Role of glucocorticoid receptor condensates in transcriptional modulation

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

Cuidad Autónoma de Buenos Aires

Simposio; Frontiers in Biosciences 4 Symposium; 2023

Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA)

The cell nucleus is highly organized into a variety of membrane-free compartments that concentrate certain biomolecules with specific functions, including those involved in transcriptional regulation. Recent evidence supports that many of these compartments are formed by a liquid-liquid phase separation (LLPS) process. The glucocorticoid receptor (GR) is a ligand-activatable transcription factor that translocates to the nucleus upon hormone binding and partitions between the nucleoplasm and multiple discrete nuclear foci. Our group has shown that the GR foci have properties compatible with those expected for condensates formed by LLPS in living cells. However, the biological role of these structures remains unknown. Here, we explore the role of intranuclear GR condensates in transcriptional modulation using advanced fluorescence microscopy techniques that allow us to analyze in living cells the dynamics of the interaction between GR and other protein factors involved in the transcriptional response. We observed that active GR condensates colocalize with multivalent transcription-related coactivators, eg, NCoA2 and Mediator complex. In addition, we study the existence of a correlation between foci formation and local chromatin condensation and corroborate that GR foci are excluded from condensed chromatin regions, suggesting that GR foci formation does not require a certain state of chromatin compaction for its formation. Additionally, we analyze the role of nascent RNAs on the formation of GR condensates; we show that the inhibition of transcription elongation leads to an increase in the size of the GR and Mediator condensates. Taken together, our results suggest that GR condensates are fused with a possible modulatory role in transcription.