The long-term goal of this application is to improve our understanding of the mechanisms through which Notch signaling, a major cellular communication pathway, regulates mammalian development and stem cell-based maintenance of adult tissues, and to apply such insights to tissue engineering and disease abatement. Pathway activation occurs when ligand binding to any of the four vertebrate Notch receptors triggers proteolytic release of a signal "unit" (the Notch intracellular domain;NICD). All 4 NICDs engage in transcription by forming a complex with RBPjk, a DNA-binding protein. Since all NICDs bind to RBPjk with equal affinity, co-expression of Notch paralogs results in redundancy, thereby leading to robustness (insensitivity to loss of one allele). However, several observations suggest that Notch receptors are not always redundant when co-expressed, resulting in developmental syndromes when one copy of a specific mammalian Notch receptor is mutated despite the presence (and in some cases, activation) of other highly conserved Notch paralogs. In addition to this context-specific activity, we identified NICD paralog-specific activities in 3 tissues where Notch paralogs are individually expressed: T-cells, B-cell and endothelial cells. This application will use a multi-pronged approach aimed to determine the mechanistic basis for paralog-specific Notch activities in these tissues. Attaining a better understanding of how context affects Notch signaling output goes beyond the academic interest in the mechanism of Notch signaling, paving the way for novel, receptor- and tissue-specific treatment of developmental syndromes associated with Notch loss, receptor-specific inhibition in cancer, Notch receptor- specific contribution to the stem cell-niche interactions and selective activation of desired paralogs for organ engineering initiatives.
The Notch pathway constitutes a short-range communication channel used to regulate proliferation, stem cells and stem cell niche maintenance, cell fate acquisition, differentiation and cell death. In humans, two structurally similar receptors (Notch1 and 2) seem to work redundantly in many cells, but have unique properties in others. Loss of one Notch1 allele leads to aortic valve defects despite the presence of Notch2, and loss of one Notch2 allele leads to Alagille syndrome despite the presence of Notch1. Clues we obtained from the immune system suggest that part of the answer lies in the composition of the intracellular domain, perhaps permitting association with receptor specific partners. Our proposal aims to understand better how Notch1 and Notch2 work to produce unique cellular outcomes. Finding partners will allow us to target the pathway in a context specific manner. We therefore believe that the proposed research will improve our ability to manipulate Notch signaling where desired as a therapeutic key to populations with rare diseases and in stem cell based therapies.
|Kopan, Raphael (2016) The Unaimed Arrow Never Misses. Curr Top Dev Biol 116:547-50|
|Thomas, Jane J; Abed, Mona; Heuberger, Julian et al. (2016) RNF4-Dependent Oncogene Activation by Protein Stabilization. Cell Rep 16:3388-400|
|Turkoz, Mustafa; Townsend, R Reid; Kopan, Raphael (2016) The Notch Intracellular Domain Has an RBPj-Independent Role during Mouse Hair Follicular Development. J Invest Dermatol 136:1106-15|
|Liu, Zhenyi; Brunskill, Eric; Boyle, Scott et al. (2015) Second-generation Notch1 activity-trap mouse line (N1IP::CreHI) provides a more comprehensive map of cells experiencing Notch1 activity. Development 142:1193-202|
|Ilagan, Ma Xenia G; Kopan, Raphael (2014) Monitoring Notch activation in cultured mammalian cells: transcriptional reporter assays. Methods Mol Biol 1187:143-54|
|Kopan, Raphael; Chen, Shuang; Liu, Zhenyi (2014) Alagille, Notch, and robustness: why duplicating systems does not ensure redundancy. Pediatr Nephrol 29:651-7|
|Liu, Zhenyi; Chen, Shuang; Boyle, Scott et al. (2013) The extracellular domain of Notch2 increases its cell-surface abundance and ligand responsiveness during kidney development. Dev Cell 25:585-98|
|Satpathy, Ansuman T; BriseÃ±o, Carlos G; Lee, Jacob S et al. (2013) Notch2-dependent classical dendritic cells orchestrate intestinal immunity to attaching-and-effacing bacterial pathogens. Nat Immunol 14:937-48|
|Liu, Zhiyong; Liu, Zhenyi; Walters, Bradley J et al. (2013) In vivo visualization of Notch1 proteolysis reveals the heterogeneity of Notch1 signaling activity in the mouse cochlea. PLoS One 8:e64903|
|Zhao, Zhong-Qiu; Huo, Fu-Quan; Jeffry, Joseph et al. (2013) Chronic itch development in sensory neurons requires BRAF signaling pathways. J Clin Invest 123:4769-80|
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