Redox Modulation of Repression by Rev-erb, a Heme-Binding Nuclear Receptor

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DESCRIPTION (provided by applicant): Nuclear hormone receptors (NRs) are eukaryotic transcription factors that recognize small signaling molecules, which in turn modulate the regulatory properties of NRs. Rev-erb¿ is a NR that binds heme leading to the recruitment of the NCoR-HDAC1 corepressor complex with concomitant repression of genes involved in circadian rhythm maintenance and metabolism. Rev-erb¿-heme binds CO and NO, gaseous signaling molecules involved in diurnal cycling; additionally, Rev-erb¿ contains a thiol-disulfide redox switch that modulates heme-binding in accordance with redox poise. The first specific aim of this proposal is to describe the interactions of pure full-length Rev-erb¿ (FLRev-erb¿) with DNA and corepressors. Rev-erb¿ exerts its transcriptional control by binding to a promoter sequence of its target genes called ROR-RE. First, the mid- point redox potential of the thiol-disulfide switch will be calculated by plotting the ratio of dithiol:disulfide populations contributing to th position of the FLRev-erb¿:heme Soret band (determined by deconvolution of the UV-visible spectrum) as a function of the ambient redox potential that will be controlled using the reduced/oxidized glutathione couple. Next, fluorescence anisotropy (FA) will be utilized to determine how variations in redox poise and heme concentrations affect the interaction between fluorescein (FSN) labeled ROR-RE oligonucleotides and FLRev-erb¿ (and site-directed variants containing substitutions of the redox switch and heme-ligands). Using FA, I will also determine the influences of redox and heme on the affinity of FLRev-erb¿ for FSN-NCoR ID1 and ID2 peptides, which mimic the binding of FLRev-erb¿ to NCoR. Additional efforts will focus on the production and purification of recombinant full-length or truncated forms of NCoR or HDAC1 and their interactions with FLRev-erb¿. The structure-function relationship of gasotransmitters binding to FLRev-erb¿-heme will be explored with UV-visible spectroscopy and electron paramagnetic resonance to determine a Kd for the interaction between CO, NO or H2S and FLRev-erb¿, and to characterize the coordination environment of heme-gas complexes. Lastly, I will determine the effect of NO, CO and H2S on the interaction between FLRev-erb¿ and ROR-RE/corepressors. The second specific aim will focus on the characterization of novel and pre-existing synthetic ligands that modulate Rev-erb¿ function. Virtual screening techniques will be used to screen chemical libraries for candidates that favorably interact with the Rev-erb¿ heme-binding pocket. The thermodynamics of candidate compounds and previously described tertiary amine- based agonists/antagonists binding to FLRev-erb¿ will be measured with ITC and the influence of the ligands on heme-binding will be tested with UV-visible spectroscopy and EPR. Lastly, I will determine the effect of synthetic ligands on the interaction between FLRev-erb¿ and ROR-RE/corepressors. Results obtained during pursuance of these specific aims will lead to a coherent biological model explaining how cellular redox poise and heme control the regulatory output of Rev-erb¿.