Glucocorticoid Receptor Quaternary Structure Drives Chromatin Occupancy and Transcriptional Outcome

GORDON L. HAGER; THOMAS A. JOHNSON; VILLE PAAKINAHO; DIEGO M. PRESMAN

San Carlos de Bariloche

Congreso; The fourth South American Spring Symposium in Signal Transduction and Molecular Medicine; 2018

SISTAM

The multimeric structure adopted by transcription factor complexes at their genomic sites of interaction is a longstanding problem in transcription biology. Information bearing on this question is often inferred from indirect data sources. Most transcription factors, including nuclear receptors, are widely modeled as binding regulatory elements as monomers, homodimers, or heterodimers. In particular, glucocorticoid receptor (GR)?s dimeric/monomeric status is widely believed to drive pharmacological output of synthetic glucocorticoids. Recent findings using quantitative fluorescence microscopy techniques in live cells show that the GR likely forms tetramers on enhancers during gene activation. These results suggest that higher oligomerization states are important for the gene regulatory responses of GR. To unveil the relationship between GR?s oligomerization and transcriptional outcome, we developed a GR null cell system to study how wild type GR and three different receptor mutants with unique quaternary structure characteristics bind chromatin and affect transcription at the genomic level. Our results indicate that GR must form dimers to bind even pre-accessible chromatin. The GRtetra, shown to mimic the DNA bound conformation of wild type receptor and form tetramers throughout the nucleus in live cells, acts as a super receptor by binding glucocorticoid response elements not accessible to wild type receptor, yet shared in numerous other cell types. GRtetra both induces and, more importantly, represses more genes in response to hormone. These results argue that a common mode of GR binding via higher order structures drives both the activating and repressive actions of glucocorticoids. This has important implications for the therapeutic uses of steroid hormones and the goal of finding selective anti-inflammatory drugs that do not create unwanted side-effects.