LMO1 Synergizes with MYCN to Promote Neuroblastoma Initiation and Metastasis

A genome-wide association study identified LMO1, which encodes an LIM-domain-only transcriptional cofactor, as a neuroblastoma susceptibility gene that functions as an oncogene in high-risk neuroblastoma. Here we show that dβh promoter-mediated expression of LMO1 in zebrafish synergizes with MYCN to increase the proliferation of hyperplastic sympathoadrenal precursor cells, leading to a reduced latency and increased penetrance of neuroblastomagenesis. The transgenic expression of LMO1 also promoted hematogenous dissemination and distant metastasis, which was linked to neuroblastoma cell invasion and migration, and elevated expression levels of genes affecting tumor cell-extracellular matrix interaction, including loxl3, itga2b, itga3, and itga5. Our results provide in vivo validation of LMO1 as an important oncogene that promotes neuroblastoma initiation, progression, and widespread metastatic dissemination.

Machine Learning-Assisted Network Inference Approach to Identify a New Class of Genes that Coordinate the Functionality of Cancer Networks

Emerging evidence indicates the existence of a new class of cancer genes that act as "signal linkers" coordinating oncogenic signals between mutated and differentially expressed genes. While frequently mutated oncogenes and differentially expressed genes, which we term Class I cancer genes, are readily detected by most analytical tools, the new class of cancer-related genes, i.e., Class II, escape detection because they are neither mutated nor differentially expressed. Given this hypothesis, we developed a Machine Learning-Assisted Network Inference (MALANI) algorithm, which assesses all genes regardless of expression or mutational status in the context of cancer etiology. We used 8807 expression arrays, corresponding to 9 cancer types, to build more than 2 × 108 Support Vector Machine (SVM) models for reconstructing a cancer network. We found that ~3% of ~19,000 not differentially expressed genes are Class II cancer gene candidates. Some Class II genes that we found, such as SLC19A1 and ATAD3B, have been recently reported to associate with cancer outcomes. To our knowledge, this is the first study that utilizes both machine learning and network biology approaches to uncover Class II cancer genes in coordinating functionality in cancer networks and will illuminate our understanding of how genes are modulated in a tissue-specific network contribute to tumorigenesis and therapy development.

Abstract 1040: LIN28B-mediated let-7 independent activation of AKT promotes neuroblastoma pathogenesis

LIN28 is well known as a RNA-binding protein and a suppressor of microRNA biogenesis, by selectively blocking the processing of let-7 precursors. It plays diverse functions in cellular reprogramming, development, metabolism and tumorigenesis. Many of these functions are executed through its ability to inhibit let-7 maturation. However, little is known about its function independent of let-7. Here we made zebrafish transgenic lines expressing high levels of either wild-type or mutant LIN28B (does not block the maturation of let-7) in the peripheral sympathetic nervous system driven by the dopamine beta-hydroxylase promoter. We bred these lines with a transgenic zebrafish line overexpressing the MYCN oncogene in these cells. Either wild-type or mutant LIN28B overexpression accelerated the onset and increased the penetrance of MYCN-induced neuroblastoma, despite the fact that only wild-type LIN28B blocked let-7 maturation compared to MYCN-only tumors. Mechanistically, both wild-type and mutant LIN28B overexpression enhanced MYCN-induced hyperplasia by increasing cell proliferation in the sympathoadrenal lineage. Further studies revealed that overexpression of either wild-type or mutant LIN28B resulted in hyperphosphorylation of AKT on both Ser473 and Thr308 in zebrafish tumors and also serum-deprived human neuroblastoma cell lines. Both wild-type and mutant LIN28B interacted with IGF2BP1, a known interactor that increases stability and translation of a subset of RNAs. We found IGF2 RNA levels to be increased in response to either form of LIN28B. Coincident with IGF2 overexpression, IGF1R was phosphorylated, providing an explanation for PI3K-AKT activation in LIN28B overexpressing cells. Finally, overexpression of a constitutively active, myristoylated murine Akt2 (myr-mAkt2) alone in zebrafish induced ganglioneuroma in the interregnal gland (the zebrafish equivalent of the human adrenal medulla), without a requirement for MCYN overexpression. Thus, our studies indicate that overexpression of LIN28B leads to AKT activation mediated through its interaction with IGF2BP1 and subsequent upregulation of IGF2. This pathway provides a mechanism underlying enhanced transformation in LIN28B overexpressing neuroblastomas, which is independent of the inhibitory activity of LIN28B on let-7 maturation.

Citation Format: Ting Tao, John T. Powers, Hui Shi, Pavlos Missios, Antonio R. Perez-Atayde, Shizhen Zhu, George Q. Daley, Thomas A. Look. LIN28B-mediated let-7 independent activation of AKT promotes neuroblastoma pathogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1040. doi:10.1158/1538-7445.AM2017-1040

Abstract 3871: Modeling the chromatin and transcriptional landscape of MYC and MYCN driven neuroblastoma in zebrafish

Elevated expression levels of MYC family genes are frequently observed in human cancer cells and correlate with tumor aggressiveness and poor prognosis. In neuroblastoma 40% of all cases are high-risk, of which 20% harbor amplification of the MYCN proto-oncogene. In high-risk cases lacking MYCN gene amplification, high expression levels of c-MYC (MYC) are often present and are associated with unfavorable histology and a poor survival. Unlike MYCN amplification, which is frequently observed in the presence of segmental chromosomal aberrations, MYC overexpression is not associated with genetic abnormalities or somatic mutations. In order to study this newly defined subgroup, we have created a novel transgenic zebrafish model in which overexpression of MYC alone in the peripheral sympathetic nervous system (PSNS) drives early-onset neuroblastoma in nearly every fish by seven weeks of age. The tumors resulting from MYC overexpression arise in the interrenal gland, which is the fish counterpart of the adrenal medulla, and are histologically identical to human neuroblastoma. We next performed the Assay for Transposase Accessible Chromatin (ATAC) sequencing and RNA-seq to identify open chromatin regions that correlate with activation of gene transcription. Lineage specific genes essential for neuronal precursor cell identity, such as PHOX2B, HAND2, and TFAP2A are highly expressed in both MYC-expressing and MYCN-amplified human neuroblastoma cell lines and are actively transcribed in zebrafish models of MYC and MYCN driven neuroblastoma. Furthermore, these studies reveal shared and differential regulatory of effects of MYC relative to MYCN activity in maintaining the malignant phenotype of neuroblastoma in vivo. Additional insight into the mechanisms of aberrant transcriptional regulation will inform the future design and use of therapeutic strategies targeting transcription in this high-risk malignancy of childhood.

Citation Format: Mark W. Zimmerman, Shuning He, Shizhen Zhu, Song Yang, Yi Zhou, Leonard I. Zon, A Thomas Look. Modeling the chromatin and transcriptional landscape of MYC and MYCN driven neuroblastoma in zebrafish [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3871. doi:10.1158/1538-7445.AM2017-3871

Neuroblastoma, a Paradigm for Big Data Science in Pediatric Oncology

Pediatric cancers rarely exhibit recurrent mutational events when compared to most adult cancers. This poses a challenge in understanding how cancers initiate, progress, and metastasize in early childhood. Also, due to limited detected driver mutations, it is difficult to benchmark key genes for drug development. In this review, we use neuroblastoma, a pediatric solid tumor of neural crest origin, as a paradigm for exploring "big data" applications in pediatric oncology. Computational strategies derived from big data science-network- and machine learning-based modeling and drug repositioning-hold the promise of shedding new light on the molecular mechanisms driving neuroblastoma pathogenesis and identifying potential therapeutics to combat this devastating disease. These strategies integrate robust data input, from genomic and transcriptomic studies, clinical data, and in vivo and in vitro experimental models specific to neuroblastoma and other types of cancers that closely mimic its biological characteristics. We discuss contexts in which "big data" and computational approaches, especially network-based modeling, may advance neuroblastoma research, describe currently available data and resources, and propose future models of strategic data collection and analyses for neuroblastoma and other related diseases.

Abstract 2433: Loss of chd5-mediated gene repression synergizes with MYCN to accelerate neuroblastoma tumorigenesis in zebrafish

Neuroblastoma is a malignancy of the peripheral sympathetic nervous system (PSNS) and accounts for 10-15% of cancer deaths among children. For the 40% of patients presenting with high-risk disease, current therapeutic approaches are insufficient and long-term survival is less than 50%. Along with genomic amplification of the MYCN oncogene, hemizygous loss of the 1p36 chromosomal region is a major risk factor in neuroblastoma. The human CHD5 gene is a neuronal specific chromatin remodeling helicase that maps to 1p36, and is thus frequently lost in high-risk neuroblastoma. Our laboratory has previously generated a faithful model of pediatric neuroblastoma in the zebrafish driven by overexpression of the MYCN oncogene in the PSNS (dbh:MYCN). Additionally, zebrafish chd5 mutant alleles were created using the newly developed gene editing technologies TALEN and CRISPR-Cas9. The resulting chd5 mutant fish exhibit abnormal development of the PSNS in the form of expansion of the superior cervical ganglia and enlargement of the interrenal gland (adrenal medulla). Haploinsufficiency for Chd5 combined with dbh:MYCN expression accelerates the onset and increases the penetrance of neuroblastoma tumorigenesis in zebrafish, indicating a tumor suppressive function. Elevated p-ERK and PCNA+ cells in tumor tissue indicates that loss of Chd5, cooperates with MYCN overexpression to accelerate neuroblast proliferation in vivo. Chd5 (in addition to Chd3 and Chd4) is a core member of the epigenetic regulatory NuRD complex, which also contains HDAC1-2, MTA1-3, MBD2-3, GATAD2A/B and RBBP4/7. The conserved biological function of Chd5 is to silence gene expression through the maintenance of a repressed chromatin state. Tumors deficient for Chd5 expression exhibit reduced levels of the H3K27me3 histone modification, a marker of facultatively repressed genes. Future studies will further explore the mechanism and function of Chd5 so that the pathways mediating tumor suppression can be elucidated and that essential proteins in these pathways can be targeted in ways that exploit the synthetic lethal relationships that are established.

Citation Format: Mark W. Zimmerman, Shuning He, Jimann Shin, Shizhen Zhu, Feng Guo, Marc Mansour, Deepak Reyon, J Keith Joung, Jinhua Quan, Timur Yusufzai, A Thomas Look. Loss of chd5-mediated gene repression synergizes with MYCN to accelerate neuroblastoma tumorigenesis in zebrafish. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2433.

Abstract 2456: Synergy between loss of NF1 and overexpression of MYCN in neuroblastoma is mediated by the GAP-related domain

Earlier reports indicated that the role of Nf1 tumor suppressor gene in limiting sympathoadrenal cell growth during embryologic development is independent of its ability to down-modulate RAS-MAPK signaling. This finding raised the question of whether neuroblastoma pathogenesis was also accelerated by loss of a similar non-canonical function of NF1. To elucidate how loss of the NF1 tumor suppressor gene contributes to the development of high-risk neuroblastoma, we relied on a transgenic zebrafish model that overexpresses MYCN and harbors loss-of-function nf1 mutations. We show here that loss of nf1 leads to aberrant activation of RAS signaling in MYCN-induced neuroblastoma, promoting both increased tumor cell survival and rapid tumor cell proliferation. We demonstrate further that the GTPase-activating protein (GAP) activity of the (GAP)-related domain (GRD) is sufficient to suppress accelerated initiation of neuroblastoma in nf1-deficient zebrafish, even though this transgene is unable to restrict abnormal sympathoadrenal cell growth during embryologic development. Hence NF1 exhibits different activities in vivo in the normal development and tumorigenesis of the peripheral sympathetic nervous system. Our findings establish nf1-deficient zebrafish that overexpress MYCN as an ideal animal model system for investigating new strategies to improve treatment of very high risk neuroblastomas with aberrant RAS-MAPK activation. We are currently performing high-throughput in vivo drug analysis using these zebrafish with primary tumors.

Citation Format: Shuning He, Marc R. Mansour, Mark W. Zimmerman, Dong Hyuk Ki, Hillary M. Layden, Koshi Akahane, Eric D. de Groh, Antonio R. Perez-Atayde, Shizhen Zhu, Jonathan A. Epstein, A Thomas Look. Synergy between loss of NF1 and overexpression of MYCN in neuroblastoma is mediated by the GAP-related domain. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2456.

Synergy between loss of NF1 and overexpression of MYCN in neuroblastoma is mediated by the GAP-related domain

Earlier reports showed that hyperplasia of sympathoadrenal cell precursors during embryogenesis in Nf1-deficient mice is independent of Nf1’s role in down-modulating RAS-MAPK signaling. We demonstrate in zebrafish that nf1 loss leads to aberrant activation of RAS signaling in MYCN-induced neuroblastomas that arise in these precursors, and that the GTPase-activating protein (GAP)-related domain (GRD) is sufficient to suppress the acceleration of neuroblastoma in nf1-deficient fish, but not the hypertrophy of sympathoadrenal cells in nf1 mutant embryos. Thus, even though neuroblastoma is a classical “developmental tumor”, NF1 relies on a very different mechanism to suppress malignant transformation than it does to modulate normal neural crest cell growth. We also show marked synergy in tumor cell killing between MEK inhibitors (trametinib) and retinoids (isotretinoin) in primary nf1a-/- zebrafish neuroblastomas. Thus, our model system has considerable translational potential for investigating new strategies to improve the treatment of very high-risk neuroblastomas with aberrant RAS-MAPK activation.

DOI:http://dx.doi.org/10.7554/eLife.14713.001

Neuroblastoma is one of the most common childhood cancers and is responsible for about 15% of childhood deaths due to cancer. The neuroblastoma tumors arise in cells that develop into and form part of the body’s nervous system. Many researchers have studied the genetics of this disease and have recognised common patterns. In particular, neuroblastomas can occur when a protein called MYCN is over-produced and a tumor suppressor protein called NF1 is lost.

NF1 is a large protein with several distinct parts or domains. The most studied domain of NF1 is called the GRD, and it is mainly responsible for dampening down signals that cause cells to grow, specialize and survive. However, experiments in mice have revealed that this protein uses its other domains to control the normal development of part of the nervous system.

He et al. wanted to know which domains of NF1 are important for suppressing the growth of neuroblastomas. The experiments were conducted in zebrafish that had been engineered to produce an excess of the human version of MYCN. When He et al. also deleted the gene for the zebrafish’s version of NF1, the fish quickly developed neuroblastomas. Supplying the zebrafish with just the GRD of NF1 was enough to supress the growth of the tumors. These experiments show that NF1 uses different domains and signalling pathways to regulate the normal development of part of the nervous system and to prevent formation of neuroblastoma.

These engineered zebrafish represent an animal model of neuroblastoma that mimics the human disease in many ways. This model will make it possible to test new drug combinations and to find more effective treatments for neuroblastoma patients.

DOI:http://dx.doi.org/10.7554/eLife.14713.002

Neuroblastoma and Its Zebrafish Model

Neuroblastoma, an important developmental tumor arising in the peripheral sympathetic nervous system (PSNS), accounts for approximately 10 % of all cancer-related deaths in children. Recent genomic analyses have identified a spectrum of genetic alterations in this tumor. Amplification of the MYCN oncogene is found in 20 % of cases and is often accompanied by mutational activation of the ALK (anaplastic lymphoma kinase) gene, suggesting their cooperation in tumor initiation and spread. Understanding how complex genetic changes function together in oncogenesis has been a continuing and daunting task in cancer research. This challenge was addressed in neuroblastoma by generating a transgenic zebrafish model that overexpresses human MYCN and activated ALK in the PSNS, leading to tumors that closely resemble human neuroblastoma and new opportunities to probe the mechanisms that underlie the pathogenesis of this tumor. For example, coexpression of activated ALK with MYCN in this model triples the penetrance of neuroblastoma and markedly accelerates tumor onset, demonstrating the interaction of these modified genes in tumor development. Further, MYCN overexpression induces adrenal sympathetic neuroblast hyperplasia, blocks chromaffin cell differentiation, and ultimately triggers a developmentally-timed apoptotic response in the hyperplastic sympathoadrenal cells. In the context of MYCN overexpression, activated ALK provides prosurvival signals that block this apoptotic response, allowing continued expansion and oncogenic transformation of hyperplastic neuroblasts, thus promoting progression to neuroblastoma. This application of the zebrafish model illustrates its value in rational assessment of the multigenic changes that define neuroblastoma pathogenesis and points the way to future studies to identify novel targets for therapeutic intervention.

The ZrO₂ Formation in ZrB₂/SiC Composite Irradiated by Laser

In order to clearly understand the details of ZrO₂ formation during ablation, high intensity continuous laser was chosen to irradiate ZrB₂/SiC. The results reveal that there are two different modes of ZrO₂ formation depending on whether liquid SiO₂ is present. When liquid SiO₂ is present, ZrO₂ generated by the oxidation of ZrB₂ is firstly dissolved into SiO₂. Then, ZrO₂ will precipitate again, the temperature will decrease and the SiO₂ will evaporate. Otherwise, the ZrB₂ will be oxidized to ZrO₂ directly.

Genetic predisposition to neuroblastoma mediated by a LMO1 super-enhancer polymorphism

Neuroblastoma is a paediatric malignancy that typically arises in early childhood, and is derived from the developing sympathetic nervous system. Clinical phenotypes range from localized tumours with excellent outcomes to widely metastatic disease in which long-term survival is approximately 40% despite intensive therapy. A previous genome-wide association study identified common polymorphisms at the LMO1 gene locus that are highly associated with neuroblastoma susceptibility and oncogenic addiction to LMO1 in the tumour cells. Here we investigate the causal DNA variant at this locus and the mechanism by which it leads to neuroblastoma tumorigenesis. We first imputed all possible genotypes across the LMO1 locus and then mapped highly associated single nucleotide polymorphism (SNPs) to areas of chromatin accessibility, evolutionary conservation and transcription factor binding sites. We show that SNP rs2168101 G>T is the most highly associated variant (combined P = 7.47 × 10(-29), odds ratio 0.65, 95% confidence interval 0.60-0.70), and resides in a super-enhancer defined by extensive acetylation of histone H3 lysine 27 within the first intron of LMO1. The ancestral G allele that is associated with tumour formation resides in a conserved GATA transcription factor binding motif. We show that the newly evolved protective TATA allele is associated with decreased total LMO1 expression (P = 0.028) in neuroblastoma primary tumours, and ablates GATA3 binding (P < 0.0001). We demonstrate allelic imbalance favouring the G-containing strand in tumours heterozygous for this SNP, as demonstrated both by RNA sequencing (P < 0.0001) and reporter assays (P = 0.002). These findings indicate that a recently evolved polymorphism within a super-enhancer element in the first intron of LMO1 influences neuroblastoma susceptibility through differential GATA transcription factor binding and direct modulation of LMO1 expression in cis, and this leads to an oncogenic dependency in tumour cells.

Abstract 476: Loss of chd5-mediated tumor suppression accelerates MYCN-driven neuroblastoma tumorigenesis in zebrafish

Neuroblastoma is a childhood tumor of the peripheral sympathetic nervous system (PSNS) that originates from cells of the primitive neural crest. For the 40% of patients with high-risk disease, current therapies are often ineffective and long-term survival remains obstinately low. A major risk factor in neuroblastoma is hemizygous loss of the 1p36 chromosomal region, which has long been suspected to harbor one or more powerful tumor suppressor genes. Our studies indicate that loss of Chromodomain helicase DNA-binding protein 5 (chd5), which is in this deleted region, cooperates with MYCN overexpression to accelerate in vivo neuroblastoma tumorigenesis. Zebrafish chd5-null alleles were created utilizing both zinc-finger nuclease and TALEN technology. The resulting chd5 mutant fish exhibit abnormal development of the PSNS in the form of expansion of the superior cervical ganglia and enlargement of the interrenal gland (adrenal medulla). In order to examine the effect of chd5 haploinsuficiency on in vivo neuroblastoma tumorigenesis, chd5 mutant fish were crossed with the dbh:MYCN transgenic model resulting in neuroblastoma tumors. Consistent with a tumor suppressor function, chd5 haploinsufficient fish exhibit an accelerated neuroblastoma phenotype with tumors present beginning as early as 6 weeks compared to 15 weeks observed in wildtype fish. The chd5 protein can serve as one of two enzymatic components of the nucleosome remodeling and histone deacetylase (NuRD) complex, which is a repressor of gene expression and is reported to have diverse roles in regulating chromatin organization, developmental signaling and gene stability. Future studies will examine the mechanism and function of chd5 so that the pathways mediating tumor suppression can be elucidated and that essential proteins in these pathways can be targeted in ways that exploit the synthetic lethal relationships that are established.

Citation Format: Mark W. Zimmerman, Shuning He, Jimann Shin, Shizhen Zhu, Marc Mansour, Keith Joung, Jinhua Quan, Timur Yusufzai, A. Thomas Look. Loss of chd5-mediated tumor suppression accelerates MYCN-driven neuroblastoma tumorigenesis in zebrafish. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 476. doi:10.1158/1538-7445.AM2015-476

Mosaic zebrafish transgenesis for functional genomic analysis of candidate cooperative genes in tumor pathogenesis

Comprehensive genomic analysis has uncovered surprisingly large numbers of genetic alterations in various types of cancers. To robustly and efficiently identify oncogenic "drivers" among these tumors and define their complex relationships with concurrent genetic alterations during tumor pathogenesis remains a daunting task. Recently, zebrafish have emerged as an important animal model for studying human diseases, largely because of their ease of maintenance, high fecundity, obvious advantages for in vivo imaging, high conservation of oncogenes and their molecular pathways, susceptibility to tumorigenesis and, most importantly, the availability of transgenic techniques suitable for use in the fish. Transgenic zebrafish models of cancer have been widely used to dissect oncogenic pathways in diverse tumor types. However, developing a stable transgenic fish model is both tedious and time-consuming, and it is even more difficult and more time-consuming to dissect the cooperation of multiple genes in disease pathogenesis using this approach, which requires the generation of multiple transgenic lines with overexpression of the individual genes of interest followed by complicated breeding of these stable transgenic lines. Hence, use of a mosaic transient transgenic approach in zebrafish offers unique advantages for functional genomic analysis in vivo. Briefly, candidate transgenes can be coinjected into one-cell-stage wild-type or transgenic zebrafish embryos and allowed to integrate together into each somatic cell in a mosaic pattern that leads to mixed genotypes in the same primarily injected animal. This permits one to investigate in a faster and less expensive manner whether and how the candidate genes can collaborate with each other to drive tumorigenesis. By transient overexpression of activated ALK in the transgenic fish overexpressing MYCN, we demonstrate here the cooperation of these two oncogenes in the pathogenesis of a pediatric cancer, neuroblastoma that has resisted most forms of contemporary treatment.

Abstract 356: Role of the LMO1 oncogene in neuroblastoma pathogenesis

Neuroblastoma, an embryonic tumor of the peripheral sympathetic nervous system (PSNS), accounts for 10% of all childhood cancer deaths. We recently developed a robust zebrafish model of neuroblastoma and demonstrated that activated ALK synergizes with MYCN by inhibiting a developmentally-timed apoptotic response that is otherwise induced by MYCN (Zhu et.al. Cancer Cell, 2012). We have now used this model to provide evidence in support of the results of a neuroblastoma genome-wide association study (GWAS) showing that common variation within the LIM domain-only 1 (LMO1) gene locus is highly associated with the development of advanced neuroblastoma and may function as an oncogene in established disease (Wang K et.al. Nature, 2011). We are collaborating because our zebrafish system provides a robust in vivo tumor model to investigate the underlying mechanisms through which LMO1 overexpression contributes to malignant transformation. Here we developed transgenic lines in which LMO1 is overexpressed in the PSNS under control of the dopamine-beta-hydroxylase (dβh) promoter. We observed that overexpression of LMO1 in three individual transgenic lines synergized with MYCN to accelerate the onset of neuroblastoma in the interrenal gland (IRG), the zebrafish analogue of the adrenal medulla. Tumors began to appear at 13 weeks in transgenic fish overexpressing MYCN alone and this latency was shortened dramatically to 5 weeks (p=0.02) and the penetrance was increased more than three-fold in the transgenic fish coexpressing both MYCN and LMO1. In addition, we found that coexpression of LMO1 with activated ALK induced neuroblastoma, which is the first time in our model system that neuroblastoma has been induced without MYCN overexpression. Thus, the zebrafish model system appears to be robust for “functional genomics analysis” to provide in vivo evidence and investigate mechanisms and pathways underlying new associations emerging from GWAS, tumor genome resequencing and other genome-wide technologies that are currently under intense investigation in human cancers.

Citation Format: Shizhen Zhu, Andrew Wood, Shuning He, Rebecca Stanton, Feng Guo, John Maris, A. Thomas Look. Role of the LMO1 oncogene in neuroblastoma pathogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 356. doi:10.1158/1538-7445.AM2013-356

Abstract 4252: Activated ALK collaborates with MYCN in neuroblastoma pathogenesis

Neuroblastoma is a developmental tumor that arises in the peripheral sympathetic nervous system and accounts for 10% of all cancer-related deaths in children. The anaplastic lymphoma kinase (ALK) gene is mutationally activated in a subset of primary neuroblastomas, including those with MYCN gene amplification, suggesting pathogenic cooperation. Because the mechanism underlying this cooperation is unclear, we generated a novel transgenic zebrafish model that overexpresses human MYCN and activated ALK in the peripheral sympathetic nervous system to analyze their interaction. The expression of MYCN in this model induces neuroblastomas in the inter-renal gland, the zebrafish analogue of the adrenal medulla, which is the site of origin observed in approximately half of childhood neuroblastomas. Furthermore, the tumors resemble human neuroblastomas histologically, immunohistochemically and ultrastructurally. Concomitant expression of activated ALK with MYCN in this model profoundly accelerates the onset of neuroblastoma and markedly increases disease penetrance. Detailed in vivo analyses show that MYCN overexpression induces adrenal sympathetic neuroblast hyperplasia, blocks chromaffin cell differentiation, and triggers a developmentally-timed apoptotic response in the hyperplastic sympathoadrenal cells. Coexpression of activated ALK with MYCN provides prosurvival signals that block this apoptotic response and allow continued expansion and oncogenic transformation of hyperplastic neuroblasts. Taken together, these findings provide a mechanism for the synergistic interplay of MYCN with activated ALK in neuroblastoma pathogenesis and demonstrate the utility of the zebrafish model in understanding human disease processes that may aid the development of improved therapeutic strategies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4252. doi:1538-7445.AM2012-4252

Activated ALK collaborates with MYCN in neuroblastoma pathogenesis

Amplification of the MYCN oncogene in childhood neuroblastoma is often accompanied by mutational activation of ALK (anaplastic lymphoma kinase), suggesting their pathogenic cooperation. We generated a transgenic zebrafish model of neuroblastoma in which MYCN-induced tumors arise from a subpopulation of neuroblasts that migrate into the adrenal medulla analog following organogenesis. Coexpression of activated ALK with MYCN in this model triples the disease penetrance and markedly accelerates tumor onset. MYCN overexpression induces adrenal sympathetic neuroblast hyperplasia, blocks chromaffin cell differentiation, and ultimately triggers a developmentally-timed apoptotic response in the hyperplastic sympathoadrenal cells. Coexpression of activated ALK with MYCN provides prosurvival signals that block this apoptotic response and allow continued expansion and oncogenic transformation of hyperplastic neuroblasts, thus promoting progression to neuroblastoma.

Using zebrafish for studying Rho GTPases signaling in vivo

Rho small GTPases play pivotal roles in a variety of dynamic cellular processes including cytoskeleton rearrangement, cell migration, cell proliferation, cell survival, and gene regulation. However, their functions in vivo are much less understood. Recently, the zebrafish, Danio rerio has emerged as a powerful model organism for developmental and genetic studies. Zebrafish embryos have many unique characteristics, such as optical transparency, external fertilization and development, and amenability for various molecular manipulations including morpholino oligo-mediated gene knockdown, mRNA or DNA overexpression-induced gain of function or rescue, in situ hybridization (ISH) with riboprobes for gene expression, western blot for protein analysis, small-molecule inhibition on signaling pathways, and bioimaging for tracking of molecular events. Taking many of such advantages, we have demonstrated the role of rhoA small GTPase in the control of gastrulation cell movements and cell survival during early zebrafish embryogenesis, linking RhoA functions to at least the noncanonical Wnt, Mek/Erk, and Bcl2 signaling nodes in vivo. Here, we describe the use of such techniques, including gene knockdown by morpholino oligo, functional rescue by mRNA overexpression, microinjection, ISH, western blot analysis and pharmacological inhibition of signaling pathways by small molecule inhibitors, with special considerations on their merits, potential drawbacks, and adaptation which could pave the way to our better understanding of the roles of various classes of small GTPases in regulating cell dynamics and development in vivo.

Pten mediates Myc oncogene dependence in a conditional zebrafish model of T cell acute lymphoblastic leukemia

Loss-of-function mutations in pten genes, or expression of a constitutively active version of Akt2, render T-ALL cell survival and disease progression independent of Myc.

The MYC oncogenic transcription factor is overexpressed in most human cases of T cell acute lymphoblastic leukemia (T-ALL), often downstream of mutational NOTCH1 activation. Genetic alterations in the PTEN–PI3K–AKT pathway are also common in T-ALL. We generated a conditional zebrafish model of T-ALL in which 4-hydroxytamoxifen (4HT) treatment induces MYC activation and disease, and withdrawal of 4HT results in T-ALL apoptosis and tumor regression. However, we found that loss-of-function mutations in zebrafish pten genes, or expression of a constitutively active Akt2 transgene, rendered tumors independent of the MYC oncogene and promoted disease progression after 4HT withdrawal. Moreover, MYC suppresses pten mRNA levels, suggesting that Akt pathway activation downstream of MYC promotes tumor progression. Our findings indicate that Akt pathway activation is sufficient for tumor maintenance in this model, even after loss of survival signals driven by the MYC oncogene.

Abstract 4296: Activated ALK accelerates the onset of neuroblastoma in MYCN-transgenic zebrafish

Neuroblastoma is the most common extracranial solid tumor in children and originates during development of the peripheral sympathetic nervous system. Advanced-stage disease and a poor outcome are associated with amplification of the MYCN oncogene, often in combination with mutational activation or amplification of another oncogene ALK (anaplastic lymphoma kinase), suggesting that they cooperate in neuroblastoma pathogenesis. To investigate this possibility, we generated a transgenic zebrafish model of neuroblastoma in which human MYCN is expressed under the control of the dopamine-beta-hydroxylase promoter, and show that the resultant tumors recapitulate childhood neuroblastomas histologically, immunohistochemically, and ultrastructurally. Surprisingly, the tumors arise from a subpopulation of neuroblasts that migrate into the adrenal analogue (interrenal gland) in the zebrafish after organogenesis is complete. Coexpression of activated ALK with MYCN markedly increased the frequency of neuroblastoma and accelerated the time of onset, providing conclusive evidence for synergistic interplay between these two oncogenes in neuroblastoma pathogenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4296. doi:10.1158/1538-7445.AM2011-4296

Oligodendrocyte progenitor cell numbers and migration are regulated by the zebrafish orthologs of the NF1 tumor suppressor gene

Neurofibromatosis type 1 is the most commonly inherited human cancer predisposition syndrome. Neurofibromin (NF1) gene mutations lead to increased risk of neurofibromas, schwannomas, low grade, pilocytic optic pathway gliomas, as well as malignant peripheral nerve sheath tumors and glioblastomas. Despite the evidence for NF1 tumor suppressor function in glial cell tumors, the mechanisms underlying transformation remain poorly understood. In this report, we used morpholinos to knockdown the two nf1 orthologs in zebrafish and show that oligodendrocyte progenitor cell (OPC) numbers are increased in the developing spinal cord, whereas neurons are unaffected. The increased OPC numbers in nf1 morphants resulted from increased proliferation, as detected by increased BrdU labeling, whereas TUNEL staining for apoptotic cells was unaffected. This phenotype could be rescued by the forced expression of the GTPase-activating protein (GAP)-related domain of human NF1. In addition, the in vivo analysis of OPC migration following nf1 loss using time-lapse microscopy demonstrated that olig2-EGFP(+) OPCs exhibit enhanced cell migration within the developing spinal cord. OPCs pause intermittently as they migrate, and in nf1 knockdown animals, they covered greater distances due to a decrease in average pause duration, rather than an increase in velocity while in motion. Interestingly, nf1 knockdown also leads to an increase in ERK signaling, principally in the neurons of the spinal cord. Together, these results show that negative regulation of the Ras pathway through the GAP activity of NF1 limits OPC proliferation and motility during development, providing insight into the oncogenic mechanisms through which NF1 loss contributes to human glial tumors.

Abstract LB-162: The onset of MYCN overexpression-induced neuroblastoma is accelerated by ALK mutation in zebrafish

Neuroblastoma (NB) is the most common extracranial solid tumor in infancy and originates in the peripheral sympathetic nervous system (PSNS). High-risk NB is fatal in the majority of patients, despite intensive myeloablative chemotherapy. The MYCN oncogene is amplified in over 20% of NB, particularly in those with highest risk treatment failure. We have developed a zebrafish NB model by overexpressing human MYCN under the control of the dopamine-beta-hydroxylase (D) promoter specific for noradrenergic cells in the PSNS. Fish from this stable transgenic line developed tumors as early as 4 months of age with approximately 20% penetrance at 8 months of age. The tumors resemble human NB histologically, immunohistochemically, and ultrastructurally. The expression of MYCN suppressed the normal development of PSNS neurons and chromaffin cells in the head kidney during embryogenesis and in young adult fish. In some fish, tumor cells began to repopulate the interrenal gland of the head kidney by 2 months of age. Germline and somatic activating mutations have been identified in the ALK gene, which encodes a receptor tyrosine kinase, in human NB, including those with MYCN amplification. To assess cooperativity between amplified MYCN and mutant ALK genes in transformation, we generated a zebrafish stable transgenic line in which the activated mutant form of ALK (F1174L) was expressed under the control of the DßH promoter. These transgenic animals did not display an abnormal phenotype nor did they develop tumors during the first 6 months of life. In contrast, mutant ALK expression accelerated the onset of MYCN-induced neuroblastoma when the 2 genes were co-expressed in double transgenic fish, indicating that MYCN over-expression and activating ALK mutations can cooperate in tumorigenesis. Although co-expression of mutant ALK accelerated the onset of tumors, it did not rescue the MYCN-induced suppression of PSNS development, suggesting that an as-yet-unidentified tumor suppressor gene, possibly located on distal 1p in the human genome, may be lost to fulfill this role in NB tumorigenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-162.

RhoA acts downstream of Wnt5 and Wnt11 to regulate convergence and extension movements by involving effectors Rho Kinase and Diaphanous: Use of zebrafish as an in vivo model for GTPase signaling

Gastrulation shapes the early embryos by forming three germ layers, ectoderm, mesoderm and endoderm. In vertebrates, this process requires massive cell rearrangement including convergence and extension (CE) movements that involve narrowing and lengthening of embryonic tissues as well as cell elongation. Such polarization and movements require precise reorganization and regulation of the cytoskeleton network and cell adhesion. Rho small GTPases are key regulators for dynamic actin cytoskeleton. However, the signaling mechanisms underlying their functions in CE remain to be further elucidated. We have cloned the zebrafish Danio rerio rhoA and by capitalizing on the specific functional knockdown using morpholinos against rhoA and the availability of CE mutants defective in Wnt signaling, we showed that rhoA morphants were reminiscent to noncanonical wnt mutants with serious disruption in CE movements. Injection of rhoA mRNA effectively rescued such defects in wnt5 and wnt11 mutants. Furthermore, CE defects in rhoA knockdown or wnt mutants can be suppressed through functional bypass after ectopic expression of the two mammalian Rho effectors, the Rho kinase and Diaphanous (mDia). These results provide the first evidence that the RhoA in vivo acts downstream of Wnt5 and Wnt11 to effect, without affecting cell fates, on the CE movements in zebrafish embryos. Significantly, it elicits such effect via both effectors, Rho kinase and Dia. These findings also support the versatility of the zebrafish as a model to further investigate the roles of various classes of small GTPases in regulating cell dynamics in vivo.

A monomeric L-aspartase obtained by in vitro selection

By mimicking the partial spatial structure of the dimer of the l-aspartase subunit, the central ten-helix bundle, and an "active site" between the cleft of domain 1 (D1) and domain 3 (D3) from different subunits, we designed l-aspartase variants, in which D1D2 and D2D3 were ligated with a random hexapeptide loop. As expected, we obtained the variant with the highest activity (relative activity is 21.3% of the native enzyme, named as drAsp017) by in vitro selection. The molecular weight of this variant, obtained from size-exclusion column chromatography, is about 81 kDa, which indicates that it is indeed a monomer, whereas native l-aspartase is a tetramer. The activity-reversibility of drAsp017 (10(-7) m) was 80% after incubation for 30 min at 50 degrees C, while native enzyme only retained about 17% under the same conditions. Reactivation of drAsp017 denatured in 4 m guanidine HCl was independent of protein concentration at up to 20 x 10(-8) m at 25 degrees C, whereas the protein concentration of native enzyme strongly affected its reactivation under the above conditions. The sensitivity of drAsp017 (10(-7) m) to effective factors in the fumarate-amination reaction compared with native enzyme was also determined. Half-saturating concentrations of the activator l-aspartate and Mg2+ for drAsp017 (0.8 and 0.5 mm, respectively) are much higher than that of the native enzyme (0.10 and 0.15 mm, respectively). The data show that a monomeric l-aspartase is obtained by in vitro selection. Thus, the conversion of oligomeric proteins into their functional monomers could have important applications.