PPAR gamma lipodystrophy mutants reveal intermolecular interactions required for enhancer activation

Mutations in PPAR gamma lead to lipodystrophy, but the mechanisms by which the mutations affect the activity in chromatin is unknown. Here, Madsen, Broekema et al. showed that mutations affecting two intermolecular interactions compromise chromatin remodeling. Peroxisome proliferator-activated receptor gamma (PPAR gamma) is the master regulator of adipocyte differentiation, and mutations that interfere with its function cause lipodystrophy. PPAR gamma is a highly modular protein, and structural studies indicate that PPAR gamma domains engage in several intra- and inter-molecular interactions. How these interactions modulate PPAR gamma's ability to activate target genes in a cellular context is currently poorly understood. Here we take advantage of two previously uncharacterized lipodystrophy mutations, R212Q and E379K, that are predicted to interfere with the interaction of the hinge of PPAR gamma with DNA and with the interaction of PPAR gamma ligand binding domain (LBD) with the DNA-binding domain (DBD) of the retinoid X receptor, respectively. Using biochemical and genome-wide approaches we show that these mutations impair PPAR gamma function on an overlapping subset of target enhancers. The hinge region-DNA interaction appears mostly important for binding and remodelling of target enhancers in inaccessible chromatin, whereas the PPAR gamma-LBD:RXR-DBD interface stabilizes the PPAR gamma:RXR:DNA ternary complex. Our data demonstrate how in-depth analyses of lipodystrophy mutants can unravel molecular mechanisms of PPAR gamma function.