Abnormal Expression of REST/NRSF and Myc in Neural Stem/Progenitor Cells Causes Cerebellar Tumors by Blocking Neuronal Differentiation

Abstract

Medulloblastoma, one of the most malignant brain tumors in children, is thought to arise from undifferentiated neural stem/progenitor cells (NSCs) present in the external granule layer of the cerebellum. However, the mechanism of tumorigenesis remains unknown for the majority of medulloblastomas. In this study, we found that many human medulloblastomas express significantly elevated levels of both myc oncogenes, regulators of neural progenitor proliferation, and REST/NRSF, a transcriptional repressor of neuronal differentiation genes. Previous studies have shown that neither c-Myc nor REST/NRSF alone could cause tumor formation. To determine whether c-Myc and REST/NRSF act together to cause medulloblastomas, we used a previously established cell line derived from external granule layer stem cells transduced with activated c-myc (NSC-M). These immortalized NSCs were able to differentiate into neurons in vitro. In contrast, when the cells were engineered to express a doxycycline-regulated REST/NRSF transgene (NSC-M-R), they no longer underwent terminal neuronal differentiation in vitro. When injected into intracranial locations in mice, the NSC-M cells did not form tumors either in the cerebellum or in the cerebral cortex. In contrast, the NSC-M-R cells did produce tumors in the cerebellum, the site of human medulloblastoma formation, but not when injected into the cerebral cortex. Furthermore, the NSC-M-R tumors were blocked from terminal neuronal differentiation. In addition, countering REST/NRSF function blocked the tumorigenic potential of NSC-M-R cells. To our knowledge, this is the first study in which abnormal expression of a sequence-specific DNA-binding transcriptional repressor has been shown to contribute directly to brain tumor formation. Our findings indicate that abnormal expression of REST/NRSF and Myc in NSCs causes cerebellum-specific tumors by blocking neuronal differentiation and thus maintaining the "stemness" of these cells. Furthermore, these results suggest that such a mechanism plays a role in the formation of human medulloblastoma.

NRSF/REST levels are decreased in cholangiocellular carcinoma but not hepatocellular carcinoma compared with normal liver tissues: A tissue microarray study

“…A similar downregulation of NRSF/REST was also demonstrated in other studies using different neuroblastoma cell lines (9,10). In addition, high NRSF/REST levels have been detected in human medulloblastoma cell lines and tumors (11)(12)(13). Similarly, in human glioblastoma multiforme (GBM), NRSF/REST is highly expressed (14) and its inhibition suppresses the proliferation and migration of GBM cells (15).…”

“…Numerous studies have investigated the expression and, to a lesser extent, the function of NRSF/REST in tumors of the nervous system (8)(9)(10)(11)(12)(13)(14)(15). Certain tumors, including neuroblastoma, share a number of biological properties with neuronal progenitor cells and, thus, can acquire neuronal phenotypes in response to a variety of agents.…”

Regulation of the NRSF/REST gene by methylation and CREB affects the cellular phenotype of small-cell lung cancer

“…In neuroblastoma and medulloblastoma cell lines, NRSF/REST expression is enhanced (Palm et al, 1999;Fuller et al, 2005). NRSF/REST and MYC overexpression induces tumour development in neuronal stem cells (Su et al, 2006). NRSF/REST is known to be degraded by SCFbeta-TRP, in which failure to degrade NRSF/REST attenuated neuronal cell differentiation (Westbrook et al, 2008).…”

Epigenetic Mechanisms in Stroke and Epilepsy

“…The interplay between REST and microRNAs is a new, emerging topic (Conaco et al, 2006;Singh et al, 2008;Johnson et al, 2008;Packer et al, 2008). During the late stages of neuronal differentiation, loss of REST is critical to acquisition of the neuronal phenotype (Su et al, 2006).…”