Crosstalk interactions between transcription factors ERRalpha and PPARalpha assist PPARalpha-mediated gene expression

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a crucial transcription factor governing genes associated with fatty acid beta-oxidation. How various interacting proteins modulate PPARalpha's transcriptional function remains incompletely understood. Employing an unbiased mammalian protein-protein interaction trap with liganded PPARalpha as bait, we identified an interaction with the orphan nuclear receptor estrogen-related receptor alpha (ERRalpha). Random mutagenesis scanning of the PPARalpha ligand-binding domain and coregulator profiling experiments implicated bridging coregulators, while in vitro studies suggested a trimeric interaction involving RXRalpha. The PPARalpha-ERRalpha interaction, dependent on three C-terminal residues within ERRalpha's helix 12, was reinforced by PGC1α and serum deprivation. Pharmacological inhibition of ERRalpha reduced its interaction with ligand-activated PPARalpha, revealing a transcriptome indicative of ERRalpha functioning as a transcriptional repressor on prototypical PPARalpha target genes. Intriguingly, ERRalpha exhibited opposite behavior on other PPARalpha targets, including the isolated PDK4 enhancer. Chromatin immunoprecipitation analyses demonstrated PPARalpha ligand-dependent recruitment of ERRalpha onto specific chromatin regions where PPARalpha binds in mouse livers. These findings highlight intricate transcriptional crosstalk mechanisms between PPARalpha and ERRalpha, suggesting a multi-layered regulatory network fine-tuning PPARalpha's activity as a nutrient-sensing transcription factor. ### Competing Interest Statement The authors have declared no competing interest.