Gaq-stimulated gene expression is insensitive to Bromo extra terminal domain inhibitors in HEK 293 cells

Bromodomain and extraterminal domain (BET) family proteins are ubiquitous transcriptional co-activators that function broadly in gene expression programs associated with cellular differentiation, proliferation, and stress responses. Pharmacological inhibition of BET proteins with small molecules that disrupt bromodomain engagement with acetyllysine residues (such as JQ1), or that drive their degradation through the ubiquitin-proteasome system (such as dBET6), ameliorates pathological gene expression in a range of systems and shows promise as a potential therapeutic strategy. BET involvement in gene expression responses is not universal, and understanding of the cell-type and signaling pathway requirements that dictate BET dependence remains incomplete. We previously demonstrated that, in neonatal rat cardiomyocytes, GPCR-induced hypertrophy response depended strongly on the BET protein Brd4 when signaling was coupled to Gs, but not Gq. Here we tested whether Brd4 was differentially responsive to G protein isoforms in another cell type by expressing Gs or Gq-coupled Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in HEK 293 cells. Gq induced expression of a group of early response genes and inflammatory genes in a manner largely insensitive to pharmacological BET inhibition, consistent with our previous data in cardiomyocytes. Gs activated a small subset of the Gq-induced genes, but this effect was largely reversed by the BET degrader molecule dBET6. Our data further suggest that there may be general signaling requirements to activate Brd4 across cell types.