| Ubiquitination is an enzymatic, post-translational modification carried out by a set of three enzymes, E1, E2and E3. Ubiquitin labelling does not always mean degradation for the substrate proteins. It can also affect cellular sub-location and function of the substrate proteins. Recently, it has been shown that ubiquitination also occurrs in both innate and adaptive immunity. Macrophages are versatile immunocytes that play many roles as scavengers, APC (antigen presenting cells), or secretory cells in both innate immunity and adaptive immunity. Macrophage activation, which including classical activation (M1) and alternative activation (M1), plays an important role in host defense. However, the role of ubiquitination during Ml versus M2polarization is poorly explored.In this work, a proteomic study on Nrdpl transgenic (Nrdpl-TG) mouse peritoneal macrophages was carried out. We found that Nrdpl, an E3ubiquitin ligase, highly up-regulated the expression of arginase1(Argl) in macrophages, which was verified by western blotting and real-time PCR subsequently. Argl is a well recognized marker of M2macrophage activation. Further studies showed that other M2activation markers like Fizzl, Ym1, and MR were also up-regulated in peritoneal macrophages of Nrdpl-TG mice compared with those of wild-type mice, after IL-4stimulation. The Nrdp1silencing experiment showed consistent results. Furthermore, Nrdp1suppressed LPS-induced iNOS expression in Nrdp1-TG macrophages, as well as pro-inflammatory cytokines like TNF-a, IL-1β, and IL-6. To further investigate the mechanism underlying Nrdpl's up-regulation of Argl, we used co-immunoprecipitation, and found that Nrdpl interacted with and polyubiquitinated transcriptional factor C/EBPβ. The subsequent Argl luciferase reporter assay showed that C/EBPβ-induced transcriptional activity of Argl was enhanced by Nrdpl in the presence of IL-4stimulation. These data indicated that, Nrdpl up-regulate Argl by ubiquitinating and activating C/EBPβ in macrpohages. |
PDF Full Text Request