Precise control of inflammation is essential for effective immunity and the maintenance of normal tissue homeostasis. Work performed under the current period of support led to the discovery of two co-repressor dependent mechanisms that enable nuclear receptors to inhibit Toll-like receptor (TLR)-dependent gene expression in a context and gene-specific manner. The first mechanism involves NCoR and SMRT co- repressor complexes. These complexes reside on the promoters of many TLR-responsive genes under basal conditions and are cleared in response to TLR ligation as a prerequisite to gene activation. These complexes can therefore be considered to impose 'checkpoint'functions that prevent spurious gene activation in the absence of a strong activating signal. PPARs and LXRs exert repressive effects on this subset of genes by inhibiting the signal-dependent clearance of NCoR/SMRT complexes. The second repression mechanism involves Co-REST/LSD1 corepressor complexes, which we recently found to function in an anti-inflammatory pathway in microglia, the main innate immune cells of the brain. In this pathway, the orphan nuclear receptor Nurr1 is induced in response to TLR signaling and recruits CoREST/LSD1 co-repressor complexes to p65 at NFkB-responsive promoters. This acts to facilitate p65 turnover and re-establish a basal state of gene expression. Several new questions have emerged from these findings that will be addressed in this proposal.
Specific Aim 1 will be to define the molecular mechanisms that enable NCoR complexes to exert their checkpoint functions at TLR4 target genes.
Specific Aim 2 will be to define mechanisms underlying signal dependent turnover of NCoR from TLR-responsive genes and the molecular basis for inhibition of this step by LXRs and PPAR3.
Specific Aim 3 will be to define roles of the NR4/CoREST/LSD1 transrepression pathway in resolution of pro-inflammatory gene expression and the functional relationship of this pathway to the NCoR/SMRT checkpoint functions. Overall, these studies will provide new insights into molecular mechanisms that are utilized to integrate pro- and anti-inflammatory signaling pathways at the level of individual promoters and are likely to identify new points for intervention in transcriptional programs that contribute to cancer, insulin resistance and chronic inflammatory diseases.
Precise control of inflammation is essential for effective immunity and the maintenance of normal tissue function. Research proposed in this application will define mechanisms that integrate pro- and anti- inflammatory processes and identify new targets for therapeutic intervention in cancer, diabetes and chronic inflammatory diseases. )
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