Orphan nuclear receptor Nur77 Inhibits Oxidized LDL-induced differentiation of RAW264.7 murine macrophage cell line into dendritic like cells

Background: Nur77 is an orphan nuclear receptor expressed in human atheroma. In vascular cells in vitro, Nur77 expression is induced by pro-inflammatory factors, such as oxidized LDL (oxLDL). Methods: We analyze the role of Nur77 in the oxLDL-induced differentiation of macrophages into dendritic cells (DC). The murine RAW264.7 macrophage cell line was stably transfected with expression plasmids encoding either GFP or GFP fusions with either full-length Nur77(GFP-Nur77), Nur77 lacking the DNA binding domain ( GFP-Nur77-Delta DBD) or Nur77 lacking the transactivation domain(GFP-Nur77-Delta TAD). Results: GFP-Nur77 overexpression significantly suppressed the effect of oxLDL treatment on DC morphologic changes, expression of DC maturation markers, endocytic activity, allogeneic activation of T cell proliferation, and the activity and secretion of pro-inflammatory cytokines. Analysis of GFP-Nur77-Delta TAD and GFP-Nur77-Delta DBD indicated that the Nur77 DNA binding and transactivation domains were both required for this effect. GFP-Nur77-Delta DBD consistently had the opposite effect to GFP-Nur77, increasing DC-type differentiation in all assays. Interestingly, GFP-Nur77-Delta DBD protein was cytosolic, whereas GFP-Nur77 and GFP-Nur77-Delta TAD were both nuclear. Conclusions: These data show that GFP-Nur77 inhibited differentiation of oxLDL-treated macrophages into DC. The effects of Nur77 on the macrophage phenotype may involve changes in its subcellular distribution.