Silencing BMI1 eliminates tumor formation of pediatric glioma CD133+ cells not by affecting known targets but by down-regulating a novel set of core genes.

Hon Chiu Eastwood Leung ,Tsz-Kwong Man,Karin M Muraszko ,Patrícia Baxter ,Robert C Dauser ,Xing Fan,Zhigang Liu,Xuezhi Zhao ,Xiao Nan Li ,Horatiu Voicu,Qi Lin,Sivashankarappa Gurusiddappa,Yulun Huang,Ching C Lau ,Adekunle M Adesina ,Mari Kogiso,Jack Su ,Jason Heth ,László Perlaky ,Murali Chintagumpala,Hua Mao

doi:10.1186/s40478-014-0160-4

Abstract

Clinical outcome of children with malignant glioma remains dismal. Here, we examined the role of over-expressed BMI1, a regulator of stem cell self-renewal, in sustaining tumor formation in pediatric glioma stem cells. Our investigation revealed BMI1 over-expression in 29 of 54 (53.7%) pediatric gliomas, 8 of 8 (100%) patient derived orthotopic xenograft (PDOX) mouse models, and in both CD133+ and CD133− glioma cells. We demonstrated that lentiviral-shRNA mediated silencing of suppressed cell proliferation in vitro in cells derived from 3 independent PDOX models and eliminated tumor-forming capacity of CD133+ and CD133− cells derived from 2 PDOX models in mouse brains. Gene expression profiling showed that most of the molecular targets of BMI1 ablation in CD133+ cells were different from that in CD133- cells. Importantly, we found that silencing BMI1 in CD133+ cells derived from 3 PDOX models did not affect most of the known genes previously associated with the activated BMI1, but modulated a novel set of core genes, including RPS6KA2, ALDH3A2, FMFB, DTL, API5, EIF4G2, KIF5c, LOC650152, C20ORF121, LOC203547, LOC653308, and LOC642489, to mediate the elimination of tumor formation. In summary, we identified the over-expressed BMI1 as a promising therapeutic target for glioma stem cells, and suggest that the signaling pathways associated with activated BMI1 in promoting tumor growth may be different from those induced by silencing BMI1 in blocking tumor formation. These findings highlighted the importance of careful re-analysis of the affected genes following the inhibition of abnormally activated oncogenic pathways to identify determinants that can potentially predict therapeutic efficacy.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-014-0160-4) contains supplementary material, which is available to authorized users.

Highlights

Tumors of the central nervous system are the second most common cancer in children
We examined if BMI1 is over-expressed in pediatric gliomas of various pathologic grades and if the over-expression of BMI1 was replicated in our new panel of 8 patient tumor-derived orthotopic xenograft (PDOX) mouse models
Elevated expression of BMI1 mRNA in pediatric malignant gliomas To determine the mRNA expression of BMI1 in pediatric gliomas, we applied Quantitative real-time RT-PCR (qRT-PCR) in a panel of 54 pediatric gliomas

Summary

Introduction

Tumors of the central nervous system are the second most common cancer in children. Glioblastoma multiforme (GBM) is one of the most malignant brain tumors that occur both in children and adults. The primary treatment for GBM is surgical resection followed by Recent isolation of cancer stem cells (CSCs), termed tumor-initiating cells [3,4,5,6,7,8], has created a new conceptual model for examining tumorigenesis and treatment failure. Baxter et al Acta Neuropathologica Communications (2014): recurrence [9,10,11,12,13]. The capability of self-renewal [3,4,15] plays the most important role in sustaining tumor growth. Genes and genetic pathways promoting abnormal self-renewal in CSCs should be prioritized for therapeutic targeting

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