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Polycomb group protein BMI1 prevents neuroblastoma cells from DNA-damage-induced apoptotic cell death

ABSTRACT: BMI1 is a polycomb protein and its overexpression has been correlated with cancer development and aggressiveness. We previously reported that v-myc avian myelocytomatosis viral oncogene neuroblastoma-derived homolog (MYCN)-induced BMI1 positively regulated neuroblastoma (NB) cell proliferation via the transcriptional suppression of tumor suppressors in NB cells. In order to evaluate the potential of BMI1 as a new target for NB therapy, we herein examined the effects of BMI1 reductions on NB cell differentiation and apoptotic NB cell death. BMI1 knockdown (KD) up to 7 days in NB cells significantly induced their differentiation. BMI1 depletion up to 14 days significantly induced apoptotic NB cell death along with the activation of p53, increases in p73, and induction of p53 family downstream molecules. BMI1 depletion in vivo markedly suppressed NB xenograft tumor growth. A pathological analysis using the TUNEL assay indicated the induction of apoptotic cell death. BMI1 reductions activated ATM and increased γ-H2AX in NB cells. Importantly, these DNA damage signals and apoptotic cell death were not canceled by transduction of polycomb group molecules EZH2 and RING1B. Further, EZH2 or RING1B knockdown could not induce apoptotic NB cell death at the same level of BMI1 KD. Together, BMI1 appears to be a promising target of molecular therapy for NB tumors and our report clarified, for the first time, the shared role of PcG proteins in DNA damage response of NB cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE189449 | GEO | 2022/11/08

REPOSITORIES: GEO

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

Project description:NguyenLK2011 - Ubiquitination dynamics in Ring1B-Bmi1 system This theoretical model investigates the dynamics of Ring1B/Bmi1 ubiquitination to identify bistable switch-like and oscillatory behaviour in the system. Michaelis-Menten (MM) equations are used to formulate the model. However, the authors show that the dynamics persist even for Mass-Action kinetics. This SBML file is the MM version of the model. This model is described in the article: Switches, excitable responses and oscillations in the Ring1B/Bmi1 ubiquitination system. Nguyen LK, Muñoz-García J, Maccario H, Ciechanover A, Kolch W, Kholodenko BN. PLoS Comput. Biol. 2011 Dec; 7(12): e1002317 Abstract: In an active, self-ubiquitinated state, the Ring1B ligase monoubiquitinates histone H2A playing a critical role in Polycomb-mediated gene silencing. Following ubiquitination by external ligases, Ring1B is targeted for proteosomal degradation. Using biochemical data and computational modeling, we show that the Ring1B ligase can exhibit abrupt switches, overshoot transitions and self-perpetuating oscillations between its distinct ubiquitination and activity states. These different Ring1B states display canonical or multiply branched, atypical polyubiquitin chains and involve association with the Polycomb-group protein Bmi1. Bistable switches and oscillations may lead to all-or-none histone H2A monoubiquitination rates and result in discrete periods of gene (in)activity. Switches, overshoots and oscillations in Ring1B catalytic activity and proteosomal degradation are controlled by the abundances of Bmi1 and Ring1B, and the activities and abundances of external ligases and deubiquitinases, such as E6-AP and USP7. This model is hosted on BioModels Database and identified by: BIOMD0000000622. To cite BioModels Database, please use: BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information.

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Polycomb group protein BMI1 prevents neuroblastoma cells from DNA-damage-induced apoptotic cell death

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