Sumoylation of peroxisome proliferator-activated receptor gamma by apoptotic cells prevents lipopolysaccharide-induced NCoR removal from kappaB binding sites mediating transrepression of proinflammatory cytokines.

Efficient clearance of apoptotic cells (AC) by professional phagocytes is crucial for tissue homeostasis and resolution of inflammation. Macrophages respond to AC with an increase in antiinflammatory cytokine production but a diminished release of proinflammatory mediators. Mechanisms to explain attenuated proinflammatory cytokine formation remain elusive. We provide evidence that peroxisome proliferator-activated receptor γ (PPARγ) coordinates antiinflammatory responses following its activation by AC. Exposing murine RAW264.7 macrophages to AC before LPS stimulation reduced NF-κB transactivation and lowered target gene expression of, that is, TNF-α and IL-6 compared with controls. In macrophages overexpressing a dominant negative mutant of PPARγ, NF-κB transactivation in response to LPS was restored, while macrophages from myeloid lineage-specific conditional PPARγ knockout mice proved that PPARγ transmitted an antiinflammatory response, which was delivered by AC. Expressing a PPARγ-Δaa32–250 deletion mutant, we observed no inhibition of NF-κB. Analyzing the PPARγ domain structures within aa 32–250, we anticipated PPARγ sumoylation in mediating the antiinflammatory effect in response to AC. Interfering with sumoylation of PPARγ by mutating the predicted sumoylation site (K77R), or knockdown of the small ubiquitin-like modifier (SUMO) E3 ligase PIAS1 (protein inhibitor of activated STAT1), eliminated the ability of AC to suppress NF-κB. Chromatin immunoprecipitation analysis demonstrated that AC prevented the LPS-induced removal of nuclear receptor corepressor (NCoR) from the κB site within the TNF-α promoter. We conclude that AC induce PPARγ sumoylation to attenuate the removal of NCoR, thereby blocking transactivation of NF-κB. This contributes to an antiinflammatory phenotype shift in macrophages responding to AC by lowering proinflammatory cytokine production.