LPS independent activation of the pro-inflammatory receptor Trem1 by C/EBPϵ in granulocytes

Abstract

C/EBPϵ is a critical transcriptional factor for granulocyte differentiation and function. Individuals with germline mutations of C/EBPϵ fail to develop normal granulocytes and suffer from repeated infections. In order to gain a global view of the transcriptional machinery regulated by C/EBPϵ, we performed whole-genome ChIP-Seq using mouse bone marrow cells. To complement the C/EBPϵ DNA binding analyses, RNA-Sequencing was done in parallel using sorted mature and immature granulocytes from WT and C/EBPϵ KO bone marrow. This approach led to the identification of several direct targets of C/EBPϵ, which are potential effectors of its role in granulocytic differentiation and function. Interestingly, Trem1, a gene critical to granulocyte function, was identifed as a direct C/EBPϵ target gene. Trem1 expression overlaps very closely with expression signature of C/EBPϵ during hematopoietic development. Luciferase reporter and EMSA assays revealed that C/EBPϵ binds to the regulatory elements of Trem1 and regulates its expression during granulocytic differentiation. In addition, we provide evidence that inflammatory stimuli (LPS) can also control the expression of Trem1 independent of C/EBPϵ. Overall, this study provides comprehensive profiling of the transcriptional network controlled by C/EBPϵ during granulopoiesis and identifies Trem1 as one of its downstream effectors involved in eliciting an immune response.