The Role of MYCN in Symmetric vs. Asymmetric Cell Division of Human Neuroblastoma Cells

MYCN in human development and diseases

Somatic mutations in MYCN have been identified across various tumors, playing pivotal roles in tumorigenesis, tumor progression, and unfavorable prognoses. Despite its established notoriety as an oncogenic driver, there is a growing interest in exploring the involvement of MYCN in human development. While MYCN variants have traditionally been associated with Feingold syndrome type 1, recent discoveries highlight gain-of-function variants, specifically p.(Thr58Met) and p.(Pro60Leu), as the cause for megalencephaly-polydactyly syndrome. The elucidation of cellular and murine analytical data from both loss-of-function (Feingold syndrome model) and gain-of-function models (megalencephaly-polydactyly syndrome model) is significantly contributing to a comprehensive understanding of the physiological role of MYCN in human development and pathogenesis. This review discusses the MYCN's functional implications for human development by reviewing the clinical characteristics of these distinct syndromes, Feingold syndrome, and megalencephaly-polydactyly syndrome, providing valuable insights into the understanding of pathophysiological backgrounds of other syndromes associated with the MYCN pathway and the overall comprehension of MYCN's role in human development.

Gain-of-function MYCN causes a megalencephaly-polydactyly syndrome manifesting mirror phenotypes of Feingold syndrome

MYCN, a member of the MYC proto-oncogene family, regulates cell growth and proliferation. Somatic mutations of MYCN are identified in various tumors, and germline loss-of-function variants are responsible for Feingold syndrome, characterized by microcephaly. In contrast, one megalencephalic patient with a gain-of-function variant in MYCN, p.Thr58Met, has been reported, and additional patients and pathophysiological analysis are required to establish the disease entity. Herein, we report two unrelated megalencephalic patients with polydactyly harboring MYCN variants of p.Pro60Leu and Thr58Met, along with the analysis of gain-of-function and loss-of-function Mycn mouse models. Functional analyses for MYCN-Pro60Leu and MYCN-Thr58Met revealed decreased phosphorylation at Thr58, which reduced protein degradation mediated by FBXW7 ubiquitin ligase. The gain-of-function mouse model recapitulated the human phenotypes of megalencephaly and polydactyly, while brain analyses revealed excess proliferation of intermediate neural precursors during neurogenesis, which we determined to be the pathomechanism underlying megalencephaly. Interestingly, the kidney and female reproductive tract exhibited overt morphological anomalies, possibly as a result of excess proliferation during organogenesis. In conclusion, we confirm an MYCN gain-of-function-induced megalencephaly-polydactyly syndrome, which shows a mirror phenotype of Feingold syndrome, and reveal that MYCN plays a crucial proliferative role, not only in the context of tumorigenesis, but also organogenesis.

Space Microgravity Alters Neural Stem Cell Division: Implications for Brain Cancer Research on Earth and in Space

Considering the imminence of long-term space travel, it is necessary to investigate the impact of space microgravity (SPC-µG) in order to determine if this environment has consequences on the astronauts' health, in particular, neural and cognitive functions. Neural stem cells (NSCs) are the basis for the regeneration of the central nervous system (CNS) cell populations and learning how weightlessness impacts NSCs in health and disease provides a critical tool for the potential mitigation of specific mechanisms leading to neurological disorders. In previous studies, we found that exposure to SPC-µG resulted in enhanced proliferation, a shortened cell cycle, and a larger cell diameter of NSCs compared to control cells. Here, we report the frequent occurrence of abnormal cell division (ACD) including incomplete cell division (ICD), where cytokinesis is not successfully completed, and multi-daughter cell division (MDCD) of NSCs following SPC-µG as well as secretome exposure compared to ground control (1G) NSCs. These findings provide new insights into the potential health implications of space travel and have far-reaching implications for understanding the mechanisms leading to the deleterious effects of long-term space travel as well as potential carcinogenic susceptibility. Knowledge of these mechanisms could help to develop preventive or corrective measures for successful long-term SPC-µG exposure.

Multifarious Functions of Butyrylcholinesterase in Neuroblastoma: Impact of BCHE Deletion on the Neuroblastoma Growth In Vitro and In Vivo

The physiological functions of butyrylcholinesterase (BChE) and its role in malignancy remain unexplained. Our studies in children newly diagnosed with neuroblastoma indicated that BChE expressions is proportional to MYCN amplification suggesting that pathogenesis of high-risk disease may be related to the persistent expression of abnormally high levels of tumor-associated BChE. BChE-deficient neuroblastoma cells (KO [knockout]) were produced from MYCN -amplified BE(2)-C cells (WT [wild-type]) by the CRISPR-Cas9 targeted disruption of the BCHE locus. KO cells have no detectable BChE activity. The compensatory acetylcholinesterase activity was not detected. The average population doubling time of KO cells is 47.0±2.4 hours, >2× longer than WT cells. Reduced proliferation rates of KO cells were accompanied by the loss of N-Myc protein and a significant deactivation of tyrosine kinase receptors associated with the aggressive neuroblastoma phenotype including Ros1, TrkB, and Ltk. Tumorigenicity of WT and KO cells in male mice was essentially identical. In contrast, KO xenografts in female mice were very small (0.37±0.10 g), ~3× smaller compared with WT xenografts (1.11±0.30 g). Unexpectedly, KO xenografts produced changes in plasma BChE similarly to WT tumors but lesser in magnitude. The disruption of BCHE locus in MYCN -amplified neuroblastoma cells decelerates proliferation and produces neuroblastoma cells that are less aggressive in female mice.

Recent advances in the developmental origin of neuroblastoma: an overview

Neuroblastoma (NB) is a pediatric tumor that originates from neural crest-derived cells undergoing a defective differentiation due to genomic and epigenetic impairments. Therefore, NB may arise at any final site reached by migrating neural crest cells (NCCs) and their progeny, preferentially in the adrenal medulla or in the para-spinal ganglia.

NB shows a remarkable genetic heterogeneity including several chromosome/gene alterations and deregulated expression of key oncogenes that drive tumor initiation and promote disease progression.

NB substantially contributes to childhood cancer mortality, with a survival rate of only 40% for high-risk patients suffering chemo-resistant relapse. Hence, NB remains a challenge in pediatric oncology and the need of designing new therapies targeted to specific genetic/epigenetic alterations become imperative to improve the outcome of high-risk NB patients with refractory disease or chemo-resistant relapse.

In this review, we give a broad overview of the latest advances that have unraveled the developmental origin of NB and its complex epigenetic landscape.

Single-cell RNA sequencing with spatial transcriptomics and lineage tracing have identified the NCC progeny involved in normal development and in NB oncogenesis, revealing that adrenal NB cells transcriptionally resemble immature neuroblasts or their closest progenitors. The comparison of adrenal NB cells from patients classified into risk subgroups with normal sympatho-adrenal cells has highlighted that tumor phenotype severity correlates with neuroblast differentiation grade.

Transcriptional profiling of NB tumors has identified two cell identities that represent divergent differentiation states, i.e. undifferentiated mesenchymal (MES) and committed adrenergic (ADRN), able to interconvert by epigenetic reprogramming and to confer intra-tumoral heterogeneity and high plasticity to NB.

Chromatin immunoprecipitation sequencing has disclosed the existence of two super-enhancers and their associated transcription factor networks underlying MES and ADRN identities and controlling NB gene expression programs.

The discovery of NB-specific regulatory circuitries driving oncogenic transformation and maintaining the malignant state opens new perspectives on the design of innovative therapies targeted to the genetic and epigenetic determinants of NB. Remodeling the disrupted regulatory networks from a dysregulated expression, which blocks differentiation and enhances proliferation, toward a controlled expression that prompts the most differentiated state may represent a promising therapeutic strategy for NB.

Transcriptional Control of Apical-Basal Polarity Regulators

Cell polarity is essential for many functions of cells and tissues including the initial establishment and subsequent maintenance of epithelial tissues, asymmetric cell division, and morphogenetic movements. Cell polarity along the apical-basal axis is controlled by three protein complexes that interact with and co-regulate each other: The Par-, Crumbs-, and Scrib-complexes. The localization and activity of the components of these complexes is predominantly controlled by protein-protein interactions and protein phosphorylation status. Increasing evidence accumulates that, besides the regulation at the protein level, the precise expression control of polarity determinants contributes substantially to cell polarity regulation. Here we review how gene expression regulation influences processes that depend on the induction, maintenance, or abolishment of cell polarity with a special focus on epithelial to mesenchymal transition and asymmetric stem cell division. We conclude that gene expression control is an important and often neglected mechanism in the control of cell polarity.

Analysis of Asymmetric Cell Division Using Human Neuroblastoma Cell Lines as a Model System

Neuroblastoma is one of the most common childhood solid tumors and develops from neural stem cells that normally comprise the embryonic structure termed the neural crest. Human neuroblastoma cell lines have special properties as they exhibit cell growth and are induced to become mature neurons by drugs such as retinoid. Therefore, we examined asymmetric cell division (ACD) using human neuroblastoma cells as an ACD model, and confirmed that ACD in human cancer cells is evolutionally conserved. Furthermore, we demonstrated that MYCN is involved in cell division fate. We introduce the brief history of ACD study using neuroblastoma cell lines and discuss why human neuroblastoma cells are an ideal model system for clarifying the mechanism of ACD.

Molecular Mechanisms of MYCN Dysregulation in Cancers

MYCN, a member of MYC proto-oncogene family, encodes a basic helix-loop-helix transcription factor N-MYC. Abnormal expression of N-MYC is correlated with high-risk cancers and poor prognosis. Initially identified as an amplified oncogene in neuroblastoma in 1983, the oncogenic effect of N-MYC is expanded to multiple neuronal and nonneuronal tumors. Direct targeting N-MYC remains challenge due to its "undruggable" features. Therefore, alternative therapeutic approaches for targeting MYCN-driven tumors have been focused on the disruption of transcription, translation, protein stability as well as synthetic lethality of MYCN. In this review, we summarize the latest advances in understanding the molecular mechanisms of MYCN dysregulation in cancers.