Doctor of Philosophy
Dr. Gianni M. Di Guglielmo
The transforming growth factor beta (TGFbeta) pathway has been conserved throughout evolution and plays important roles in tissue homeostasis. Dysregulation of the TGFbeta pathway has been implicated in a number of disorders, including cancer, fibrosis, and vascular conditions. The signalling potential of the TGFbeta pathway is regulated by the route of internalization of its cell-surface receptors: Receptors internalized by clathrin-mediated endocytosis propagate signal transduction while those internalized by membrane rafts are targeted for degradation. Given the importance of trafficking of the TGFbeta receptors to signal propagation, this thesis focuses on evaluating proteins which direct TGFb receptor internalization and trafficking. Initial work in this thesis shows that the extracellular domain of the type II TGFbeta receptor (TbRII) and the glycosylation state of the cell are important factors in permitting membrane-raft localization of TbRII. Using this information I assessed the ability of TbRIII, a glycosylated cell surface protein, to direct TbRII internalization. I found that TbRIII increases membrane-raft independent internalization of TbRII, increases TbRII/TbRI complex half-life, and basal TGFbeta signalling. I next assessed the role of beta arrestin2, a protein which interacts with TbRIII, in regulating TbRII trafficking and signalling. I show that beta arrestin2 interacts with TbRII and traffics with TbRII to the early endosome to increase Smad-dependent signalling. Also, I show that depletion of beta arrestin2 increases Smad-independent signal transduction. In the last data chapter of this thesis, I evaluate the role of TGFbeta1 and TGFbeta3, to direct TGFbeta trafficking and signalling. I found that TGFbeta3 is less potent than TGFbeta1 at propagating TGFbeta signalling. I also show that TGFbeta3 induces a different binding ratio of TbRII/TbRI cell-surface complexes, which could explain its decreased potency. Overall my studies highlight the role of receptor-interacting proteins in directing TGFbeta receptor trafficking and signal transduction. Since this pathway is dysregulated in a number of pathologies, my studies suggest that TGFbeta receptor trafficking is an important avenue to modifying TGFbeta signal transduction.
McLean, Sarah E.A., "Transforming Growth Factor Beta Receptor Partitioning: Molecular Mechanisms and Functional Consequences" (2012). Electronic Thesis and Dissertation Repository. 752.