Hyper MAPK/ERK signaling in DCs causes increased LPS-induced TNFa at the post-transcriptional level

Abstract

Abstract Background: Langerhans Cell Histiocytosis (LCH) is an inflammatory disease driven by abnormal dendritic cells (DCs) with hyper-MAPK/ERK signaling, usually due to Braf-V600E mutation. Since DCs are poised with Toll like Receptors (TLRs), which utilize MAPK/ERK signaling to incite an immune response, we hypothesize that LCH cells have a hyper-TLR response. Methods: We use an animal model of LCH (CD11c-Cre:BRAFV600E-flox; which expresses Braf-V600E in DCs) to measure serum TNFa and tnfa transcripts in CD11c+ splenocytes after LPS injection. Cultured BMDCs were pre-treated with/without a V600E-inhibitor before LPS stimulation. We measured intracellular TNFa, secretion and reuptake of TNFa, tnfa transcripts, NFkB signaling, TNFa degradation, and TACE activity. Results: LCH mice have increased LPS-induced circulating TNFa compared to WT. LCH-BMDCs have reversible LPS-induced increase in TNFa secretion and intracellular accumulation, but decreased tnfa and tlr4 transcripts and NFkB signaling compared to WT. There is no difference in TACE activity, TNFa reuptake, or protein degradation. Conclusions: Hyper-MAPK/ERK signaling in DCs causes a hyper LPS-induced TNFa response, despite diminished LPS signaling. Increased intracellular TNFa indicates a cell intrinsic, post-transcriptional mechanism. Current experiments are analyzing translation of TNFa, which is implicated by MAPK/ERK signaling. These data indicate novel effects of Braf-V600E on LPS-induced TNFa production, and current studies are investigating whether this is a more global phenomenon.