Sumoylation of peroxisome proliferator-activated receptor γ by apoptotic cells prevents lipopolysaccharide-induced NCoR removal from κB binding sites 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 gamma (PPAR gamma) coordinates antiinflammatory responses following its activation by AC. Exposing murine RAW264.7 macrophages to AC before LPS stimulation reduced NF-kappa B transactivation and lowered target gene expression of, that is, TNF-alpha and IL-6 compared with controls. In macrophages overexpressing a dominant negative mutant of PPAR gamma, NF-kappa B transactivation in response to LPS was restored, while macrophages from myeloid lineage-specific conditional PPAR gamma knockout mice proved that PPAR gamma transmitted an antiinflammatory response, which was delivered by AC. Expressing a PPAR gamma-Delta aa32-250 deletion mutant, we observed no inhibition of NF-kappa B. Analyzing the PPAR gamma domain structures within aa 32-250, we anticipated PPAR-gamma sumoylation in mediating the antiinflammatory effect in response to AC. Interfering with sumoylation of PPAR gamma 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-kappa B Chromatin immunoprecipitation analysis demonstrated that AC prevented the LPS-induced removal of nuclear receptor corepressor (NCoR) from the kappa B site within the TNF-alpha promoter. We conclude that AC induce PPAR gamma sumoylation to attenuate the removal of NCoR, thereby blocking transactivation of NF-kappa B This contributes to an antiinflammatory phenotype shift in macrophages responding to AC by lowering proinflammatory cytokine production.