Co-depletion of cathepsin B and uPAR induces G0/G1 arrest in glioma via FOXO3a mediated p27 upregulation

Proteomic profiling and ROC analysis identify CD151 and ELAVL1 as potential therapy response markers for the antiviral drug in resistant TNBC

Triple-negative breast cancer is high heterogeneous, aggressive, and metastatic with poor prognosis. Despite of advances in targeted therapies, TNBC has been reported to cause high morbidity and mortality. A rare subpopulation within the tumor microenvironment organized into a hierarchy of cancer stem cells is responsible for therapy resistance and tumor recurrence. Repurposing of antiviral drugs for cancer treatment is gaining momentum due to reduced cost, labour, and research time, but limited due to lack of prognostic, and predictive markers. The present study investigates proteomic profiling and ROC analysis to identify CD151 and ELAVL1 as potential therapy response markers for the antiviral drug 2-thio-6-azauridine (TAU) in resistant TNBC. The stemness of MDA-MB 231 and MDA-MD 468 adherent cells was enriched by culturing them under non-adherent and non-differentiation conditions. Then, CD151⁺ subpopulation was isolated and characterized for the enrichment of stemness. This study found that CD151 has overexpressed in stemness enriched subpopulations, and also showed CD44 high and CD24 low expression along with stem cell-related transcription factors octamer-binding transcription factor 4 (OCT4) and Sex determining Y-box 2 (SOX2). This study also found that TAU induced significant cytotoxicity and genotoxicity in the CD151⁺TNBC subpopulation and inhibited their proliferation by inducing DNA damage, cell cycle arrest at the G₂M phase, and apoptosis. Further, a proteomic profiling study showed that the expression of CD151 along with ELAVL1, an RNA-binding protein, was significantly reduced with TAU treatment. KM plotter showed correlation of CD151 and ELAVL1 gene expression with a poor prognosis of TNBC. ROC analysis predicted and validated CD151 and ELAVL1 as best therapy response marker for TAU in TNBC. These findings provide new insight into repurposing antiviral drug TAU for treatment of metastatic and drug resistant TNBC.

Loss of p27Kip1 leads to expansion of CD4+ effector memory T cells and accelerates colitis-associated colon cancer in mice with a T cell lineage restricted deletion of Smad4

The cyclin-dependent kinase inhibitor p27^Kip1 is a tumor suppressor whose intrinsic activity in cancer cells correlates with tumor aggressiveness, invasiveness, and impaired tumor cell differentiation. Here we explore whether p27^Kip1 indirectly influences tumor progression by restricting expansion and survival of effector memory T cell (T_EM) populations in a preclinical model of spontaneous colitis-associated colorectal cancer (CAC). We show mRNA and protein expression of p27^Kip1 to be significantly decreased in the colons of mice with a T cell-restricted deletion of the TGF-β intermediate, SMAD4 (Smad4^TKO). Loss of p27^Kip1 expression in T cells correlates with the onset of spontaneous CAC in Smad4^TKO mice by 8 months of age. This phenotype is greatly accelerated by the introduction of a germline deletion of CDKN1b (the gene encoding p27^Kip1) in Smad4^TKO mice (Smad4^TKO/p27^Kip1-/-, DKO). DKO mice display colon carcinoma by 3 months of age and increased mortality compared to Smad4^TKO. Importantly, the phenotype in DKO mice is associated with a significant increase in the frequency of effector CD4 T cells expressing abundant IFN-γ and with a concomitant decrease in Foxp3⁺ regulatory T cells, both in the intestinal mucosa and in the periphery. In addition, induction of inflammatory mediators (IFN-γ, TNF-γ, IL-6, IL-1β, iNOS) and activation of Stat1, Stat3, and IκB is also observed in the colon as early as 1–2 months of age. Our data suggest that genomic alterations known to influence p27^Kip1 abundance in gastrointestinal cancers may indirectly promote epithelial malignancy by augmenting the production of inflammatory mediators from a spontaneously expanding pool of T_EM cells.

CDKL1 promotes the chemoresistance of human oral squamous cell carcinoma cells to hydroxycamptothecin

CDKL1 is a cyclin-dependent kinase-like kinase that is highly expressed in diverse types of cancer cells. However, the role of CDKL1 in the chemoresistance of oral squamous cell carcinoma (OSCC) remains largely undefined. Here, we explored the role of CDKL1 in the chemoresistance of the human OSCC cell line CAL27 to hydroxycamptothecin (HCPT). Real-time quantitative polymerase chain reaction and western blotting revealed that exposure of CAL27 cells to HCPT led to a marked increase in the expression of CDKL1 at the mRNA and protein levels. Knockdown of CDKL1 significantly suppressed cell proliferation and induced cell cycle G0/G1 phase arrest in CAL27 cells based on the results of MTT and flow cytometry assays, respectively. CAL27 cells displayed attenuated biological activity of the cell population. After treatment with HCPT, whereas CDKL1 overexpression increased the resistance to HCPT of the remaining cells. Moreover, the western blot showed that the expression of cleaved-caspase 3 and phosphorylated ataxia telangiectasia mutated proteins was upregulated by HCPT treatment in CAL27 cells. Furthermore, CDKL1 overexpression partially reversed the inhibitory effects of HCPT in CAL27 cells. These results suggest that CDKL1 overexpression decreased the chemosensitivity of OSCC cells to HCPT, indicating a potential strategic approach for reversing the HCPT resistance in human OSCC.

Receptor tyrosine kinase-Ras-PI 3 kinase-Akt signaling network in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most malignant form of the brain tumors and shows different genetic and epigenetic abnormalities. Gene amplification, genetic instability, disruption of apoptotic pathways, deregulated oncogene expression, invasive phenotypical changes, abnormal angiogenesis, and epigenetic changes have all been described in GBMs. These abnormalities indicate that a number of different signaling pathways are deregulated in GBM. Increasing number of studies provide a better understanding of the tumor biology, genetic, and epigenetic background of the GBM. Also, current research provides us useful approaches in designing novel therapies for GBM. In this review, we summarize the receptor tyrosine kinase-Ras-PI 3 kinase-Akt signaling network, focusing on the potential molecular targets for anti-signaling molecular therapies in this pathway.

Towards Targeting PI3K-Dependent Regulation of Gene Expression in Brain Cancer

The PI3K pathway is one of the most highly perturbed cell signaling pathways in human cancer, including the most common malignant brain tumors, gliomas, where either activating mutations of positive pathway effectors or loss/inactivation of pathway inhibitors occurs. Knowledge of the precise transcription factors modulated by PI3K in tumor cells remains elusive but there are numerous PI3K-responsive signaling factors, including kinases, which can activate many transcription factors. In the context of cancer, these transcription factors participate in the regulation of target genes expression networks to support cancer cell characteristics such as survival, proliferation, migration and differentiation. This review focuses on the role of PI3K signaling-regulated transcription in brain cancer cells from a series of recent investigations. A deeper understanding of this regulation is beginning to provide the hope of developing more sophisticated anti-cancer targeting approaches, where both upstream and downstream components of the PI3K pathway may be targeted by existing and novel drugs.

Icariside II induces cell cycle arrest and apoptosis in human glioblastoma cells through suppressing Akt activation and potentiating FOXO3a activity

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor, and currently chemotherapeutic options for GBM are very limited. Given the poor prognosis, the development of novel anti-GBM agents is quite urgent. Using two human glioma cells (U87 and A172 cells), we demonstrated that Icariside II (ICA II), an active flavonoid compound derived from Epimedium koreanum, could inhibit GBM cell growth in a dose dependent manner. Wound healing data suggested that ICA II also inhibited the migration of human glioma cells. Mechanistically, ICA II induced apoptosis and cell cycle arrest, and this cytotoxic effect was dependent on the reduction of Forkhead box O3a(FOXO3a) phosphorylation mediated by Akt and the enrichment of nuclear FOXO3a, which initiated the transcription of p21/p27. Importantly, the cytotoxic effect induced by ICA II could be reversed by silencing the expression of FOXO3a, suggesting the critical role of FOXO3a in this process. Taken together, we propose ICA II as a potential novel anti-GBM candidate with a mechanism of inhibiting cell proliferation and inducing apoptosis through suppressing Akt activation and potentiating FOXO3a activity.

Cathepsin B-deficient mice as source of monoclonal anti-cathepsin B antibodies

Cathepsin B has been demonstrated to be involved in several proteolytic processes that support tumor progression and metastasis and neurodegeneration. To further clarify its role, defined monoclonal antibodies are needed. As the primary structure of human cathepsin B is almost identical to that of the mouse, cathepsin B-deficient mice were used in a novel approach for generating such antibodies, providing the chance of an increased immune response to the antigen, human cathepsin B. Thirty clones were found to produce cathepsin B-specific antibodies. Seven of these antibodies were used to detect cathepsin B in MCF10-DCIS human breast cancer cells by immunocytochemistry and immunoblotting. Five different binding sites were identified by epitope mapping giving the opportunity to combine these antibodies in oligoclonal antibody mixtures for an improved detection of cathepsin B.

CELF1 is Up-Regulated in Glioma and Promotes Glioma Cell Proliferation by Suppression of CDKN1B

BACKGROUND

As a member of the CELF family, CELF1 (CUG-binding protein 1, CUGBP1) is involved in cardiac and embryonic development, skeletal muscle differentiation and mammary epithelial cell proliferation. CELF1 is also observed in many kinds of cancer and may play a great role in tumorigenesis and deterioration. However, the expression and mechanism of its function in human glioma remain unclear.

METHODS

We examined CELF1 expression in 62 glioma patients by immunohistochemistry and Western blot. The association between the expression of CELF1 protein and clinicopathological characteristics was analysed using SPSS 17.0. Survival analyses were performed using the Kaplan-Meier method. Small-interfering RNA was utilised to specifically knockdown CELF1 mRNA in U87 and U251 cells. Cell proliferation, cell cycle and cell apoptosis were tested by Cell Counting Kit-8 and flow cytometry. The expression of cell cycle-related gene CDKN1B was investigated by Western blot. The interactions between CELF1 and CDKN1B were detected with immune co-precipitation. Subcutaneous tumour models were used to study the effect of CELF1 on the growth of glioma cells in vivo.

RESULTS

Our results showed that CELF1 protein was frequently up-regulated in human glioma tissues. The expression level of this protein was positively correlated with glioma World Health Organisation grade and inversely correlated with patient survival (P < 0.05). Knockdown of CELF1 inhibited the glioma cell cycle process and proliferation potential, possibly by down-regulating its target, CDKN1B protein.

CONCLUSIONS

Results indicated that CELF1 may be a novel independent prognostic predictor of survival for glioma patients. It may promote glioma cell proliferation and cell cycle process during glioma carcinogenesis.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: focus on the cancer hallmark of tumor angiogenesis

One of the important 'hallmarks' of cancer is angiogenesis, which is the process of formation of new blood vessels that are necessary for tumor expansion, invasion and metastasis. Under normal physiological conditions, angiogenesis is well balanced and controlled by endogenous proangiogenic factors and antiangiogenic factors. However, factors produced by cancer cells, cancer stem cells and other cell types in the tumor stroma can disrupt the balance so that the tumor microenvironment favors tumor angiogenesis. These factors include vascular endothelial growth factor, endothelial tissue factor and other membrane bound receptors that mediate multiple intracellular signaling pathways that contribute to tumor angiogenesis. Though environmental exposures to certain chemicals have been found to initiate and promote tumor development, the role of these exposures (particularly to low doses of multiple substances), is largely unknown in relation to tumor angiogenesis. This review summarizes the evidence of the role of environmental chemical bioactivity and exposure in tumor angiogenesis and carcinogenesis. We identify a number of ubiquitous (prototypical) chemicals with disruptive potential that may warrant further investigation given their selectivity for high-throughput screening assay targets associated with proangiogenic pathways. We also consider the cross-hallmark relationships of a number of important angiogenic pathway targets with other cancer hallmarks and we make recommendations for future research. Understanding of the role of low-dose exposure of chemicals with disruptive potential could help us refine our approach to cancer risk assessment, and may ultimately aid in preventing cancer by reducing or eliminating exposures to synergistic mixtures of chemicals with carcinogenic potential.

Urokinase-type plasminogen activator receptor regulates apoptotic sensitivity of colon cancer HCT116 cell line to TRAIL via JNK-p53 pathway

The urokinase-type plasminogen activator receptor (uPAR) serves not only as an anchor for urokinase-type plasminogen activator but also participates in intracellular signal transduction events. In this study, we investigated whether uPAR could modulate TRAIL-induced apoptosis in human colon cancer cells HCT116. Using an antisense strategy, we established a stable HCT116 cell line with down-regulated uPAR. The sensitivity to TRAIL-induced apoptosis was evaluated by FACS analysis. Our results show that the inhibition of uPAR could sensitize HCT116 to TRAIL-induced apoptosis. uPAR inhibition changed the expression of mitochondrial apoptotic pathway proteins, including Bcl-2, Bax, Bid and p53, in a pro-apoptotic manner. We also found that the inhibition of uPAR down-regulated the phosphorylation of FAK, ERK and JNK. The inhibition of p53 by RNA interference rescued cells from enhanced apoptosis, thus indicating that p53 is critical for enhancing TRAIL-induced apoptosis. Furthermore, JNK, but not ERK, inhibition involved in the up-regulation of p53. JNK negatively regulated p53 protein level. Overall, our results show that uPAR inhibition can sensitize colon cancer cells HCT116 to TRAIL-induced apoptosis via active p53 and mitochondrial apoptotic pathways that JNK inhibition is involved.

Dysregulation of apoptotic signaling pathways by interaction of RPLP0 and cathepsin X/Z in gastric cancer

Cathepsin X (CTSX, also called cathepsin Z/P) is a cysteine protease that still plays an unknown role in human cancer. It has been shown to bind cell surface heparin sulphate proteoglycans and integrins, indicating possible functions of CTSX in cellular adhesion, phagocytosis, and immune response. Our previous studies have shown an association between Helicobacter pylori (H. pylori) infection, a strong up-regulation of CTSX, and development of gastric cancer. In this study, yeast two-hybrid analysis revealed that RPLP0, a ribosomal protein P0, interacts with the human CTSX protein in gastric cancer. The CTSX/RPLP0 interaction was confirmed by co-immunoprecipitation assays. In addition, co-localization studies in cancer cell line N87 and gastric cancer tissue samples were performed. Laserscan microscopy revealed a shuttling of RPLP0 (and CTSX) from cytoplasm to the nucleus after CTSX knockdown. Down-regulation of RPLP0 resulted in G1 arrest of gastric cancer cells, whereas knockdown of CTSX led to G1 arrest and apoptosis after 48 h. Knockdown of both proteins caused increased apoptosis. RPLP0 deficiency could suppress cell growth and cell cycle progression by down-regulating CDK2. It was further demonstrated that RPLP0 affected p21 expression, but did not change the expression of Cyclin E. Down-regulation of both proteins at least through CDK2 suggests an anti-apoptotic effect on gastric cancer cells and opens up new possibilities for apoptotic immune modulation and gastric cancer therapy.

Knockdown of cathepsin B and uPAR inhibits CD151 and α3β1 integrin-mediated cell adhesion and invasion in glioma

Glioma is a highly complex brain tumor characterized by the dysregulation of proteins and genes that leads to tumor metastasis. Cathepsin B and uPAR are overexpressed in gliomas and they are postulated to play central roles in glioma metastasis. In this study, efficient downregulation of cathepsin B and uPAR by siRNA treatments significantly reduced glioma cell adhesion to laminin as compared to vitronectin, fibronectin, or collagen I in U251 and 4910 glioma cell lines. Brain glioma tissue array analysis showed high expression of CD151 in clinical samples when compared with normal brain tissue. Cathepsin B and uPAR siRNA treatment led to the downregulation of CD151 and laminin-binding integrins α3 and β1. Co-immunoprecipitation experiments revealed that downregulation of cathepsin B and uPAR decreased the interaction of CD151 with uPAR cathepsin B, and α3β1 integrin. Studies on the downstream signaling cascade of uPAR/CD151/α3β1 integrin have shown that phosphorylation of FAK, SRC, paxillin, and expression of adaptor cytoskeletal proteins talin and vinculin were reduced with knockdown of cathepsin B, uPAR, and CD151. Treatment with the bicistronic construct reduced interactions between uPAR and CD151 as well as lowering α3β1 integrin, talin, and vinculin expression levels in pre-established glioma tumors of nude mice. In conclusion, our results show that downregulation of cathepsin B and uPAR alone and in combination inhibit glioma cell adhesion by downregulating CD151 and its associated signaling molecules in vitro and in vivo. Taken together, the results of the present study show that targeting the uPAR-cathepsin B system has possible therapeutic potential.

Platelet-derived growth factor-A regulates lung fibroblast S-phase entry through p27(kip1) and FoxO3a

BACKGROUND

Secondary pulmonary alveolar septal formation requires platelet derived growth factor (PDGF-A) and platelet derived growth factor receptor-alpha (PDGFRα), and their regulation influences alveolar septal areal density and thickness. Insufficient PDGFRα expression in lung fibroblasts (LF) results in failed septation.

METHODS

Mice in which the endogenous PDGFRα-gene regulates expression of the green fluorescent protein were used to temporally and spatially track PDGFRα-signaling. Transition from the G₁/G₀ to the S-phase of the cell cycle was compared in PDGFRα-expressing and non-expressing LF using flow cytometry. Laser scanning confocal microscopy was used to quantify p27(kip1) and forkhead box "other" 3a (FoxO3a) in the nuclei of alveolar cells from mice bearing the PDGFRα-GFP knock-in, and p27(kip1) in mice with a conditional deletion of PDGFRα-gene function. The effects of PDGF-A on the phosphorylation and the intracellular location of FoxO3a were examined using Western immuoblotting and immunocytochemistry.

RESULTS

In neonatal mouse lungs, entry of the PDGFRα-expressing LF subpopulation into the S-phase of the cell cycle diminished sooner than in their non-expressing LF counterparts. This preferential diminution was influenced by PDGFRα-mediated signaling, which phosphorylates and promotes cytoplasmic localization of FoxO3a. Comparative observations of LF at different ages during secondary septation and in mice that lack PDGFRα in alveolar LF demonstrated that nuclear localization of the G₁ cyclin-dependent kinase inhibitor p27(kip1) correlated with reduced LF entry into S-phase.

CONCLUSIONS

Nuclear localization of FoxO3a, an important regulator of p27(kip1) gene-expression, correlates with diminished proliferation of the PDGFRα-expressing LF subpopulation. These mechanisms for diminishing the effects of PDGFRα-mediated signaling likely regulate secondary septal formation and their derangement may contribute to imbalanced fibroblast cell kinetics in parenchymal lung diseases.

Cathepsin B as a cancer target

INTRODUCTION

Cathepsin B is of significant importance to cancer therapy as it is involved in various pathologies and oncogenic processes in humans. Numerous studies have shown that abnormal regulation of cathepsin B overexpression is correlated with invasive and metastatic phenotypes in cancers. Cathepsin B is normally associated with the lysosomes involved in autophagy and immune response, but its aberrant expression has been shown to lead to cancers.

AREAS COVERED

This review highlights the oncogenic role of cathepsin B, discusses the regulation of cathepsin B in light of oncogenesis, discusses the role of cathepsin B as a signaling molecule, and highlights the therapeutic potential of targeting cathepsin B.

EXPERT OPINION

Targeting cathepsin B alone does not appear to abolish tumor growth, and this is probably because cathepsin B appears to have diverse functions and influence numerous pathways. It is not clear whether global suppression of cathepsin B activity or expression would produce unintended effects or cause the activation or suppression of unwanted pathways. A localized approach for targeting the expression of cathepsin B would be more relevant. Moreover, a combination of targeting cathepsin B with other relevant oncogenic molecules has significant therapeutic potential.

Anthocyanins in the black soybean (Glycine max L.) protect U2OS cells from apoptosis by inducing autophagy via the activation of adenosyl monophosphate-dependent protein kinase

Anthocyanins (ATCs) have been reported to induce apoptosis in various types of cancer cells, stimulating the development of ATCs as a cancer chemotherapeutic or chemopreventive agent. It was recently reported that ATCs can induce autophagy, however, the mechanism for this remains unclear. In the present report, we carried out mechanistic studies of the mechanism involved in ATC-induced autophagy using ATCs extracted from black soybeans (cv. Cheongja 3, Glycine max L.). ATCs clearly induced hallmarks of autophagy, including LC3 puncta formation and the conversion of LC3-I to LC3-II in U2OS human osteosarcoma cells. The induction of autophagy was accompanied by the phosphorylation of multiple protein kinases including extracellular signal-regulated kinase (ERK)1/2, p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), protein kinase B (AKT) and adenosyl mono-phosphate-dependent protein kinase (AMPK). While chemical inhibitors against ERK1/2, p38 MAPK, JNK and AKT failed to inhibit ATC-induced autophagy, the suppression of AMPK by compound C (CC) as well as siRNA against AMPK reduced ATC-induced autophagy. The treatment of ATCs resulted in a decrease in intracellular ATP contents and the activation of AMPK by AICAR treatment also induced autophagy. It is noteworthy that the reduction of autophagy via the inhibition of AMPK resulted in enhanced apoptosis in ATC-treated cells. In addition, siRNA against forkhead box O3A (FOXO3a), a downstream target of AMPK, suppressed ATC-induced autophagy and p27KIP1 siRNA increased apoptosis in ATC-treated cells. Collectively, it can be concluded that ATCs induce autophagy in U2OS cells via activation of the AMPK-FOXO3a pathway and protect cells from ATC-induced apoptosis via the AMPK-p27KIP1 pathway. These results also suggest that autophagy-modulating agents could contribute to the efficient development of ATCs as anticancer therapy.

uPAR and cathepsin B knockdown inhibits radiation-induced PKC integrated integrin signaling to the cytoskeleton of glioma-initiating cells

Despite advances in radiotherapeutic and chemotherapeutic techniques and aggressive surgical resection, the prognosis of glioblastoma patients is dismal. Accumulation of evidence indicates that some cancer cells survive even the most aggressive treatments, and these surviving cells, which are resistant to therapy and are perhaps essential for the malignancy, may be cancer stem cells. The CD133 surface marker is commonly used to isolate these extremely resistant glioma-initiating cells (GICs). In the present study, GICs which tested positive for the CD133 marker (CD133⁺) were isolated from both the established U251 cell line and the 5310 xenograft glioma cell line to study the events related to the molecular pathogenesis of these cells. Simultaneous down-regulation of uPAR and cathepsin B by shRNA (pUC) treatment caused the disruption of radiation-induced complex formation of pPKC θ/δ, integrin β1 and PKC ζ, integrin β1 in glioma cells. Further, pUC treatment inhibited PKC/integrin signaling via FAK by causing disassociation of FAK and the cytoskeletal molecules vinculin and α-actinin. Also, we observed the inhibition of ERK phosphorylation. This inhibition was mediated by pUC and directed a negative feedback mechanism over the FAK signaling molecules, which led to an extensive reduction in the signal for cytoskeletal organization generating migratory arrest. Altogether, it can be hypothesized that knockdown of uPAR and cathepsin B using shRNA is an effective strategy for controlling highly invasive glioma cells and extremely resistant glioma-initiating cells.

uPAR and cathepsin B inhibition enhanced radiation-induced apoptosis in gliomainitiating cells

Glioblastomas present as diffuse tumors with invasion into normal brain tissue and frequently recur or progress after radiation as focal masses because of glioma-initiating cells. The role of the urokinase-type plasminogen activator receptor (uPAR) and cathepsin B in stem-like phenotype has been extensively studied in several solid tumors. In the present study, we demonstrated that selection of glioma-initiating cells using CD133 expression leads to a specific enrichment of CD133(+) cells in both U87 and 4910 cells. In addition, CD133(+) cells exhibited a considerable amount of other stem cell markers, such as Nestin and Sox-2. Radiation treatment significantly enhanced uPAR and cathepsin B levels in glioma-initiating cells. To downregulate radiation-induced uPAR and cathepsin B expression, we used a bicistronic shRNA construct that simultaneously targets both uPAR and cathepsin B (pCU). Downregulation of uPAR and cathepsin B using pCU decreased radiation-enhanced uPAR and cathepsin B levels and caused DNA damage-induced apoptosis in glioma cell lines and glioma-initiating cells. The most striking finding of this study is that knockdown of uPAR and cathepsin B inhibited ongoing transcription by suppressing BrUTP incorporation at γH2AX foci. In addition, uPAR and cathepsin B gene silencing inversely regulated survivin and H2AX expression in both glioma cells and glioma-initiating cells. Pretreatment with pCU reduced radiation-enhanced expression of uPAR, cathepsin B, and survivin and enhanced DNA damage in pre-established glioma in nude mice. Taken together, our in vitro and in vivo findings suggest that uPAR and cathepsin B inhibition might serve as an adjunct to radiation therapy to target glioma-initiating cells and, therefore, for the treatment of glioma.

Inhibition of cathepsin B activity attenuates extracellular matrix degradation and inflammatory breast cancer invasion

Introduction

Inflammatory breast cancer (IBC) is an aggressive, metastatic and highly angiogenic form of locally advanced breast cancer with a relatively poor three-year survival rate. Breast cancer invasion has been linked to proteolytic activity at the tumor cell surface. Here we explored a role for active cathepsin B on the cell surface in the invasiveness of IBC.

Methods

We examined expression of the cysteine protease cathepsin B and the serine protease urokinase plasminogen activator (uPA), its receptor uPAR and caveolin-1 in two IBC cell lines: SUM149 and SUM190. We utilized a live cell proteolysis assay to localize in real time the degradation of type IV collagen by IBC cells. IBC patient biopsies were examined for expression of cathepsin B and caveolin-1.

Results

Both cell lines expressed comparable levels of cathepsin B and uPA. In contrast, levels of caveolin-1 and uPAR were greater in SUM149 cells. We observed that uPA, uPAR and enzymatically active cathepsin B were colocalized in caveolae fractions isolated from SUM149 cells. Using a live-cell proteolysis assay, we demonstrated that both IBC cell lines degrade type IV collagen. The SUM149 cells exhibit predominantly pericellular proteolysis, consistent with localization of proteolytic pathway constitutents to caveolar membrane microdomains. A functional role for cathepsin B was confirmed by the ability of CA074, a cell impermeable and highly selective cathepsin B inhibitor, to significantly reduce pericellular proteolysis and invasion by SUM149 cells. A statistically significant co-expression of cathepsin B and caveolin-1 was found in IBC patient biopsies, thus validating our in vitro data.

Conclusion

Our study is the first to show that the proteolytic activity of cathepsin B and its co-expression with caveolin-1 contributes to the aggressiveness of IBC.

Regulation of DNA repair mechanism in human glioma xenograft cells both in vitro and in vivo in nude mice

BACKGROUND

Glioblastoma Multiforme (GBM) is the most lethal form of brain tumor. Efficient DNA repair and anti-apoptotic mechanisms are making glioma treatment difficult. Proteases such as MMP9, cathepsin B and urokinase plasminogen activator receptor (uPAR) are over expressed in gliomas and contribute to enhanced cancer cell proliferation. Non-homologous end joining (NHEJ) repair mechanism plays a major role in double strand break (DSB) repair in mammalian cells.

METHODOLOGY/PRINCIPAL FINDINGS

Here we show that silencing MMP9 in combination with uPAR/cathepsin B effects NHEJ repair machinery. Expression of DNA PKcs and Ku70/80 at both mRNA and protein levels in MMP9-uPAR (pMU) and MMP9-cathepsin B (pMC) shRNA-treated glioma xenograft cells were reduced. FACS analysis showed an increase in apoptotic peak and proliferation assays revealed a significant reduction in the cell population in pMU- and pMC-treated cells compared to untreated cells. We hypothesized that reduced NHEJ repair led to DSBs accumulation in pMU- and pMC-treated cells, thereby initiating cell death. This hypothesis was confirmed by reduced Ku70/Ku80 protein binding to DSB, increased comet tail length and elevated γH2AX expression in treated cells compared to control. Immunoprecipitation analysis showed that EGFR-mediated lowered DNA PK activity in treated cells compared to controls. Treatment with pMU and pMC shRNA reduced the expression of DNA PKcs and ATM, and elevated γH2AX levels in xenograft implanted nude mice. Glioma cells exposed to hypoxia and irradiation showed DSB accumulation and apoptosis after pMU and pMC treatments compared to respective controls.

CONCLUSION/SIGNIFICANCE

Our results suggest that pMU and pMC shRNA reduce glioma proliferation by DSB accumulation and increase apoptosis under normoxia, hypoxia and in combination with irradiation. Considering the radio- and chemo-resistant cancers favored by hypoxia, our study provides important therapeutic potential of MMP9, uPAR and cathepsin B shRNA in the treatment of glioma from clinical stand point.

uPAR and cathepsin B downregulation induces apoptosis by targeting calcineurin A to BAD via Bcl-2 in glioma

Cathepsin B and urokinase plasminogen activator receptor (uPAR) are postulated to play key roles in glioma invasion. Calcineurin is one of the key regulators of mitochondrial-dependent apoptosis, but its mechanism is poorly understood. Hence, we studied subcellular localization of calcineurin after transcriptional downregulation of uPAR and cathepsin B in glioma. In the present study, efficient downregulation of uPAR and cathepsin B increased the translocation of calcineurin A from the mitochondria to the cytosol, decreased pBAD (S136) expression and its interaction with 14-3-3ζ and increased the interaction of BAD with Bcl-xl. Co-depletion of uPAR and cathepsin B induced mitochondrial translocation of BAD, activation of caspase 3 as well as PARP and cytochrome c and SMAC release. These effects were inhibited by FK506 (10 μM), a specific inhibitor of calcineurin. Calcineurin A was co-localized and also co-immunoprecipitated with Bcl-2. This interaction decreased with co-depletion of uPAR and cathepsin B and also with Bcl-2 inhibitor, HA 14-1 (20 μg/ml). Altered localization and interaction of calcineurin A with Bcl-2 was also observed in vivo when uPAR and cathepsin B were downregulated. In conclusion, downregulation of uPAR and cathepsin B induced apoptosis by targeting calcineurin A to BAD via Bcl-2 in glioma.

MMP-9 silencing regulates hTERT expression via β1 integrin-mediated FAK signaling and induces senescence in glioma xenograft cells

In more than 90% of cancers including glioma, telomere elongation reverse transcriptase (hTERT) is overexpressed. In the present study, we sought to explore whether matrix metalloproteinase-9 (MMP-9) shRNA could alter hTERT-mediated proliferation in glioma cells. MMP-9 shRNA induced senescence and apoptosis in glioma cells by inhibiting hTERT expression and telomere activity. MMP-9 silencing decreased oncogenic c-Myc expression (hTERT activator), whereas the expression of the c-Myc antagonist MAD increased drastically (hTERT repressor); both c-Myc and MAD are transcription factors for hTERT. In addition, MMP-9 suppression turns the switch from c-Myc/MAX to MAD/MAX heterodimer binding to the hTERT promoter as determined by chromatin immunoprecipitation assay. We also show that silencing MAD via siRNA restored hTERT expression and inhibited senescence in glioma cells. MMP-9 transcriptional suppression decreased the expression of FAK, phospho FAK and β1 integrin in glioma xenograft cells. Further, MMP-9 suppression decreased the interaction of β1 integrin/FAK and also MMP-9/β1 integrin as confirmed by immunoprecipitation analysis. Studies with either function blocking β1 integrin or FAK shRNA indicate that suppression of MMP-9 decreased β1 integrin-mediated induction of FAK, which led to decreased hTERT expression. Moreover, 4910 and 5310 glioma xenograft tissue sections from mice treated with MMP-9 shRNA showed reduced expression of FAK/c-Myc and elevated MAD levels. Decreased co-localization of β1 integrin and MMP-9 was associated with MMP-9-suppressed tumor sections. Further, immunoprecipitation analysis showed decreased association of proteins involved in telomere end repair in MMP-9 shRNA-treated glioma cells. Elevated levels of p73 and TRAIL and the results of the FACS analysis show induction of apoptosis in MMP-9-silenced glioma cells. Taken together, these data provide new insights into the mechanisms underlying MMP-9-mediated hTERT expression in glioma proliferation.

Mechanism of p27 upregulation induced by downregulation of cathepsin B and uPAR in glioma

Cathepsin B and urokinase plasminogen activator receptor (uPAR) are overexpressed in gliomas. Deregulation of the G1 phase cell cycle machinery is a common feature of cancers. p27(Kip1) (p27) is one of the major cyclin-CDK regulators in the G1 phase. uPAR and cathepsin B downregulation was recently shown to induce p27 expression through PI3K/Akt/FOXO3a signaling. Since uPAR and cathepsin B knockdown also decreased phosphorylation of ERK, we hypothesized that ERK also has a role to play in p27 induction. As induction of p27 is due to an increase in gene transcription, we investigated the roles of c-Myc and E2F1 transcription factors which have been shown to potently affect p27 promoter activity. In the present study, shRNA against cathepsin B and uPAR as well as specific inhibitors, Wortmannin (10 μM) and U0126 (10 μM), were used to determine the roles of AKT and ERK signaling on p27 expression. Immunoblot analysis demonstrated that downregulation of both p-ERK and p-AKT downstream of EGFR and β1 integrin are involved in the p27 upregulation. Cathepsin B and uPAR downregulation induced E2F1 and decreased phosphorylaion of pocket proteins and c-Myc expression. CHIP analysis and luciferase expression studies confirmed the functional association of transcription factor E2F1 to the p27 promoter. Further, c-Myc-Max interaction inhibitor studies showed an inverse pattern of c-Myc and p27 expression. Also, cathepsin B and uPAR downregulation reduced tumor growth and increased p27 nuclear expression in vivo. In summary, cathepsin B and uPAR downregulation reduced p-ERK levels and c-Myc expression, increased expression of E2F1 and FOXO3a, decreased phosphorylation of pocket proteins and thus upregulated p27 expression in glioma cells.

Akt, FoxO and regulation of apoptosis

Forkhead box O (FoxO) transcription factors are downstream targets of the serine/threonine protein kinase B (PKB)/Akt. The Akt kinase regulates processes of cellular proliferation and survival. Phosphorylation of FoxOs by Akt inhibits transcriptional functions of FoxOs and contributes to cell survival, growth and proliferation. Emerging evidence suggests involvement of FoxOs in diverse intracellular signaling pathways with critical roles in a number of physiological as well as pathological conditions including cancer. The FoxO signaling is regulated by their interactions with other intracellular proteins as well as their post-translational modifications such as phosphorylation. FoxOs promote cell growth inhibitory and/or apoptosis signaling by either inducing expression of multiple pro-apoptotic members of the Bcl2-family of mitochondria-targeting proteins, stimulating expression of death receptor ligands such as Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), or enhancing levels of various cyclin-dependent kinase inhibitors (CDKIs). Coupled with their ability to cross-talk with p53, FoxOs represent an important class of tumor suppressors in a variety of cancers. This review summarizes our current understanding of mechanisms by which Akt and FoxOs regulate cell growth and survival that in turn offers opportunities for development of novel strategies to combat cancer. This article is part of a Special Issue entitled: P13K-AKT-FOxO axis in cancer and aging.

Downregulation of uPAR and cathepsin B induces apoptosis via regulation of Bcl-2 and Bax and inhibition of the PI3K/Akt pathway in gliomas

BACKGROUND

Glioma is the most commonly diagnosed primary brain tumor and is characterized by invasive and infiltrative behavior. uPAR and cathepsin B are known to be overexpressed in high-grade gliomas and are strongly correlated with invasive cancer phenotypes.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study, we observed that simultaneous downregulation of uPAR and cathepsin B induces upregulation of some pro-apoptotic genes and suppression of anti-apoptotic genes in human glioma cells. uPAR and cathepsin B (pCU)-downregulated cells exhibited decreases in the Bcl-2/Bax ratio and initiated the collapse of mitochondrial membrane potential. We also observed that the broad caspase inhibitor, Z-Asp-2, 6-dichlorobenzoylmethylketone rescued pCU-induced apoptosis in U251 cells but not in 5310 cells. Immunoblot analysis of caspase-9 immunoprecipitates for Apaf-1 showed that uPAR and cathepsin B knockdown activated apoptosome complex formation in U251 cells. Downregulation of uPAR and cathepsin B also retarded nuclear translocation and interfered with DNA binding activity of CREB in both U251 and 5310 cells. Further western blotting analysis demonstrated that downregulation of uPAR and cathepsin B significantly decreased expression of the signaling molecules p-PDGFR-β, p-PI3K and p-Akt. An increase in the number of TUNEL-positive cells, increased Bax expression, and decreased Bcl-2 expression in nude mice brain tumor sections and brain tissue lysates confirm our in vitro results.

CONCLUSIONS/SIGNIFICANCE

In conclusion, RNAi-mediated downregulation of uPAR and cathepsin B initiates caspase-dependent mitochondrial apoptosis in U251 cells and caspase-independent mitochondrial apoptosis in 5310 cells. Thus, targeting uPAR and cathepsin B-mediated signaling using siRNA may serve as a novel therapeutic strategy for the treatment of gliomas.