ATF3 is a stress-inducible gene that encodes a member of the ATF/CREB family of bZip transcription factors that binds to the consensus CRE. Its mRNA level is low or not detectable in most cells, but it is greatly upregulated in response to a variety of stress signals including cytokines, TLR ligands, genotoxic agents and compounds that induce cell death. In macrophages, ATF3 has been shown to be induced by the TLR4 ligand, LPS. Chemically defined LPS, Kdo2-Lipid A, is fully active as an endotoxin based on various biological criteria and highly selective for TLR4.
Here, we report that Kdo2-Lipid A induces ATF3 expression in wild type MEF cells and induces NF-κB and JNK activation via the TLR4 signaling pathway, but that no activation of either of these pathways is observed in ATF3 knockout MEF cells. Interestingly, in contrast to Kdo2-Lipid A, the activation of both NF-kB and JNK by TNF-α was normal in ATF3 knockout MEF cells. To investigate the mechanism underlying this phenomenon, we examined the difference in gene expression between ATF3 wild type and knockout MEF cells using microarray technology. We found that several of the genes showed dramatically increased expression in wild type MEF cells in response to Kdo2-Lipid A treatment, while little difference was observed in the ATF3 knockout MEF cells. Our findings indicate that the ATF3 deficiency affects Kdo2-Lipid A-induced TLR4 signaling pathways in MEF cells, and that it may upregulate IkBz expression. Additionally, ATF3 is required in TLR4-dependent gene expressions through the NF-κB pathway and it functions as a cell type specific manner.