Stress via p53 pathway causes apoptosis by mitochondrial Noxa upregulation in doxorubicin-treated neuroblastoma cells

A common cellular response to broad splicing perturbations is characterized by metabolic transcript downregulation driven by the Mdm2-p53 axis

Disruptions in core cellular processes elicit stress responses that drive cell-state changes leading to organismal phenotypes. Perturbations in the splicing machinery cause widespread mis-splicing, resulting in p53-dependent cell-state changes that give rise to cell-type-specific phenotypes and disease. However, a unified framework for how cells respond to splicing perturbations, and how this response manifests itself in nuanced disease phenotypes, has yet to be established. Here, we show that a p53-stabilizing Mdm2 alternative splicing event and the resulting widespread downregulation of metabolic transcripts are common events that arise in response to various splicing perturbations in both cellular and organismal models. Together, our results classify a common cellular response to splicing perturbations, put forth a new mechanism behind the cell-type-specific phenotypes that arise when splicing is broadly disrupted, and lend insight into the pleiotropic nature of the effects of p53 stabilization in disease.

The PRC2 molecule EED is a target of epigenetic therapy for neuroblastoma

Epigenetic modifications by polycomb repressive complex (PRC) molecules appear to play a role in the tumorigenesis and aggressiveness of neuroblastoma (NB). Embryonic ectoderm development (EED) is a member of the PRC2 complex that binds to the H3K27me3 mark deposited by EZH2 via propagation on adjacent nucleosomes. We herein investigated the molecular roles of EED in MYCN-amplified NB cells using EED-knockdown (KD) shRNAs, EED-knockout sgRNAs, and the EED small molecule inhibitor EED226. The suppression of EED markedly inhibited NB cell proliferation and flat and soft agar colony formation. A transcriptome analysis using microarrays of EED-KD NB cells indicated the de-repression of cell cycle-regulated and differentiation-related genes. The results of a GSEA analysis suggested that inhibitory cell cycle-regulated gene sets were markedly up-regulated. Furthermore, an epigenetic treatment with the EED inhibitor EED226 and the HDAC inhibitors valproic acid/SAHA effectively suppressed NB cell proliferation and colony formation. This combined epigenetic treatment up-regulated cell cycle-regulated and differentiation-related genes. The ChIP sequencing analysis of histone codes and PRC molecules suggested an epigenetic background for the de-repression of down-regulated genes in MYCN-amplified/PRC2 up-regulated NB.

Oridonin induces Mdm2-p60 to promote p53-mediated apoptosis and cell cycle arrest in neuroblastoma

Oridonin could induce NB (neuroblastoma) cells growth inhibition by inducing apoptosis and cell cycle arrest, and the molecular mechanisms behind the effects deserve to be further explored. Here, oridonin was confirmed to cause the reactivation of p53 (cellular tumor antigen p53) to promote the expression of a series of apoptosis‐ and cell cycle arrest‐related proteins for the biological effects. During the process, oridonin relied on the caspase activation to cleave p53‐induced Mdm2 (E3 ubiquitin‐protein ligase Mdm2) to generate Mdm2‐p60. The generation of Mdm2‐p60 stabilized p53, and resulted in p53 accumulation for p53 continuous activation. In our research, it was also found that the reactivation of p53 induced by oridonin was closely related with the generation of ROS (reactive oxygen species). Taken together, these findings explain that oridonin exerts its anticancer activity partially by targeting the Mdm2‐p53 axis in NB cells, which lay an experimental base for future research of exploring the effects and molecular mechanisms of oridonin.

CFC1 is a cancer stemness-regulating factor in neuroblastoma

Background

Despite the use of aggressive therapy, survival rates among high-risk neuroblastoma (NB) patients remain poor. Cancer stem cells (CSCs) are considered to be critically involved in the recurrence and metastasis of NB and are isolated as NB spheres.

Methods

The gene expression profiling of adherent (control) and sphere-forming primary NB cells was conducted using a gene expression microarray. CFC1, which functions in the development of embryos and decides the left-right axis, was strongly expressed in sphere-forming cells only and was related to the unfavorable prognosis of NB patients. The knockdown and overexpression of CFC1 were performed using a lentiviral system in NB cell lines. Sphere formation, cell proliferation, colony formation in soft agar, and xenograft tumor formation were analyzed.

Results

The overexpression of CFC1 increased sphere formation, cell growth, and colony formation. These phenotypes, particularly sphere formation, and xenograft tumor formation were significantly suppressed by the knockdown of CFC1. CFC1 inhibited Activin A-induced NB cell differentiation and Smad2 phosphorylation in NB cell lines, indicating its involvement in tumorigenesis related to EGF-CFC co-receptor family molecule pathways. Collectively, these results indicate that CFC1 is a candidate molecule for the development of CSC-targeted therapy for NB.

EZH2 regulates neuroblastoma cell differentiation via NTRK1 promoter epigenetic modifications

The polycomb repressor complex 2 molecule EZH2 is now known to play a role in essential cellular processes, namely, cell fate decisions, cell cycle regulation, senescence, cell differentiation, and cancer development/progression. EZH2 inhibitors have recently been developed; however, their effectiveness and underlying molecular mechanisms in many malignancies have not yet been elucidated in detail. Although the functional role of EZH2 in tumorigenesis in neuroblastoma (NB) has been investigated, mutations of EZH2 have not been reported. A Kaplan–Meier analysis on the event free survival and overall survival of NB patients indicated that the high expression of EZH2 correlated with an unfavorable prognosis. In order to elucidate the functional roles of EZH2 in NB tumorigenesis and its aggressiveness, we knocked down EZH2 in NB cell lines using lentivirus systems. The knockdown of EZH2 significantly induced NB cell differentiation, e.g., neurite extension, and the neuronal differentiation markers, NF68 and GAP43. EZH2 inhibitors also induced NB cell differentiation. We performed a comprehensive transcriptome analysis using Human Gene Expression Microarrays and found that NTRK1 (TrkA) is one of the EZH2-related suppression targets. The depletion of NTRK1 canceled EZH2 knockdown-induced NB cell differentiation. Our integrative methylome, transcriptome, and chromatin immunoprecipitation assays using NB cell lines and clinical samples clarified that the NTRK1 P1 and P2 promoter regions were regulated differently by DNA methylation and EZH2-related histone modifications. The NTRK1 transcript variants 1/2, which were regulated by EZH2-related H3K27me3 modifications at the P1 promoter region, were strongly expressed in favorable, but not unfavorable NB. The depletion and inhibition of EZH2 successfully induced NTRK1 transcripts and functional proteins. Collectively, these results indicate that EZH2 plays important roles in preventing the differentiation of NB cells and also that EZH2-related NTRK1 transcriptional regulation may be the key pathway for NB cell differentiation.

Mechanistic clues to the protective effect of chrysin against doxorubicin-induced cardiomyopathy: Plausible roles of p53, MAPK and AKT pathways

Doxorubicin (DOX) is the mainstay chemotherapeutic agent against a variety of human neoplasmas. However, its clinical utility is limited by its marked cardiotoxicity. Chrysin, is a natural flavone which possesses antioxidant, anti-inflammatory and anti-cancer properties. The current study aimed to investigate the potential protective effect of chrysin against DOX-induced chronic cardiotoxicity and the underlying molecular mechanisms. Male Sprague-Dawley rats were treated with either DOX (5 mg/kg, once a week) and/or chrysin (50 mg/kg, four times a week) for four weeks. Chrysin prevented DOX-induced cardiomyopathy which was evident by conduction abnormalities, elevated serum CKMB and LDH and histopathological changes. Chrysin also ameliorated DOX-induced oxidative stress by decreasing lipid peroxidation and upregulating the antioxidant enzymes. Moreover, chrysin attenuated DOX-induced apoptosis via decreasing expression of p53, Bax, Puma, Noxa, cytochrome c and caspase-3 while increasing expression of Bcl-2. DOX induced activation of MAPK; p38 and JNK and increased expression of NF-κB. Meanwhile, DOX suppressed AKT pathway via decreasing expression of its upstream activator VEGF and increasing expression of PTEN. Conversely, chrysin effectively neutralised all these effects. Collectively, these findings indicate that chrysin effectively protected against DOX-induced cardiomyopathy via suppressing oxidative stress, p53-dependent apoptotic pathway, MAPK and NF-κB pathways while augmenting the VEGF/AKT pathway.

Low Dose of Doxorubicin Potentiates the Effect of Temozolomide in Glioblastoma Cells

Glioblastoma (GBM) is an aggressive brain tumor with temozolomide (TMZ)-based chemotherapy as the main therapeutic strategy. Doxorubicin (DOX) is not used in gliomas due to its low bioavailability in the brain; however, new delivery strategies and low doses may be effective in the long term, especially as part of a drug cocktail. Our aim was to evaluate the chronic effects of low doses of DOX and TMZ in GBM. Human U87-ATCC cells and a primary GBM culture were chronically treated with TMZ (5 μM) and DOX (1 and 10 nM) alone or combined. DOX resulted in a reduction in the number of cells over a period of 35 days and delayed the cell regrowth. In addition, DOX induced cell senescence and reduced tumor sphere formation and the proportion of NANOG- and OCT4-positive cells after 7 days. Low doses of TMZ potentiated the effects of DOX on senescence and sphere formation. This combined response using low doses of DOX may pave the way for its use in glioma therapy, with new technologies to overcome its low blood-brain barrier permeability.

Inhibitory Effect of Ginseng on Breast Cancer Cell Line Growth Via Up-Regulation of Cyclin Dependent Kinase Inhibitor, p21 and p53

Objective:

Breast cancer is global female health problem worldwide. Most of the currently used agents for breast cancer treatment have toxic side-effects. Ginseng root, an oriental medicine, has many health benefits and may exhibit direct anti-cancer properties. This study was performed to assess the effects of ginseng on breast cancer cell lines.

Materials and Methods:

Cytotoxicity of ginseng extract was measured by MTT assay after exposure of MDA-MB-231, MCF-10A and MCF-7 breast cancer cells to concentrations of 0.25, 0.5, 1, 1.5, 2 and 2.5 mg/well. Expression levels of p21WAF, p16INK4A, Bcl-2, Bax and P53 genes were analyzed by quantitative real time PCR.

Results:

The treatment resulted in inhibition of cell proliferation in a dose-and time-dependent manner. p53, p21WAF1and p16INK4A expression levels were up-regulated in ginseng treated MDA-MB-231 and MCF-7 cancer cells compared to untreated controls and in MCF-10A cells. The expression levels of Bcl2 in the MDA-MB-231 and MCF-7 cells were down-regulated. In contrast, that of Bax was significantly up-regulated.

Conclusion:

The results of this study revealed that ginseng may inhibit breast cancer cell growth by activation of the apoptotic pathway.

Editor's Highlight: Hydroxyurea Exposure Activates the P53 Signaling Pathway in Murine Organogenesis-Stage Embryos

Hydroxyurea, an anticancer agent and potent teratogen, induces oxidative stress and activates a DNA damage response pathway in the gestation day (GD) 9 mouse embryo. To delineate the stress response pathways activated by this drug, we investigated the effect of hydroxyurea exposure on the transcriptome of GD 9 embryos. Timed pregnant CD-1 mice were treated with saline or hydroxyurea (400 mg/kg or 600 mg/kg) on GD 9; embryonic gene and protein expression were examined 3 h later. Microarray analysis revealed that the expression of 1346 probe sets changed significantly in embryos exposed to hydroxyurea compared with controls; the P53 signaling pathway was highly affected. In addition, P53 related family members, P63 and P73, were predicted to be activated and had common and unique downstream targets. Western blot analysis revealed that active phospho-P53 was significantly increased in drug-exposed embryos; confocal microscopy showed that the translocation of phospho-P53 to the nucleus was widespread in the embryo. Furthermore, qRT-PCR showed that the expression of P53-regulated genes (Cdkn1A, Fas, and Trp53inp1) was significantly upregulated in hydroxyurea-exposed embryos; the concentration of the redox sensitive P53INP1 protein was also increased in a hydroxyurea dose-dependent fashion. Thus, hydroxyurea elicits a significant effect on the transcriptome of the organogenesis stage murine embryo, activating several key developmental signaling pathways related to DNA damage and oxidative stress. We propose that the P53 pathway plays a central role in the embryonic stress response and the developmental outcome after teratogen exposure.

MTO1 mediates tissue specificity of OXPHOS defects via tRNA modification and translation optimization, which can be bypassed by dietary intervention

Mitochondrial diseases often exhibit tissue-specific pathologies, but this phenomenon is poorly understood. Here we present regulation of mitochondrial translation by the Mitochondrial Translation Optimization Factor 1, MTO1, as a novel player in this scenario. We demonstrate that MTO1 mediates tRNA modification and controls mitochondrial translation rate in a highly tissue-specific manner associated with tissue-specific OXPHOS defects. Activation of mitochondrial proteases, aberrant translation products, as well as defects in OXPHOS complex assembly observed in MTO1 deficient mice further imply that MTO1 impacts translation fidelity. In our mouse model, MTO1-related OXPHOS deficiency can be bypassed by feeding a ketogenic diet. This therapeutic intervention is independent of the MTO1-mediated tRNA modification and involves balancing of mitochondrial and cellular secondary stress responses. Our results thereby establish mammalian MTO1 as a novel factor in the tissue-specific regulation of OXPHOS and fine tuning of mitochondrial translation accuracy.

Nanoformulated cell-penetrating survivin mutant and its dual actions

In this study, we investigated the differential actions of a dominant-negative survivin mutant (SurR9-C84A) against cancerous SK-N-SH neuroblastoma cell lines and differentiated SK-N-SH neurons. In both the cases, the mutant protein displayed dual actions, where its effects were cytotoxic toward cancerous cells and proliferative toward the differentiated neurons. This can be explained by the fact that tumorous (undifferentiated SK-N-SH) cells have a high endogenous survivin pool and upon treatment with mutant SuR9-C84A causes forceful survivin expression. These events significantly lowered the microtubule dynamics and stability, eventually leading to apoptosis. In the case of differentiated SK-N-SH neurons that express negligible levels of wild-type survivin, the mutant indistinguishably behaved in a wild-type fashion. It also favored cell-cycle progression, forming the chromosome-passenger complex, and stabilized the microtubule-organizing center. Therefore, mutant SurR9-C84A represents a novel therapeutic with its dual actions (cytotoxic toward tumor cells and protective and proliferative toward neuronal cells), and hence finds potential applications against a variety of neurological disorders. In this study, we also developed a novel poly(lactic-co-glycolic acid) nanoparticulate formulation to surmount the hurdles associated with the delivery of SurR9-C84A, thus enhancing its effective therapeutic outcome.

Receptor-type protein tyrosine phosphatase κ directly dephosphorylates CD133 and regulates downstream AKT activation

Although CD133 has been considered to be a molecular marker for cancer stem cells, its functional roles in tumorigenesis remain unclear. We here examined the molecular basis behind CD133-mediated signaling. Knockdown of CD133 resulted in the retardation of xenograft tumor growth of colon cancer-derived HT-29 and LoVo cells accompanied by hypophosphorylation of AKT, which diminished β-catenin/T-cell factor-mediated CD44 expression. As tyrosine residues of CD133 at positions 828 and 852 were phosphorylated in HT-29 and SW480 cells, we further addressed the significance of this phosphorylation in the tumorigenesis of SW480 cells expressing mutant CD133, with substitution of these tyrosine residues by glutamate (CD133-EE) or phenylalanine (CD133-FF). Forced expression of CD133-EE promoted much more aggressive xenograft tumor growth relative to wild-type CD133-expressing cells accompanied by hyperphosphorylation of AKT; however, CD133-FF expression had negligible effects on AKT phosphorylation and xenograft tumor formation. Intriguingly, the tyrosine phosphorylation status of CD133 was closely linked to the growth of SW480-derived spheroids. Using yeast two-hybrid screening, we finally identified receptor-type protein tyrosine phosphatase κ (PTPRK) as a binding partner of CD133. In vitro studies demonstrated that PTPRK associates with the carboxyl-terminal region of CD133 through its intracellular phosphatase domains and also catalyzes dephosphorylation of CD133 at tyrosine-828/tyrosine-852. Silencing of PTPRK elevated the tyrosine phosphorylation of CD133, whereas forced expression of PTPRK reduced its phosphorylation level markedly and abrogated CD133-mediated AKT phosphorylation. Endogenous CD133 expression was also closely associated with higher AKT phosphorylation in primary colon cancer cells, and ectopic expression of CD133 enhanced AKT phosphorylation. Furthermore, lower PTPRK expression significantly correlated with the poor prognosis of colon cancer patients with high expression of CD133. Thus, our present findings strongly indicate that the tyrosine phosphorylation of CD133, which is dephosphorylated by PTPRK, regulates AKT signaling and has a critical role in colon cancer progression.

One siRNA pool targeting the λ constant region stops λ light-chain production and causes terminal endoplasmic reticulum stress

Immunoglobulin light-chain and antibody production by plasma cells is significantly reduced by siRNA for the light-chain constant region. In plasma cells making intact antibodies, knockdown of light chains can cause terminal ER stress because of unpaired heavy chains.

Discrepant NOXA (PMAIP1) transcript and NOXA protein levels: a potential Achilles' heel in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm with transient response to conventional chemotherapy. We here investigated the role of the Bcl-2 homology domain 3-only protein NOXA for life–death decision in MCL. Surprisingly, NOXA (PMAIP1) mRNA and NOXA protein levels were extremely discrepant in MCL cells: NOXA mRNA was found to be highly expressed whereas NOXA protein levels were low. Chronic active B-cell receptor signaling and to a minor degree cyclin D1 overexpression contributed to high NOXA mRNA expression levels in MCL cells. The phoshatidyl-inositol-3 kinase/AKT/mammalian target of rapamycin pathway was identified as the major downstream signaling pathway involved in the maintenance of NOXA gene expression. Interestingly, MCL cells adapt to this constitutive pro-apoptotic signal by extensive ubiquitination and rapid proteasomal degradation of NOXA protein (T_½∼15–30 min). In addition to the proteasome inhibitor Bortezomib, we identified the neddylation inhibitor MLN4924 and the fatty acid synthase inhibitor Orlistat as potent inducers of NOXA protein expression leading to apoptosis in MCL. All inhibitors targeted NOXA protein turnover. In contrast to Bortezomib, MLN4924 and Orlistat interfered with the ubiquitination process of NOXA protein thereby offering new strategies to kill Bortezomib-resistant MCL cells. Our data, therefore, highlight a critical role of NOXA in the balance between life and death in MCL. The discrepancy between NOXA transcript and protein levels is essential for sensitivity of MCL to ubiquitin-proteasome system inhibitors and could therefore provide a druggable Achilles' heel of MCL cells.

p53, SKP2, and DKK3 as MYCN Target Genes and Their Potential Therapeutic Significance

Neuroblastoma is the most common extra-cranial solid tumor of childhood. Despite significant advances, it currently still remains one of the most difficult childhood cancers to cure, with less than 40% of patients with high-risk disease being long-term survivors. MYCN is a proto-oncogene implicated to be directly involved in neuroblastoma development. Amplification of MYCN is associated with rapid tumor progression and poor prognosis. Novel therapeutic strategies which can improve the survival rates whilst reducing the toxicity in these patients are therefore required. Here we discuss genes regulated by MYCN in neuroblastoma, with particular reference to p53, SKP2, and DKK3 and strategies that may be employed to target them.

Bmi1 regulates cell fate via tumor suppressor WWOX repression in small-cell lung cancer cells

Mortality from lung cancer is important worldwide. Recently, epigenetic aberration of lung cancer, not only genomic DNA methylation but also chromatin modification, has become an important target for lung cancer research, although previous research has demonstrated that lung cancer develops as a result of both environmental and genetic factors. Here, we demonstrated that an epigenetic regulator/polycomb group protein Bmi1 is more highly expressed in small-cell lung cancer (SCLC) than in non-small-cell lung cancer by immunohistochemical analysis. In vitro experiments indicated that Bmi1 reduction by lentivirus-derived shRNA significantly suppressed proliferation, colony formation and in vivo tumor formation. Importantly, apoptosis was induced by Bmi1 depletion in small-cell lung cancer cells. Furthermore, a tumor suppressor WWOX was identified as a Bmi1 target in the cells by a chromatin immunoprecipitation assay and a quantitative real-time PCR assay; WWOX had a role as a tumor suppressor in SCLC cells; therefore, the Bmi1/WWOX pathway could be a new candidate for a new therapeutic approach for SCLC.

MYCN sensitizes human neuroblastoma to apoptosis by HIPK2 activation through a DNA damage response

MYCN amplification occurs in approximately 20% of human neuroblastomas and is associated with early tumor progression and poor outcome, despite intensive multimodal treatment. However, MYCN overexpression also sensitizes neuroblastoma cells to apoptosis. Thus, uncovering the molecular mechanisms linking MYCN to apoptosis might contribute to designing more efficient therapies for MYCN-amplified tumors. Here we show that MYCN-dependent sensitization to apoptosis requires activation of p53 and its phosphorylation at serine 46. The p53(S46) kinase HIPK2 accumulates on MYCN expression, and its depletion by RNA interference impairs p53(S46) phosphorylation and apoptosis. Remarkably, MYCN induces a DNA damage response that accounts for the inhibition of HIPK2 degradation through an ATM- and NBS1-dependent pathway. Prompted by the rare occurrence of p53 mutations and by the broad expression of HIPK2 in our human neuroblastoma series, we evaluated the effects of the p53-reactivating compound Nutlin-3 on this pathway. At variance from other tumor histotypes, in MYCN-amplified neuroblastoma, Nutlin-3 further induced HIPK2 accumulation, p53(S46) phosphorylation, and apoptosis, and in combination with clastogenic agents purged virtually the entire cell population. Altogether, our data uncover a novel mechanism linking MYCN to apoptosis that can be triggered by the p53-reactivating compound Nutlin-3, supporting its use in the most difficult-to-treat subset of neuroblastoma.

TAp63 plays compensatory roles in p53-deficient cancer cells under genotoxic stress

p53, p63, and p73 belong to the p53 family of proteins, which mediate development, differentiation, and various other cellular responses. p53 is involved in many anti-cancer mechanisms, such as cell cycle regulation, apoptosis, and the maintenance of genomic integrity. The p63 gene is controlled by two promoters that direct the expression of two isoforms, one with and one without transactivating properties, known as TAp63 and ΔNp63. In this study, p53-deficient cells (Hep3B and PC-3) and p53-expressing cells (A549 and HepG2) were treated with doxorubicin to examine the possible roles of TAp63 in these cells under genotoxic stress; TAp63 expression was induced in p53-deficient cell lines, but not in p53-expressing cell lines. The ectopic expression of p53 in p53-deficient cells (Hep3B) reduced TAp63 promoter activity, and knockdown of TAp63 attenuated doxorubicin-induced cell growth arrest by promoting cell cycle progression, leading to an increase in the percentage of G(2)/M cells. Moreover, knockdown of TAp63 increased cell sensitivity to doxorubicin-induced genomic damage. Our results suggest that TAp63 may play a compensatory role in cell cycle regulation and DNA damage repair in p53-deficient cancer cells.

Transcriptional activity of TAp63 promoter is regulated by c-jun

The transcription factor p63 belongs to the p53 protein family and plays an important role in epithelial development. Recent studies showed that p63 is over-expressed in some human squamous cell carcinomas of the head and neck, suggesting a role in carcinogenesis. The p63 gene contains two promoters and alternative promoter usage generates two groups of proteins with (TAp63) or without (ΔNp63) the transactivation domain. Although the roles of TAp63 in epithelial development have been described in numerous recent studies, the regulation of its expression has not been elucidated. In this study, we showed that the transcriptional activity of the TAp63 promoter and TAp63 protein level were both up-regulated by an increased c-jun activity in Hep3B human hepatocellular carcinoma cell. Moreover, the elevated TAp63 expression was coincided with an increased binding of c-jun to the TAp63 promoter. Point mutation of the sp1 binding site within the TAp63 promoter region attenuated the effect of c-jun on TAp63 expression. Knockdown of TAp63 expression by shRNA led to increased proliferation of Hep3B cell compared to that of the mock cell, suggesting a growth suppressive effect of TAp63.

CD133 suppresses neuroblastoma cell differentiation via signal pathway modification

CD133 (prominin-1) is a transmembrane glycoprotein expressed on the surface of normal and cancer stem cells (tumor-initiating cells), progenitor cells, rod photoreceptor cells and a variety of epithelial cells. Although CD133 is widely used as a marker of various somatic and putative cancer stem cells, its contribution to the fundamental properties of cancer cells, such as tumorigenesis and differentiation, remains to be elucidated. In the present report, we found that CD133 was expressed in several neuroblastoma (NB) cell lines/tumor samples. Intriguingly, CD133 repressed NB cell differentiation, for example neurite extension and the expression of differentiation marker proteins, and was decreased by several differentiation stimuli, but accelerated cell proliferation, anchorage-independent colony formation and in vivo tumor formation of NB cells. NB cell line and primary tumor-sphere experiments indicated that the molecular mechanism of CD133-related differentiation suppression in NB was in part dependent on neurotrophic receptor RET tyrosine kinase regulation. RET transcription was suppressed by CD133 in NB cells and glial cell line-derived neurotrophic factor treatment failed to induce RET in CD133-expressing cells; RET overexpression rescued CD133-related inhibition of neurite elongation. Of note, CD133-related NB cell differentiation and RET repression were mainly dependent on p38MAPK and PI3K/Akt pathways. Furthermore, CD133 has a function in growth and RET expression in NB cell line- and primary tumor cell-derived tumor spheres. To the best of our knowledge, this is the first report of the function of CD133 in cancer cells and our findings may be applied to improve differentiation induction therapy for NB patients.

Polycomb group molecule PHC3 regulates polycomb complex composition and prognosis of osteosarcoma

Polyhomeotic homolog 3 (PHC 3) is a member of the human polycomb complex and has been regarded as a candidate tumor suppressor of osteosarcoma. In the present paper, we performed a mutation survey and PHC3 expression analysis by quantitative real-time PCR using 10 osteosarcoma cell lines and 42 primary osteosarcoma samples. Relative PHC3 expression values of clinical samples were analyzed with clinical outcomes, and it was suggested that lower PHC3-expressing patients had significantly worse overall survival. Relative PHC3 values of clinical samples were less than those of normal bone tissues, whereas they were greater than those of cell lines. By denaturing high performance liquid chromatography analysis and direct sequencing, we found a PHC3 missense mutation in U2OS cells, which resulted in arginine56 to proline substitution. The same point mutation existed in four of 42 primary osteosarcoma samples. Regarding functional analysis, PHC3 expression significantly suppressed the colony formation of tumor cells. Intriguingly, polycomb repressive complex 1 members, Bmi1 and Ring1b proteins, were reduced in PHC3-expressing osteosarcoma cells. Deletion mutant PHC3 expression suggested that the carboxyl terminus of PHC3 has a role in suppression; the above-mentioned point mutation of PHC3 also lost inhibitory activities. Conversely, Bmi1 expression reduced PHC3 at the mRNA level and induced the proliferation of osteosarcoma cells. Taken together, we confirmed the role of PHC3 as a tumor suppressor in osteosarcoma cells and found that PHC3-dependent tumor suppression may be caused by modification of the composition of polycomb repressive complex 1 in cancer cells.

HDM2 impairs Noxa transcription and affects apoptotic cell death in a p53/p73-dependent manner in neuroblastoma

HDM2, a human homologue of MDM2, is a major negative regulator of p53 function, and increased expression of HDM2 by its promoter polymorphism SNP309 resulted in p53 inactivation and an increased risk of several tumours, including neuroblastoma (NB). Herein, we show that increased expression of HDM2 is related to a worse prognosis in MYCN-amplified NB patients. HDM2 plays an important role in the expression of Noxa, a pro-apoptotic molecule of the Bcl-2 family, which induces NB cell apoptotic death after doxorubcin (Doxo) treatment. Knockdown of HDM2 by siRNA resulted in the upregulation of Noxa at mRNA/protein levels and improved the sensitivity of Doxo-resistant NB cells, although these were not observed in p53-mutant NB cells. Noxa-knockdown abolished the recovered Doxo-induced cell death by HDM2 reduction. Intriguingly, resistance to Doxo was up-regulated by over-expression of HDM2 in Doxo-sensitive NB cells. By HDM2 expression, p53 was inactivated but its degradation was not accelerated, suggesting that p53 was degraded in a proteasome-independent manner in NB cells; downstream effectors of p53, p21(Cip1/Waf1) and Noxa were suppressed by HDM2. Noxa transcription was considerably regulated by both p53 and p73 in NB cells. Furthermore, in vivo binding of p53 and p73 to Noxa promoter was suppressed and Noxa promoter activation was inhibited by HDM2. Taken together, our results may indicate that the HDM2-related resistance to chemotherapeutic drugs of NB is regulated by p53/p73-dependent Noxa expression in NB.

p53 family: Therapeutic targets in neuroblastoma

Survival rates for metastatic neuroblastoma remain poor, despite significant increase in the intensity of therapy. Although it represents approximately 7% of pediatric cancer, neuroblastoma accounts for approximately 15% of childhood cancer deaths. Thus, novel approaches to enhance neuroblastoma chemotherapy sensitivity and prevent or bypass chemoresistance are required. Disruption of the p53 pathway is a common mechanism leading to defects in apoptosis in cancer cells. Increasing evidence suggests that the p53 pathway may be inactivated in neuroblastoma. Inactivation of the p53 pathway occurs most commonly at the time of relapse, and probably contributes to chemoresistance. The p53 family proteins, p73 and p63, can also induce apoptosis, and early studies suggest that p73 may be important in neuroblastoma pathogenesis and response to treatment. This article focuses on current therapies and novel drugs targeting p53 and p73 signaling pathways in neuroblastoma. Understanding the balance between the p53 family proteins in neuroblastoma and how their expression and activity are regulated will hopefully lead to the discovery of agents that target these pathways to induce neuroblastoma cell death, alone or in combination with chemotherapies.

Bmi1 is a MYCN target gene that regulates tumorigenesis through repression of KIF1Bbeta and TSLC1 in neuroblastoma

Recent advances in neuroblastoma (NB) research addressed that epigenetic alterations such as hypermethylation of promoter sequences, with consequent silencing of tumor-suppressor genes, can have significant roles in the tumorigenesis of NB. However, the exact role of epigenetic alterations, except for DNA hypermethylation, remains to be elucidated in NB research. In this paper, we clarified the direct binding of MYCN to Bmi1 promoter and upregulation of Bmi1 transcription by MYCN. Mutation introduction into an MYCN binding site in the Bmi1 promoter suggests that MYCN has more important roles in the transcription of Bmi1 than E2F-related Bmi1 regulation. A correlation between MYCN and polycomb protein Bmi1 expression was observed in primary NB tumors. Expression of Bmi1 resulted in the acceleration of proliferation and colony formation in NB cells. Bmi1-related inhibition of NB cell differentiation was confirmed by neurite extension assay and analysis of differentiation marker molecules. Intriguingly, the above-mentioned Bmi1-related regulation of the NB cell phenotype seems not to be mediated only by p14ARF/p16INK4a in NB cells. Expression profiling analysis using a tumor-specific cDNA microarray addressed the Bmi1-dependent repression of KIF1Bbeta and TSLC1, which have important roles in predicting the prognosis of NB. Chromatin immunoprecipitation assay showed that KIF1Bbeta and TSLC1 are direct targets of Bmi1 in NB cells. These findings suggest that MYCN induces Bmi1 expression, resulting in the repression of tumor suppressors through Polycomb group gene-mediated epigenetic chromosome modification. NB cell proliferation and differentiation seem to be partially dependent on the MYCN/Bmi1/tumor-suppressor pathways.

Mcl1 downregulation sensitizes neuroblastoma to cytotoxic chemotherapy and small molecule Bcl2-family antagonists

Neuroblastoma (NB) is a common, highly lethal pediatric cancer, with treatment failures largely attributable to the emergence of chemoresistance. The pro-survival Bcl2 homology (BH) proteins critically regulate apoptosis, and may represent important therapeutic targets for restoring drug sensitivity in NB. We used a human NB tumor tissue microarray to survey the expression of pro-survival BH proteins Mcl1 and Bcl2, and correlated expression to clinical prognostic factors and survival. Primary NB tumors heterogeneously expressed Mcl1 or Bcl2, with high expression correlating to high-risk phenotype. Co-expression is infrequent (11%), but correlates to reduced survival. Using RNA interference, we investigated the functional relevance of Mcl1 and Bcl2 in high-risk NB cell lines (SK-N-AS, IMR-5, NLF). Mcl1 knockdown induced apoptosis in all NB cell lines, while Bcl2 knockdown inhibited only NLF, suggesting functional heterogeneity. Finally, we determined the relevance of Mcl1 in resistance to conventional chemotherapy (etoposide, doxorubicin) and small molecule Bcl2-family antagonists (ABT-737 and AT-101). Mcl1 silencing augmented sensitivity to chemotherapeutics 2- to 300-fold, while Bcl2 silencing did not, even in Bcl2-sensitive NLF cells. Resistance to ABT-737, which targets Bcl2/-w/-x, was overcome by Mcl1 knockdown. AT-101, which also neutralizes Mcl1, had single-agent cytotoxicity, further augmented by Mcl1 knockdown. In conclusion, Mcl1 appears a predominant pro-survival protein contributing to chemoresistance in NB, and Mcl1 inactivation may represent a novel therapeutic strategy. Optimization of compounds with higher Mcl1 affinity, or combination with additional Mcl1 antagonists, may enhance the clinical utility of this approach.

Toll-like receptor 4 mediates synergism between alcohol and HCV in hepatic oncogenesis involving stem cell marker Nanog

Alcohol synergistically enhances the progression of liver disease and the risk for liver cancer caused by hepatitis C virus (HCV). However, the molecular mechanism of this synergy remains unclear. Here, we provide the first evidence that Toll-like receptor 4 (TLR4) is induced by hepatocyte-specific transgenic (Tg) expression of the HCV nonstructural protein NS5A, and this induction mediates synergistic liver damage and tumor formation by alcohol-induced endotoxemia. We also identify Nanog, the stem/progenitor cell marker, as a novel downstream gene up-regulated by TLR4 activation and the presence of CD133/Nanog-positive cells in liver tumors of alcohol-fed NS5A Tg mice. Transplantation of p53-deficient hepatic progenitor cells transduced with TLR4 results in liver tumor development in mice following repetitive LPS injection, but concomitant transduction of Nanog short-hairpin RNA abrogates this outcome. Taken together, our study demonstrates a TLR4-dependent mechanism of synergistic liver disease by HCV and alcohol and an obligatory role for Nanog, a TLR4 downstream gene, in HCV-induced liver oncogenesis enhanced by alcohol.

Characterization of the cytotoxic activity of the indoloquinoline alkaloid cryptolepine in human tumour cell lines and primary cultures of tumour cells from patients

The plant derived indoloquinoline alkaloid cryptolepine was investigated for its cytotoxic properties in 12 human tumour cell lines and in primary cultures of tumour cells from patients. The fluorometric microculture cytotoxicity assay was used to assess cytotoxicity and DNA micro-array analysis to evaluate gene expression. Cryptolepine mean IC(50) in the cell line panel was 0.9 microM compared with 1.0 and 2.8 microM in haematological and solid tumour malignancies, respectively. Among patient solid tumour samples, those from breast cancer were the most sensitive and essentially as sensitive as haematological malignancies. Cryptolepine activity showed highest correlations to topoisomerase II and microtubule targeting drugs. In the cell lines cryptolepine activity was essentially unaffected by established mechanisms of drug resistance. A number of genes were identified as associated with cryptolepine activity. In conclusion, cryptolepine shows interesting in vitro cytotoxic properties and its further evaluation as an anti-cancer drug seems warranted.

Cytotoxic diarylheptanoid induces cell cycle arrest and apoptosis via increasing ATF3 and stabilizing p53 in SH-SY5Y cells

PURPOSE

The aim of the study is to dissect the cytotoxic mechanisms of 1-(4-hydroxy-3-methoxyphenyl)-7-(3,4-dihydroxyphenyl)-4E-en-3-heptanone (compound 1) in SH-SY5Y cells and therefore to provide new insight into neuroblastoma chemotherapy.

METHODS

Nine diarylheptanoids were isolated from Alpinia officinarum by chromatography and their cytotoxicity was evaluated by an MTS assay. Flow cytometry, BrdU incorporation assay and fluorescence staining were employed to investigate cytostatic and apoptotic effects induced by the compound 1. In addition, Western blot, qPCR and siRNA techniques were used to elucidate the molecular mechanisms of the cytotoxicity.

RESULTS

The study to elucidate the cytotoxic mechanisms of compound 1, the most potent diarylheptanoid showed that cell cycle-related proteins, cyclins, CDKs and CDKIs, as well as two main apoptotic related families, caspase and Bcl 2 were involved in S phase arrest and apoptosis in neuroblastoma cell line SH-SY5Y. Furthermore, following the drug treatment, the protein expression of p53, phospho-p53 (Ser20) as well as the p53 transcriptional activated genes ATF3, puma and Apaf-1 were increased dramatically; MDM2 and Aurora A, the two p53 negative regulators were decreased; the p53 protein stability was enhanced, whereas the p53 mRNA expression level slightly decreased and ATF3 mRNA expression apparently increased. In addition, the knockdown of ATF3 gene by siRNA partially suppressed p53, caspase 3, S phase arrest and apoptosis triggered by compound 1.

CONCLUSION

These results suggest that compound 1 induces S phase arrest and apoptosis via up regulation of ATF3 and stabilization of p53 in SH-SY5Y cell line. Therefore, compound 1 might be a promising lead structure for neuroblastoma therapy.