A Comprehensive Proteomic and Transcriptomic Approach to Understand Novel Features of Adaptor Protein ShcD

Most cellular processes are modulated by protein-protein interactions, which serve as the basis for intracellular signaling cascades. Perturbations in these cascades lead to abnormal signaling events and ultimately result in diseases like cancer. Specialized phosphotyrosine circuitry translates extracellular signals into cellular responses through altered phosphorylation states of tyrosine residues using receptor tyrosine kinases, phosphatases, as well as phosphotyrosine binding domains found in adaptor proteins. The Shc (Src homology 2 domain-containing) family of cytosolic adaptors consists of four evolutionarily related proteins that share structural homology yet possess distinct functional roles. The more recently identified and least characterized member, ShcD, is of clinical relevance on account of its overexpression in malignant gliomas. However, its exact role remains speculative and therefore warrants further inquiry. The purpose of this project, accordingly, is to identify and better understand the mechanisms through which ShcD interacts with other signaling proteins to modulate pathways that likely contribute to glioma occurrence and/or progression. Using a comprehensive, dual-pronged proteomic and transcriptomic approach, I demonstrate that ShcD associates with receptor Tie2 to synergistically promote invasion in glioma cells. Additionally, I show that the ShcD signaling repertoire is not only limited to receptor tyrosine kinases, but it also associates with the phosphatase Shp2 and suppresses Erk activation downstream of neurotrophic receptor TrkB. Lastly, this project examines the regulatory landscape of ShcD by identifying its upstream and alternative promoters that reveal tissue-specific adaptation as well as dynamic usage across embryonic and postnatal development. Contribution of ShcD to signaling pathways implicated in glioma progression, as reported here, can be used to delineate neurogenesis as well as to understand instances of disease occurrence and progression, including cancer and neurodegenerative disorders. The data presented in this thesis can, therefore, serve as a foundation to identify ShcD as a potential diagnostic marker and/or a therapeutic target. 2021-01-01