Regulation of Id2 gene expression in plasmacytoid dendritic cells

Abstract

Abstract Plasmacytoid dendritic cells (pDCs) are specialized type I interferon (IFN-I) producing cells that mediate anti-viral responses, anti-tumor immunity, and autoimmunity. When exposed to Toll-like receptor 7 (TLR7)- and TLR9-ligands, pDCs mature and produce IFN-Is; pDCs also acquire conventional DC (cDC)-like morphology and features, including the cell surface expression of antigen presentation and co-stimulatory molecules, secretion of additional cytokines, and ability to activate adaptive T cell responses. Yet, the transcriptional pathways regulating TLR-induced pDC maturation are poorly characterized. We found the mRNA and protein expression of the inhibitor of DNA binding protein 2 (Id2) was induced in TLR7/9-stimulated pDCs, and Id2 expression correlated with greater cDC-like features. Id2 normally blocks pDC development by antagonizing the pDC-master regulator, E2-2, while E2-2 suppresses Id2 transcription. Thus, we hypothesize TLR-activated signaling pathways in pDCs control the abundance of transcriptional regulators (e.g., E2-2) at the Id2 promoter as well as the promoter chromatin state, leading to induction of Id2 transcription during pDC maturation. Using genetic knockout mouse models, we found Id2 induction was independent of interferon alpha receptor and nuclear factor kappa beta signaling pathways. Chromatin-immunoprecipitation assays suggested E2-2 abundance at the Id2 promoter decreased following TLR stimulation, while activating histone modifications increased. These data are consistent with transcriptional induction of Id2 upon TLR stimulation. Future work will investigate the effect of additional regulators and TLR-regulated pathways on Id2 induction in TLR7/9-stimulated pDCs.