPR-driven pathways transit from a protective to a killing modality with favorable immunogenic and proinflammatory output remains unresolved. Here, we discuss key aspects of the functional dichotomy of UPR in cancer cells and how this signal can be harnessed for therapeutic benefit in the context of ICD, especially from the aspect of inflammation aroused by the UPR.

Gremlin-1 Promotes Colorectal Cancer Cell Metastasis by Activating ATF6 and Inhibiting ATF4 Pathways

Cancer cell survival, function and fate strongly depend on endoplasmic reticulum (ER) proteostasis. Although previous studies have implicated the ER stress signaling network in all stages of cancer development, its role in cancer metastasis remains to be elucidated. In this study, we investigated the role of Gremlin-1 (GREM1), a secreted protein, in the invasion and metastasis of colorectal cancer (CRC) cells in vitro and in vivo. Firstly, public datasets showed a positive correlation between high expression of GREM1 and a poor prognosis for CRC. Secondly, GREM1 enhanced motility and invasion of CRC cells by epithelial–mesenchymal transition (EMT). Thirdly, GREM1 upregulated expression of activating transcription factor 6 (ATF6) and downregulated that of ATF4, and modulation of the two key players of the unfolded protein response (UPR) was possibly through activation of PI3K/AKT/mTOR and antagonization of BMP2 signaling pathways, respectively. Taken together, our results demonstrate that GREM1 is an invasion-promoting factor via regulation of ATF6 and ATF4 expression in CRC cells, suggesting GREM1 may be a potential pharmacological target for colorectal cancer treatment.

Role of UPR Sensor Activation in Cell Death-Survival Decision of Colon Cancer Cells Stressed by DPE Treatment

Polyphenols have been shown to possess several beneficial properties, including properties involved in the prevention or treatment of cancer. Among these polyphenols, a leading role is played by dihydroxyphenylethanol (DPE), the most powerful antioxidant compound contained in the olive oil. DPE has been previously reported to induce endoplasmic reticulum (ER) stress and to reduce cell survival in colon cancer, one of the most common and aggressive cancers in developed countries. In this study, we further investigated the activation of UPR by DPE and explored the roles of the three UPR sensors, inositol-requiring enzyme (IRE) 1 alpha, protein kinase RNA-like endoplasmic reticulum kinase (PERK), and activating transcription factor (ATF6), in the cell death-survival decision of wt and mutp53 colon cancer cells and the underlying mechanisms involved. We also unveiled a new interplay between ATF6 and wt, as well as mutp53, which may have important implications in cancer therapy.

2-Hydroxypropyl-β-cyclodextrin Regulates the Epithelial to Mesenchymal Transition in Breast Cancer Cells by Modulating Cholesterol Homeostasis and Endoplasmic Reticulum Stress

Cholesterol metabolism affects endoplasmic reticulum (ER) stress and modulates epithelial-mesenchymal transition (EMT). Our previous study demonstrated that 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) attenuated EMT by blocking the transforming growth factor (TGF)-β/Smad signaling pathway and activating ER stress in MDA-MB-231 cells. To further assess the detailed mechanisms between cholesterol metabolism, ER stress, and EMT, LXR-623 (an agonist of LXRα) and simvastatin were used to increase and decrease cholesterol efflux and synthesis, respectively. Here, we found that high HP-β-CD concentrations could locally increase cholesterol levels in the ER by decreasing LXRα expression and increasing Hydroxymethylglutaryl-Coenzyme A reductase (HMGCR) expression in MDA-MB-231 and BT-549 cells, which triggered ER stress and inhibited EMT. Meanwhile, tunicamycin-induced ER stress blocked the TGF-β/Smad signaling pathway. However, low HP-β-CD concentrations can decrease the level of membrane cholesterol, enhance the TGF-β receptor I levels in lipid rafts, which helped to activate TGF-β/Smad signaling pathway, inhibit ER stress and elevate EMT. Based on our findings, the use of high HP-β-CD concentration can lead to cholesterol accumulation in the ER, thereby inducing ER stress, which directly suppresses TGF-β pathway-induced EMT. However, HP-β-CD is proposed to deplete membrane cholesterol at low concentrations and concurrently inhibit ER stress and induce EMT by promoting the TGF-β signaling pathways.

The change of intracellular zinc distribution after strong acid challenge

Zinc (Zn2+) is stored in the nucleus, endoplasmic reticulum (ER), Golgi apparatus, mitochondria, lysosomes, and zinc-binding proteins. The acidity of the microenvironment affects the binding between zinc and proteins in which zinc become free or loosely bound. In this study, when cells were treated with an acidic medium, we started seeing free zinc 'hot spots' or zincosomes where we found bright zinc fluorescence. The rising free zinc quickly across whole cells with both intensity and distribution were pH-dependent. Interestingly, the nucleus was more sensitive to acidic treatment as the increase of nuclear zinc was faster and higher than the increase of cytosolic zinc. In addition, we re-cultured strong acid-challenged cells in a normal medium. Comparing to the control, these cells exhibited multiple zinc 'hot spots' beside the nucleus, suggesting that free zinc became more extensively distributed. To investigate further the function of zinc in cell shaping and morphological changes, we categorized strong acid-challenged cells into different shapes and found that the proportion of each cell shape had changed after the acid challenge. These acid-induced changes of the cell shape percentage were partially reversed by the reduction of zinc, suggesting that zinc participated in directing the cell shapes and morphologies during cell growth. Our findings reveal that acidic pH affects the dynamics of cellular zinc by making zinc more accessible to cellular compartments and zinc-binding proteins, which provided new insights into understanding the cellular behavior and the function of zinc in it.

[A Review of the Roles of Endoplasmic Reticulum Stress in Cancer Cell Metastasis]

Metastasis is a multistep and low-efficiency biological process driven by acquisition of genetic and/or epigenetic alterations within tumor cells. These evolutionary alterations enable tumor cells to thrive in the inhospitable microenvironment they encounter in the process of metastasis and eventually lead to macroscopic metastases in distant organs. The unfolded protein response (UPR) induced by endoplasmic reticulum (ER) stress is one of the most important mechanisms regulating cellular adaptation to an adverse microenvironment. UPR is involved in all stages of metastasis, playing an important role in tumor cell growth, survival, and differentiation and the process of maintaining protein hemostasis. Sustained activation of ER stress sensors endows tumor cells with better epithelial-mesenchymal transition (EMT), survival, immune escape, angiogenesis, cellular adhesion, dormancy-to reactivation capacity in the process of metastasis. Here, we discussed the role of UPR in regulating the above-mentioned abilities of tumor cells during metastasis, providing a reference for development of new targets for the treatment of tumor metastasis.UPR in regulating the above-mentioned characteristics and mechanisms of tumor cells during metastasis, providing a reference for development of new targets for the treatment of tumor metastasis.

Emerging Concepts of Hybrid Epithelial-to-Mesenchymal Transition in Cancer Progression

Epithelial mesenchymal transition (EMT) is a complex process through which epithelial (E) cells lose their adherens junctions, transform into mesenchymal (M) cells and attain motility, leading to metastasis at distant organs. Nowadays, the concept of EMT has shifted from a binary phase of interconversion of pure E to M cells and vice versa to a spectrum of E/M transition states preferably coined as hybrid/partial/intermediate EMT. Hybrid EMT, being a plastic transient state, harbours cells which co-express both E and M markers and exhibit high tumourigenic properties, leading to stemness, metastasis, and therapy resistance. Several preclinical and clinical studies provided the evidence of co-existence of E/M phenotypes. Regulators including transcription factors, epigenetic regulators and phenotypic stability factors (PSFs) help in maintaining the hybrid state. Computational and bioinformatics approaches may be excellent for identifying new factors or combinations of regulatory elements that govern the different EMT transition states. Therapeutic intervention against hybrid E/M cells, though few, may evolve as a rational strategy against metastasis and drug resistance. This review has attempted to present the recent advancements on the concept and regulation of the process of hybrid EMT which generates hybrid E/M phenotypes, evidence of intermediate EMT in both preclinical and clinical setup, impact of partial EMT on promoting tumourigenesis, and future strategies which might be adapted to tackle this phenomenon.

Metformin: Metabolic Rewiring Faces Tumor Heterogeneity

Tumor heterogeneity impinges on all the aspects of tumor history, from onset to metastasis and relapse. It is growingly recognized as a propelling force for tumor adaptation to environmental and micro-environmental cues. Metabolic heterogeneity perfectly falls into this process. It strongly contributes to the metabolic plasticity which characterizes cancer cell subpopulations-capable of adaptive switching under stress conditions, between aerobic glycolysis and oxidative phosphorylation-in both a convergent and divergent modality. The mitochondria appear at center-stage in this adaptive process and thus, targeting mitochondria in cancer may prove of therapeutic value. Metformin is the oldest and most used anti-diabetic medication and its relationship with cancer has witnessed rises and falls in the last 30 years. We believe it is useful to revisit the main mechanisms of action of metformin in light of the emerging views on tumor heterogeneity. We first analyze the most consolidated view of its mitochondrial mechanism of action and then we frame the latter in the context of tumor adaptive strategies, cancer stem cell selection, metabolic zonation of tumors and the tumor microenvironment. This may provide a more critical point of view and, to some extent, may help to shed light on some of the controversial evidence for metformin's anticancer action.

KSHV dysregulates bulk macroautophagy, mitophagy and UPR to promote endothelial to mesenchymal transition and CCL2 release, key events in viral-driven sarcomagenesis

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of KS, an aggressive neoplasm that mainly occurs in immune-compromised patients. Spindle cells represent the main feature of this aggressive malignancy and arise from KSHV-infected endothelial cells undergoing endothelial to mesenchymal transition (EndMT), which changes their cytoskeletal composition and organization. As in epithelial to mesenchymal transition (EMT), EndMT is driven by transcription factors such as SNAI1 and ZEB1 and implies a cellular reprogramming mechanism regulated by several molecular pathways, particularly PI3K/AKT/MTOR. Here we found that KSHV activated MTOR and its targets 4EBP1 and ULK1 and reduced bulk macroautophagy and mitophagy to promote EndMT, activate ER stress/unfolded protein response (UPR), and increase the release of the pro-angiogenic and pro-inflammatory chemokine CCL2 by HUVEC cells. Our study suggests that the manipulation of macroautophagy, mitophagy and UPR and the interplay between the three could be a promising strategy to counteract EndMT, angiogenesis and inflammation, the key events of KSHV-driven sarcomagenesis.

Role of Epithelial-Mesenchymal Transition in Retinal Pigment Epithelium Dysfunction

Retinal pigment epithelial (RPE) cells maintain the health and functional integrity of both photoreceptors and the choroidal vasculature. Loss of RPE differentiation has long been known to play a critical role in numerous retinal diseases, including inherited rod-cone degenerations, inherited macular degeneration, age-related macular degeneration, and proliferative vitreoretinopathy. Recent studies in post-mortem eyes have found upregulation of critical epithelial-mesenchymal transition (EMT) drivers such as TGF-β, Wnt, and Hippo. As RPE cells become less differentiated, they begin to exhibit the defining characteristics of mesenchymal cells, namely, the capacity to migrate and proliferate. A number of preclinical studies, including animal and cell culture experiments, also have shown that RPE cells undergo EMT. Taken together, these data suggest that RPE cells retain the reprogramming capacity to move along a continuum between polarized epithelial cells and mesenchymal cells. We propose that movement along this continuum toward a mesenchymal phenotype be defined as RPE Dysfunction. Potential mechanisms include impaired tight junctions, accumulation of misfolded proteins and dysregulation of several key pathways and molecules, such as TGF-β pathway, Wnt pathway, nicotinamide, microRNA 204/211 and extracellular vesicles. This review synthesizes the evidence implicating EMT of RPE cells in post-mortem eyes, animal studies, primary RPE, iPSC-RPE and ARPE-19 cell lines.

Expression of R345W-Fibulin-3 Induces Epithelial-Mesenchymal Transition in Retinal Pigment Epithelial Cells

Purpose

To investigate the role of protein misfolding in retinal pigment epithelial (RPE) cell dysfunction, the effects of R345W-Fibulin-3 expression on RPE cell phenotype were studied.

Methods

Primary RPE cells were cultured to confluence on Transwells and infected with lentivirus constructs to express wild-type (WT)- or R345W-Fibulin-3. Barrier function was assessed by evaluating zonula occludens-1 (ZO-1) distribution and trans-epithelial electrical resistance (TER). Polarized secretion of vascular endothelial growth factor (VEGF), was measured by Enzyme-linked immunosorbent assay (ELISA). Differentiation status was assessed by qPCR of genes known to be preferentially expressed in terminally differentiated RPE cells, and conversion to an epithelial–mesenchymal transition (EMT) phenotype was assessed by a migration assay.

Results

Compared to RPE cells expressing WT-Fibulin-3, ZO-1 distribution was disrupted and TER values were significantly lower in RPE cells expressing R345W-Fibulin-3. In cells expressing mutant Fibulin-3, VEGF secretion was attenuated basally but not in the apical direction, whereas Fibulin-3 secretion was reduced in both the apical and basal directions. Retinal pigment epithelial signature genes were downregulated and multiple genes associated with EMT were upregulated in the mutant group. Migration assays revealed a faster recovery rate in ARPE-19 cells overexpressing R345W-Fibulin-3 compared to WT.

Conclusions

The results suggest that expression of R345W-Fibulin-3 promotes EMT in RPE cells.

Antitumor effects and mechanisms of pyropheophorbide‑α methyl ester‑mediated photodynamic therapy on the human osteosarcoma cell line MG‑63

Photodynamic therapy (PDT) is a promising treatment for osteosarcoma, and pyropheophorbide-α methyl ester (MPPa) is a second-generation photosensitizer for tumor treatment. The present study aimed to determine the efficacy and possible mechanisms of MPPa-PDT in the treatment of osteosarcoma MG-63 cells. Flow cytometry and western blotting were used to detect cell cycle-related indicators Cyclin D1, Cyclin E, Cyclin A and Cyclin B1. Cell migration and invasion abilities were detected using wound-healing and Transwell chamber assays. Cellular endoplasmic reticulum stress (ERS), autophagy and apoptosis-related indicators were detected by flow cytometry and western blotting. The results demonstrated that MPPa-PDT blocked the MG-63 cell cycle and inhibited cell migration and invasion. Additionally, MPPa-PDT inhibited the activation of the Akt/mammalian target of rapamycin (mTOR) pathway. MG-63 cells underwent ERS-induced apoptosis following MPPa-PDT treatment. Pretreatment with the mTOR phosphorylation inhibitor rapamycin affected the autophagy of MPPa-PDT-induced osteosarcoma MG-63 cells and enhanced apoptosis through targeting mTOR.

The P5-type ATPase Spf1 is required for development and virulence of the rice blast fungus Pyricularia oryzae

Pyricularia oryzae (synonym Magnaporthe oryzae) is a plant pathogen causing major yield losses in cultivated rice and wheat. The P-type ATPases play important roles in cellular processes of fungi, plants, and animals via transporting specific substrates through ATP hydrolysis. Here, we characterized the roles of a P5-ATPase, Spf1, in the development and virulence of P. oryzae. Deletion of SPF1 led to decreased hyphal growth and conidiation, delayed spore germination and appressorium formation, reduced penetration and invasive hyphal extension, and attenuated virulence. Appressorium turgor, however, was not affected by deletion of SPF1. The co-localization of Spf1-GFP and an endoplasmic reticulum (ER) marker protein, Lhs1-DsRed2, indicated that Spf1 is an ER-localized P5-ATPase. An ER stress factor, 0.5 μg/ml tunicamycin (TUNI), inhibited the growth of ∆spf1, but another ER stress factor, 5 mM dithiothreitol (DTT), promoted the growth of ∆spf1. Treatment with chemicals for oxidative stress (5 mM H₂O₂ and 0.8 mM paraquat) also promoted the growth of ∆spf1. Gene expression assays showed that unfolded protein response (UPR) components KAR2, OST1, PMT1, ERV29, PDI1, SCJ1, SEC61, a Ca²⁺ channel-related P-type ATPase gene PMR1, and a calcineurin-dependent transcription factor CRZ1 were significantly up-regulated in ∆spf1, suggesting activation of UPR in the mutant. These lines of experimental evidence indicate that SPF1 is involved in some basal ER mechanisms of P. oryzae including UPR pathway and responses to ER related stresses, therefore, affecting fungal development and virulence. However, the detailed mechanism between Spf1 and virulence still awaits future researches.

Contribution of Epithelial Plasticity to Therapy Resistance

Therapy resistance is responsible for tumour recurrence and represents one of the major challenges in present oncology. Significant advances have been made in the understanding of the mechanisms underlying resistance to conventional and targeted therapies improving the clinical management of relapsed patients. Unfortunately, in too many cases, resistance reappears leading to a fatal outcome. The recent introduction of immunotherapy regimes has provided an unprecedented success in the treatment of specific cancer types; however, a good percentage of patients do not respond to immune-based treatments or ultimately become resistant. Cellular plasticity, cancer cell stemness and tumour heterogeneity have emerged as important determinants of treatment resistance. Epithelial-to-mesenchymal transition (EMT) is associated with resistance in many different cellular and preclinical models, although little evidence derives directly from clinical samples. The recognition of the presence in tumours of intermediate hybrid epithelial/mesenchymal states as the most likely manifestation of epithelial plasticity and their potential link to stemness and tumour heterogeneity, provide new clues to understanding resistance and could be exploited in the search for anti-resistance strategies. Here, recent evidence linking EMT/epithelial plasticity to resistance against conventional, targeted and immune therapy are summarized. In addition, future perspectives for related clinical approaches are also discussed.