In Vivo RNAi Screen for BMI1 Targets Identifies TGF-β/BMP-ER Stress Pathways as Key Regulators of Neural- and Malignant Glioma-Stem Cell Homeostasis

Abstract

In mouse and human neural progenitor and glioblastoma "stem-like" cells, we identified key targets of the Polycomb-group protein BMI1 by combining ChIP-seq with in vivo RNAi screening. We discovered that Bmi1 is important in the cellular response to the transforming growth factor-β/bone morphogenetic protein (TGF-β/BMP) and endoplasmic reticulum (ER) stress pathways, in part converging on the Atf3 transcriptional repressor. We show that Atf3 is a tumor-suppressor gene inactivated in human glioblastoma multiforme together with Cbx7 and a few other candidates. Acting downstream of the ER stress and BMP pathways, ATF3 binds to cell-type-specific accessible chromatin preloaded with AP1 and participates in the inhibition of critical oncogenic networks. Our data support the feasibility of combining ChIP-seq and RNAi screens in solid tumors and highlight multiple p16(INK4a)/p19(ARF)-independent functions for Bmi1 in development and cancer.

Physiological/pathological ramifications of transcription factors in the unfolded protein response

“…In contrast to the above results, ATF3 expression is decreased in human colorectal cancer (Bottone et al 2003), cervical cancer (Wang et al 2010), and glioma (Gargiulo et al 2013) compared with normal tissues, suggesting that ATF3 may act as a tumor suppressor. ATF3 activates p53 by preventing its ubiquitination and degradation in cervical cancer (Wang et al 2010).…”

“…In colorectal cancer, ATF3 activates DR5 to enhance sensitivity to apoptotic cell death (Taketani et al 2012;Edagawa et al 2014). In addition, bone morphogenetic protein (BMP) signaling activates ATF3 to bind open chromatin structures at AP1-preloaded sites and inhibit the oncogenic network (Gargiulo et al 2013). ATF3 also suppresses bladder cancer metastasis through promoting gelsolin-mediated actin remodeling (Yuan et al 2013) and maintains genomic stability by activating ataxia telangiectasia mutated (ATM) signaling (Cui et al 2015).…”

Plk2 regulates mitotic spindle orientation and mammary gland development

“…Therefore, it is imperative to identify signaling pathways that contribute to the etiology of breast cancer in an attempt to discover novel therapeutic targets. RNA interference (RNAi) has been used successfully in high-throughput screens to identify potential drug targets (Gargiulo et al, 2013;Liu et al, 2013). In particular, RNAi has been used to identify putative tumor suppressors in forward genetic screens (Westbrook et al, 2005;Krastev et al, 2011;Iorns et al, 2012).…”

MicroRNA-31 Is a Transcriptional Target of Histone Deacetylase Inhibitors and a Regulator of Cellular Senescence

“…In addition to cellular senescence, BMI1 also promotes cancer stem cell phenotype and therapy resistance in cancer cells (11,21). In addition to p16, BMI1 is known to regulate expression of other cancer and aging relevant genes, such as p57, and genes involved in TGF-␤ signaling, endoplasmic reticulum stress, and WNT pathways (22)(23)(24)(25). Because of their role in promoting various cancers, inhibitors of BMI1 and EZH2 are of clinical importance.…”