Grace Grifferty

Biochemistry, '18


Identification of novel therapeutic targets of the Notch1 signaling pathway

Mentor: Jon Aster, MD (Brigham and Women's Hospital)

The canonical Notch1 pathway is well known for its role in regulating the differentiation of multipotent progenitor cells during development. Activation of Notch1 through binding of cognate ligands triggers a proteolyic cascade that releases the Notch1 intracellular domain, which translocates to the nucleus and forms a transcriptional complex with RBPJ and MAML family cofactor that upregulates the expression of key target genes. Mutations that lead to ligand-independent activation of Notch1 are oncogenic drivers in a number of cancers, such as T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) and a subset of triple negative breast cancers. Thus, understanding the epigenetic mechanisms that regulate Notch1 expression and downstream signaling events will allow identification of potential therapeutic targets. To this end, we are taking two parallel approaches. Firstly, we are characterizing the enhancer elements and transcription factors that regulate Notch1 expression in T-ALL cells through the use of luciferase assays and CRISPR technology. Secondly, we are constructing an endogenous BioTAP-XL tag system that will enable concomitant whole genome ChIP-Seq and unbiased proteomic studies. This will allow us to identify Notch1-RBPJ DNA binding sites as well as novel protein effectors that directly interact with Notch1-RBPJ transcriptional machinery. By doing so, we hope to illuminate new facets of oncogenic Notch signaling in cancer cells.

The structure of the Notch1 protein is depicted at the top of this image. The Notch1 signaling pathway is illustrated below it. Notch signaling occurs between ligands of the sending cell (bottom left) and EGF repeat region on Notch1 receptor protein on the receiving cell (bottom right). Notch1 is then cleaved by ADAM and gamma-secretase. This cleavage releases intracellular Notch from the cell membrane, which translocates into the nucleus. Intracellular Notch forms the Notch transcription complex with RBPJ and MAML, which recruits other co-activators and transcriptional machinery. This process turns on target gene expression. Source: Wang H et al. J Cell Physiol. 2015 May; 230(5): 982–988. Source: