MYCN-Directed Centrosome Amplification Requires MDM2-Mediated Suppression of p53 Activity in Neuroblastoma Cells

Repurposing a plant alkaloid homoharringtonine targets insulinoma associated-1 in N-Myc-activated neuroblastoma

High-risk neuroblastoma (NB) is a heterogeneous and malignant childhood cancer that is frequently characterized by MYCN proto-oncogene amplification or elevated N-Myc protein (N-Myc) expression. An N-Myc downstream target gene, insulinoma associated-1 (INSM1) has emerged as a biomarker that plays a critical role in facilitating NB tumor cell growth and transformation. N-Myc activates endogenous INSM1 gene expression through binding to the E2-box of the INSM1 proximal promoter in NB. We identified a plant alkaloid, homoharringtonine (HHT), from a chemical library screening showing potent inhibition of INSM1 promoter activity. This positive-hit plant alkaloid exemplifies an effective screening approach for repurposed compound targeting INSM1 expression in NB cancer therapy. The elevated N-Myc and INSM1 expression in NB constitutes a positive-loop through INSM1 activation that promotes N-Myc stability. In the present study, the biological effects and anti-tumor properties of HHT against NB were examined. HHT either down regulates and/or interferes with the binding of N-Myc to the E2-box of the INSM1 promoter and the inhibition of PI3K/AKT-mediated N-Myc stability could lead to the NB cell apoptosis. HHT inhibition of NB cell proliferation is consistent with the INSM1 expression as higher level of INSM1 exhibits a more sensitive IC50 value. The combination treatment of HHT and A674563 provides a better option of increasing potency and reducing cellular cytotoxicity than HHT or A674563 treatment alone. Taken together, the suppression of the INSM1-associated signaling pathway axis promotes the inhibition of NB tumor cell growth. This study developed a feasible approach for repurposing an effective anti-NB drug.

Interplay: The Essential Role between INSM1 and N-Myc in Aggressive Neuroblastoma

Simple Summary

Neuroblastoma (NB) is a cancer that starts in certain very early forms of nerve cells of the sympathetic nervous system, most often found in an embryo or fetus. Symptoms may include bone pain, an abdominal mass, frequent urination, limping, anemia, spinal cord weakness, or bruising of the eye area. N-Myc is a key driver of high-risk NB. An elevated expression of N-Myc often predicts a poorer prognosis, in both time to tumor progression and overall survival rate. We discovered a transcription factor, insulinoma-associated-1 (INSM1), as the downstream target gene of N-Myc. INSM1 has emerged as a novel NB biomarker that plays a critical role in facilitating NB tumor cell development. Both N-Myc and INSM1 demonstrate high clinical relevance to NB. Therefore, further understanding the association of INSM1 and N-Myc functions in aggressive NB should be beneficial for future NB treatment.

Abstract

An aggressive form of neuroblastoma (NB), a malignant childhood cancer derived from granule neuron precursors and sympathoadrenal lineage, frequently comprises MYCN amplification/elevated N-Myc expression, which contributes to the development of neural crest-derived embryonal malignancy. N-Myc is an oncogenic driver in NB. Persistent N-Myc expression during the maturation of SA precursor cells can cause blockage of the apoptosis and induce abnormal proliferation, resulting in NB development. An insulinoma-associated-1 (INSM1) zinc-finger transcription factor has emerged as an NB biomarker that plays a critical role in facilitating tumor cell growth and transformation. INSM1 plays an essential role in sympathoadrenal cell differentiation. N-Myc activates endogenous INSM1 through an E2-box of the INSM1 proximal promoter, whereas INSM1 enhances N-Myc stability via RAC-α-serine/threonine protein kinase (AKT) phosphorylation in NB. The ectopic expression of INSM1 stimulates NB tumor growth in contrast to the knockdown of INSM1 that inhibits NB cell proliferation. The clinical pathological result and bioinformatics analysis show that INSM1 is a strong diagnostic and a prognostic biomarker for the evaluation of NB progression. The INSM1/N-Myc expression shows high clinical relevance in NB. Therefore, targeting the INSM1/N-Myc-associated signaling axis should be a feasible approach to identifying new drugs for the suppression of NB tumor growth.

Filamin A increases aggressiveness of human neuroblastomas

Background

The actin-binding protein filamin A (FLNA) regulates oncogenic signal transduction important for tumor growth, but the role of FLNA in the progression of neuroblastoma (NB) has not been explored.

Methods

We analyzed FLNA mRNA expression in the R2 NB-database and FLNA protein expression in human NB tumors. We then silenced FLNA expression in human SKNBE2 and IMR32 NB cells by lentiviral vector encoding shRNA FLNA and assayed the cells for proliferation, migration, colony, spheroid formation, and apoptosis. SKNBE2 xenografts expressing or lacking FLNA in BALB/c nude mice were analyzed by both routine histopathology and immunohistochemistry.

Results

We observed shorter patient survival with higher expression of FLNA mRNA than patients with lower FLNA mRNA expression, and high-risk NB tumors expressed higher FLNA levels. SKNBE2 cells expressing higher FLNA levels proliferated more than IMR32 cells expressing lower FLNA levels. NB cell lines transfected with siRNA FLNA proliferated and migrated less, expressed lower levels of phosphorylated AKT and ERK1/2, formed smaller colonies and spheroids, as well as increased apoptosis. After inoculation of SKNBE2 cells infected with lentivirus expressing shRNA FLNA, size of NB tumors and number of proliferating cells were decreased. Furthermore, we identified STAT3 as an interacting partner of FLNA. Silencing FLNA mRNA reduced levels of phosphorylated STAT3 and MYCN, and induced expression NF-κB, cleaved caspase 3, and p53.

Conclusion

Inhibition of FLNA impaired NB cell signaling and function and reduced NB tumor size in vivo, suggesting that drugs targeting either FLNA or its interaction with STAT3 may be useful in the treatment of NB.

Keep Calm and Carry on with Extra Centrosomes

Simple Summary

Precise chromosome segregation during mitosis is a vital event orchestrated by formation of bipolar spindle poles. Supernumerary centrosomes, caused by centrosome amplification, deteriorates mitotic processes, resulting in segregation defects leading to chromosomal instability (CIN). Centrosome amplification is frequently observed in various types of cancer and considered as a significant contributor to destabilization of chromosomes. This review provides a comprehensive overview of causes and consequences of centrosome amplification thoroughly describing molecular mechanisms.

Abstract

Aberrations in the centrosome number and structure can readily be detected at all stages of tumor progression and are considered hallmarks of cancer. Centrosome anomalies are closely linked to chromosome instability and, therefore, are proposed to be one of the driving events of tumor formation and progression. This concept, first posited by Boveri over 100 years ago, has been an area of interest to cancer researchers. We have now begun to understand the processes by which these numerical and structural anomalies may lead to cancer, and vice-versa: how key events that occur during carcinogenesis could lead to amplification of centrosomes. Despite the proliferative advantages that having extra centrosomes may confer, their presence can also lead to loss of essential genetic material as a result of segregational errors and cancer cells must deal with these deadly consequences. Here, we review recent advances in the current literature describing the mechanisms by which cancer cells amplify their centrosomes and the methods they employ to tolerate the presence of these anomalies, focusing particularly on centrosomal clustering.

From DNA Copy Number Gains and Tumor Dependencies to Novel Therapeutic Targets for High-Risk Neuroblastoma

Neuroblastoma is a pediatric tumor arising from the sympatho-adrenal lineage and a worldwide leading cause of childhood cancer-related deaths. About half of high-risk patients die from the disease while survivors suffer from multiple therapy-related side-effects. While neuroblastomas present with a low mutational burden, focal and large segmental DNA copy number aberrations are highly recurrent and associated with poor survival. It can be assumed that the affected chromosomal regions contain critical genes implicated in neuroblastoma biology and behavior. More specifically, evidence has emerged that several of these genes are implicated in tumor dependencies thus potentially providing novel therapeutic entry points. In this review, we briefly review the current status of recurrent DNA copy number aberrations in neuroblastoma and provide an overview of the genes affected by these genomic variants for which a direct role in neuroblastoma has been established. Several of these genes are implicated in networks that positively regulate MYCN expression or stability as well as cell cycle control and apoptosis. Finally, we summarize alternative approaches to identify and prioritize candidate copy-number driven dependency genes for neuroblastoma offering novel therapeutic opportunities.

Long Noncoding RNA NHEG1 Drives β-Catenin Transactivation and Neuroblastoma Progression through Interacting with DDX5

Recent studies suggest that long noncoding RNAs (lncRNAs) play essential roles in tumor progression. However, the functional roles and underlying mechanisms of lncRNAs in neuroblastoma (NB), the most common malignant solid tumor in pediatric population, still remain elusive. Herein, through integrating analysis of a public RNA sequencing dataset, neuroblastoma highly expressed 1 (NHEG1) was identified as a risk-associated lncRNA, contributing to an unfavorable outcome of NB. Depletion of NHEG1 led to facilitated differentiation and decreased growth and aggressiveness of NB cells. Mechanistically, NHEG1 bound to and stabilized DEAD-box helicase 5 (DDX5) protein through repressing proteasome-mediated degradation, resulting in β-catenin transactivation that altered target gene expression associated with NB progression. We further determined a lymphoid enhancer binding factor 1 (LEF1)/transcription factor 7-like 2 (TCF7L2)/NHEG1/DDX5/β-catenin axis with a positive feedback loop and demonstrated that NHEG1 harbored oncogenic properties via its interplay with DDX5. Administration of small interfering RNAs against NHEG1 or DDX5 reduced tumor growth and prolonged survival of nude mice bearing xenografts. High NHEG1 or DDX5 expression was associated with poor survival of NB patients. These results indicate that lncRNA NHEG1 exhibits oncogenic activity that affects NB progression via stabilizing the DDX5 protein, which might serve as a potential therapeutic target for NB.

Resveratrol attenuates diabetes-associated cell centrosome amplification via inhibiting the PKCα-p38 to c-myc/c-jun pathway

Type 2 diabetes increases the risk for cancer. Centrosome amplification can initiate tumorigenesis. We have described that type 2 diabetes increases the centrosome amplification of peripheral blood mononuclear cells, with high glucose, insulin, and palmitic acid as the triggers, which suggests that centrosome amplification is a candidate biological mechanism linking diabetes to cancer. In this study, we aimed to further investigate the signaling pathways of the diabetes-associated centrosome amplification and to examine whether and how resveratrol inhibits the centrosome amplification. The results showed that treatment with high glucose, insulin, and palmitic acid, alone or in combination, could increase the protein levels of phospho-protein kinase C alpha (p-PKCα), phospho-p38 mitogen-activated protein kinases (p-p38), c-myc, and c-jun, as well as the mRNA levels of c-myc and c-jun. PKCα inhibitor could inhibit the treatment-induced increase in the protein levels of p-p38, c-myc, and c-jun. Inhibitor or siRNA of p38 was also able to inhibit the treatment-induced increase in the levels of p-p38, c-myc, and c-jun. Meanwhile, knockdown of c-myc or c-jun did not alter the treatment-induced increase in the phosphorylation of PKCα or p38. Importantly, inhibition of the phosphorylation of PKCα or p38 and knockdown of c-myc or c-jun could attenuate the centrosome amplification. In diabetic mice, the levels of p-PKCα, p-p38, c-myc, and c-jun were all increased in the colon tissues. Interestingly, resveratrol, but not metformin, was able to attenuate the treatment-induced increase in the levels of p-PKCα, p-p38, c-myc, and c-jun, as well as the centrosome amplification. In conclusion, our results suggest that PKCα-p38 to c-myc/c-jun is the signaling pathway of the diabetes-associated centrosome amplification, and resveratrol attenuates the centrosome amplification by inhibiting this signaling pathway.

Bioinformatics analysis of the CDK2 functions in neuroblastoma

The present study aimed to elucidate the potential mechanism of cyclin-dependent kinase 2 (CDK2) in neuroblastoma progression and to identify the candidate genes associated with neuroblastoma with CDK2 silencing. The microarray data of GSE16480 were obtained from the gene expression omnibus database. This dataset contained 15 samples: Neuroblastoma cell line IMR32 transfected with CDK2 shRNA at 0, 8, 24, 48 and 72 h (n=3 per group; total=15). Significant clusters associated with differentially expressed genes (DEGs) were identified using fuzzy C‑Means algorithm in the Mfuzz package. Gene ontology and pathway enrichment analysis of DEGs in each cluster were performed, and a protein‑protein interaction (PPI) network was constructed. Additionally, functional annotation of DEGs in clusters was performed for the detection of transcription factors and tumor‑associated genes. A total of 4 clusters with significant change tendency and 1,683 DEGs were identified. The hub nodes of the PPI network constructed by DEGs in Cluster 1, Cluster 2, Cluster 3 and Cluster 4 were MDM2 oncogene, E3 ubiquitin protein ligase (MDM2), cyclin‑dependent kinase 1 (CDK1), proteasome (prosome, macropain) 26S subunit, non‑ATPase, 14 (PSMD14) and translocator protein (18 kDa) (TSPO) respectively. These genes were significantly enriched in the p53 signaling pathway, cell cycle, proteasome and systemic lupus erythematosus pathways. MDM2, CDK1, PSMD14 and TSPO may be key target genes of CDK2. CDK2 may have key functions in neuroblastoma progression by regulating the expression of these genes.

Prognostic value of CA20, a score based on centrosome amplification-associated genes, in breast tumors

Centrosome amplification (CA) is a hallmark of cancer, observable in ≥75% of breast tumors. CA drives aggressive cellular phenotypes such as chromosomal instability (CIN) and invasiveness. Thus, assessment of CA may offer insights into the prognosis of breast cancer and identify patients who might benefit from centrosome declustering agents. However, it remains unclear whether CA is correlated with clinical outcomes after adjusting for confounding factors. To gain insights, we developed a signature, “CA20”, comprising centrosome structural genes and genes whose dysregulation is implicated in inducing CA. We found that CA20 was a significant independent predictor of worse survival in two large independent datasets after adjusting for potentially confounding factors. In multivariable analyses including both CA20 and CIN25 (a gene expression-based score that correlates with aneuploidy and has prognostic value in many types of cancer), only CA20 was significant, suggesting CA20 captures the risk-predictive information of CIN25 and offers information beyond it. CA20 correlated strongly with CIN25, so a high CA20 score may reflect tumors with high CIN and potentially other aggressive features that may require more aggressive treatment. Finally, we identified processes and pathways differing between CA20-low and high groups that may be valuable therapeutic targets.

INSM1 increases N-myc stability and oncogenesis via a positive-feedback loop in neuroblastoma

Insulinoma associated-1 (IA-1/INSM1) gene is exclusively expressed during early embryonic development, but has been found to be re-expressed at high levels in neuroendocrine tumors including neuroblastoma. Using over-expression and knockdown experiments in neuroblastoma cells, we showed that INSM1 is critical for cell proliferation, BME-coated invasion, and soft agar colony formation. Here, we identified INSM1 as a novel target gene activated by N-myc in N-myc amplified neuroblastoma cells. The Sonic hedgehog signaling pathway induced INSM1 by increasing N-myc expression. INSM1 activated PI3K/AKT/GSK3β pathways to suppress N-myc phosphorylation (Thr-58) and inhibited degradation of N-myc. Inversely, N-myc protein bound to the E2-box region of the INSM1 promoter and activated INSM1 expression. The invasion assay and the xenograft nude mouse tumor model revealed that the INSM1 factor facilitated growth and oncogenesis of neuroblastoma. The current data supports our hypothesis that a positive-feedback loop of sonic hedgehog signaling induced INSM1 through N-myc and INSM1 enhanced N-myc stability contributing to the transformation of human neuroblastoma.

Functional Significance of Aurora Kinases-p53 Protein Family Interactions in Cancer

Aurora kinases play critical roles in regulating spindle assembly, chromosome segregation, and cytokinesis to ensure faithful segregation of chromosomes during mitotic cell division cycle. Molecular and cell biological studies have revealed that Aurora kinases, at physiological levels, orchestrate complex sequential cellular processes at distinct subcellular locations through functional interactions with its various substrates. Aberrant expression of Aurora kinases, on the other hand, cause defects in mitotic spindle assembly, checkpoint response activation, and chromosome segregation leading to chromosomal instability. Elevated expression of Aurora kinases correlating with chromosomal instability is frequently detected in human cancers. Recent genomic profiling of about 3000 human cancer tissue specimens to identify various oncogenic signatures in The Cancer Genome Atlas project has reported that recurrent amplification and overexpression of Aurora kinase-A characterize distinct subsets of human tumors across multiple cancer types. Besides the well-characterized canonical pathway interactions of Aurora kinases in regulating assembly of the mitotic apparatus and chromosome segregation, growing evidence also supports the notion that deregulated expression of Aurora kinases in non-canonical pathways drive transformation and genomic instability by antagonizing tumor suppressor and exacerbating oncogenic signaling through direct interactions with critical proteins. Aberrant expression of the Aurora kinases–p53 protein family signaling axes appears to be critical in the abrogation of p53 protein family mediated tumor suppressor pathways frequently deregulated during oncogenic transformation process. Recent findings reveal the existence of feedback regulatory loops in mRNA expression and protein stability of these protein families and their consequences on downstream effectors involved in diverse physiological functions, such as mitotic progression, checkpoint response pathways, as well as self-renewal and pluripotency in embryonic stem cells. While these investigations have focused on the functional consequences of Aurora kinase protein family interactions with wild-type p53 family proteins, those involving Aurora kinases and mutant p53 remain to be elucidated. This article presents a comprehensive review of studies on Aurora kinases–p53 protein family interactions along with a prospective view on the possible functional consequences of Aurora kinase–mutant p53 signaling pathways in tumor cells. Additionally, we also discuss therapeutic implications of these findings in Aurora kinases overexpressing subsets of human tumors.

NSC-87877 inhibits DUSP26 function in neuroblastoma resulting in p53-mediated apoptosis

Dual specificity protein phosphatase 26 (DUSP26) is overexpressed in high-risk neuroblastoma (NB) and contributes to chemoresistance by inhibiting p53 function. In vitro, DUSP26 has also been shown to effectively inhibit p38 MAP kinase. We hypothesize that inhibiting DUSP26 will result in decreased NB cell growth in a p53 and/or p38-mediated manner. NSC-87877 (8-hydroxy-7-[(6-sulfo-2-naphthyl)azo]-5-quinolinesulfonic acid), a novel DUSP26 small molecule inhibitor, shows effective growth inhibition and induction of apoptosis in NB cell lines. NB cell lines treated with small hairpin RNA (shRNA) targeting DUSP26 also exhibit a proliferation defect both in vitro and in vivo. Treatment of NB cell lines with NSC-87877 results in increased p53 phosphorylation (Ser37 and Ser46) and activation, increased activation of downstream p38 effector proteins (heat shock protein 27 (HSP27) and MAP kinase-activated protein kinase 2 (MAPKAPK2)) and poly ADP ribose polymerase/caspase-3 cleavage. The cytotoxicity resulting from DUSP26 inhibition is partially reversed by knocking down p53 expression with shRNA and also by inhibiting p38 activity with SB203580 (4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]pyridine). In an intrarenal mouse model of NB, NSC-87877 treatment results in decreased tumor growth and increased p53 and p38 activity. Together, these results suggest that DUSP26 inhibition with NSC-87877 is an effective strategy to induce NB cell cytotoxicity in vitro and in vivo through activation of the p53 and p38 mitogen-activated protein kinase (MAPK) tumor-suppressor pathways.

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.

N-Myc and L-Myc are essential for hair cell formation but not maintenance

Sensorineural hearing loss results from damage to the hair cells of the organ of Corti and is irreversible in mammals. While hair cell regeneration may prove to be the ideal therapy after hearing loss, prevention of initial hair cell loss could provide even more benefit at a lower cost. Previous studies have shown that the deletion of Atoh1 results in embryonic loss of hair cells while the absence of Barhl1, Gfi1, and Pou4f3 leads to the progressive loss of hair cells in newborn mice. We recently reported that in the early embryonic absence of N-Myc (using Pax2-Cre), hair cells in the organ of Corti develop and remain until at least seven days after birth, with subsequent progressive loss. Thus, N-Myc plays a role in hair cell viability; however, it is unclear if this is due to its early expression in hair cell precursors and throughout the growing otocyst as it functions through proliferation or its late expression exclusively in differentiated hair cells. Furthermore, the related family member L-Myc is mostly co-expressed in the ear, including in differentiated hair cells, but its function has not been studied and could be partially redundant to N-Myc. To test for a long-term function of the Mycs in differentiated hair cells, we generated nine unique genotypes knocking out N-Myc and/or L-Myc after initial formation of hair cells using the well-characterized Atoh1-Cre. We tested functionality of the auditory and vestibular systems at both P21 and four months of age and under the administration of the ototoxic drug cisplatin. We conclude that neither N-Myc nor L-Myc is likely to play important roles in long-term hair cell maintenance. Therefore, it is likely that the late-onset loss of hair cells resulting from early deletion of the Mycs leads to an unsustainable developmental defect.

p53 in the CNS: Perspectives on Development, Stem Cells, and Cancer

The p53 tumor suppressor potently limits the growth of immature and mature neurons under conditions of cellular stress. Although loss of p53 function contributes to the pathogenesis of central nervous system (CNS) tumors, excessive p53 function is implicated in neural tube defects, embryonic lethality, and neuronal degeneration. Thus, p53 function must be tightly controlled. The anti-proliferative properties of p53 are mediated, in part, through the induction of apoptosis, cell cycle arrest, and senescence. Although there is still much to be learned about the role of p53 in these processes, recent evidence supports exciting new roles for p53 in a wide range of processes, including neural precursor cell self-renewal, differentiation, and cell fate decisions. Understanding the full repertoire of p53 function in CNS development and tumorigenesis may provide us with novel points of therapeutic intervention for human diseases of the CNS.

A clinical overview of centrosome amplification in human cancers

The turn of the 21st century had witnessed a surge of interest in the centrosome and its causal relation to human cancer development - a postulate that has existed for almost a century. Centrosome amplification (CA) is frequently detected in a growing list of human cancers, both solid and haematological, and is a candidate "hallmark" of cancer cells. Several lines of evidence support the progressive involvement of CA in the transition from early to advanced stages of carcinogenesis, being also found in pre-neoplastic lesions and even in histopathologically-normal tissue. CA constitutes the major mechanism leading to chromosomal instability and aneuploidy, via the formation of multipolar spindles and chromosomal missegregation. Clinically, CA may translate to a greater risk for initiation of malignant transformation, tumour progression, chemoresistance and ultimately, poor patient prognosis. As mechanisms underlying CA are progressively being unravelled, the centrosome has emerged as a novel candidate target for cancer treatment. This Review summarizes mainly the clinical studies performed to date focusing on the mechanisms underlying CA in human neoplasia, and highlights the potential utility of centrosomes in the diagnosis, prognosis and treatment of human cancers.

Tripeptidyl Peptidase II Is Required for c-MYC-Induced Centriole Overduplication and a Novel Therapeutic Target in c-MYC-Associated Neoplasms

Centrosome aberrations are frequently detected in c-MYC-associated human malignancies. Here, we show that c-MYC-induced centrosome and centriole overduplication critically depend on the protease tripeptidyl peptidase II (TPPII). We found that TPPII localizes to centrosomes and that overexpression of TPPII, similar to c-MYC, can disrupt centriole duplication control and cause centriole multiplication, a process during which maternal centrioles nucleate the formation of more than a single daughter centriole. We report that inactivation of TPPII using chemical inhibitors or siRNA-mediated protein knockdown effectively reduced c-MYC-induced centriole overduplication. Remarkably, the potent and selective TPPII inhibitor butabindide not only potently suppressed centriole aberrations but also caused significant cell death and growth suppression in aggressive human Burkitt lymphoma cells with c-MYC overexpression. Taken together, these results highlight the role of TPPII in c-MYC-induced centriole overduplication and encourage further studies to explore TPPII as a novel antineoplastic drug target.

Suppression of Aurora-A oncogenic potential by c-Myc downregulation

The abnormality of serine/threonine kinase Aurora-A is seen in many types of cancers. Although in physiological context it has been shown to play a vital role in cellular mitosis, how this oncogene contributes to tumorigenesis remains unclear. Here we demonstrate that Aurora-A overexpression enhances both the expression level and transcriptional activity of c-Myc. The inhibition of c-Myc expression by RNA interference significantly impaired the oncogenic potential of Aurora-A, resulting in attenuated cellular proliferation and transformation rates as well as fewer centrosomal aberrations. Furthermore, downregulation of c-Myc effectively overcame Aurora-A-induced resistance to cisplatin in esophageal cancer cells. Taken together, our results suggest an important role for c-Myc in mediating the oncogenic activity of Aurora-A, which may in turn allow for future targeting of c-Myc as a potential therapeutic strategy for tumors with Aurora-A overexpression.

Pharmacological inhibition of Mdm2 triggers growth arrest and promotes DNA breakage in mouse colon tumors and human colon cancer cells

The p53 tumor suppressor protein performs a number of cellular functions, ranging from the induction of cell cycle arrest and apoptosis to effects on DNA repair. Modulating p53 activity with Mdm2 inhibitors is a promising approach for treating cancer; however, it is presently unclear how the in vivo application of Mdm2 inhibitors impact the myriad processes orchestrated by p53. Since approximately half of all colon cancers (predominately cancers with microsatellite instability) are p53-normal, we assessed the anticancer activity of the Mdm2 inhibitor Nutlin-3 in the mouse azoxymethane (AOM) colon cancer model, in which p53 remains wild type. Using a cell line derived from an AOM-induced tumor, we found that four daily exposures to Nutlin-3 induced persistent p53 stabilization and cell cycle arrest without significant apoptosis. A 4-day dosing schedule in vivo generated a similar response in colon tumors; growth arrest without significantly increased apoptosis. In adjacent normal colon tissue, Nutlin-3 treatment reduced both cell proliferation and apoptosis. Surprisingly, Nutlin-3 induced a transient DNA damage response in tumors but not in adjacent normal tissue. Nutlin-3 likewise induced a transient DNA damage response in human colon cancer cells in a p53-dependent manner, and enhanced DNA strand breakage and cell death induced by doxorubicin. Our findings indicate that Mdm2 inhibitors not only trigger growth arrest, but may also stimulate p53's reported ability to slow homologous recombination repair. The potential impact of Nutlin-3 on DNA repair in tumors suggests that Mdm2 inhibitors may significantly accentuate the tumoricidal actions of certain therapeutic modalities.

Development of target protein-selective degradation inducer for protein knockdown

Our previous technique for inducing selective degradation of target proteins with ester-type SNIPER (Specific and Nongenetic Inhibitor-of-apoptosis-proteins (IAPs)-dependent Protein ERaser) degrades both the target proteins and IAPs. Here, we designed a small-molecular amide-type SNIPER to overcome this issue. As proof of concept, we synthesized and biologically evaluated an amide-type SNIPER which induces selective degradation of cellular retinoic acid binding protein II (CRABP-II), but not IAPs. Such small-molecular, amide-type SNIPERs that induce target protein-selective degradation without affecting IAPs should be effective tools to study the biological roles of target proteins in living cells.

MYCN oncoprotein targets and their therapeutic potential

The MYCN oncogene encodes a transcription factor which is amplified in up to 40% of high risk neuroblastomas. MYCN amplification is a well-established poor prognostic marker in neuroblastoma, however the role of MYCN expression and the mechanisms by which it acts to promote an aggressive phenotype remain largely unknown. This review discusses the current evidence identifying the direct and indirect downstream transcriptional targets of MYCN from recent studies, with particular reference to how MYCN affects the cell cycle, DNA damage response, differentiation and apoptosis in neuroblastoma.

Escape from p53-mediated tumor surveillance in neuroblastoma: switching off the p14(ARF)-MDM2-p53 axis

A primary failsafe program against unrestrained proliferation and oncogenesis is provided by the p53 tumor suppressor protein, inactivation of which is considered as a hallmark of cancer. Intriguingly, mutations of the TP53 gene are rarely encountered in neuroblastoma tumors, suggesting that alternative p53-inactivating lesions account for escape from p53 control in this childhood malignancy. Several recent studies have shed light on the mechanisms by which neuroblastoma cells circumvent the p53-driven antitumor barrier. We review here these mechanisms for evasion of p53-mediated growth control and conclude that deregulation of the p14(ARF)-MDM2-p53 axis seems to be the principal mode of p53 inactivation in neuroblastoma, opening new perspectives for targeted therapeutic intervention.

Combining chromosomal arm status and significantly aberrant genomic locations reveals new cancer subtypes

Many types of tumors exhibit characteristic chromosomal losses or gains, as well as local amplifications and deletions. Within any given tumor type, sample specific amplifications and deletions are also observed. Typically, a region that is aberrant in more tumors, or whose copy number change is stronger, would be considered as a more promising candidate to be biologically relevant to cancer. We sought for an intuitive method to define such aberrations and prioritize them. We define V, the "volume" associated with an aberration, as the product of three factors: (a) fraction of patients with the aberration, (b) the aberration's length and (c) its amplitude. Our algorithm compares the values of V derived from the real data to a null distribution obtained by permutations, and yields the statistical significance (p-value) of the measured value of V. We detected genetic locations that were significantly aberrant, and combine them with chromosomal arm status (gain/loss) to create a succinct fingerprint of the tumor genome. This genomic fingerprint is used to visualize the tumors, highlighting events that are co-occurring or mutually exclusive. We apply the method on three different public array CGH datasets of Medulloblastoma and Neuroblastoma, and demonstrate its ability to detect chromosomal regions that were known to be altered in the tested cancer types, as well as to suggest new genomic locations to be tested. We identified a potential new subtype of Medulloblastoma, which is analogous to Neuroblastoma type 1.

Human neuroblastoma cells rapidly enter cell cycle arrest and apoptosis following exposure to C-28 derivatives of the synthetic triterpenoid CDDO

Synthetic triterpenoids, such as 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) and its derivatives, are an extremely potent class of new anti-cancer therapeutic agents, characterized by high anti-tumor potency and low toxicity to normal tissues. This report is the first to investigate the effects of C-28 derivatives of CDDO on 22 pediatric solid tumor cell lines, including neuroblastoma, rhabdomyosarcoma, osteosarcoma, and Ewing's sarcoma. We determined IC(50)s in the range of 5-170 nM for inhibition of colony formation and DNA synthesis, and 110-630 nM for metabolic cell death and decrease in cell number, using the C-28 CDDO analogs, CDDO methyl ester (CDDO-Me), CDDO imidazolide (CDDO-Im), CDDO ethyl amide (CDDO-EA), CDDO trifluoroethyl amide (CDDO-TFEA), and CDDO diethylamide (CDDO-DE). After treatment of human neuroblastoma cells with CDDO-Me, cell cycle studies show depletion of the S-phase, while apoptosis studies show conformational activation and mitochondrial translocation of Bax protein, as well as activation of caspases -3 and -8. These data demonstrate the potential utility of CDDO analogs as promising novel therapeutic agents for high-risk pediatric solid tumors.