Promoter hypermethylation as a mechanism for Lamin A/C silencing in a subset of neuroblastoma cells

Targeting c-Myc transactivation by LMNA inhibits tRNA processing essential for malate-aspartate shuttle and tumour progression

BACKGROUND

A series of studies have demonstrated the emerging involvement of transfer RNA (tRNA) processing during the progression of tumours. Nevertheless, the roles and regulating mechanisms of tRNA processing genes in neuroblastoma (NB), the prevalent malignant tumour outside the brain in children, are yet unknown.

METHODS

Analysis of multi-omics results was conducted to identify crucial regulators of downstream tRNA processing genes. Co-immunoprecipitation and mass spectrometry methods were utilised to measure interaction between proteins. The impact of transcriptional regulators on expression of downstream genes was measured by dual-luciferase reporter, chromatin immunoprecipitation, western blotting and real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) methods. Studies have been conducted to reveal impact and mechanisms of transcriptional regulators on biological processes of NB. Survival differences were analysed using the log-rank test.

RESULTS

c-Myc was identified as a transcription factor driving tRNA processing gene expression and subsequent malate-aspartate shuttle (MAS) in NB cells. Mechanistically, c-Myc directly promoted the expression of glutamyl-prolyl-tRNA synthetase (EPRS) and leucyl-tRNA synthetase (LARS), resulting in translational up-regulation of glutamic-oxaloacetic transaminase 1 (GOT1) as well as malate dehydrogenase 1 (MDH1) via inhibiting general control nonrepressed 2 or activating mechanistic target of rapamycin signalling. Meanwhile, lamin A (LMNA) inhibited c-Myc transactivation via physical interaction, leading to suppression of MAS, aerobic glycolysis, tumourigenesis and aggressiveness. Pre-clinically, lobeline was discovered as a LMNA-binding compound to facilitate its interaction with c-Myc, which inhibited aminoacyl-tRNA synthetase expression, MAS and tumour progression of NB, as well as growth of organoid derived from c-Myc knock-in mice. Low levels of LMNA or elevated expression of c-Myc, EPRS, LARS, GOT1 or MDH1 were linked to a worse outcome and a shorter survival time of clinical NB patients.

CONCLUSIONS

These results suggest that targeting c-Myc transactivation by LMNA inhibits tRNA processing essential for MAS and tumour progression.

A biomechanical view of epigenetic tumor regulation

The occurrence and development of tumors depend on a complex regulation by not only biochemical cues, but also biomechanical factors in tumor microenvironment. With the development of epigenetic theory, the regulation of biomechanical stimulation on tumor progress genetically is not enough to fully illustrate the mechanism of tumorigenesis. However, biomechanical regulation on tumor progress epigenetically is still in its infancy. Therefore, it is particularly important to integrate the existing relevant researches and develop the potential exploration. This work sorted out the existing researches on the regulation of tumor by biomechanical factors through epigenetic means, which contains summarizing the tumor epigenetic regulatory mode by biomechanical factors, exhibiting the influence of epigenetic regulation under mechanical stimulation, illustrating its existing applications, and prospecting the potential. This review aims to display the relevant knowledge through integrating the existing studies on epigenetic regulation in tumorigenesis under mechanical stimulation so as to provide theoretical basis and new ideas for potential follow-up research and clinical applications. Mechanical factors under physiological conditions stimulate the tumor progress through epigenetic ways, and new strategies are expected to be found with the development of epidrugs and related delivery systems.

Mechanical profile of human keratinocytes expressing HPV-18 oncogenes

During tumorigenesis, the mechanical properties of cancer cells change markedly, with decreased stiffness often accompanying a more invasive phenotype. Less is known about the changes in mechanical parameters at intermediate stages in the process of malignant transformation. We have recently developed a pre-tumoral cell model by stably transducing the immortalized but non-tumorigenic human keratinocyte cell line HaCaT with the E5, E6 and E7 oncogenes from HPV-18, one of the leading causes of cervical cancer and other types of cancer worldwide. We have used atomic force microscopy (AFM) to measure cell stiffness and to obtain mechanical maps of parental HaCaT and HaCaT E5/E6/E7-18 cell lines. We observed a significant decrease in Young's modulus in HaCaT E5/E6/E7-18 cells measured by nanoindentation in the central region, as well as decreased cell rigidity in regions of cell-cell contact measured by Peakforce Quantitative Nanomechanical Mapping (PF-QNM). As a morphological correlate, HaCaT E5/E6/E7-18 cells displayed a significantly rounder cell shape than parental HaCaT cells. Our results therefore show that decreased stiffness with concomitant perturbations in cell shape are early mechanical and morphological changes during the process of malignant transformation.

Tumoral heterogeneity in neuroblastoma

Neuroblastoma is a solid, neuroendocrine tumor with divergent clinical behavior ranging from asymptomatic to fatal. The diverse clinical presentations of neuroblastoma are directly linked to the high intra- and inter-tumoral heterogeneity it presents. This heterogeneity is strongly associated with therapeutic resistance and continuous relapses, often leading to fatal outcomes. The development of successful risk assessment and tailored treatment strategies lies in evaluating the extent of heterogeneity via the accurate genetic and epigenetic profiling of distinct cell subpopulations present in the tumor. Recent studies have focused on understanding the molecular mechanisms that drive tumoral heterogeneity in pursuing better therapeutic and diagnostic approaches. This review describes the cellular, genetic, and epigenetic aspects of neuroblastoma heterogeneity. In addition, we summarize the recent findings on three crucial factors that can lead to heterogeneity in solid tumors: the inherent diversity of the progenitor cells, the presence of cancer stem cells, and the influence of the tumor microenvironment.

Lamin A and telomere maintenance in aging: Two to Tango

Lamin proteins which constitute the nuclear lamina in almost all higher eukaryotes, are mainly of two types A & B encoded by LMNA and LMNB1/B2 genes respectively. While lamin A remains the principal product of LMNA gene, variants like lamin C, C2 and A∆10 are also formed as alternate splice products. Role of lamin A in aging has been highlighted in recent times due to its association with progeroid or premature aging syndromes which is classified as a type of laminopathy. Progeria caused by accelerated accumulation of lamin A Δ50 or progerin occurs due to a mutation in this LMNA gene leading to defects in post translational modification of lamin A. One of the most common and severe symptoms of progeroid laminopathy is accelerated cellular senescence or aging along with bone resorption, muscle weakness, lipodystrophy and cardiovascular disorders. On the other hand, progerin accumulation and telomere dysfunction merge as common traits in the process of chronological aging. Two major hallmarks of physiological aging in humans include loss of genomic integrity and telomere attrition which can result from defective laminar organization leading to deformed nuclear architecture and culminates into replicative senescence. This also adversely affects epigenetic landscape, mitochondrial dysfunction and several signalling pathways like DNA repair, mTOR, MAPK, TGFβ. In this review, we discuss the telomere-lamina interplay in the context of physiological aging and progeria.

Lamin A and the LINC complex act as potential tumor suppressors in Ewing Sarcoma

Lamin A, a main constituent of the nuclear lamina, is involved in mechanosignaling and cell migration through dynamic interactions with the LINC complex, formed by the nuclear envelope proteins SUN1, SUN2 and the nesprins. Here, we investigated lamin A role in Ewing Sarcoma (EWS), an aggressive bone tumor affecting children and young adults. In patients affected by EWS, we found a significant inverse correlation between LMNA gene expression and tumor aggressiveness. Accordingly, in experimental in vitro models, low lamin A expression correlated with enhanced cell migration and invasiveness and, in vivo, with an increased metastatic load. At the molecular level, this condition was linked to altered expression and anchorage of nuclear envelope proteins and increased nuclear retention of YAP/TAZ, a mechanosignaling effector. Conversely, overexpression of lamin A rescued LINC complex organization, thus reducing YAP/TAZ nuclear recruitment and preventing cell invasiveness. These effects were also obtained through modulation of lamin A maturation by a statin-based pharmacological treatment that further elicited a more differentiated phenotype in EWS cells. These results demonstrate that drugs inducing nuclear envelope remodeling could be exploited to improve therapeutic strategies for EWS.

Revealing the heterogeneity in neuroblastoma cells via nanopillar-guided subnuclear deformation

Neuroblastoma is a hard-to-treat childhood cancer that is well known for the heterogeneity of its clinical phenotypes. Although the risk levels of neuroblastoma have been defined from a complex matrix of clinical and tumor biological factors to guide treatment, the accuracy in predicting cancer relapse and related fatality is still poor in many cases, where heterogeneity with subpopulations in highly malignant or drug-resistant tumors is believed to be underestimated by the current analysis methods. Therefore, new technologies to probe neuroblastoma heterogeneity are needed for the improvement of risk stratification. In this study, we introduce the nanopillar-guided subnuclear morphology as an effective indicator for heterogeneity evaluation among individual neuroblastoma cells. Nuclear polymorphisms, especially the generation of subnuclear irregularities, are well-known markers of high cancer metastasis risk and poor prognosis. By quantitatively evaluating the orientation of nanopillar-guided nuclear envelope features in neuroblastoma cells, we identified two subpopulations with differential motilities and EMT marker levels. Moreover, with endogenous expression, cells with high levels of the nuclear structure protein lamin A exhibit anisotropic deformation on nanopillars and migrate faster than low-lamin A cells, indicating a greater potential for metastasis. Overexpression of lamin A, however, reduces both the coherency and migration speed, suggesting that subpopulations with similar lamin A levels may have different metastatic potentials. We further verified that nanopillar-generated nuclear deformation patterns can quantitatively reveal individual cells' responses to anti-cancer drug treatment. Overall, we envision that the nanopillar-based assessment of subnuclear irregularities brings new additions to our toolkits for both precise risk stratification in neuroblastoma and the evaluation of related anti-cancer therapeutics.

NTRK1/TrkA Signaling in Neuroblastoma Cells Induces Nuclear Reorganization and Intra-Nuclear Aggregation of Lamin A/C

Simple Summary

Neuroblastoma (NB) accounts for 15% of all cancer-related deaths of children. While the amplification of the Myc-N proto-oncogene (MYCN) is a major driver of aggressive NB, the expression of the neurotrophin receptor, NTRK1/TrkA, has been shown to be associated with an excellent outcome. MYCN downregulates NTRK1 expression, but it is unknown if the molecular effects of NTRK1 signaling also affect MYCN-induced networks. The aim of this study was to decipher NTRK1 signaling using an unbiased proteome and phosphoproteome approach. To this end, we realized inducible ectopic NTRK1 expression in a NB cell line with MYCN amplification and analyzed the proteomic changes upon NTRK1 activation in a time-dependent manner. In line with the phenotypes observed, NTRK1 activation induced markers of neuronal differentiation and cell cycle arrest. Most prominently, NTRK1 upregulated the expression and phosphorylation of the nuclear lamina component Lamin A/C. Moreover, NTRK1 signaling also induced the aggregation of LMNA within nucleic foci, which accompanies differentiation in other cell types.

Abstract

(1) Background: Neuroblastomas (NBs) are the most common extracranial solid tumors of children. The amplification of the Myc-N proto-oncogene (MYCN) is a major driver of NB aggressiveness, while high expression of the neurotrophin receptor NTRK1/TrkA is associated with mild disease courses. The molecular effects of NTRK1 signaling in MYCN-amplified NB, however, are still poorly understood and require elucidation. (2) Methods: Inducible NTRK1 expression was realized in four NB cell lines with (IMR5, NGP) or without MYCN amplification (SKNAS, SH-SY5Y). Proteome and phosphoproteome dynamics upon NTRK1 activation by its ligand, NGF, were analyzed in a time-dependent manner in IMR5 cells. Target validation by immunofluorescence staining and automated image processing was performed using the three other NB cell lines. (3) Results: In total, 230 proteins and 134 single phosphorylated class I phosphosites were found to be significantly regulated upon NTRK1 activation. Among known NTRK1 targets, Stathmin and the neurosecretory protein VGF were recovered. Additionally, we observed the upregulation and phosphorylation of Lamin A/C (LMNA) that accumulated inside nuclear foci. (4) Conclusions: We provide a comprehensive picture of NTRK1-induced proteome and phosphoproteome dynamics. The phosphorylation of LMNA within nucleic aggregates was identified as a prominent feature of NTRK1 signaling independent of the MYCN status of NB cells.

Hyperglycemia and hyperlipidemia can induce morphophysiological changes in rat cardiac cell line

H9c2 cardiac cells were incubated under the control condition and at different hyperglycemic and hyperlipidemic media, and the following parameters were determined and quantified: a) cell death, b) type of cell death, and c) changes in cell length, width and height. Of all the proven media, the one that showed the greatest differences compared to the control was the medium glucose (G) 33 mM + 500 μM palmitic acid. This condition was called the hyperglycemic and hyperlipidemic condition (HHC). Incubation of H9c2 cells in HHC promoted 5.2 times greater total cell death when compared to the control. Of the total death ofthe HHC cells, 38.6% was late apoptotic and 8.3% early apoptotic. HHC also changes cell morphology. The reordering of the actin cytoskeleton and cell stiffness was also studied in control and HHC cells. The actin cytoskeleton was quantified and the number and distance of actin bundles were not the same in the control as under HHC. Young's modulus images show a map of cell stiffness. Cells incubated in HHC with the reordered actin cytoskeleton were stiffer than those incubated in control. The region of greatest stiffness was the peripheral zone of HHC cells (where the number of actin bundles was higher and the distance between them smaller). Our results suggest a correlation between the reordering of the actin cytoskeleton and cell stiffness. Thus, our study showed that HHC can promote morphophysiological changes in rat cardiac cells confirming that gluco-and lipotoxicity may play a central role in the development of diabetic cardiomyopathy.

Lamin A/C: Function in Normal and Tumor Cells

Simple Summary

The aim of this review is to summarize lamin A/C’s currently known functions in both normal and diseased cells. Lamin A/C is a nuclear protein with many functions in cells, such as maintaining a cell’s structural stability, cell motility, mechanosensing, chromosome organization, gene regulation, cell differentiation, DNA damage repair, and telomere protection. Mutations of the lamin A/C gene, incorrect processing of the protein, and lamin A/C deregulation can lead to various diseases and cancer. This review touches on diseases caused by mutation and incorrect processing of lamin A/C, called laminopathies. The effect of lamin A/C deregulation in cancer is also reviewed, and lamin A/C’s potential in helping to diagnose prostate cancers more accurately is discussed.

Abstract

This review is focused on lamin A/C, a nuclear protein with multiple functions in normal and diseased cells. Its functions, as known to date, are summarized. This summary includes its role in maintaining a cell’s structural stability, cell motility, mechanosensing, chromosome organization, gene regulation, cell differentiation, DNA damage repair, and telomere protection. As lamin A/C has a variety of critical roles within the cell, mutations of the lamin A/C gene and incorrect processing of the protein results in a wide variety of diseases, ranging from striated muscle disorders to accelerated aging diseases. These diseases, collectively termed laminopathies, are also touched upon. Finally, we review the existing evidence of lamin A/C’s deregulation in cancer. Lamin A/C deregulation leads to various traits, including genomic instability and increased tolerance to mechanical insult, which can lead to more aggressive cancer and poorer prognosis. As lamin A/C’s expression in specific cancers varies widely, currently known lamin A/C expression in various cancers is reviewed. Additionally, Lamin A/C’s potential as a biomarker in various cancers and as an aid in more accurately diagnosing intermediate Gleason score prostate cancers is also discussed.

Correlating nuclear morphology and external force with combined atomic force microscopy and light sheet imaging separates roles of chromatin and lamin A/C in nuclear mechanics

Nuclei are often under external stress, be it during migration through tight constrictions or compressive pressure by the actin cap, and the mechanical properties of nuclei govern their subsequent deformations. Both altered mechanical properties of nuclei and abnormal nuclear morphologies are hallmarks of a variety of disease states. Little work, however, has been done to link specific changes in nuclear shape to external forces. Here, we utilize a combined atomic force microscope and light sheet microscope to show SKOV3 nuclei exhibit a two-regime force response that correlates with changes in nuclear volume and surface area, allowing us to develop an empirical model of nuclear deformation. Our technique further decouples the roles of chromatin and lamin A/C in compression, showing they separately resist changes in nuclear volume and surface area, respectively; this insight was not previously accessible by Hertzian analysis. A two-material finite element model supports our conclusions. We also observed that chromatin decompaction leads to lower nuclear curvature under compression, which is important for maintaining nuclear compartmentalization and function. The demonstrated link between specific types of nuclear morphological change and applied force will allow researchers to better understand the stress on nuclei throughout various biological processes.

Correlating nuclear morphology and external force with combined atomic force microscopy and light sheet imaging separates roles of chromatin and lamin A/C in nuclear mechanics

Nuclei are often under external stress, be it during migration through tight constrictions or compressive pressure by the actin cap, and the mechanical properties of nuclei govern their subsequent deformations. Both altered mechanical properties of nuclei and abnormal nuclear morphologies are hallmarks of a variety of disease states. Little work, however, has been done to link specific changes in nuclear shape to external forces. Here, we utilize a combined atomic force microscope and light sheet microscope to show SKOV3 nuclei exhibit a two-regime force response that correlates with changes in nuclear volume and surface area, allowing us to develop an empirical model of nuclear deformation. Our technique further decouples the roles of chromatin and lamin A/C in compression, showing they separately resist changes in nuclear volume and surface area, respectively; this insight was not previously accessible by Hertzian analysis. A two-material finite element model supports our conclusions. We also observed that chromatin decompaction leads to lower nuclear curvature under compression, which is important for maintaining nuclear compartmentalization and function. The demonstrated link between specific types of nuclear morphological change and applied force will allow researchers to better understand the stress on nuclei throughout various biological processes.

Modeling of Cell Nuclear Mechanics: Classes, Components, and Applications

Cell nuclei are paramount for both cellular function and mechanical stability. These two roles of nuclei are intertwined as altered mechanical properties of nuclei are associated with altered cell behavior and disease. To further understand the mechanical properties of cell nuclei and guide future experiments, many investigators have turned to mechanical modeling. Here, we provide a comprehensive review of mechanical modeling of cell nuclei with an emphasis on the role of the nuclear lamina in hopes of spurring future growth of this field. The goal of this review is to provide an introduction to mechanical modeling techniques, highlight current applications to nuclear mechanics, and give insight into future directions of mechanical modeling. There are three main classes of mechanical models-schematic, continuum mechanics, and molecular dynamics-which provide unique advantages and limitations. Current experimental understanding of the roles of the cytoskeleton, the nuclear lamina, and the chromatin in nuclear mechanics provide the basis for how each component is subsequently treated in mechanical models. Modeling allows us to interpret assay-specific experimental results for key parameters and quantitatively predict emergent behaviors. This is specifically powerful when emergent phenomena, such as lamin-based strain stiffening, can be deduced from complimentary experimental techniques. Modeling differences in force application, geometry, or composition can additionally clarify seemingly conflicting experimental results. Using these approaches, mechanical models have informed our understanding of relevant biological processes such as migration, nuclear blebbing, nuclear rupture, and cell spreading and detachment. There remain many aspects of nuclear mechanics for which additional mechanical modeling could provide immediate insight. Although mechanical modeling of cell nuclei has been employed for over a decade, there are still relatively few models for any given biological phenomenon. This implies that an influx of research into this realm of the field has the potential to dramatically shape both future experiments and our current understanding of nuclear mechanics, function, and disease.

Lamin A and Prelamin A Counteract Migration of Osteosarcoma Cells

A type lamins are fundamental components of the nuclear lamina. Changes in lamin A expression correlate with malignant transformation in several cancers. However, the role of lamin A has not been explored in osteosarcoma (OS). Here, we wanted to investigate the role of lamin A in normal osteoblasts (OBs) and OS cells. Thus, we studied the expression of lamin A/C in OS cells compared to OBs and evaluated the effects of lamin A overexpression in OS cell lines. We show that, while lamin A expression increases during osteoblast differentiation, all examined OS cell lines express lower lamin A levels relative to differentiated OBs. The condition of low LMNA expression confers to OS cells a significant increase in migration potential, while overexpression of lamin A reduces migration ability of OS cells. Moreover, overexpression of unprocessable prelamin A also reduces cell migration. In agreement with the latter finding, OS cells which accumulate the highest prelamin A levels upon inhibition of lamin A maturation by statins, had significantly reduced migration ability. Importantly, OS cells subjected to statin treatment underwent apoptotic cell death in a RAS-independent, lamin A-dependent manner. Our results show that pro-apoptotic effects of statins and statin inhibitory effect on OS cell migration are comparable to those obtained by prelamin A accumulation and further suggest that modulation of lamin A expression and post-translational processing can be a tool to decrease migration potential in OS cells.

Causes and consequences of genomic instability in laminopathies: Replication stress and interferon response

Mammalian nuclei are equipped with a framework of intermediate filaments that function as a karyoskeleton. This nuclear scaffold, formed primarily by lamins (A-type and B-type), maintains the spatial and functional organization of the genome and of sub-nuclear compartments. Over the past decade, a body of evidence has highlighted the significance of these structural nuclear proteins in the maintenance of nuclear architecture and mechanical stability, as well as genome function and integrity. The importance of these structures is now unquestioned given the wide range of degenerative diseases that stem from LMNA gene mutations, including muscular dystrophy disorders, peripheral neuropathies, lipodystrophies, and premature aging syndromes. Here, we review our knowledge about how alterations in nuclear lamins, either by mutation or reduced expression, impact cellular mechanisms that maintain genome integrity. Despite the fact that DNA replication is the major source of DNA damage and genomic instability in dividing cells, how alterations in lamins function impact replication remains minimally explored. We summarize recent studies showing that lamins play a role in DNA replication, and that the DNA damage that accumulates upon lamins dysfunction is elicited in part by deprotection of replication forks. We also discuss the emerging model that DNA damage and replication stress are “sensed” at the cytoplasm by proteins that normally survey this space in search of foreign nucleic acids. In turn, these cytosolic sensors activate innate immune responses, which are materializing as important players in aging and cancer, as well as in the response to cancer immunotherapy.

Lamin B1 loss promotes lung cancer development and metastasis by epigenetic derepression of RET

Although abnormal nuclear structure is an important criterion for cancer diagnostics, remarkably little is known about its relationship to tumor development. Here we report that loss of lamin B1, a determinant of nuclear architecture, plays a key role in lung cancer. We found that lamin B1 levels were reduced in lung cancer patients. Lamin B1 silencing in lung epithelial cells promoted epithelial-mesenchymal transition, cell migration, tumor growth, and metastasis. Mechanistically, we show that lamin B1 recruits the polycomb repressive complex 2 (PRC2) to alter the H3K27me3 landscape and repress genes involved in cell migration and signaling. In particular, epigenetic derepression of the RET proto-oncogene by loss of PRC2 recruitment, and activation of the RET/p38 signaling axis, play a crucial role in mediating the malignant phenotype upon lamin B1 disruption. Importantly, loss of a single lamin B1 allele induced spontaneous lung tumor formation and RET activation. Thus, lamin B1 acts as a tumor suppressor in lung cancer, linking aberrant nuclear structure and epigenetic patterning with malignancy.

Cancer Stem Cells in Neuroblastoma: Expanding the Therapeutic Frontier

Neuroblastoma (NB) is the most common extracranial solid tumor often diagnosed in childhood. Despite intense efforts to develop a successful treatment, current available therapies are still challenged by high rates of resistance, recurrence and progression, most notably in advanced cases and highly malignant tumors. Emerging evidence proposes that this might be due to a subpopulation of cancer stem cells (CSCs) or tumor-initiating cells (TICs) found in the bulk of the tumor. Therefore, the development of more targeted therapy is highly dependent on the identification of the molecular signatures and genetic aberrations characteristic to this subpopulation of cells. This review aims at providing an overview of the key molecular players involved in NB CSCs and focuses on the experimental evidence from NB cell lines, patient-derived xenografts and primary tumors. It also provides some novel approaches of targeting multiple drivers governing the stemness of CSCs to achieve better anti-tumor effects than the currently used therapeutic agents.

Methylation of DNA and chromatin as a mechanism of oncogenesis and therapeutic target in neuroblastoma

Neuroblastoma (NB), a developmental cancer, is often fatal, emphasizing the need to understand its pathogenesis and identify new therapeutic targets. The heterogeneous pathological and clinical phenotype of NB underscores the cryptic biological and genetic features of this tumor that result in outcomes ranging from rapid progression to spontaneous regression. Despite recent genome-wide mutation analyses, most primary NBs do not harbor driver mutations, implicating epigenetically-mediated gene regulatory mechanisms in the initiation and maintenance of NB. Aberrant epigenomic mechanisms, as demonstrated by global changes in DNA methylation signatures, acetylation, re-distribution of histone marks, and change in the chromatin architecture, are hypothesized to play a role in NB oncogenesis. This paper reviews the evidence for, putative mechanisms underlying, and prospects for therapeutic targeting of NB oncogenesis related to DNA methylation.