Live cell imaging unveils multiple domain requirements for in vivo dimerization of the glucocorticoid receptor

PRESMAN D.; OGARA M.F.; STORTZ M.; ALVAREZ L.D.; GRØNTVED L.; JOHNSON TA; BURTON G.; LEVI V.; HAGER G.L.; PECCI A.

Sorrento

Conferencia; EMBO CONFERENCE: NUCLEAR RECEPTORS: LINKING MOLECULES, GENOMES & PHYSIOLOGY; 2013

EMBO

Glucocorticoid receptor (GR) transcriptional activity and clinical outcome have been associated with its oligomerization state. Current models propose that upon ligand binding GR translocates into the nucleus, forms homodimers, binds to DNA, and recruits transcription co-modulators. However, the hierarchical succession of these events is not clearly established. Moreover, although GR homodimerization is considered essential for the GR-transactivation pathway, there are several discrepancies related to the identification of regions involved in homodimerization and the mechanisms underlying this process. According to crystal structure analysis, three putative dimerization regions have been reported; one located in the DNA binding domain (DBD) and the other two in the Ligand-binding domain (LBD) of the receptor. A point mutation within the mouse GR DBD (A465T) named GRdim, has been reported as crucial for receptor dimerization and DNA binding. Here, we analyzed GR oligomerization state in vivo by using the Number and Brightness assay. Our results suggest a complete, reversible and DNA-independent, ligand-induced model for GR dimerization. We demonstrate that the GRdim forms dimers in vivo while an additional mutation in the ligand-binding domain (I634A) severely compromises homodimer formation. Moreover, GR dimerization also seems to be dependent on the ligand structure, indicating that the dimerization process is more complex than previously described. Contrary to dogma, no correlation between the GR monomeric/dimeric state and its transcriptional activity was observed. These results will have major implications on the future search for therapeutic glucocorticoids with reduced side effects.