A transcriptional cofactor GRIP1 drives PPARγ DNA binding and p300-dependent enhancer activity during homeostatic...

Homeostatic macrophages maintain tissue health and resolve inflammation. Upon sustained exposure to type II cytokine IL4, transcription factors STAT6, KLF4, EGR2 and a ligand-regulated nuclear receptor PPARγ orchestrate the M2_IL4 'polarization', marked by enhancer RNA (eRNA) production near multiple M2 genes. The mechanisms of enhancer activation by unliganded PPARγ are poorly understood. We interrogated cofactor requirements for PPARγ-driven gene expression in M2_IL4, including those lacking PPARγ or a ligand-dependent nuclear receptor coregulator NCoA2/GRIP1 vs. macrophages treated with the PPARγ agonist rosiglitazone. As expected, rosiglitazone activated conventional PPARγ targets; GRIP1 deletion blunted their induction and depleted GRIP1-interacting histone acetyltransferase p300 from PPARγ-bound sites. Surprisingly, GRIP1 colocalized with unliganded PPARγ in M0 and M2_IL4, and GRIP1 ablation dramatically reduced genome-wide DNA binding of PPARγ itself while promoting broad deposition of CTCF insulator. Functionally, GRIP1 deletion mirrored PPARγ deficiency, establishing GRIP1 as a central regulator of unliganded PPARγ DNA binding, required for both eRNA and mRNA transcription of PPARγ targets in homeostatic macrophages.