Characterization of macromolecular complexes mediating glucocorticoid effects in skeletal muscles
Description: Glucocorticoids (GC) are widely prescribed drugs for chronic inflammatory conditions, including rheumatoid arthritis, multiple sclerosis and asthma that have revolutionized the field of medicine. However, long-term treatments have important side effects as they induce diabetes, osteoporosis and muscle wasting. GC functions are mediated by the GC receptor (GR), a member of the nuclear receptor superfamily. GR modulates the expression of a large number of genes, by recruiting coregulatory proteins. Whereas the interaction between GR and various coregulators has been characterized in vitro and in cell culture models, the tissue-specific composition and the structure of the functional GR-associated macromolecular complexes still remain to be determined. Interestingly, functional data from Team 2 of this consortium show that GR cooperates with the myogenic factor MYOD1 in muscle fibers at physiological GC levels. Co-immunoprecipitation experiments on muscle nuclear extracts revealed that GR and MYOD1 interact. However, this interaction might be mediated by specific DNA binding sites and/or might require additional proteins. In this respect, likely candidates are 2 members of the p160 family of coactivators, SRC1 and TIF2, since they interact with both GR and MYOD1. Preliminary data of Team 1 confirmed the interaction between GR and TIF2, and provided evidence that recombinant full-length GR forms a complex with full-length SRC1. In addition, Team 2 showed that GR and MYOD1 act in concert to negatively regulate muscle mass, as does TIF2, whereas SRC1 has an opposite function. This suggests that various combinations of coregulators recruited by GR to specific DNA binding sites lead to different functional outputs. Importantly, since various GR ligands induce selective GR conformation changes that might impact coregulator recruitment and DNA binding specificity, a molecular understanding of such complexes might allow to identify compounds that promote or impair selective complexes, and thus exert selective activities. The MYOGLUCO project focuses on the structure-function studies of GR-containing macromolecular complexes bound to various GR-responsive elements in skeletal muscles in the presence of natural and synthetic GCs. Using a multidisciplinary approach combining functional, molecular and structural analyses, MYOGLUCO aims at identifying the genes coregulated by these proteins and the associated signaling pathways, and determining the architecture of these ligand-dependent GR-associated macromolecular complexes using integrative cutting-edge structural methods, such as cryo electron microscopy and X-ray crystallography. To this end, the MYOGLUCO project will be set up in two work packages. WP1 aims at characterizing the GR-Myod1-SRC1/TIF2 complexes in skeletal muscle in the presence of various GR ligands, and will coordinated by the Team 2 that has a long-standing expertise in physiology and molecular biology. WP2 will provide the first biophysical and structural characterization of GR-Myod1-SRC1/TIF2 complexes bound to selective DNA sequences, and will be carried out by the Team 1 that is expert in structural biology. Unravelling the molecular underpinnings through which ligands impact GR-containing macromolecular complexes in skeletal muscles will provide invaluable information on the molecular and structural determinants of the GR action, which is of fundamental importance for the field of nuclear receptors and transcriptional regulation. Moreover, identifying actionable tissue/promoter specific GR-containing complexes will open novel therapeutic perspectives to reduce GC-induced side effects.
Funder: Agence Nationale de la Recherche
Amount: €471,900
Funding type: research
Funder scheme: AAPG2022
Start date: 2023-01-01
Investigator: Isabelle BILLAS (lead)
Institutions: Institut de génétique et de biologie moléculaire et cellulaire, Centre Européen de Recherche en Biologie et en Médecine
Subfield: Endocrinology
Domain: Life Sciences
Funded outputs count: 4
Funder award ID: ANR-22-CE11-0014
OpenAlex ID: G6569471908