Date of Award

Spring 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Biophysics and Biochemistry

First Advisor

Koleske, Anthony

Abstract

The catalytic activity of Abl family kinases is tightly regulated in cells by a complex set of intra- and intermolecular interactions and post-translational modifications. Abl family kinases are activated by diverse cellular stimuli, including receptor tyrosine kinase signaling. For example, the platelet-derived growth factor receptor beta (PDGFRβ) is a potent activator of Abl family kinases. However, the molecular mechanism by which PDGFRβ engages and activates Abl family kinases is not known. We find that the Abl2 Src Homology 2 (SH2) domain directly binds to phospho–tyrosine Y771 in the PDGFRβ cytoplasmic domain. PDGFRβ directly phosphorylates Abl2 N-terminal half on multiple novel sites including Y116, Y139 and Y161 within the SH3 domain, and Y299, Y303 and Y310 on the kinase domain. Y116, Y161, Y272 and Y310 are all located at or near the SH3/SH2-kinase linker interface, which helps maintain Abl family kinases in an auto-inhibited conformation. We found that PDGFRβ-mediated phosphorylation of Abl2 in vitro activates Abl2 kinase activity, but mutation of these four tyrosine (Y116, Y161, Y272 and Y310) to phenylalanine abrogated PDGFRβ-mediated activation of Abl2. These findings reveal how the PDGFRβ engages and phosphorylates Abl2 and how this leads to activation of the kinase, providing a framework to understand how growth factor receptors engage and activate Abl family kinases. Finally, the biological importance of PDGFR-mediated activation on Abl2 is unclear. Our lab recently showed that Abl2 directly binds and phosphorylates the integrin β1 cytoplasmic tail. Here, I provide initial findings suggesting that PDGFR-mediated activation on Abl2 promotes Abl2-integrin β1 interaction and β1 phosphorylation by Abl2. This process also inhibits talin-integrin interaction. Since talin is the most important integrin activator, Abl2 may regulate talin-integrin interaction, and potentially acts as an integrin inactivator. Abl2 acting downstream of PDGFR to regulate integrin activation may provide a mechanism to allow PDGFR to crosstalk with integrin to regulate many processes including cancer metastasis, angiogenesis and embryonic development.

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