The Dead Receptor Paradox: Insights into Receptor Tyrosine Kinases with Intracellular Pseudokinase Domains
Date of Award
Doctor of Philosophy (PhD)
Receptor tyrosine kinases, or RTKs, are key transducers of cellular signals in metazoans. All RTKs utilize a common architecture—an extracellular ligand binding region, a single-pass transmembrane helix, and an intracellular kinase domain—to control diverse biological processes from cellular metabolism to migration. Our understanding of how most receptors relay signals, however, remains incomplete. A particular puzzle is the collection of ~10% of RTKs that lack catalytic activity in their intracellular kinase homology domains, owing to altered amino acid residues thought necessary for phosphorylation. These so-called pseudokinases are highly evolutionarily conserved and are mutated, overexpressed, or otherwise dysregulated in certain cancers or developmental disorders. This observation serves as the basis for what I refer to herein as the dead receptor paradox; despite containing ‘dead’ kinase domains in their intracellular regions, these RTK pseudokinases are competent to bind ligands in their extracellular regions and mediate signaling. In this thesis, I ask the basic question: how do the human RTK pseudokinases detect and relay extracellular cues? Recent studies, in addition to my work described here, have led me to conclude that conformational dynamics of the pseudokinase domains is an essential component to the signaling mechanisms of these receptors. In this body of work, I demonstrate that the WNT-associated RTK pseudokinases bear close resemblance to the insulin receptor kinase domain in their structures and dynamics. I further show that RTK pseudokinases, regardless of their ability to bind nucleotides, can be targeted with small molecules to induce conformational changes. Finally, to gain insights into signaling by ‘dead receptors,’ I explored the mechanisms of WNT recognition by RTK extracellular regions. Overall, my findings support a role for pseudokinase conformational dynamics as a key step in signal transduction by these receptors, helping make sense of the dead receptor paradox and setting the stage for pseudokinase-targeted therapeutics.
Sheetz, Joshua B., "The Dead Receptor Paradox: Insights into Receptor Tyrosine Kinases with Intracellular Pseudokinase Domains" (2022). Yale Graduate School of Arts and Sciences Dissertations. 522.