Date of Award
Doctor of Philosophy (PhD)
G protein coupled receptors transduce diverse extracellular signals like hormones, neurotransmitters, and photons to specific cellular responses through heterotrimeric G proteins. G proteins activate numerous effectors and signal transduction pathways, and therefore the regulation of G proteins is crucial for faithful propagation of specific cellular and physiological responses. A better understanding of the mechanisms that regulate G proteins should provide new insight into signaling pathways that govern healthy and disease states, and also provide opportunities for discovery of novel therapeutic targets.Regulator of G protein signaling (RGS) proteins are crucial regulators of G proteins, for they control amplitude and duration of G protein signaling responses. RGS2 is particularly important because it is associated with many physiological and disease processes. A key concept that has emerged is that physiological and disease processes are extremely sensitive to even modest changes in RGS2 expression levels. The goals of this dissertation were to investigate the mechanism that controls RGS2 levels and to determine how dynamic RGS2 levels affect GPCR signaling. The particular focus was on the ubiquitin proteasome pathway (UPP), which is one of the key mechanisms that control RGS2 expression levels. Rather than looking for components of the UPP that recognize and degrade RGS2, a comprehensive analysis was performed on the RGS2 N-terminal domain to identify signals required for degradation. This analysis revealed a novel bipartite hydrophobic motif that is required for degradation. Intriguingly, deletion of these hydrophobic motifs did not abrogate binding with E3 ligases associated with RGS2 degradation, suggesting additional mechanisms are involved. The effect of UPP mediated degradation of RGS2 on regulation of GPCR signaling was also explored. Using a cell based, kinetically resolved, GPCR reporter assay, it was demonstrated that proteasome degradation of RGS2 dynamically regulates GPCR signaling, influencing both agonist efficacy and the rate of receptor resensitization.G protein signaling pathways also can be modulated by small molecule inhibitors. YM-254890 and FR900359 are a class of small molecule inhibitors for G proteins that are selective and cell permeable. They are promising research tools and leads for therapeutic agents, but the exact molecular mechanism of action of these inhibitors is not known. The second part of the dissertation describes early stages of a study that aims to elucidate the mechanism of action of YM and FR. Preliminary results that support an allosteric model of inhibition are reported, followed by a discussion of future work that will further test this model.
Chair and Committee
Kendall J. Blumer
Thomas J. Baranski, Robert W. Mercer, Paul H. Schlesinger, Conrad C. Weihl,
Kanai, Stanley Michinobu, "Mechanisms of G Protein Regulation by RGS Proteins and Small Molecule Inhibitors" (2017). Arts & Sciences Electronic Theses and Dissertations. 1116.