Enhancement of Acetate-Induced Apoptosis of Colorectal Cancer Cells by Cathepsin D Inhibition Depends on Oligomycin A-Sensitive Respiration

Colorectal cancer (CRC) is a leading cause of death worldwide. Conventional therapies are available with varying effectiveness. Acetate, a short-chain fatty acid produced by human intestinal bacteria, triggers mitochondria-mediated apoptosis preferentially in CRC but not in normal colonocytes, which has spurred an interest in its use for CRC prevention/therapy. We previously uncovered that acetate-induced mitochondrial-mediated apoptosis in CRC cells is significantly enhanced by the inhibition of the lysosomal protease cathepsin D (CatD), which indicates both mitochondria and the lysosome are involved in the regulation of acetate-induced apoptosis. Herein, we sought to determine whether mitochondrial function affects CatD apoptotic function. We found that enhancement of acetate-induced apoptosis by CatD inhibition depends on oligomycin A-sensitive respiration. Mechanistically, the potentiating effect is associated with an increase in cellular and mitochondrial superoxide anion accumulation and mitochondrial mass. Our results provide novel clues into the regulation of CatD function and the effect of tumor heterogeneity in the outcome of combined treatment using acetate and CatD inhibitors.

Myricitrin from bayberry as a potential inhibitor of cathepsin-D: Prospects for squamous lung carcinoma prevention

Cathepsin-D (CATD) inhibitors' design and development drawn interest due to their potential therapeutic applications in managing different cancer types, including lung cancer. This study investigated myricitrin, a flavonol-3-O-rhamnoside, for its binding affinity to CATD. Molecular docking experiments revealed a strong binding affinity (-7.8 kcal/mol). Molecular dynamics (MD) simulation confirmed the complex's stability, while enzyme activity studies showed inhibitory concentration (IC50) of 35.14 ± 6.08 μM (in cell-free) and 16.00 ± 3.48 μM (in cell-based) test systems. Expression analysis indicated downregulation of CATD with a fold change of 1.35. Myricitrin demonstrated antiproliferative effects on NCIH-520 cells [IC50: 64.11 μM in Sulphorhodamine B (SRB), 24.44 μM in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)], but did not affect healthy CHANG cells. It also prolonged the G2/M phase (at 10 μM: 1.19-fold; at 100 μM: 1.13-fold) and increased sub-diploid population by 1.35-fold. Based on the analysis done using SwissADME program, it is predicted that myricitrin is not a cytochrome p450s (CYPs) inhibitor, followed the rule of Ghose and found not permeable to the blood-brain barrier (BBB) which suggests it as a safe molecule. In summary, the experimental findings may establish the foundation for myricitrin and its analogues to be used therapeutically in CATD-mediated lung cancer prevention.

Functional Analysis of the Cathepsin D Gene Response to SGIV Infection in the Orange-Spotted Grouper, Epinephelus coioides

(1) Background: Lysosomal aspartic protease Cathepsin D (CD) is a key regulator and signaling molecule in various biological processes including activation and degradation of intracellular proteins, the antigen process and programmed cell death. However, the function of fish CD in virus infection remains largely unknown. (2) Methods: The functions of the CD gene response to SGIV infection was determined with light microscopy, reverse transcription quantitative PCR, Western blot and flow cytometry. (3) Results: In this study, Ec-Cathepsin D (Ec-CD) was cloned and identified from the orange-spotted grouper, Epinephelus coioides. The open reading frame (ORF) of Ec-CD consisted of 1191 nucleotides encoding a 396 amino acid protein with a predicted molecular mass of 43.17 kDa. Ec-CD possessed typical CD structural features including an N-terminal signal peptide, a propeptide region and a mature domain including two glycosylation sites and two active sites, which were conserved in other CD sequences. Ec-CD was predominantly expressed in the spleen and kidneys of healthy groupers. A subcellular localization assay indicated that Ec-CD was mainly distributed in the cytoplasm. Ec-CD expression was suppressed by SGIV stimulation and Ec-CD-overexpressing inhibited SGIV replication, SGIV-induced apoptosis, caspase 3/8/9 activity and the activation of reporter gene p53 and activating protein-1 (AP-1) in vitro. Simultaneously, Ec-CD overexpression obviously restrained the activated mitogen-activated protein kinase (MAPK) pathways, including extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). In addition, Ec-CD overexpression negatively regulated the transcription level of pro-inflammatory cytokines and activation of the NF-κB promotor. (4) Conclusions: Our findings revealed that the Ec-CD possibly served a function during SGIV infection.

Itch and autophagy-mediated NF-κB activation contributes to inhibition of cathepsin D-induced sensitizing effect on anticancer drugs

Inhibition of cathepsin D (Cat D) sensitizes cancer cells to anticancer drugs via RNF183-mediated downregulation of Bcl-xL expression. Although NF-κB activation is involved in the upregulation of RNF183 expression, the molecular mechanism of NF-κB activation by Cat D inhibition is unknown. We conducted this study to investigate the molecular mechanism underlying Cat D-mediated NF-κB activation. Interestingly, Cat D inhibition-induced IκB degradation in an autophagy-dependent manner. Knockdown of autophagy-related genes (ATG7 and Beclin1) and lysosome inhibitors (chloroquine and bafilomycin A1) blocked IκB degradation via Cat D inhibition. Itch induced K63-linked ubiquitination of IκB and then modulated the protein stability of IκB by Cat D inhibition. Inhibition of Cat D-mediated Itch activation was modulated by the JNK signaling pathway, and phosphorylated Itch could bind to IκB, resulting in polyubiquitination of IκB. Additionally, inhibition of Cat D increased autophagy flux via activation of the LKB1-AMPK-ULK1 pathway. Therefore, our results suggested that Cat D inhibition activated NF-κB signaling via degradation of autophagy-dependent IκB, which is associated with the upregulation of RNF183, an E3 ligase of Bcl-xL. Cat D inhibition enhances TRAIL-induced apoptosis through Bcl-xL degradation via upregulation of RNF183.

High Expression of the Lysosomal Protease Cathepsin D Confers Better Prognosis in Neuroblastoma Patients by Contrasting EGF-Induced Neuroblastoma Cell Growth

Neuroblastoma is a malignant extracranial solid tumor arising from the sympathoadrenal lineage of the neural crest and is often associated with N-MYC amplification. Cathepsin D has been associated with chemoresistance in N-MYC-overexpressing neuroblastomas. Increased EGFR expression also has been associated with the aggressive behavior of neuroblastomas. This work aimed to understand the mechanisms linking EGFR stimulation and cathepsin D expression with neuroblastoma progression and prognosis. Gene correlation analysis in pediatric neuroblastoma patients revealed that individuals bearing a high EGFR transcript level have a good prognosis only when CTSD (the gene coding for the lysosomal protease Cathepsin D, CD) is highly expressed. Low CTSD expression was associated with poor clinical outcome. CTSD expression was negatively correlated with CCNB2, CCNA2, CDK1 and CDK6 genes involved in cell cycle division. We investigated the biochemical pathways downstream to EGFR stimulation in human SH-SY5Y neuroblastoma cells engineered for overexpressing or silencing of CD expression. Cathepsin D overexpression decreased the proliferative potential of neuroblastoma cells through downregulation of the pro-oncogenic MAPK signaling pathway. EGFR stimulation downregulated cathepsin D expression, thus favoring cell cycle division. Our data suggest that chemotherapeutics that inhibit the EGFR pathway, along with stimulators of cathepsin D synthesis and activity, could benefit neuroblastoma prognosis.

Cathepsin D as a potential therapeutic target to enhance anticancer drug-induced apoptosis via RNF183-mediated destabilization of Bcl-xL in cancer cells

Cathepsin D (Cat D) is well known for its roles in metastasis, angiogenesis, proliferation, and carcinogenesis in cancer. Despite Cat D being a promising target in cancer cells, effects and underlying mechanism of its inhibition remain unclear. Here, we investigated the plausibility of using Cat D inhibition as an adjuvant or sensitizer for enhancing anticancer drug-induced apoptosis. Inhibition of Cat D markedly enhanced anticancer drug-induced apoptosis in human carcinoma cell lines and xenograft models. The inhibition destabilized Bcl-xL through upregulation of the expression of RNF183, an E3 ligase of Bcl-xL, via NF-κB activation. Furthermore, Cat D inhibition increased the proteasome activity, which is another important factor in the degradation of proteins. Cat D inhibition resulted in p62-dependent activation of Nrf2, which increased the expression of proteasome subunits (PSMA5 and PSMB5), and thereby, the proteasome activity. Overall, Cat D inhibition sensitized cancer cells to anticancer drugs through the destabilization of Bcl-xL. Furthermore, human renal clear carcinoma (RCC) tissues revealed a positive correlation between Cat D and Bcl-xL expression, whereas RNF183 and Bcl-xL expression indicated inverse correlation. Our results suggest that inhibition of Cat D is promising as an adjuvant or sensitizer for enhancing anticancer drug-induced apoptosis in cancer cells.

An Integrated Meta-Analysis of Secretome and Proteome Identify Potential Biomarkers of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is extremely aggressive, has an unfavorable prognosis, and there are no biomarkers for early detection of the disease or identification of individuals at high risk for morbidity or mortality. The cellular and molecular complexity of PDAC leads to inconsistences in clinical validations of many proteins that have been evaluated as prognostic biomarkers of the disease. The tumor secretome, a potential source of biomarkers in PDAC, plays a crucial role in cell proliferation and metastasis, as well as in resistance to treatments, which together contribute to a worse clinical outcome. The massive amount of proteomic data from pancreatic cancer that has been generated from previous studies can be integrated and explored to uncover secreted proteins relevant to the diagnosis and prognosis of the disease. The present study aimed to perform an integrated meta-analysis of PDAC proteome and secretome public data to identify potential biomarkers of the disease. Our meta-analysis combined mass spectrometry data obtained from two systematic reviews of the pancreatic cancer literature, which independently selected 20 studies of the secretome and 35 of the proteome. Next, we predicted the secreted proteins using seven in silico tools or databases, which identified 39 secreted proteins shared between the secretome and proteome data. Notably, the expression of 31 genes of these secretome-related proteins was upregulated in PDAC samples from The Cancer Genome Atlas (TCGA) when compared to control samples from TCGA and The Genotype-Tissue Expression (GTEx). The prognostic value of these 39 secreted proteins in predicting survival outcome was confirmed using gene expression data from four PDAC datasets (validation set). The gene expression of these secreted proteins was able to distinguish high- and low-survival patients in nine additional tumor types from TCGA, demonstrating that deregulation of these secreted proteins may also contribute to the prognosis in multiple cancers types. Finally, we compared the prognostic value of the identified secreted proteins in PDAC biomarkers studies from the literature. This analysis revealed that our gene signature performed equally well or better than the signatures from these previous studies. In conclusion, our integrated meta-analysis of PDAC proteome and secretome identified 39 secreted proteins as potential biomarkers, and the tumor gene expression profile of these proteins in patients with PDAC is associated with worse overall survival.

Mitochondria-Mediated Programmed Cell Death in Saccharomyces cerevisiae Induced by Betulinic Acid Is Accelerated by the Deletion of PEP4 Gene

In this work, using Saccharomyces cerevisiae as a model, we showed that BetA could inhibit cell proliferation and lead to lethal cytotoxicity accompanying programmed cell death (PCD). Interestingly, it was found that vacuolar protease Pep4p played a pivotal role in BetA-induced S. cerevisiae PCD. The presence of Pep4p reduced the damage of BetA-induced cells. This work implied that BetA may induce cell death of S. cerevisiae through mitochondria-mediated PCD, and the deletion of Pep4 gene possibly accelerated the effect of PCD. The present investigation provided the preliminary research for the complicated mechanism of BetA-induced cell PCD regulated by vacular protease Pep4p and lay the foundation for understanding of the Pep4p protein in an animal model.

Autocrine mechanisms of cancer chemoresistance

An ever-increasing number of studies highlight the role of cancer secretome in the modification of tumour microenvironment and in the acquisition of cancer cell resistance to therapeutic drugs. The knowledge of the mechanisms underlying the relationship between cancer cell-secreted factors and chemoresistance is becoming fundamental for the identification of novel anticancer therapeutic strategies overcoming drug resistance and novel prognostic secreted biomarkers. In this review, we summarize the novel findings concerning the regulation of secreted molecules by cancer cells compromising drug sensitivity. In particular, we highlight data from available literature describing the involvement of cancer cell-secreted molecules determining chemoresistance in an autocrine manner, including: i) growth factors; ii) glycoproteins; iii) inflammatory cytokines; iv) enzymes and chaperones; and v) tumor-derived exosomes.

Autophagy and the invisible line between life and death

For a considerable time cell death has been considered to represent mutually exclusive states with cell death modalities that are governed by their inherent and unique mode of action involving specific molecular entities and have therefore been studied primarily in isolation. It is now, however, becoming increasingly clear that these modalities are regulated by similar pathways and share a number of initiator and effector molecules that control both cell death as well as cell survival mechanisms, demanding a newly aligned and integrative approach of cell death assessment. Frequently cell death is triggered through a dual action that incorporates signaling events associated with more than one death modality. Apoptosis and necrosis regularly co-operate in a tightly balanced interplay that involves autophagy to serve context dependently either as a pro-survival or a pro-death mechanism. In this review we will assess current cell death modalities and their molecular overlap with the goal of clarifying the controversial role of autophagy in the cell death response. By dissecting the key molecular pathways and their positioning within a network of regulatory signalling hubs and checkpoints we discuss a distinct approach that integrates autophagy with a resultant cell death manifestation. In doing so, former classifications of cell death modalities fade and reveal the intricate molecular proportions and complexities of the cell death response that may contribute towards an enhanced means of cell death control.

Inhibition of cathepsin proteases attenuates migration and sensitizes aggressive N-Myc amplified human neuroblastoma cells to doxorubicin

Neuroblastoma arises from the sympathetic nervous system and accounts for 15% of childhood cancer mortality. Amplification of the oncogene N-Myc is reported to occur in more than 20% of patients. While N-Myc amplification status strongly correlates with higher tumour aggression and resistance to treatment, the role of N-Myc in the aggressive progression of the disease is poorly understood. N-Myc being a transcription factor can modulate the secretion of key proteins that may play a pivotal role in tumorigenesis. Characterising the soluble secreted proteins or secretome will aid in understanding their role in the tumour microenvironment, such as promoting cancer cell invasion and resistance to treatment. The aim of this study is to characterise the secretome of human malignant neuroblastoma SK-N-BE2 (N-Myc amplified, more aggressive) and SH-SY5Y (N-Myc non-amplified, less aggressive) cells. Conditioned media from SK-N-BE2 and SH-SY5Y cell lines were subjected to proteomics analysis. We report a catalogue of 894 proteins identified in the secretome isolated from the two neuroblastoma cell lines, SK-N-BE2 and SH-SY5Y. Functional enrichment analysis using FunRich software identified enhanced secretion of proteins implicated in cysteine peptidase activity in the aggressive N-Myc amplified SK-N-BE2 secretome compared to the less tumorigenic SH-SY5Y cells. Protein-protein interaction-based network analysis highlighted the enrichment of cathepsin and epithelial-to-mesenchymal transition sub-networks. For the first time, inhibition of cathepsins by inhibitors sensitized the resistant SK-N-BE2 cells to doxorubicin as well as decreased its migratory potential. The dataset of secretome proteins of N-Myc amplified (more aggressive) and non-amplified (less aggressive) neuroblastoma cells represent the first inventory of neuroblastoma secretome. The study also highlights the prominent role of cathepsins in the N-Myc amplified neuroblastoma pathogenesis. As N-Myc amplification correlates with aggressive neuroblastoma and chemotherapy-based treatment failure, co-treatment with cathepsin inhibitors might be a better avenue for disease management.

Enzymatically active cathepsin D sensitizes breast carcinoma cells to TRAIL

Cathepsin D (CD), a ubiquitously expressed lysosomal aspartic protease, is upregulated in human breast carcinoma and many other tumor types. CD has been repeatedly reported to act as key mediator of apoptosis induced by various chemotherapeutics. However, there is still controversy over the role of enzymatic/proteolytic versus protein-protein interaction activities of CD in apoptotic signaling. The elucidation of molecular mechanism responsible for the effect of CD in the chemotherapy-induced cell death is crucial for development of an appropriate strategy to target this protease in cancer treatment. Therefore, the objective of this study was to investigate the molecular mechanism behind the CD-mediated regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cell death. For this purpose, MDA-MB-231 breast carcinoma cells with an increased level of wt CD (CD) or mutant enzymatically inactive CD (ΔCD) were subjected to TRAIL and the frequency of apoptosis was determined. Our results show that CD facilitates the TRAIL-induced apoptosis of MDA-MB-231 breast cancer cells in enzymatic activity-dependent manner. Moreover, the importance of endosomal/lysosomal acidification in this process was documented. Analysis of the potential substrates specifically cleaved by CD during the TRAIL-induced apoptosis confirmed caspase-8 and Bid proteins as the CD targets. Moreover, in search for protein regulators of apoptosis that can be cleaved by CD at physiologically relevant pH, we identified the Bcl-2 protein as a suitable candidate. The modulatory role of CD in cell response to TRAIL was also confirmed in another breast cancer cell line SKBR3. These experiments identified the CD enzymatic activity as a new factor affecting sensitivity of breast cancer cells to TRAIL.

Autophagic flux promotes cisplatin resistance in human ovarian carcinoma cells through ATP-mediated lysosomal function

Lysosomes are involved in promoting resistance of cancer cells to chemotherapeutic agents. However, the mechanisms underlying lysosomal influence of cisplatin resistance in ovarian cancer remain incompletely understood. We report that, compared with cisplatin-sensitive SKOV3 cells, autophagy increases in cisplatin-resistant SKOV3/DDP cells treated with cisplatin. Inhibition of early-stage autophagy enhanced cisplatin-mediated cytotoxicity in SKOV3/DDP cells, but autophagy inhibition at a later stage by disturbing autophagosome-lysosome fusion is more effective. Notably, SKOV3/DDP cells contained more lysosomes than cisplatin-sensitive SKOV3 cells. Abundant lysosomes and lysosomal cathepsin D activity were required for continued autolysosomal degradation and maintenance of autophagic flux in SKOV3/DDP cells. Furthermore, SKOV3/DDP cells contain abundant lysosomal ATP required for lysosomal function, and inhibition of lysosomal ATP accumulation impaired lysosomal function and blocked autophagic flux. Therefore, our findings suggest that lysosomes at least partially contribute to cisplatin resistance in ovarian cancer cells through their role in cisplatin-induced autophagic processes, and provide insight into the mechanism of cisplatin resistance in tumors.

Aspartic cathepsin D degrades the cytosolic cysteine cathepsin inhibitor stefin B in the cells

Stefin B is the major general cytosolic protein inhibitor of cysteine cathepsins. Its main function is to protect the organism against the activity of endogenous potentially hazardous proteases accidentally released from lysosomes. In this study, we investigated the possible effect of endosomal/lysosomal aspartic cathepsins D and E on stefin B after membrane permeabilization. Loss of membrane integrity of lysosomes and endosomes was induced by a lysosomotropic agent L-Leucyl-L-leucine methyl ester (Leu-Leu-OMe). The rat thyroid cell line FRTL-5 was selected as a model cell line owing to its high levels of proteases, including cathepsin D and E. Permeabilization of acid vesicles from FRTL-5 cells induced degradation of stefin B. The process was inhibited by pepstatin A, a potent inhibitor of aspartic proteases. However, degradation of stefin B was prevented by siRNA-mediated silencing of cathepsin D expression. In contrast, cathepsin E silencing had no effect on stefin B degradation. These results showed that cathepsin D and not cathepsin E degrades stefin B. It can be concluded that the presence of cathepsin D in the cytosol affects the inhibitory potency of stefin B, thus preventing the regulation of cysteine cathepsin activities in various biological processes.

Yeast as a tool to explore cathepsin D function

Cathepsin D has garnered increased attention in recent years, mainly since it has been associated with several human pathologies. In particular, cathepsin D is often overexpressed and hypersecreted in cancer cells, implying it may constitute a therapeutic target. However, cathepsin D can have both anti- and pro-survival functions depending on its proteolytic activity, cellular context and stress stimulus. Therefore, a more detailed understanding of cathepsin D regulation and how to modulate its apoptotic functions is clearly needed. In this review, we provide an overview of the role of cathepsin D in physiological and pathological scenarios. We then focus on the opposing functions of cathepsin D in apoptosis, particularly relevant in cancer research. Emphasis is given to the role of the yeast protease Pep4p, the vacuolar counterpart of cathepsin D, in life and death. Finally, we discuss how insights from yeast cathepsin D and its role in regulated cell death can unveil novel functions of mammalian cathepsin D in apoptosis and cancer.

Cathepsin D protects colorectal cancer cells from acetate-induced apoptosis through autophagy-independent degradation of damaged mitochondria

Acetate is a short-chain fatty acid secreted by Propionibacteria from the human intestine, known to induce mitochondrial apoptotic death in colorectal cancer (CRC) cells. We previously established that acetate also induces lysosome membrane permeabilization in CRC cells, associated with release of the lysosomal protease cathepsin D (CatD), which has a well-established role in the mitochondrial apoptotic cascade. Unexpectedly, we showed that CatD has an antiapoptotic role in this process, as pepstatin A (a CatD inhibitor) increased acetate-induced apoptosis. These results mimicked our previous data in the yeast system showing that acetic acid activates a mitochondria-dependent apoptosis process associated with vacuolar membrane permeabilization and release of the vacuolar protease Pep4p, ortholog of mammalian CatD. Indeed, this protease was required for cell survival in a manner dependent on its catalytic activity and for efficient mitochondrial degradation independently of autophagy. In this study, we therefore assessed the role of CatD in acetate-induced mitochondrial alterations. We found that, similar to acetic acid in yeast, acetate-induced apoptosis is not associated with autophagy induction in CRC cells. Moreover, inhibition of CatD with small interfering RNA or pepstatin A enhanced apoptosis associated with higher mitochondrial dysfunction and increased mitochondrial mass. This effect seems to be specific, as inhibition of CatB and CatL with E-64d had no effect, nor were these proteases significantly released to the cytosol during acetate-induced apoptosis. Using yeast cells, we further show that the role of Pep4p in mitochondrial degradation depends on its protease activity and is complemented by CatD, indicating that this mechanism is conserved. In summary, the clues provided by the yeast model unveiled a novel CatD function in the degradation of damaged mitochondria when autophagy is impaired, which protects CRC cells from acetate-induced apoptosis. CatD inhibitors could therefore enhance acetate-mediated cancer cell death, presenting a novel strategy for prevention or therapy of CRC.

Cell biology of the NCL proteins: What they do and don't do

The fatal, primarily childhood neurodegenerative disorders, neuronal ceroid lipofuscinoses (NCLs), are currently associated with mutations in 13 genes. The protein products of these genes (CLN1 to CLN14) differ in their function and their intracellular localization. NCL-associated proteins have been localized mostly in lysosomes (CLN1, CLN2, CLN3, CLN5, CLN7, CLN10, CLN12 and CLN13) but also in the Endoplasmic Reticulum (CLN6 and CLN8), or in the cytosol associated to vesicular membranes (CLN4 and CLN14). Some of them such as CLN1 (palmitoyl protein thioesterase 1), CLN2 (tripeptidyl-peptidase 1), CLN5, CLN10 (cathepsin D), and CLN13 (cathepsin F), are lysosomal soluble proteins; others like CLN3, CLN7, and CLN12, have been proposed to be lysosomal transmembrane proteins. In this review, we give our views and attempt to summarize the proposed and confirmed functions of each NCL protein and describe and discuss research results published since the last review on NCL proteins. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

Proteomic Analysis between U87MG and U343MG-A Cell Lines: Searching for Candidate Proteins for Glioma Invasion

Background

To investigate the molecular basis for invasion of malignant gliomas, proteomic analysis approach was carried out using two human glioma cell lines, U87MG and U343MG-A that demonstrate different motility and invasiveness in in vitro experiments.

Methods

High-resolution two-dimensional gel electrophoresis and matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry analysis were performed.

Results

Nine distinct protein spots that were recognized with significant alteration between the two cell lines. Five of these protein spots were up-regulated in U87MG and four were up-regulated in U343MG-A.

Conclusion

Among these proteins, cathepsin D was shown to be one of the important proteins which are related with glioma invasion. However, further studies are necessary to reveal the exact role and mechanism of cathepsin D in glioma invasion.

Identification of chemoresistance-related cell-surface glycoproteins in leukemia cells and functional validation of candidate glycoproteins

Chemoresistance remains the most significant obstacle to successful chemotherapy for leukemia, and its exact mechanism is still unknown. In this work, we used the cell-surface capturing method together with quantitative proteomics to investigate differences in the glycoproteomes of adriamycin-sensitive and adriamycin-resistant leukemia cells. Two quantitative methods, isotopic dimethyl labeling and SWATH, were used to quantify glycoproteins, and 35 glycoproteins were quantified by both methods. High correlation was observed between the glycoproteins quantified by the above two methods, and 15 glycoproteins displayed a consistent significant change trend in both sets of quantitative results. These 15 proteins included classical multidrug resistance-related glycoproteins such as ABCB1 as well as a set of novel glycoproteins that have not previously been reported to be associated with chemoresistance in leukemia cells. Further validation with quantitative real-time PCR and Western blotting confirmed the proteomic screening results. Subsequent functional experiments based on RNA interference technology showed that CTSD, FKBP10, and SLC2A1 are novel genes that participate in the acquisition and maintenance of the adriamycin-resistant phenotype in leukemia cells.

A prognostic model for triple-negative breast cancer patients based on node status, cathepsin-D and Ki-67 index

Objective

The aim of this study was to evaluate clinicopathologic factors that could possibly affect the outcome of patients with triple negative breast cancer and subsequently build a prognostic model to predict patients’ outcome.

Methods

We retrospectively analyzed clinicopathologic characteristics and outcome of 504 patients diagnosed with triple-negative invasive ductal breast cancer. 185 patients enrolled between 2000 and 2002 were designated to the training set. The variables that had statistically significant correlation with prognosis were combined to build a model. The prognostic value of the model was further validated in the separate validation set containing 319 patients enrolled between 2003 and 2006.

Results

The median follow-up duration was 66 months. 174 patients experienced recurrence, and 111 patients died. Positivity for ≥4 lymph nodes, Cathepsin-D positivity, and Ki-67 index ≥20% were independent factors for DFS, while the lymph nodes status and Ki-67 index were the prognostic factors for OS. The prognostic model was established based on the sum of all three factors, where positivity for ≥4 lymph nodes, Cathepsin-D and Ki-67 index ≥20% would individually contribute 1 point to the risk score. The patients in the validation set were assigned to a low-risk group (0 and 1 point) and a high-risk group (2 and 3 points). The external validation analysis also demonstrated that our prognostic model provided the independent high predictive accuracy of recurrence.

Conclusion

This model has a considerable clinical value in predicting recurrence, and will help clinicians to design an appropriate level of adjuvant treatment and schedule adequate appointments of surveillance visits.

Dipeptide mimic oligomer transporter mediates intracellular delivery of Cathepsin D inhibitors: a potential target for cancer therapy

Implication of the intracellular proteolytic activity of Cathepsin D (CathD), a lysosomal aspartyl-protease overexpressed in numerous solid tumors, has been evidenced on tumor growth. Its intracellular inhibition by potent inhibitors such as pepstatin constitutes a relevant but challenging molecular target. Indeed the potential of pepstatin as a therapeutic molecule is hampered by its too low intracellular penetration. We addressed this limitation by designing and developing a bioconjugate combining a pepstatin derivative with a new vector of cell penetration (CPNP) specifically targeting the endolysosomal compartment. We showed that this pepstatin conjugate (JMV4463) exhibited high anti-proliferative effect on tumor cell cultures via intracellular CathD inhibition and altered cell cycle associated with apoptotic events in vitro. When tested in mice xenografted with breast cancer cells, JMV4463 delayed tumor emergence and growth.

Cathepsin D inhibits oxidative stress-induced cell death via activation of autophagy in cancer cells

Cathepsin D (CatD), a lysosomal aspartic protease, plays an essential role in tumor progression and apoptosis. However, the function of CatD in cell death is not yet fully understood. In this study, we identified CatD as one of up-regulated proteins in human malignant glioblastoma M059J cells that lack the catalytic subunit of DNA-PK compared with its isogenic M059K cells with normal DNA-PK activity. M059J cells were relatively more resistant to genotoxic stress than M059K cells. Overexpression of wild-type CatD but not catalytically inactive mutant CatD (D295N) inhibited H(2)O(2)-induced cell death in HeLa cells. Furthermore, knockdown of CatD expression abolished anti-apoptotic effect by CatD in the presence of H(2)O(2). Interestingly, high expression of CatD in HeLa cells significantly activated autophagy: increase of acidic autophagic vacuoles, LC3-II formation, and GFP-LC3 puncta. These results suggest that CatD can function as an anti-apoptotic mediator by inducing autophagy under cellular stress. In conclusion, inhibition of autophagy could be a novel strategy for the adjuvant chemotherapy of CatD-expressing cancers.

Procathepsin d involvement in chemoresistance of cancer cells

Background:

The role of pCD in cancer has been studied for a long time. We have focused on the hypothesis that increased expression and/or secretion of pCD in cancer cells causes increased chemoresistance to apoptosis inducing molecules.

Aim:

The aim was to evaluate the effects of pCD expression/release on chemoresistance.

Materials and Methods:

We tested the LC₅₀ values for various transfectants of breast cancer cell line MDA-MB-231 as well as effects of exogenous additions of pCD, its mutants, pepstatine, antibodies, and Brefeldin on the resistance.

Results:

We found that pCD levels can be correlated with chemoresistance, the pro-resistant activity seems to be localized outside the cells, proteolytic activity is not involved, and PI3-Akt signaling has an important role in antiapoptotic effects of pCD.

Conclusion:

We can conclude that overexpression of pCD has strong influence on increased resistance of tumor cells. This could, in fact, be an important contribution in the possible use of pCD level determination for prognostic and/or therapeutic purposes.

RNA interference screening identifies a novel role for autocrine fibroblast growth factor signaling in neuroblastoma chemoresistance

Chemotherapeutic drug resistance is one of the major causes for treatment failure in high-risk neuroblastoma (NB), the most common extra cranial solid tumor in children. Poor prognosis is typically associated with MYCN amplification. Here, we utilized a loss-of-function kinome-wide RNA interference screen to identify genes that cause cisplatin sensitization. We identified fibroblast growth factor receptor 2 (FGFR2) as an important determinant of cisplatin resistance. Pharmacological inhibition of FGFR2 confirmed the importance of this kinase in NB chemoresistance. Silencing of FGFR2 sensitized NB cells to cisplatin-induced apoptosis, which was regulated by the downregulation of the anti-apoptotic proteins BCL2 and BCLXL. Mechanistically, FGFR2 was shown to activate protein kinase C-δ to induce BCL2 expression. FGFR2, as well as the ligand fibroblast growth factor-2, were consistently expressed in primary NB and NB cell lines, indicating the presence of an autocrine loop. Expression analysis revealed that FGFR2 correlates with MYCN amplification and with advanced stage disease, demonstrating the clinical relevance of FGFR2 in NB. These findings suggest a novel role for FGFR2 in chemoresistance and provide a rational to combine pharmacological inhibitors against FGFR2 with chemotherapeutic agents for the treatment of NB.

Marine cyanobacteria compounds with anticancer properties: a review on the implication of apoptosis

Marine cyanobacteria have been considered a rich source of secondary metabolites with potential biotechnological applications, namely in the pharmacological field. Chemically diverse compounds were found to induce cytoxicity, anti-inflammatory and antibacterial activities. The potential of marine cyanobacteria as anticancer agents has however been the most explored and, besides cytotoxicity in tumor cell lines, several compounds have emerged as templates for the development of new anticancer drugs. The mechanisms implicated in the cytotoxicity of marine cyanobacteria compounds in tumor cell lines are still largely overlooked but several studies point to an implication in apoptosis. This association has been related to several apoptotic indicators such as cell cycle arrest, mitochondrial dysfunctions and oxidative damage, alterations in caspase cascade, alterations in specific proteins levels and alterations in the membrane sodium dynamics. In the present paper a compilation of the described marine cyanobacterial compounds with potential anticancer properties is presented and a review on the implication of apoptosis as the mechanism of cell death is discussed.

Shared Copy Number Variation in Simultaneous Nephroblastoma and Neuroblastoma due to Fanconi Anemia

Concurrent emergence of nephroblastoma (Wilms Tumor; WT) and neuroblastoma (NB) is rare and mostly observed in patients with severe subtypes of Fanconi anemia (FA) with or without VACTER-L association (VL). We investigated the hypothesis that early consequences of genomic instability result in shared regions with copy number variation in different precursor cells that originate distinct embryonal tumors. We observed a newborn girl with FA and VL (aplasia of the thumbs, cloacal atresia (urogenital sinus), tethered cord at L3/L4, muscular ventricular septum defect, and horseshoe-kidney with a single ureter) who simultaneously acquired an epithelial-type WT in the left portion of the kidney and a poorly differentiated adrenal NB in infancy. A novel homozygous germline frameshift mutation in PALB2 (c.1676_c1677delAAinsG) leading to protein truncation (pGln526ArgfsX1) inherited from consanguineous parents formed the genetic basis of FA-N. Spontaneous and induced chromosomal instability was detected in the majority of cells analyzed from peripheral lymphocytes, bone marrow, and cultured fibroblasts. Bone marrow cells also showed complex chromosome rearrangements consistent with the myelodysplastic syndrome at 11 months of age. Array-comparative genomic hybridization analyses of both WT and NB showed shared gains or amplifications within the chromosomal regions 11p15.5 and 17q21.31-q25.3, including genes that are reportedly implicated in tumor development such as IGF2, H19, WT2, BIRC5, and HRAS.

Protein alterations associated with temozolomide resistance in subclones of human glioblastoma cell lines

Temozolomide (TMZ) is the standard chemotherapeutic agent for human malignant glioma, but intrinsic or acquired chemoresistance represents a major obstacle to successful treatment of this highly lethal group of tumours. Obtaining better understanding of the molecular mechanisms underlying TMZ resistance in malignant glioma is important for the development of better treatment strategies. We have successfully established a passage control line (D54-C10) and resistant variants (D54-P5 and D54-P10) from the parental TMZ-sensitive malignant glioma cell line D54-C0. The resistant sub-cell lines showed alterations in cell morphology, enhanced cell adhesion, increased migration capacities, and cell cycle arrests. Proteomic analysis identified a set of proteins that showed gradual changes in expression according to their 50% inhibitory concentration (IC(50)). Successful validation was provided by transcript profiling in another malignant glioma cell line U87-MG and its resistant counterparts. Moreover, three of the identified proteins (vimentin, cathepsin D and prolyl 4-hydroxylase, beta polypeptide) were confirmed to be upregulated in high-grade glioma. Our data suggest that acquired TMZ resistance in human malignant glioma is associated with promotion of malignant phenotypes, and our reported molecular candidates may serve not only as markers of chemoresistance but also as potential therapeutic targets in the treatment of TMZ-resistant human malignant glioma, providing a platform for future investigations.

Vacuole-mitochondrial cross-talk during apoptosis in yeast: a model for understanding lysosome-mitochondria-mediated apoptosis in mammals

The yeast apoptosis field emerged with the finding that key components of the apoptotic machinery are conserved in these simple eukaryotes. Thus it became possible to exploit these genetically tractable organisms to improve our understanding of the intricate mechanisms of cell death in higher eukaryotes and of severe human diseases associated with apoptosis dysfunctions. Early on, it was recognized that a mitochondria-mediated apoptotic pathway showing similarities to the mammalian intrinsic pathway was conserved in yeast. Recently, lysosomes have also emerged as central players in mammalian apoptosis. Following LMP (lysosomal membrane permeabilization), lysosomal proteases such as cathepsins B, D and L are released into the cytosol and can trigger a mitochondrial apoptotic cascade. CatD (cathepsin D) can also have anti-apoptotic effects in some cellular types and specific contexts. Nonetheless, the mechanisms underlying LMP and the specific role of cathepsins after their release into the cytosol remain poorly understood. We have recently shown that yeast vacuoles, membrane-bound acidic organelles, which share many similarities to plant vacuoles and mammalian lysosomes, are also involved in the regulation of apoptosis and that the vacuolar protease Pep4p, orthologue of the human CatD, is released from the vacuole into the cytosol in response to acetic acid. Here, we discuss how the conservation of cell-death regulation mechanisms in yeast by the lysosome-like organelle and mitochondria may provide new insights into the understanding of the complex interplay between the mitochondria and lysosome-mediated signalling routes during mammalian apoptosis.

Perifosine-induced inhibition of Akt attenuates brain-derived neurotrophic factor/TrkB-induced chemoresistance in neuroblastoma in vivo

BACKGROUND

Neuroblastoma (NB) tumors expressing high levels of brain-derived neurotrophic factor (BDNF) and its receptor TrkB or activated Akt are associated with decreased event-free or overall survival in patients with NB. In the current study, the effect of perifosine, an Akt inhibitor, on the chemosensitivity of TrkB-expressing NB cells or tumors was evaluated.

METHODS

A tetracycline-regulated TrkB-expressing isogenic NB cell model system was tested. In this system, NB cells were treated with etoposide and/or perifosine both in vitro and in vivo. Inhibition of the target by perifosine was evaluated by Western blot analysis or kinase activity assay. Cell survival and tumor growth were investigated.

RESULTS

In vitro BDNF treatment induced Akt phosphorylation and rescued cells from etoposide-induced cell death in cells with high TrkB expression, but not in cells with low TrkB expression. Pretreatment of high TrkB-expressing TB3 cells with perifosine blocked BDNF/TrkB-induced Akt phosphorylation and inhibited BDNF's protection of TB3 cells from etoposide treatment. In vivo, tumors with high TrkB expression were found to have elevated levels of phosphorylated Akt and were less sensitive to etoposide treatment compared with tumors with low TrkB expression. Mice treated with a combination of perifosine and etoposide were found to have a statistically significant decrease in tumor growth compared with mice treated with either etoposide or perifosine alone. Activation of Akt through the BDNF/TrkB signaling pathway induced chemoresistance in NB in vivo.

CONCLUSIONS

Perifosine-induced inhibition of Akt increased the sensitivity of NB to chemotherapy. The results of the current study support the future clinical evaluation of an Akt inhibitor combined with cytotoxic drugs for the improvement of treatment efficacy.

The prognostic importance of cathepsin D and E-cadherin in early breast cancer: A single-institution experience

Molecular tools have increasingly been used for decision-making in patients with early breast cancer (EBC). Nevertheless, simple tools such as immunohistochemistry may still be required in particular cases to complement traditional and molecular prognosticators. In this study, the prognostic significance of three well-known immunohistochemical biomarkers, cathepsin D, E-cadherin and Ki67, was studied in 270 patients with EBC, followed by a median time of 126 months in a single institution. Histological examination was performed to confirm the histopathological diagnosis and select specimens. The specimens were evaluated using immunohistochemistry and survival curves were plotted. Results revealed the following patient characteristics: node-negative/1-3 lymph nodes in 228 (86%) patients, hormone receptor-positive in 217 (80%); triple-negative in 31 (11%), and Her2-overexpression in 23 (9%) patients. Breast cancer-related events occurred in 37 patients (14%). A total of 217 patients (80%) survived. Receiver operating characteristic analysis for breast cancer-specific survival showed an area under curve for the clinicopathological model of 0.75 (95% CI, 0.64-0.86), 0.79 (95% CI, 0.68-0.90) for the three-biomarker model, and 0.82 (95% CI, 0.72-0.92) for the E-cadherin and cathepsin D only model. We propose that a simple prognostic model based on combined scores of E-cadherin and cathepsin D may aid treatment decisions in patients with EBC.

The propeptide of yeast cathepsin D inhibits programmed necrosis

The lysosomal endoprotease cathepsin D (CatD) is an essential player in general protein turnover and specific peptide processing. CatD-deficiency is associated with neurodegenerative diseases, whereas elevated CatD levels correlate with tumor malignancy and cancer cell survival. Here, we show that the CatD ortholog of the budding yeast Saccharomyces cerevisiae (Pep4p) harbors a dual cytoprotective function, composed of an anti-apoptotic part, conferred by its proteolytic capacity, and an anti-necrotic part, which resides in the protein's proteolytically inactive propeptide. Thus, deletion of PEP4 resulted in both apoptotic and necrotic cell death during chronological aging. Conversely, prolonged overexpression of Pep4p extended chronological lifespan specifically through the protein's anti-necrotic function. This function, which triggered histone hypoacetylation, was dependent on polyamine biosynthesis and was exerted via enhanced intracellular levels of putrescine, spermidine and its precursor S-adenosyl-methionine. Altogether, these data discriminate two pro-survival functions of yeast CatD and provide first insight into the physiological regulation of programmed necrosis in yeast.

PTEN status switches cell fate between premature senescence and apoptosis in glioma exposed to ionizing radiation

Loss of the tumor suppressor phosphatase and tensin homolog (PTEN) has frequently been observed in human gliomas, conferring AKT activation and resistance to ionizing radiation (IR) and drug treatments. Recent reports have shown that PTEN loss or AKT activation induces premature senescence, but many details regarding this effect remain obscure. In this study, we tested whether the status of PTEN determined fate of the cell by examining PTEN-deficient U87, U251, and U373, and PTEN-proficient LN18 and LN428 glioma cells after exposure to IR. These cells exhibited different cellular responses, senescence or apoptosis, depending on the PTEN status. We further observed that PTEN-deficient U87 cells with high levels of both AKT activation and intracellular reactive oxygen species (ROS) underwent senescence, whereas PTEN-proficient LN18 cells entered apoptosis. ROS were indispensable for inducing senescence in PTEN-deficient cells, but not for apoptosis in PTEN-proficient cells. Furthermore, transfection with wild-type (wt) PTEN or AKT small interfering RNA induced a change from premature senescence to apoptosis and depletion of p53 or p21 prevented IR-induced premature senescence in U87 cells. Our data indicate that PTEN acts as a pivotal determinant of cell fate, regarding senescence and apoptosis in IR-exposed glioma cells. We conclude that premature senescence could have a compensatory role for apoptosis in the absence of the tumor suppressor PTEN through the AKT/ROS/p53/p21 signaling pathway.

Interactions of the proteins of neuronal ceroid lipofuscinosis: clues to function

Neuronal ceroid lipofuscinoses (NCL) are caused by mutations in eight different genes, are characterized by lysosomal accumulation of autofluorescent storage material, and result in a disease that causes degeneration of the central nervous system (CNS). Although functions are defined for some of the soluble proteins that are defective in NCL (cathepsin D, PPT1, and TPP1), the primary function of the other proteins defective in NCLs (CLN3, CLN5, CLN6, CLN7, and CLN8) remain poorly defined. Understanding the localization and network of interactions for these proteins can offer clues as to the function of the NCL proteins and also the pathways that will be disrupted in their absence. Here, we present a review of the current understanding of the localization, interactions, and function of the proteins associated with NCL.

Transcriptional repression of SKP2 is impaired in MYCN-amplified neuroblastoma

The cell cycle regulator, SKP2, is overexpressed in various cancers and plays a key role in p27 degradation, which is involved in tumor cell dedifferentiation. Little is known about the mechanisms leading to impaired SKP2 transcriptional control in tumor cells. We used neuroblastoma as a model to study SKP2 regulation because SKP2 transcript levels gradually increase with aggressiveness of neuroblastoma subtypes. The highest SKP2 levels are found in neuroblastomas with amplified MYCN. Accordingly, we found 5.5-fold (range, 2-9.5) higher SKP2 core promoter activity in MYCN-amplified cells. Higher SKP2 core promoter activity in MYCN-amplified cells is mediated through a defined region at the transcriptional start site. This region includes a specific E2F-binding site that makes SKP2 activation largely independent of mitogenic signals integrated through the SP1/ELK-1 site. We show by chromatin immunoprecipitation that SKP2 activation through the transcriptional start site in MYCN-amplified cells is associated with the low abundance of pRB-E2F1 complexes bound to the SKP2 promoter. Transcriptional control of SKP2 through this regulatory mechanism can be reestablished in MYCN-amplified cells by restoring pRB activity using selective small compound inhibitors of CDK4. In contrast, doxorubicin or nutlin-3 treatment-both leading to p53-p21 activation-or CDK2 inhibition had no effect on SKP2 regulation in MYCN-amplified cells. Together, this implies that deregulated MYCN protein levels in MYCN-amplified neuroblastoma cells activate SKP2 through CDK4 induction, abrogating repressive pRB-E2F1 complexes bound to the SKP2 promoter.

Comparative genome-wide screening identifies a conserved doxorubicin repair network that is diploid specific in Saccharomyces cerevisiae

The chemotherapeutic doxorubicin (DOX) induces DNA double-strand break (DSB) damage. In order to identify conserved genes that mediate DOX resistance, we screened the Saccharomyces cerevisiae diploid deletion collection and identified 376 deletion strains in which exposure to DOX was lethal or severely reduced growth fitness. This diploid screen identified 5-fold more DOX resistance genes than a comparable screen using the isogenic haploid derivative. Since DSB damage is repaired primarily by homologous recombination in yeast, and haploid cells lack an available DNA homolog in G1 and early S phase, this suggests that our diploid screen may have detected the loss of repair functions in G1 or early S phase prior to complete DNA replication. To test this, we compared the relative DOX sensitivity of 30 diploid deletion mutants identified under our screening conditions to their isogenic haploid counterpart, most of which (n = 26) were not detected in the haploid screen. For six mutants (bem1Delta, ctf4Delta, ctk1Delta, hfi1Delta,nup133Delta, tho2Delta) DOX-induced lethality was absent or greatly reduced in the haploid as compared to the isogenic diploid derivative. Moreover, unlike WT, all six diploid mutants displayed severe G1/S phase cell cycle progression defects when exposed to DOX and some were significantly enhanced (ctk1Delta and hfi1Delta) or deficient (tho2Delta) for recombination. Using these and other "THO2-like" hypo-recombinogenic, diploid-specific DOX sensitive mutants (mft1Delta, thp1Delta, thp2Delta) we utilized known genetic/proteomic interactions to construct an interactive functional genomic network which predicted additional DOX resistance genes not detected in the primary screen. Most (76%) of the DOX resistance genes detected in this diploid yeast screen are evolutionarily conserved suggesting the human orthologs are candidates for mediating DOX resistance by impacting on checkpoint and recombination functions in G1 and/or early S phases.

Regulation of BIRC5 and its isoform BIRC5-2B in neuroblastoma

We analysed the expression of BIRC5 and BIRC5-2B in primary neuroblastoma (NB) tumors and NB model systems. In tumors, overexpression of BIRC5 correlated closely with its isoform BIRC5-2B. Expression of both transcripts was stage-dependent, associated with poor prognosis and with the expression of the transcription factor E2F1. In cell culture, we identified BIRC5 as a direct transcriptional target of activating E2Fs, primarily when p21(Cip1) and p27(Kip1), two other E2F1 targets, are strongly suppressed. Deregulated MYCN indirectly induces BIRC5 through suppression of CDKN1A/p21(Cip1) and induction of Skp2, which in turn favors the degradation of p27(Kip1). In addition, increased BIRC5 protein stability via phosphorylation is mediated by expression of E2F targets such as CDC2. In line with this, selective knock down of CDC2 inhibited BIRC5 abundance and suppressed its anti-apoptotic activities. We conclude that BIRC5 is induced via a functional cooperation between MYCN and E2F1.

Astrocyte elevated gene-1 contributes to the pathogenesis of neuroblastoma

Neuroblastoma, derived from neural crest progenitor cells, is the most common extracranial solid tumor of childhood. Astrocyte elevated gene-1 (AEG-1) is a primary mediator of tumor progression and metastasis in several human cancers. In this study, we investigated the potential contribution of AEG-1 in human neuroblastoma pathogenesis. AEG-1 expression was significantly elevated in neuroblastoma patient-derived samples and neuroblastoma cell lines as compared with normal peripheral nerve tissues, normal astrocytes and immortalized melanocytes. Knockdown of AEG-1 by small interfering RNA reduced the tumorigenic properties of highly aggressive neuroblastoma cells. Conversely, over-expression of AEG-1 enhanced proliferation and expression of the transformed state in less aggressive neuroblastoma cells through activation of the phosphatidylinositol 3-kinase-Akt-signaling pathway and stabilization of MYCN. These provocative results indicate that AEG-1 may play a crucial role in the pathogenesis of neuroblastoma and could represent a potential target for therapeutic intervention.