Identification of non-canonical NF-κB signaling as a critical mediator of Smac mimetic-stimulated migration and invasion of glioblastoma cells

Idiopathic Pulmonary Fibrosis Caused by Damaged Mitochondria and Imbalanced Protein Homeostasis in Alveolar Epithelial Type II Cell

Alveolar epithelial Type II (ATII) cells are closely associated with early events of Idiopathic pulmonary fibrosis (IPF). Proteostasis dysfunction, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction are known causes of decreased proliferation of alveolar epithelial cells and the secretion of pro-fibrotic mediators. Here, a large body of evidence is systematized and a cascade relationship between protein homeostasis, endoplasmic reticulum stress, mitochondrial dysfunction, and fibrotropic cytokines is proposed, providing a theoretical basis for ATII cells dysfunction as a possible pathophysiological initiating event for idiopathic pulmonary fibrosis.

Research on the signaling pathways related to the intervention of traditional Chinese medicine in Parkinson's disease:A literature review

ETHNOPHARMACOLOGICAL RELEVANCE

Parkinson's disease (PD) is the most common progressive neurodegenerative disorder affecting more than 10 million people worldwide and is characterized by the progressive loss of Daergic (DA) neurons in the substantia nigra pars compacta. It has been reported that signaling pathways play a crucial role in the pathogenesis of PD, while the active ingredients of traditional Chinese medicine (TCM) have been found to possess a protective effect against PD. TCM has demonstrated significant potential in mitigating oxidative stress (OS), neuroinflammation, and apoptosis of DA neurons via the regulation of signaling pathways associated with PD.

AIM OF THE REVIEW

This study discussed and analyzed the signaling pathways involved in the occurrence and development of PD and the mechanism of active ingredients of TCM regulating PD via signaling pathways, with the aim of providing a basis for the development and clinical application of therapeutic strategies for TCM in PD.

MATERIALS AND METHODS

With "Parkinson's disease", "Idiopathic Parkinson's Disease", "Lewy Body Parkinson's Disease", "Parkinson's Disease, Idiopathic", "Parkinson Disease, Idiopathic", "Parkinson's disorders", "Parkinsonism syndrome", "Traditional Chinese medicine", "Chinese herbal medicine", "active ingredients", "medicinal plants" as the main keywords, PubMed, Web of Science and other online search engines were used for literature retrieval.

RESULTS

PD exhibits a close association with various signaling pathways, including but not limited to MAPKs, NF-κB, PI3K/Akt, Nrf2/ARE, Wnt/β-catenin, TLR/TRIF, NLRP3, Notch. The therapeutic potential of TCM lies in its ability to regulate these signaling pathways. In addition, the active ingredients of TCM have shown significant effects in improving OS, neuroinflammation, and DA neuron apoptosis in PD.

CONCLUSION

The active ingredients of TCM have unique advantages in regulating PD-related signaling pathways. It is suggested to combine network pharmacology and bioinformatics to study the specific targets of TCM. This not only provides a new way for the prevention and treatment of PD with the active ingredients of TCM, but also provides a scientific basis for the selection and development of TCM preparations.

Guanine nucleotide exchange factor RABGEF1 facilitates TNF-induced necroptosis by targeting cIAP1

Necroptosis is a form of regulated cell death that depends on the receptor-interacting serine-threonine kinase 3 (RIPK3) and mixed lineage kinase domain-like (MLKL). The molecular mechanisms underlying distinct instances of necroptosis have only recently begun to emerge. In the present study, we characterized RABGEF1 as a positive regulator of RIPK1/RIPK3 activation in vitro. Based on the overexpression and knockdown experiments, we determined that RABGEF1 accelerated the phosphorylation of RIPK1 and promoted necrosome formation in L929 cells. The pro-necrotic effect of RABGEF1 is associated with its E3 ubiquitin ligase activity and guanine nucleotide exchange factor (GEF) activity. We further confirmed that RABGEF1 interacts with cIAP1 protein by inhibiting its function and plays a regulatory role in necroptosis, which can be abolished by treatment with the antagonist Smac mimetic (SM)-164. In conclusion, our study highlights a potential and novel role of RABGEF1 in promoting TNF-induced cell necrosis.

Cellular signaling in glioblastoma: A molecular and clinical perspective

Glioblastoma multiforme (GBM) is the most aggressive brain tumor with an average life expectancy of less than 15 months. Such high patient mortality in GBM is pertaining to the presence of clinical and molecular heterogeneity attributed to various genetic and epigenetic alterations. Such alterations in critically important signaling pathways are attributed to aberrant gene signaling. Different subclasses of GBM show predominance of different genetic alterations and therefore, understanding the complex signaling pathways and their key molecular components in different subclasses of GBM is extremely important with respect to clinical management. In this book chapter, we summarize the common and important signaling pathways that play a significant role in different subclasses and discuss their therapeutic targeting approaches in terms of preclinical studies and clinical trials.

Exploring the immunological role and prognostic potential of PPM1M in pan-cancer

BACKGROUND

PPM1M is a member of the metal-dependent protein phosphatase family, and its role in the immunization process has not been studied in depth. In this study, we investigated the role of PPM1M in pan-cancer.

METHODS

Samples of cancer and normal tissues were obtained from the cancer genome atlas and genotype-tissue expression. Kaplan-Meier survival curves and Cox regression were used to analyze the effect of PPM1M on prognosis. Functional and pathway enrichment analyses were performed using the R package "clusterProfiler" to explore the role of PPM1M. The Sanger Box database was used to analyze the relationship between PPM1M and tumor immune checkpoint, tumor mutational burden, and microsatellite instability. The Tumor Immune Estimation Resource 2 database and CIBERSORT method were used to analyze the relationship between PPM1M and tumor-infiltrating immune cells. Finally, the cBioPortal database was used to analyze the genomic variation in PPM1M.

RESULTS

Among the variety of tumors, the expression of PPM1M was higher in normal tissues than in cancerous tissues. The expression of PPM1M is closely associated with patient prognosis, tumor immune checkpoint, tumor mutational burden, and microsatellite instability. PPM1M is closely associated with the infiltration of immune cells into the tumor microenvironment. In addition, PPM1M is involved in the regulation of several immune-related pathways.

CONCLUSION

In pan-cancer, PPM1M affects patient prognosis and may be a potential immunological biomarker. Furthermore, PPM1M may be a potential therapeutic target in tumor immunology.

Combined Inhibition of IAPs and WEE1 Enhances TNFα- and Radiation-Induced Cell Death in Head and Neck Squamous Carcinoma

Head and neck squamous cell carcinoma (HNSCC) remains a prevalent diagnosis with current treatment options that include radiotherapy and immune-mediated therapies, in which tumor necrosis factor-α (TNFα) is a key mediator of cytotoxicity. However, HNSCC and other cancers often display TNFα resistance due to activation of the canonical IKK-NFκB/RELA pathway, which is activated by, and induces expression of, cellular inhibitors of apoptosis proteins (cIAPs). Our previous studies have demonstrated that the IAP inhibitor birinapant sensitized HNSCC to TNFα-dependent cell death in vitro and radiotherapy in vivo. Furthermore, we recently demonstrated that the inhibition of the G2/M checkpoint kinase WEE1 also sensitized HNSCC cells to TNFα-dependent cell death, due to the inhibition of the pro-survival IKK-NFκB/RELA complex. Given these observations, we hypothesized that dual-antagonist therapy targeting both IAP and WEE1 proteins may have the potential to synergistically sensitize HNSCC to TNFα-dependent cell death. Using the IAP inhibitor birinapant and the WEE1 inhibitor AZD1775, we show that combination treatment reduced cell viability, proliferation and survival when compared with individual treatment. Furthermore, combination treatment enhanced the sensitivity of HNSCC cells to TNFα-induced cytotoxicity via the induction of apoptosis and DNA damage. Additionally, birinapant and AZD1775 combination treatment decreased cell proliferation and survival in combination with radiotherapy, a critical source of TNFα. These results support further investigation of IAP and WEE1 inhibitor combinations in preclinical and clinical studies in HNSCC.

NF-κB-inducing kinase (NIK) is activated in pancreatic β-cells but does not contribute to the development of diabetes

The transcription factor nuclear factor-κB (NF-κB) has a key role in the pathogenesis of diabetes and its complications. Although activation of the canonical NF-κB pathway in β-cells is generally deleterious, little is known about the role of the non-canonical NF-κB signalling and its main regulator, the NF-κB-inducing kinase (NIK), on pancreatic β-cell survival and function. Previous studies based on models of NIK overexpression in pancreatic islet cells showed that NIK induced either spontaneous β-cell death due to islet inflammation or glucose intolerance during diet-induced obesity (DIO) in mice. Therefore, NIK has been proposed as a potential target for diabetes therapy. However, no clear studies showed whether inhibition of NIK improves diabetes development. Here we show that genetic silencing of NIK in pancreatic β-cells neither modifies diabetes incidence nor inflammatory responses in a mouse model of immune-mediated diabetes. Moreover, NIK silencing in DIO mice did not influence body weight gain, nor glucose metabolism. In vitro studies corroborated the in vivo findings in terms of β-cell survival, function, and downstream gene regulation. Taken together, our data suggest that NIK activation is dispensable for the development of diabetes.

The Pivotal Immunoregulatory Functions of Microglia and Macrophages in Glioma Pathogenesis and Therapy

Gliomas are mixed solid tumors composed of both neoplastic and nonneoplastic cells. In glioma microenvironment, the most common nonneoplastic and infiltrating cells are macrophages and microglia. Microglia are the exact phagocytes of the central nervous system, whereas macrophages are myeloid immune cells that are depicted with ardent phagocytosis. Microglia are heterogeneously located in almost all nonoverlapping sections of the brain as well as the spinal cord, while macrophages are derived from circulating monocytes. Microglia and macrophages utilize a variety of receptors for the detection of molecules, particles, and cells that they engulf. Both microglia and peripheral macrophages interact directly with vessels both in the periphery of and within the tumor. In glioma milieu, normal human astrocytes, glioma cells, and microglia all exhibited the ability of phagocytosing glioma cells and precisely apoptotic tumor cells. Also, microglia and macrophages are robustly triggered by the glioma via the expression of chemoattractants such as monocyte chemoattractant protein, stromal-derived factor-1, and macrophage-colony stimulating factor. Glioma-associated microglia and/or macrophages positively correlated with glioma invasiveness, immunosuppression, and patients' poor outcome, making these cells a suitable target for immunotherapeutic schemes.

The combination of TRAIL and the Smac mimetic LCL-161 induces an irreversible phenotypic change of MCF-7 breast cancer cells

BACKGROUND

Breast cancer is the most common malignancy affecting women. Although the prognosis generally is good, a substantial number of patients still suffer from relapse, emphasizing the need for novel treatments. Smac mimetics were developed to facilitate cell death by blocking inhibitor of apoptosis proteins (IAPs). It has been suggested that TNF-related apoptosis inducing ligand (TRAIL) can be used together with Smac mimetics to induce cancer cell death.

METHODS

Cell viability was studied with Trypan blue staining and Annexin V assay, siRNA was used to downregulate specific proteins, protein levels were estimated with Western blot, and mRNA levels were analyzed with qPCR, microarray and RNA-seq. For global expression, groups were compared with principal component analysis and the limma package in R. Gene enrichment was analyzed with Fisher's test. For other experiments, significance of difference was tested by one-way ANOVA, followed by Tukey's HSD test.

RESULTS

The combination of Smac mimetic LCL-161 and TRAIL induces an irreversible change in phenotype, but not cell death, of luminal MCF-7 breast cancer cells. The cells become small and circular and dissociate from each other and the effect could not be reversed by returning the cells to regular growth medium. The morphology change could be prevented by caspase inhibition using z-VAD-FMK and downregulation of caspase-8. Caspase-7 is also indicated to be of importance since downregulation of this caspase resulted in fewer morphologically changed cells. Enrichment analyses of changes in global gene expression demonstrated that genes associated with estrogen receptor (ER) signaling are downregulated, whereas nuclear factor kappa B- (NF-κB) and interferon- (IFN) driven genes are upregulated in altered cells. However, inhibition of these pathways did not influence the change in morphology. Induction of IFN-induced genes were potentiated but NF-ĸB-driven genes were slightly suppressed by caspase inhibition.

CONCLUSIONS

The results demonstrate that LCL-161 and TRAIL can irreversibly alter the MCF-7 breast cancer cell phenotype. However, the changes in morphology and global gene expression are mediated via separate pathways.

High expression of cluster of differentiation 276 indicates poor prognosis in glioma

Background

Glioma is the central nervous system tumor with the highest incidence rate and the molecular detection of gliomas has been the focus of research. This study aimed to investigate the guiding effect of cluster of differentiation 276 (CD276) expression on the clinical prognosis of glioma.

Methods

The TCGA and CGGA databases were used to study whether CD 276 can be used as an independent prognostic factor for gliomas. Immunohistochemistry was used to detect the expression of CD276, isocitrate dehydrogenase-1 (IDH1), matrix metallopeptidase 9 (MMP9), p53, and Ki-67, and 1p/19q co-deletion was detected by fluorescence in situ hybridization (FISH). The effects of CD276 RNA interference (RNAi) on cell invasion, cell cycle and the expression of β-catenin, tumor necrosis factor receptor 1 (TNFR1), and MMP9 were observed. Furthermore, the biological effects of CD276 gene knockout on intracranial transplanted tumors in nude mice were studied.

Results

CD276 expression was positively correlated with the extracellular matrix, collagen decomposition, and cell adhesion molecules. Immunohistochemistry and FISH showed that CD276 expression positively correlated with the glioma grade, p53 mutation, Ki-67 proliferation, and MMP9 expression; however, it negatively correlated with IDH1 mutation, 1p/19q co-deletion, and the survival rate. CD276 RNAi in U87 cells inhibited cell proliferation, migration, and invasion, but had no effect on the cell cycle. CD276 inhibited the expression of β-catenin, TNFR1, and MMP9 in U87 cells at the mRNA and protein levels. In vivo experiments showed that the tumor formation and invasion of the CD276 small interfering RNA glioma cell line in nude mice were reduced and the survival time was prolonged.

Conclusions

The present study demonstrated that high expression of CD276 in gliomas indicates a poor prognosis.

RelB and Neuroinflammation

Neuroinflammation within the central nervous system involves multiple cell types that coordinate their responses by secreting and responding to a plethora of inflammatory mediators. These factors activate multiple signaling cascades to orchestrate initial inflammatory response and subsequent resolution. Activation of NF-κB pathways in several cell types is critical during neuroinflammation. In contrast to the well-studied role of p65 NF-κB during neuroinflammation, the mechanisms of RelB activation in specific cell types and its roles during neuroinflammatory response are less understood. In this review, we summarize the mechanisms of RelB activation in specific cell types of the CNS and the specialized effects this transcription factor exerts during neuroinflammation.

Smac mimetics can provoke lytic cell death that is neither apoptotic nor necroptotic

Smac mimetics, or IAP antagonists, are a class of drugs currently being evaluated as anti-cancer therapeutics. These agents antagonize IAP proteins, including cIAP1/2 and XIAP, to induce cell death via apoptotic or, upon caspase-8 deficiency, necroptotic cell death pathways. Many cancer cells are unresponsive to Smac mimetic treatment as a single agent but can be sensitized to killing in the presence of the cytokine TNFα, provided either exogenously or via autocrine production. We found that high concentrations of a subset of Smac mimetics could provoke death in cells that did not produce TNFα, despite sensitization at lower concentrations by TNFα. The ability of these drugs to kill did not correlate with valency. These cells remained responsive to the lethal effects of Smac mimetics at high concentrations despite genetic or pharmacological impairments in apoptotic, necroptotic, pyroptotic, autophagic and ferroptotic cell death pathways. Analysis of dying cells revealed necrotic morphology, which was accompanied by the release of lactate dehydrogenase and cell membrane rupture without prior phosphatidylserine exposure implying cell lysis, which occurred over a several hours. Our study reveals that cells incapable of autocrine TNFα production are sensitive to some Smac mimetic compounds when used at high concentrations, and this exposure elicits a lytic cell death phenotype that occurs via a mechanism not requiring apoptotic caspases or necroptotic effectors RIPK3 or MLKL. These data reveal the possibility that non-canonical cell death pathways can be triggered by these drugs when applied at high concentrations.

OTUD7B suppresses Smac mimetic-induced lung cancer cell invasion and migration via deubiquitinating TRAF3

Background

Smac mimetics are a type of drug that can induce apoptosis by antagonizing IAP family members in cancer treatment. However, a recent study showed that Smac mimetics can trigger cell invasion and migration in cancer cells by activating the NF-κB pathway.

Methods

We assessed lung cancer cell elongation, invasion and migration under treatment with the Smac mimetic LCL161. Functional analyses (in vitro and in vivo) were performed to detect the contribution of NIK and OTUD7B to LCL161-induced cell invasion and migration. The role of OTUD7B in regulation of the TRAF3/NIK/NF-κB pathway under LCL161 treatment was analysed by immunoblotting, immunoprecipitation, luciferase and ubiquitin assays, shRNA silencing and plasmid overexpression. Expression levels of OTUD7B, NIK and TRAF3 in tissue samples from lung cancer patients were examined by immunohistochemistry.

Results

We found that LCL161 stimulates lung cancer cell elongation, invasion and migration at non-toxic concentrations. Mechanistically, LCL161 results in NIK accumulation and activates the non-canonical rather than the canonical NF-κB pathway to enhance the transcription of target genes, such as IL-2 and MMP-9. Importantly, knockdown of NIK dramatically suppresses LCL161-induced cell invasion and migration by reducing the proteolytic processing of p100 to p52 and target gene transcription. Interestingly, we discovered that OTUD7B increases TRAF3 and decreases NIK to inhibit the non-canonical NF-κB pathway and that overexpression of OTUD7B suppresses LCL161-induced cell invasion and migration. Notably, OTUD7B directly binds to TRAF3 rather than to NIK and deubiquitinates TRAF3, thereby inhibiting TRAF3 proteolysis and preventing NIK accumulation and NF-κB pathway activation. Furthermore, the OTU domain of OTUD7B is required for the inhibition of LCL161-induced cell invasion and migration, as demonstrated by transfection of the C194S/H358R(CH) mutant OTUD7B. Finally, we investigated whether OTUD7B inhibits LCL161-induced lung cancer cell intrapulmonary metastasis in vivo, and our analysis of clinical samples was consistent with the above findings.

Conclusions

Our study highlights the importance of OTUD7B in the suppression of LCL161-induced lung cancer cell invasion and migration, and the results are meaningful for selecting lung cancer patients suitable for LCL161 treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01751-3.

Targeting NF-κB-Inducing Kinase (NIK) in Immunity, Inflammation, and Cancer

NF-κB-inducing kinase (NIK), the essential upstream kinase, which regulates activation of the noncanonical NF-κB pathway, has important roles in regulating immunity and inflammation. In addition, NIK is vital for maintaining cellular health through its control of fundamental cellular processes, including differentiation, growth, and cell survival. As such aberrant expression or regulation of NIK is associated with several disease states. For example, loss of NIK leads to severe immune defects, while the overexpression of NIK is observed in inflammatory diseases, metabolic disorders, and the development and progression of cancer. This review discusses recent studies investigating the therapeutic potential of NIK inhibitors in various diseases.

Expression and clinical significance of CXC chemokines in the glioblastoma microenvironment

BACKGROUND

Glioblastoma (GBM) is the most common subtype of brain cancer, encompassing 16% of all primary brain cancers. The prognosis of GBM is poor, with a 5-year-survial of approximately 5%. Increasing evidence has revealed that chemokines in the tumor microenvironment (TME) are often altered, thus affecting tumor proliferation and metastasis.

METHOD

Multi-omics and bioinformatics tools were utilized to clarify the role of CXC chemokine in GBM.

RESULT

Most CXC chemokines were found to be differentially regulated in GBM, which correlated with patient prognosis. CXC chemokines were found to activate cancer-related signaling pathways, thus affecting immune infiltration. Interestingly, this was found to be associated with drug resistance. Most CXC chemokines were significantly correlated with abundance of B cells, CD8+ cells and dendritic cells. Furthermore, somatic copy number alterations of CXC chemokines can inhibit dendritic cell infiltration. Moreover, CXCL1 was selected as a hub gene, and several kinase, miRNA and transcription factor targets of CXCL1 were identified.

CONCLUSION

our study provides novel insights into CXC chemokine expression and their role in the GBM microenvironment. These results are able to provide more data about prognostic biomarkers and therapeutic targets of GBM.

In vitro analysis reveals necroptotic signaling does not provoke DNA damage or HPRT mutations

Most anticancer drugs provoke apoptotic signaling by damaging DNA or other means. Genotoxic therapies may enhance a patient’s risk of developing “therapy-related cancers” due to the accumulation of oncogenic mutations that may occur in noncancerous cells. Mutations can also form upon apoptotic signaling due to sublethal caspase activity, implying that apoptosis activating drugs may also be oncogenic. Necroptosis is a different way of killing cancer cells: this version of caspase-independent cell death is characterized by receptor-interacting protein kinase-3 (RIPK3) and mixed lineage kinase-like domain protein (MLKL) activation, leading to cell membrane rupture and controlled cell lysis. The mutagenic potential of sublethal necroptotic signaling has not yet been directly investigated. Smac mimetics drugs, which activate apoptotic or necroptotic cell death, do not induce mutations but the mechanistic basis for this lack of mutagenic activity has not been determined. In this study, we compared the mutagenic potential of these two cell death pathways by engineering cells to activate either apoptotic or necroptotic signaling by exposing them to Smac mimetics with or without TNFα, and/or enforcing or preventing expression of apoptotic or necroptotic regulators. We discovered that sublethal concentrations of Smac mimetics in contexts that activated apoptotic signaling provoked DNA damage and mutations in surviving cells. Mutagenesis was dependent on executioner caspase activation of the nuclease CAD. In contrast, RIPK3- and MLKL-dependent necroptotic signaling following Smac mimetic treatment was not mutagenic. Likewise, DNA damage was not provoked in cells expressing a lethal constitutively active MLKL mutant. These data reveal that cells surviving sublethal necroptotic signaling do not sustain genomic damage and provide hope for a reduced risk of therapy-related malignancies in patients treated with necroptosis-inducing drugs.

Roles of miR-640 and Zinc Finger Protein 91 (ZFP91) in Angiopoietin-1-Induced In Vitro Angiogenesis

Angiopoietin-1 (Ang-1) is a ligand of Tie-2 receptors that promotes angiogenesis. It has been established that regulatory loops exist between angiogenic growth factors and distinct pro or anti-angiogenic miRNAs, but the nature and the roles of Ang-1-regulated miRNAs remain unclear. In this study, we assessed the role of miR-640 in Ang-1-induced angiogenesis in human umbilical vein endothelial cells (HUVECs). Exposure to Ang-1 (300 ng/mL) from 6 to 72 h significantly decreased expression of mature miR-640, a response that was mediated by Tie-2 receptors and was also observed in response to Ang-2, the vascular endothelial growth factor, and transforming growth factor β. Increasing miR-640 levels using a mimic inhibited Ang-1-induced cell migration and capillary-like tube formation whereas inhibition of miR-640 enhanced these responses. Pull down assays of biotinylated miR-640 revealed that miR-640 directly targets Zinc Finger Protein 91 (ZFP91), an atypical E3-ubiquitin ligase. Ang-1 exposure induced ZFP91 expression through down-regulation of miR-640. Silencing of ZFP91 significantly inhibited Ang-1-induced cell migration and tube formation. We conclude that Ang-1 upregulates ZFP91 expression through transcriptional down-regulation of miR-640 and that ZFP91 plays important roles in the promotion of Ang-1-induced endothelial cell migration and differentiation.

4-1BB costimulation promotes CAR T cell survival through noncanonical NF-κB signaling

Clinical response to chimeric antigen receptor (CAR) T cell therapy is correlated with CAR T cell persistence, especially for CAR T cells that target CD19⁺ hematologic malignancies. 4-1BB-costimulated CAR (BBζ) T cells exhibit longer persistence after adoptive transfer than do CD28-costimulated CAR (28ζ) T cells. 4-1BB signaling improves T cell persistence even in the context of 28ζ CAR activation, which indicates distinct prosurvival signals mediated by the 4-1BB cytoplasmic domain. To specifically study signal transduction by CARs, we developed a cell-free, ligand-based activation and ex vivo culture system for CD19-specific CAR T cells. We observed greater ex vivo survival and subsequent expansion of BBζ CAR T cells when compared to 28ζ CAR T cells. We showed that only BBζ CARs activated noncanonical nuclear factor κB (ncNF-κB) signaling in T cells basally and that the anti-CD19 BBζ CAR further enhanced ncNF-κB signaling after ligand engagement. Reducing ncNF-κB signaling reduced the expansion and survival of anti-CD19 BBζ T cells and was associated with a substantial increase in the abundance of the most pro-apoptotic isoforms of Bim. Although our findings do not exclude the importance of other signaling differences between BBζ and 28ζ CARs, they demonstrate the necessary and nonredundant role of ncNF-κB signaling in promoting the survival of BBζ CAR T cells, which likely underlies the engraftment persistence observed with this CAR design.

Codelivery of STAT3 siRNA and BV6 by carboxymethyl dextran trimethyl chitosan nanoparticles suppresses cancer cell progression

High expression of inhibitor of apoptosis (IAP) molecules in cancer cells promotes cancer cell chemoresistance. Use of BV6, a well-known IAP inhibitor, along with inhibition of signal transducer and activator of transcription 3 (STAT3), which is an important factor in the survival of tumor cells, and NIK as a mediator of BV6 unpredicted side effects, can induce effective apoptosis in tumor cells. The present study has investigated the combination therapy of cancer cells using Carboxymethyl Dextran-conjugated trimethyl chitosan (TMC-CMD) nanoparticles (NPs) loaded with NIK/STAT3-specific siRNA and BV6 to synergistically induce apoptosis in the breast, colorectal and melanoma cancer cell lines. Our results showed that in addition to enhanced pro-apoptotic effects, this combination therapy reduced proliferation, cell migration, colony formation, and angiogenesis, along with expression of factors including IL-10 and HIF in tumor cells. The results indicate the potential of this combination therapy for further investigation in animal models of cancer.

Effects of epigenetic pathway inhibitors on corticotroph tumour AtT20 cells

Medical treatments for corticotrophinomas are limited, and we therefore investigated the effects of epigenetic modulators, a new class of anti-tumour drugs, on the murine adrenocorticotropic hormone (ACTH)-secreting corticotrophinoma cell line AtT20. We found that AtT20 cells express members of the bromo and extra-terminal (BET) protein family, which bind acetylated histones, and therefore, studied the anti-proliferative and pro-apoptotic effects of two BET inhibitors, referred to as (+)-JQ1 (JQ1) and PFI-1, using CellTiter Blue and Caspase Glo assays, respectively. JQ1 and PFI-1 significantly decreased proliferation by 95% (P < 0.0005) and 43% (P < 0.0005), respectively, but only JQ1 significantly increased apoptosis by >50-fold (P < 0.0005), when compared to untreated control cells. The anti-proliferative effects of JQ1 and PFI-1 remained for 96 h after removal of the respective compound. JQ1, but not PFI-1, affected the cell cycle, as assessed by propidium iodide staining and flow cytometry, and resulted in a higher number of AtT20 cells in the sub G1 phase. RNA-sequence analysis, which was confirmed by qRT-PCR and Western blot analyses, revealed that JQ1 treatment significantly altered expression of genes involved in apoptosis, such as NFκB, and the somatostatin receptor 2 (SSTR2) anti-proliferative signalling pathway, including SSTR2. JQ1 treatment also significantly reduced transcription and protein expression of the ACTH precursor pro-opiomelanocortin (POMC) and ACTH secretion by AtT20 cells. Thus, JQ1 treatment has anti-proliferative and pro-apoptotic effects on AtT20 cells and reduces ACTH secretion, thereby indicating that BET inhibition may provide a novel approach for treatment of corticotrophinomas.

Molecular and Clinical Insights into the Invasive Capacity of Glioblastoma Cells

The invasive capacity of GBM is one of the key tumoral features associated with treatment resistance, recurrence, and poor overall survival. The molecular machinery underlying GBM invasiveness comprises an intricate network of signaling pathways and interactions with the extracellular matrix and host cells. Among them, PI3k/Akt, Wnt, Hedgehog, and NFkB play a crucial role in the cellular processes related to invasion. A better understanding of these pathways could potentially help in developing new therapeutic approaches with better outcomes. Nevertheless, despite significant advances made over the last decade on these molecular and cellular mechanisms, they have not been translated into the clinical practice. Moreover, targeting the infiltrative tumor and its significance regarding outcome is still a major clinical challenge. For instance, the pre- and intraoperative methods used to identify the infiltrative tumor are limited when trying to accurately define the tumor boundaries and the burden of tumor cells in the infiltrated parenchyma. Besides, the impact of treating the infiltrative tumor remains unclear. Here we aim to highlight the molecular and clinical hallmarks of invasion in GBM.

RelB acts as a molecular switch driving chronic inflammation in glioblastoma multiforme

Glioblastoma multiforme (GBM) is a primary brain tumor characterized by extensive necrosis and immunosuppressive inflammation. The mechanisms by which this inflammation develops and persists in GBM remain elusive. We identified two cytokines interleukin-1β (IL-1) and oncostatin M (OSM) that strongly negatively correlate with patient survival. We found that these cytokines activate RelB/p50 complexes by a canonical NF-κB pathway, which surprisingly drives expression of proinflammatory cytokines in GBM cells, but leads to their inhibition in non-transformed astrocytes. We discovered that one allele of the gene encoding deacetylase Sirtuin 1 (SIRT1), needed for repression of cytokine genes, is deleted in 80% of GBM tumors. Furthermore, RelB specifically interacts with a transcription factor Yin Yang 1 (YY1) in GBM cells and activates GBM-specific gene expression programs. As a result, GBM cells continuously secrete proinflammatory cytokines and factors attracting/activating glioma-associated microglia/macrophages and thus, promote a feedforward inflammatory loop.

NF-κB contributes to Smac mimetic-conferred protection from tunicamycin-induced apoptosis

Smac mimetics that deplete cellular inhibitor of apoptosis (cIAP) proteins have been shown to activate Nuclear Factor-kappa B (NF-κB). Here, we report that Smac mimetic-mediated activation of NF-κB contributes to the rescue of cancer cells from tunicamycin (TM)-triggered apoptosis. The prototypic Smac mimetic BV6 activates non-canonical and canonical NF-κB pathways, while TM has little effect on NF-κB signaling. Importantly, ectopic expression of dominant-negative IκBα superrepressor (IκBα-SR), which inhibits canonical and non-canonical NF-κB activation, significantly reversed this BV6-imposed protection against TM. Similarly, transient or stable knockdown of NF-κB-inducing kinase, which accumulated upon exposure to BV6 alone and in combination with TM, significantly counteracted BV6-mediated inhibition of TM-induced apoptosis. Interestingly, while cIAP2 was initially degraded upon BV6 treatment, it was subsequently upregulated in an NF-κB-dependent manner, as this restoration of cIAP2 expression was abolished in IκBα-SR-overexpressing cells. Interestingly, upon exposure to TM/BV6 apoptosis was significantly increased in cIAP2 knockdown cells. Furthermore, NF-κB inhibition partially prevented BV6-stimulated expression of Mcl-1 upon TM treatment. Consistently, Mcl-1 silencing significantly inhibited BV6-mediated protection from TM-induced apoptosis. Thus, NF-κB activation by Smac mimetic contributes to Smac mimetic-mediated protection against TM-induced apoptosis.

Inhibitor of Apoptosis Proteins Determines Glioblastoma Stem-Like Cell Fate in an Oxygen-Dependent Manner

In glioblastomas, apoptosis inhibitor proteins (IAPs) are involved in apoptotic and nonapoptotic processes. We previously showed that IAP inhibition induced a loss of stemness and glioblastoma stem cells differentiation by activating nuclear factor-κB under normoxic conditions. Hypoxia has been shown to modulate drug efficacy. Here, we investigated how IAPs participate in glioblastoma stem-like cell maintenance and fate under hypoxia. We showed that in a hypoxic environment, IAPs inhibition by GDC-0152, a small-molecule IAPs inhibitor, triggered stem-like cell apoptosis and decreased proliferation in four human glioblastoma cell lines. We set up a three-dimensional glioblastoma spheroid model in which time-of-flight secondary ion mass spectrometry analyses revealed a decrease in oxygen levels between the periphery and core. We observed low proliferative and apoptotic cells located close to the hypoxic core of the spheres and glial fibrillary acidic protein⁺ cells at their periphery. These oxygen-dependent GDC-0152 antitumoral effects have been confirmed on human glioblastoma explants. Notably, serine-threonine kinase activation analysis revealed that under hypoxic conditions, IAP inhibition activated ataxia telangiectasia and Rad3-related protein signaling. Our findings provide new insights into the dual mechanism of action of IAP inhibitors that depends on oxygen level and are relevant to their therapeutic application in tumors. Stem Cells 2019;37:731-742.

Sustained NF-κB-STAT3 signaling promotes resistance to Smac mimetics in Glioma stem-like cells but creates a vulnerability to EZH2 inhibition

Glioblastoma is an incurable and highly aggressive brain tumor. Understanding therapeutic resistance and survival mechanisms driving this tumor type is key to finding effective therapies. Smac mimetics (SM) emerged as attractive cancer therapeutics particularly for tumor populations that are highly resistant to conventional apoptosis-inducing therapies. We evaluated the therapeutic efficacy of SM on Glioma stem-like cells (GSCs) and showed that this family of compounds stimulates an adaptive response triggered by TNFα. Increased expression of TNFα results in a prolonged and sustained activation of NF-κB and STAT3 signaling thus activating several tumor cell resistance mechanisms in GSCs. We show that STAT3 activation is contingent on EZH2 activation and uncover a synergistic lethality between SM and EZH2 inhibitors. Therapeutic inhibition of EZH2 impaired the viability of SM-treated GSCs. Our study outlines the molecular underpinnings of SM resistance in glioblastoma and provides mechanistic insight to overcome this resistance and increase therapeutic efficacy.

Smac mimetic suppresses tunicamycin-induced apoptosis via resolution of ER stress

Since Inhibitor of Apoptosis (IAP) proteins have been implicated in cellular adaptation to endoplasmic reticulum (ER) stress, we investigated the regulation of ER stress-induced apoptosis by small-molecule second mitochondria-derived activator of caspase (Smac) mimetics that antagonize IAP proteins. Here, we discover that Smac mimetic suppresses tunicamycin (TM)-induced apoptosis via resolution of the unfolded protein response (UPR) and ER stress. Smac mimetics such as BV6 selectively inhibit apoptosis triggered by pharmacological or genetic inhibition of protein N-glycosylation using TM or knockdown of DPAGT1, the enzyme that catalyzes the first step of protein N-glycosylation. In contrast, BV6 does not rescue cell death induced by other typical ER stressors (i.e., thapsigargin (TG), dithiothreitol, brefeldin A, bortezomib, or 2-deoxyglucose). The protection from TM-triggered apoptosis is found for structurally different Smac mimetics and for genetic knockdown of cellular IAP (cIAP) proteins in several cancer types, underlining the broader relevance. Interestingly, lectin microarray profiling reveals that BV6 counteracts TM-imposed inhibition of protein glycosylation. BV6 consistently abolishes TM-stimulated accumulation of ER stress markers such as glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) and reduces protein kinase RNA-like ER kinase (PERK) phosphorylation and X box-binding protein 1 (XBP1) splicing upon TM treatment. BV6-stimulated activation of nuclear factor-κB (NF-κB) contributes to the resolution of ER stress, since NF-κB inhibition by overexpression of dominant-negative IκBα superrepressor counteracts the suppression of TM-stimulated transcriptional activation of CHOP and GRP78 by BV6. Thus, our study is the first to show that Smac mimetic protects from TM-triggered apoptosis by resolving the UPR and ER stress. This provides new insights into the regulation of cellular stress responses by Smac mimetics.

Targeting the BIR Domains of Inhibitor of Apoptosis (IAP) Proteins in Cancer Treatment

Inhibitor of apoptosis (IAP) proteins are characterized by the presence of the conserved baculoviral IAP repeat (BIR) domain that is involved in protein-protein interactions. IAPs were initially thought to be mainly responsible for caspase inhibition, acting as negative regulators of apoptosis, but later works have shown that IAPs also control a plethora of other different cellular pathways. As X-linked IAP (XIAP), and other IAP, levels are often deregulated in cancer cells and have been shown to correlate with patients' prognosis, several approaches have been pursued to inhibit their activity in order to restore apoptosis. Many small molecules have been designed to target the BIR domains, the vast majority being inspired by the N-terminal tetrapeptide of Second Mitochondria-derived Activator of Caspases/Direct IAp Binding with Low pI (Smac/Diablo), which is the natural XIAP antagonist. These compounds are therefore usually referred to as Smac mimetics (SMs). Despite the fact that SMs were intended to specifically target XIAP, it has been shown that they also interact with cellular IAP-1 (cIAP1) and cIAP2, promoting their proteasome-dependent degradation. SMs have been tested in combination with several cytotoxic compounds and are now considered promising immune modulators which can be exploited in cancer therapy, especially in combination with immune checkpoint inhibitors. In this review, we give an overview of the structural hot-spots of BIRs, focusing on their fold and on the peculiar structural patches which characterize the diverse BIRs. These structures are exploited/exploitable for the development of specific and active IAP inhibitors.

Smac mimetics as novel promising modulators of apoptosis in the treatment of breast cancer

Breast cancer is the most prevalent cancer in women. Despite improvements in treatment, the rate of breast cancer-related deaths is still high, and this issue needs further, accurate investigations. Although several treatment options are available, none of them are efficient for complete remission, particularly in advanced stages of the disease. It is known that cancerous cells have dysregulated apoptosis-related pathways, by which they can remain alive for a long time, expand freely, and escape from apoptosis-inducing drugs or antitumor immune responses. Therefore, modulation of apoptosis resistance in cancer cells may be an efficient strategy to overcome current problems faced in the development of immunotherapeutic approaches for the treatment of breast cancer. The inhibitors of apoptosis protein (IAPs) are important targets for cancer therapy because it has been shown that these molecules are overexpressed and highly active in various cancer cells and suppress apoptosis process in malignant cells by blockage of caspase proteins. There is evidence of Smac mimetics efficacy as a single agent; however, recent studies have indicated the efficacy of current anticancer immunotherapeutic approaches when combined with Smac mimetics, which are potent inhibitors of IAPs and synthesized mimicking Smac/Diablo molecules. In this review, we are going to discuss the efficacy of treatment of breast cancer by Smac mimetics alone or in combination with other therapeutics.

The Multiple Roles of Peptidyl Prolyl Isomerases in Brain Cancer

Peptidyl prolyl isomerases (PPIases) are broadly expressed enzymes that accelerate the cis-trans isomerization of proline peptide bonds. The most extensively studied PPIase family member is protein interacting with never in mitosis A1 (PIN1), which isomerizes phosphorylated serine/threonine–proline bonds. By catalyzing this specific cis-trans isomerization, PIN1 can alter the structure of its target proteins and modulate their activities in a number of different ways. Many proteins are targets of proline-directed phosphorylation and thus PIN1-mediated isomerization of proline bonds represents an important step in the regulation of a variety of cellular mechanisms. Numerous other proteins in addition to PIN1 are endowed with PPIase activity. These include other members of the parvulin family to which PIN1 belongs, such as PIN4, as well as several cyclophilins and FK506-binding proteins. Unlike PIN1, however, these other PPIases do not isomerize phosphorylated serine/threonine–proline bonds and have different substrate specificities. PIN1 and other PPIases are overexpressed in many types of cancer and have been implicated in various oncogenic processes. This review will discuss studies providing evidence for multiple roles of PIN1 and other PPIases in glioblastoma and medulloblastoma, the most frequent adult and pediatric primary brain tumors.

Cell death-based treatment of glioblastoma

Cancer cells including glioblastoma have typically evolved multiple mechanisms to escape programmed cell death in order to maintain their survival. Defects in cell death mechanisms not only facilitate tumorigenesis but also ensure resistance to current anticancer therapies. This emphasizes that targeting cell death pathways may provide a means to tackle one of the Achilles' heels of cancer. Over the last decades several approaches have been developed to selectively target cell death pathways for therapeutic purposes. Some of these concepts have already been transferred into clinical application in oncology and may open new perspectives for the treatment of cancer.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Microglia in Cancer: For Good or for Bad?

Glioblastoma is a malignant tumor of astrocytic origin that is highly invasive, proliferative and angiogenic. Despite current advances in multimodal therapies, such as surgery, radio- and chemotherapy, the outcome for patients with glioblastoma is nearly always fatal. The glioblastoma microenvironment has a tremendous influence over the tumor growth and spread. Microglia and macrophages are abundant cells in the tumor mass. Increasing evidence indicates that glioblastoma recruits these cell populations and signals in a way that microglia and macrophages are subverted to promote tumor progression. In this chapter, we discuss some aspects of the interaction between microglia and glioblastoma, consequences of this interaction for tumor progression and the possibility of microglial cells being used as therapeutic vectors, which opens up new alternatives for the development of GBM therapies targeting microglia.

NF-κB Signalling in Glioblastoma

Nuclear factor-κB (NF-κB) is a transcription factor regulating a wide array of genes mediating numerous cellular processes such as proliferation, differentiation, motility and survival, to name a few. Aberrant activation of NF-κB is a frequent event in numerous cancers, including glioblastoma, the most common and lethal form of brain tumours of glial cell origin (collectively termed gliomas). Glioblastoma is characterized by high cellular heterogeneity, resistance to therapy and almost inevitable recurrence after surgery and treatment. NF-κB is aberrantly activated in response to a variety of stimuli in glioblastoma, where its activity has been implicated in processes ranging from maintenance of cancer stem-like cells, stimulation of cancer cell invasion, promotion of mesenchymal identity, and resistance to radiotherapy. This review examines the mechanisms of NF-κB activation in glioblastoma, the involvement of NF-κB in several mechanisms underlying glioblastoma propagation, and discusses some of the important questions of future research into the roles of NF-κB in glioblastoma.

cIAP2 promotes gallbladder cancer invasion and lymphangiogenesis by activating the NF-κB pathway

Several studies have produced contradictory findings about the prognostic implications for inhibitor of apoptosis proteins (IAP) in different types of cancer. Cellular inhibitor of apoptosis 2 (cIAP2/BIRC) is one of the most extensively characterized human IAP. To date, no studies have focused on the expression level of cIAP2 in human gallbladder cancer (GBC), and the mechanism of cIAP2 in GBC invasion and lymphangiogenesis remains unclear. Therefore, in the present study, cIAP2 expression in GBC was detected using quantitative real‐time polymerase chain reaction and immunohistochemistry, and the relationship between cIAP2 levels in cancer tissues and the clinicopathological characteristics of patients was analyzed. The biological effect of cIAP2 in GBC cells was tested using the Cell Counting Kit‐8 Assay, Transwell assays and the ability of human dermal lymphatic endothelial cells (HDLEC) to undergo tube formation. The role of cIAP2 in activating the NF‐κB pathway was determined using a dual‐luciferase reporter assay, immunofluorescence staining, western blotting and ELISA. Finally, an animal model was used to further confirm the role of cIAP2 in lymphangiogenesis. We showed that cIAP2 expression was elevated in human GBC tissues and correlated with a negative prognosis for patients. Moreover, cIAP2 was identified as a lymphangiogenic factor of GBC cells and, thus, promoted lymph node metastasis in GBC cells. Our study is the first to suggest that cIAP2 can promote GBC invasion and lymphangiogenesis by activating the NF‐κB pathway.

The Smac Mimetic BV6 Improves NK Cell-Mediated Killing of Rhabdomyosarcoma Cells by Simultaneously Targeting Tumor and Effector Cells

Rhabdomyosarcoma (RMS), the most common cancer of connective tissues in pediatrics, is often resistant to conventional therapies. One underlying mechanism of this resistance is the overexpression of Inhibitor of Apoptosis (IAP) proteins, leading to a dysfunctional cell death program within tumor cells. Smac mimetics (SM) are small molecules that can reactivate the cell death program by antagonizing IAP proteins and thereby compensating their overexpression. Here, we report that SM sensitize two RMS cell lines (RD and RH30) toward natural killer (NK) cell-mediated killing on the one hand, and increase the cytotoxic potential of NK cells on the other. The SM-induced sensitization of RH30 cells toward NK cell-mediated killing is significantly reduced through blocking tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on NK cells prior to coculture. In addition, the presence of zVAD.fmk, a pancaspase inhibitor, rescues tumor cells from the increase in killing, indicating an apoptosis-dependent cell death. On the NK cell side, the presence of SM in addition to IL-2 during the ex vivo expansion leads to an increase in their cytotoxic activity against RH30 cells. This effect is mainly TNFα-dependent and partially mediated by NK cell activation, which is associated with transcriptional upregulation of NF-κB target genes such as IκBα and RelB. Taken together, our findings implicate that SM represent a novel double-hit strategy, sensitizing tumor and activating NK cells with one single drug.

Cooperative TRAIL production mediates IFNα/Smac mimetic-induced cell death in TNFα-resistant solid cancer cells

Smac mimetics antagonize IAP proteins, which are highly expressed in several cancers. Recent reports indicate that Smac mimetics trigger a broad cytokine response and synergize with immune modulators to induce cell death. Here, we identify a differential requirement of TRAIL or TNFα as mediators of IFNα/Smac mimetic-induced cell death depending on the cellular context. Subtoxic concentrations of Smac mimetics cooperate with IFNα to induce cell death in various solid tumor cell lines in a highly synergistic manner as determined by combination index. Mechanistic studies show that IFNα/BV6 cotreatment promotes the formation of a caspase-8-activating complex together with the adaptor protein FADD and RIP1. Assembly of this RIP1/FADD/caspase-8 complex represents a critical event, since RIP1 silencing inhibits IFNα/BV6-induced cell death. Strikingly, pharmacological inhibition of paracrine/autocrine TNFα signaling by the TNFα scavenger Enbrel rescues HT-29 colon carcinoma cells, but not A172 glioblastoma cells from IFNα/BV6-induced cell death. By comparison, A172 cells are significantly protected against IFNα/BV6 treatment by blockage of TRAIL signaling through genetic silencing of TRAIL or its cognate receptor TRAIL receptor 2 (DR5). Despite this differential requirement of TNFα and TRAIL signaling, mRNA and protein expression is increased by IFNα/BV6 cotreatment in both cell lines. Interestingly, A172 cells turn out to be resistant to exogenously added recombinant TNFα even in the presence of BV6, whereas they display a high sensitivity towards TRAIL/BV6. In contrast, BV6 efficiently sensitizes HT-29 cells to TNFα while TRAIL only had limited efficacy. This demonstrates that a differential sensitivity towards TRAIL or TNFα determines the dependency on either death receptor ligand for IFNα/Smac mimetic-induced cell death. Thus, by concomitant stimulation of both death receptor systems IFNα/Smac mimetic combination treatment is an effective strategy to induce cell death in TNFα- or TRAIL-responsive cancers.

Promises and Challenges of Smac Mimetics as Cancer Therapeutics

Inhibitor of Apoptosis (IAP) proteins block programmed cell death and are expressed at high levels in various human cancers, thus making them attractive targets for cancer drug development. Second mitochondrial activator of caspases (Smac) mimetics are small-molecule inhibitors that mimic Smac, an endogenous antagonist of IAP proteins. Preclinical studies have shown that Smac mimetics can directly trigger cancer cell death or, even more importantly, sensitize tumor cells for various cytotoxic therapies, including conventional chemotherapy, radiotherapy, or novel agents. Currently, several Smac mimetics are under evaluation in early clinical trials as monotherapy or in rational combinations (i.e., GDC-0917/CUDC-427, LCL161, AT-406/Debio1143, HGS1029, and TL32711/birinapant). This review discusses the promise as well as some challenges at the translational interface of exploiting Smac mimetics as cancer therapeutics.

Targeting cell death signalling in cancer: minimising 'Collateral damage'

Targeting apoptosis for the treatment of cancer has become an increasingly attractive strategy, with agents in development to trigger extrinsic apoptosis via TRAIL signalling, or to prevent the anti-apoptotic activity of BCL-2 proteins or inhibitor of apoptosis (IAP) proteins. Although the evasion of apoptosis is one of the hallmarks of cancer, many cancers have intact apoptotic signalling pathways, which if unblocked could efficiently kill cancerous cells. However, it is becoming increasing clear that without a detailed understanding of both apoptotic and non-apoptotic signalling, and the key proteins that regulate these pathways, there can be dose-limiting toxicity and adverse effects associated with their modulation. Here we review the main apoptotic pathways directly targeted for anti-cancer therapy and the unforeseen consequences of their modulation. Furthermore, we highlight the importance of an in-depth mechanistic understanding of both the apoptotic and non-apoptotic functions of those proteins under investigation as anti-cancer drug targets and outline some novel approaches to sensitise cancer cells to apoptosis, thereby improving the efficacy of existing therapies when used in combination with novel targeted agents.

Smac Mimetic-Induced Upregulation of CCL2/MCP-1 Triggers Migration and Invasion of Glioblastoma Cells and Influences the Tumor Microenvironment in a Paracrine Manner

Second mitochondria-derived activator of caspase (Smac) mimetics are considered as promising anticancer therapeutics that are currently under investigation in early clinical trials. They induce apoptosis by antagonizing inhibitor of apoptosis proteins, which are frequently overexpressed in cancer. We previously reported that Smac mimetics, such as BV6, additionally exert non-apoptotic functions in glioblastoma (GBM) cells by stimulating migration and invasion in a nuclear factor kappa B (NF-κB)-dependent manner. Because NF-κB target genes mediating these effects are largely unknown, we performed whole-genome expression analyses. Here, we identify chemokine (C-C motif) ligand 2 (CCL2) as the top-listed NF-κB-regulated gene being upregulated upon BV6 treatment in GBM cells. BV6-induced upregulation and secretion of CCL2 are required for migration and invasion of GBM cells because knockdown of CCL2 in GBM cells abolishes these effects. Co-culture experiments of GBM cells with non-malignant astroglial cells reveal that BV6-stimulated secretion of CCL2 by GBM cells into the supernatant triggers migration of astroglial cells toward GBM cells because CCL2 knockdown in BV6-treated GBM cells impedes BV6-stimulated migration of astroglial cells. In conclusion, we identify CCL2 as a BV6-induced NF-κB target gene that triggers migration and invasion of GBM cells and exerts paracrine effects on the GBM's microenvironment by stimulating migration of astroglial cells. These findings provide novel insights into the biological functions of Smac mimetics with important implications for the development of Smac mimetics as cancer therapeutics.

Clipping the Wings of Glioblastoma: Modulation of WNT as a Novel Therapeutic Strategy

Glioblastoma (GBM) is the most malignant brain tumor and has a dismal prognosis. Aberrant WNT signaling is known to promote glioma cell growth and dissemination and resistance to conventional radio- and chemotherapy. Moreover, a population of cancer stem-like cells that promote glioma growth and recurrence are strongly dependent on WNT signaling. Here, we discuss the role and mechanisms of aberrant canonical and noncanonical WNT signaling in GBM. We present current clinical approaches aimed at modulating WNT activity and evaluate their clinical perspective as a novel treatment option for GBM.

PKC activation sensitizes basal-like breast cancer cell lines to Smac mimetics

There is a need for novel strategies to initiate cancer cell death. One approach is the use of Smac mimetics, which antagonize inhibitor of apoptosis proteins (IAPs). Recent studies have shown that combinations of Smac mimetics such as LBW242 or LCL161 in combination with chemotherapeutic agents increase cancer cell death. Here we show that the protein kinase C (PKC) activator TPA together with the Smac mimetic LBW242 induces cell death in two basal breast cancer cell lines (MDA-MB-468 and BT-549) that are resistant to Smac mimetic as single agent. Ten other LBW242-insensitive cancer cell lines were not influenced by the TPA+LBW242 combination. The TPA+LBW242 effect was suppressed by the PKC inhibitor GF109203X, indicating dependence on PKC enzymatic activity. The PKC effect was mediated via increased synthesis and release of TNFα, which can induce death in the presence of Smac mimetics. The cell death, coinciding with caspase-3 cleavage, was suppressed by caspase inhibition and preceded by the association of RIP1 with caspase-8, as seen in complex II formation. Smac mimetics, but not TPA, induced the non-canonical NF-κB pathway in both MDA-MB-231 and MDA-MB-468 cells. Blocking the canonical NF-κB pathway suppressed TPA induction of TNFα in MDA-MB-468 cells whereas isolated downregulation of either the canonical or non-canonical pathways did not abolish the Smac mimetic induction of the NF-κB driven genes TNFα and BIRC3 in MDA-MB-231 cells although the absolute levels were suppressed. A combined downregulation of the canonical and non-canonical pathways further suppressed TNFα levels and inhibited Smac mimetic-mediated cell death. Our data suggest that in certain basal breast cancer cell lines co-treatment of TPA with a Smac mimetic induces cell death highlighting the potential of using these pathways as molecular targets for basal-like breast cancers.

Molecular mechanisms of apoptosis and roles in cancer development and treatment

Programmed cell death (PCD) or apoptosis is a mechanism which is crucial for all multicellular organisms to control cell proliferation and maintain tissue homeostasis as well as eliminate harmful or unnecessary cells from an organism. Defects in the physiological mechanisms of apoptosis may contribute to different human diseases like cancer. Identification of the mechanisms of apoptosis and its effector proteins as well as the genes responsible for apoptosis has provided a new opportunity to discover and develop novel agents that can increase the sensitivity of cancer cells to undergo apoptosis or reset their apoptotic threshold. These novel targeted therapies include those targeting anti-apoptotic Bcl-2 family members, p53, the extrinsic pathway, FLICE-inhibitory protein (c-FLIP), inhibitor of apoptosis (IAP) proteins, and the caspases. In recent years a number of these novel agents have been assessed in preclinical and clinical trials. In this review, we introduce some of the key regulatory molecules that control the apoptotic pathways, extrinsic and intrinsic death receptors, discuss how defects in apoptotic pathways contribute to cancer, and list several agents being developed to target apoptosis.

Smac mimetic-induced upregulation of interferon-β sensitizes glioblastoma to temozolomide-induced cell death

Inhibitor of apoptosis (IAP) proteins are frequently expressed at high levels in cancer cells and represent attractive therapeutic targets. We previously reported that the Smac (second mitochondria-derived activator of caspases) mimetic BV6, which antagonizes IAP proteins, sensitizes glioblastoma cells to temozolomide (TMZ)-induced cell death in a nuclear factor-κB (NF-κB)-dependent manner. However, BV6-induced NF-κB target genes responsible for this synergistic interaction have remained elusive. Using whole-genome gene expression profiling, we here identify BV6-stimulated, NF-κB-dependent transcriptional upregulation of interferon-β (IFNβ) and IFN-mediated proapoptotic signaling as critical events that mediate BV6/TMZ-induced apoptosis. Knockdown of IFNβ significantly rescues cells from BV6/TMZ-induced cell death. Similarly, silencing of the corresponding receptor IFNα/β receptor (IFNAR) confers a significant protection against apoptosis, demonstrating that IFNβ and IFN signaling are required for BV6/TMZ-mediated cell death. Moreover, BV6 and TMZ cooperate to transcriptionally upregulate the proapoptotic B-cell lymphoma 2 family proteins Bax (Bcl-2-associated X protein) or Puma (p53-upregulated modulator of apoptosis). Knockdown of Bax or Puma significantly decreases BV6/TMZ-induced apoptosis, showing that both proteins are necessary for apoptosis. By identifying IFNβ as a key mediator of BV6/TMZ-induced apoptosis, our study provides novel insights into the underlying molecular mechanisms of Smac mimetic-mediated chemosensitization with important implications for the development of novel treatment strategies for glioblastoma.