All ETDs from UAB

Advisory Committee Chair

Matthew B Renfrow

Advisory Committee Members

Donald D Muccio

Susan M Ruppert

David A Schneider

Tim M Townes

Document Type

Dissertation

Date of Award

2012

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Nuclear receptor (NR) protein retinoid X receptor (RXR) is a ligand-inducible transcription factor that binds retinoids for regulation of target genes. Agonist binding induces a major structural rearrangement in the ligand binding domain (LBD) and formation of the coactivator binding interface. RXR-signaling pathways control proliferation, differentiation, and growth in epithelial tissues. To understand how RXR agonists enhance signaling at the molecular level requires an understanding of how agonists induce structural and dynamical changes in the LBD to recruit coactivators for activation of anti-cancer relevant transcription. While most studies of NR activation center on the position of Helix 12 (H12)/activation function-2 (AF-2), RXR agonists do not directly contact H12. RXR agonists must stabilize AF-2 through interactions with residues in the ligand binding pocket (LBP). While existing X-ray co-crystal structures show agonist-bound RXR locked in the active position, numerous in-solution studies including hydrogen deuterium exchange mass spectrometry (HDX MS) demonstrate that H12 remains dynamic in the presence of potent agonists. So while other NR-agonists can be evaluated solely on the position of H12, the structural mechanism of RXR agonist and coactivator binding is more complicated then this two-step model. X-ray crystallographic structures of agonist and coactivator-bound hRXRα-LBD are very similar. Using in-solution HDX MS, the studies in this dissertation outline the dynamical changes associated with LxxLL motif-containing glucocorticoid receptor interacting protein 1 (GRIP-1) coactivator peptide binding to the hRXRα-LBD:9cRA homodimer. More specifically, the following work demonstrates that stabilization of the hRXRα-LBD:9cRA:GRIP-1 complex is an additive effort between ligand and coactivator and identify regions that demonstrate GRIP-1 dependent stabilization (H11 and H12). The results presented within this dissertation identify a crucial role for H11 for communication between the ligand-bound LBP and coactivator binding interface. Next, it is demonstrated that structurally distinct retinoids result in unique hRXRα-LBD conformational dynamics in the presence and absence of GRIP-1. H3, H11, and H12 are identified as targets for future evaluations of RXR agonists and the importance of GRIP-1 for evaluation of RXR agonists versus the ligand alone analysis is highlighted.

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