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

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 M2IL4 '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 M2IL4, 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 M2IL4, 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.