The major focus of our current studies is to learn how the programming and reprogramming of stem cells regulate normal development and cancer and to use this information to identify and design treatments for various injuries and disorders. One of the tools we have chosen to investigate stem cell regulation is RE1-Silencing Transcription Factor (REST)/Neuron Restrictive Silencing Factor (NRSF). REST, a transcriptional repressor, contains a DNA binding domain and two repressor domains. Once bound to its target genes, REST interacts with several cellular co-repressors to modulate chromatin via all three modes: histone modification, DNA methylation, and chromatin remodeling. Thus, it is a major epigenetic regulator. REST was originally found to be a transcriptional repressor of neurogenesis.

We recently discovered that REST plays a role in the interconnected regulatory network that maintains the self-renewal and pluripotency of embryonic stem (ES) cells. ES cells have the potential for either indefinite self-renewal or differentiation into all three germ layers of the body. Understanding the mechanisms that govern self-renewal and differentiation in ES cells has important implications for biology and medicine. The current view is that of an interconnected molecular network, containing regulators such as Oct4, Nanog, and Sox2, that controls these properties in ES cells. However, the details of this network are still emerging. We found that REST maintains self-renewal, pluripotency, and concommittant expression of Oct4, Sox2, and Nanog in ES cells through suppression of microRNA-21. We are currently studying further implications of this finding.

Our other studies indicate that there is a mechanistic link between aberrant neural stem/progenitor cell differentiation and cancer. Medulloblastoma, one of the most malignant brain tumors in children, is thought to arise from undifferentiated cerebellar neural stem/progenitor cells. Although pathways regulating cerebellar development, such as Hedgehog and Wnt, have been found to be activated by genetic alterations during medulloblastoma tumorigenesis, the mechanism of tumorigenesis for the majority of medulloblastomas remained unknown. Previously, we identified REST as a critical factor overexpressed in about 50% of human medulloblastoma specimens. Our further studies indicated that abnormal expression of REST and Myc in neural stem/progenitor cells causes cerebellar tumors in mice that are very similar to human medulloblastoma. The major role of REST in these tumors was to block the differentiation of neural stem/progenitor cells. REST in these tumors is, therefore, a potential therapeutic target in medulloblastoma. We are currently analyzing how REST is activated in these tumors and how we can utilize this information for therapeutic purposes.

To reprogram the REST-mediated blockade of stem/progenitor cell differentiation, we constructed a recombinant molecule, REST-VP16, by replacing the repressor domains of REST with the VP16 activation domain. REST-VP16 countered REST activity and converted neural stem/progenitor cells, and even myoblasts, into the physiologically active neuronal phenotype. Our results suggest that direct activation of REST/NRSF target genes with a single transgene, REST-VP16, is sufficient to activate other terminal neuronal differentiation genes and override the muscle differentiation pathways and that this approach provides an efficient way of triggering neuronal differentiation in myoblasts and, possibly, other stem cells. Whether a specific subtype of neuron can be generated from heterologous stem/progenitor cells is still unclear. Our ongoing studies indicate that myoblast-derived neuronal cells produce glutamatergic neurons in the cerebellum. We are currently studying further implications of these findings in brain injury and disease.

Selected publications

• Singh S, Kagalwala M, Parker-Thornburg J, Adams H, Majumder S (2008) REST/NRSF maintains self-renewal and pluripotency of embryonic stem cells. Nature (in press).
  
  
• Majumder S (2006) REST in good times and bad: roles in tumor suppressor and oncogenic activities. Cell Cycle 5:1929–1935.
  
  
• Su X, Gopalakrishnan V, Stearns D, Aldape K, Lang FF, Fuller GN, Snyder E, Eberhart CG, Majumder S (2006) Abnormal expression of REST/NRSF and Myc in neural stem/progenitor cells causes cerebellar tumors by blocking neuronal differentiation. Mol. Cell. Biol. 26:1666–1678.
  
  
• Fuller GN, Su X, Price RE, Cohen ZR, Lang FF, Sawaya R, Majumder S (2005) Many human medulloblastoma tumors overexpress repressor element-1 silencing transcription factor (REST)/neuron-restrictive silencer factor, which can be functionally countered by REST-VP16. Mol. Cancer Therap. 4:343–349.
  
  
• Su X, Kameoka S, Lentz S, Majumder S (2004) Activation of REST/NRSF target genes in neural stem cells is sufficient to cause neuronal differentiation. Mol. Cell. Biol. 24: 8018–8025.
  
  
• Watanabe Y, Kameoka S, Gopalakrishnan V, Aldape KD, Pan ZZ, Lang FF, Majumder S (2004) Conversion of myoblasts to physiologically active neuronal phenotype. Genes & Dev. 18: 889–900.
  
  
• Rastelli L, Zhao Z, Robinson K, Majumder S (2001) Reconstitution of enhancer function in paternal pronuclei of one-cell mouse embryos. Mol Cell Biol 21, 5531–5540.
  
  
• Immaneni A, Lawinger P, Zhao Z, Lu W, Rastelli L, Morris JH, Majumder S (2000) REST-VP16 activates multiple neuronal differentiation genes in human NT2 cells. Nucleic Acids Res 28, 3403–3410.
  
  
• Lawinger P, Venugopal R, Guo ZS, Immaneni A, Sengupta D, Lu W, Rastelli L, Marin Dias Carneiro A, Levin V, Fuller GN, Echelard Y, Majumder S (2000) The neuronal repressor REST/NRSF is an essential regulator in medulloblastoma cells. Nat Med 6, 826–831.
  

Last updated 02/21/2008