ROLE OF GLUCOCORTICOID RECEPTOR CONDENSATES IN TRANSCRIPTIONAL MODULATION

BELÉN BENITEZ; MARTÍN STORTZ; ADALI PECCI; DIEGO M. PRESMAN; VALERIA LEVI

Mar del Plata

Congreso; Reunión Anual de Sociedades de Biociencias (SAIC 2023); 2023

Sociedad Argentina de Investigación Clínica

The cell nucleus is organized into a variety of membrane less compartments that concentrate certain biomolecules with specific functions, including those involved in transcriptional regulation. It has been proposed that many of these compartments are formed by a liquid-liquid phase separation process (LLPS). The glucocorticoid receptor (GR) is a pharmacologically relevant ligand-dependent transcription factor that translocates to the nucleus upon hormone binding and partitions between the nucleoplasm and multiple discrete nuclear foci or condensates. Our group has previously shown that GR foci present properties compatible with condensates formed by LLPS in the context of living cells. However, the biological role of these structures remains unclear. Here, we explore whether intranuclear GR condensates have a role in transcriptional activity. By using advanced fluorescence microscopy techniques in living cells, we characterized the behavior of GR foci and other proteins involved in the transcriptional response. Consistently with a positive role in transcription, GR foci redistribute and colocalize with a subunit of the Mediator complex (Med1), a key player in RNApol II transcription. Interestingly, we observed at least two sub-populations of GR condensates that differ in their size, relative intensity, and respond differently to Med1 overexpression. We also observed an anti-correlation between foci formation and local chromatin condensation wherein GR foci are excluded from heterochromatin regions. Finally, we show that pharmacological inhibition of RNApol II elongation leads to a decrease in foci density, while increasing their relative intensity and sizes. Taken together, our results suggest that at least a subpopulation of GR condensates are involved in GR’s transcriptional activity by recruiting proteins related to this process. A further exploration of this new layer of transcriptional regulation might open new venues for pharmacological control of GR action.