Glucocorticoid-regulated transcription networks in macrophage biology

Hospital For Special Surgery, New York NY

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Abstract

DESCRIPTION (provided by applicant): The epidemic of obesity, insulin resistance and type 2 diabetes with associated co-morbidities is a daunting problem in public health. Metabolic disease involves a strong inflammatory component in which adipose tissue macrophages (M?) play a critical pathogenic role. Glucocorticoids (GCs) remain the most common and cost-effective class of medications for managing inflammatory diseases however, GCs are themselves diabetogenic, which hampers their therapeutic utility. In M?, GCs broadly inhibit the production of proinflammatory mediators; moreover, GCs promote the polarization of 'alternatively activated' M2 M? that display an anti-inflammatory phenotype, and, paradoxically, increase insulin sensitivity. Untangling the dichotomy between the systemic vs. M2-specific metabolic actions of GCs is crucial for understanding the pathogenesis of insulin resistance and for creating anti-inflammatory drugs with improved therapeutic profiles. GCs signal through the GC receptor (GR) a ligand-regulated transcription factor of the nuclear receptor (NR) superfamily that recruits numerous coregulators to activate or repress transcription. Among those, the GR-interacting protein (GRIP) 1 is an established NR coactivator, that we have recently shown to serve as a key GR corepressor attenuating the inflammatory gene expression program in M?. Unexpectedly, GRIP1 was also found to cooperate with non-receptor regulators in the immune system. What enables GRIP1 to selectively engage in antagonistic biological pathways or display opposite transcriptional activities is unknown. Recently, we found that GRIP1 undergoes GC-induced, GR interaction-dependent phosphorylation at multiple sites that was required for the induction of a subset of GR targets. The objective of this application is to dissect the role and mechanisms of GR-induced GRIP1 phosphorylation in M? as a modulator of anti-inflammatory and metabolic effects of GCs. Our central hypothesis is that liganded GR modifies its own coregulator by enabling GC-response element (GRE)-specific recruitment of GRIP1 kinases, thus dictating GRIP1 function in distinct GR transcription complexes, or preferential utilization of its activating vs. repressing properties. Our Specific Aims are to: 1) utilize our M?-specific conditional GRIP1-deficient mice and GRIP1 phosphosite-specific antibodies to assess the genome-wide distribution of GRIP1 phospho-isoforms in M? and determine the functionally relevant binding sites; 2) dissect the function of putative GRIP1 kinases, cyclin-dependent kinase-9 and casein kinase-2, as GRE-specific components of GR transcription complexes; 3) identify (by blocking phosphorylation of endogenous GRIP1 or integrating GRIP1 phosphosite mutants into GRIP1-null cells) the role of GRIP1 phosphorylation in the assembly and gene regulation by GR transcription complexes, as well as in M? polarization and the M?:adipocyte interactions. This work will yield detailed information on a novel mechanism contributing specificity to GR-mediated gene expression, which should reveal an important facet of metabolic control and new opportunities for the design of safer therapies for inflammatory diseases.