Transcription of Tnfaip3 Is Regulated by NF-[kappa]B and p38 via C/EBP[beta] in Activated Macrophages

Macrophages play a pivotal role in the immune system through recognition and elimination of microbial pathogens. Toll-like receptors (TLRs) on macrophages interact with microbial substances and initiate signal transduction through intracellular adapters. TLR4, which recognizes the lipopolysaccharides (LPS) on Gram-positive and Gram-negative bacteria, triggers downstream signaling mediators and eventually activates I[kappa]B kinase (IKK) complex and mitogen-activated protein kinases (MAPKs) such as p38. Previous reports revealed that, in addition to NF-[kappa]B, a core transcription factor of the innate immune response, the induction of some LPS-induced genes in macrophages required another transcription factor whose activity depends on p38. However, these additional transcription factors remain to be identified. In order to identify p38-activated transcription factors that cooperate with NF-[kappa]B in response to LPS stimulation, microarrays were used to identify genes regulated by both NF-[kappa]B and p38 using wild-type, IKK-depleted, and p38 inhibitor-treated mouse bone marrow-derived macrophages (BMDMs). In silico analysis of transcription factor binding sites was used to predict the potential synergistic transcription factors from the co-expressed genes. Among these genes, NF-[kappa]B and C/EBP[beta], a p38 downstream transcription factor, were predicted to co-regulate genes in LPS-stimulated BMDMs. Based on the subsequent results of a chromatin immunoprecipitation assay and TNFAIP3 expression in C/EBP[beta]-ablated macrophages, we demonstrated that Tnfaip3 is regulated by both NF-[kappa]B and p38-dependent C/EBP[beta]. These results identify a novel regulatory mechanism in TLR4-mediated innate immunity.