ATF3 Plays a Key Role in Kdo2-Lipid A-Induced TLR4-Dependent Gene Expression via NF-κB Activation

Background: Activating transcription factor 3 (ATF3) is a negative regulator of proinflammatory cytokine expression in macrophages, and ATF3 deficient mice are more susceptible to endotoxic shock. This study addresses the role of ATF3 in the Kdo(2)-Lipid A-induced Toll-like receptor 4 (TLR4) signaling pathway in mouse embryonic fibroblasts (MEF). Kdo(2)-Lipid A upregulates ATF3 expression in wild type MEF cells and induces both nuclear factor kappa B (NF-kappa B) and c-Jun N-terminal kinase (JNK) activation via the TLR4 signaling pathway, while neither of these pathways is activated in ATF3-/- MEF cells. Interestingly, in contrast to Kdo(2)-Lipid A, the activation of both NF-kappa B and JNK by TNF-alpha was normal in ATF3-/- MEF cells. Methodology/Principal Findings: We found that several genes were dramatically upregulated in ATF3+/+ MEF cells in response to Kdo(2)-Lipid A treatment, while little difference was observed in the ATF3-/- MEF cells. However, we also found that the signal intensities of I kappa B zeta in ATF3-/- MEF cells were substantially higher than those in wild type MEF cells upon microarray analyses, and upregulated I kappa B zeta expression was detected in the cytosol fraction. Conclusions/Significance: Our findings indicate that ATF3 deficiency affects Kdo(2)-Lipid A-induced TLR4 signaling pathways in MEF cells, that it may upregulate I kappa B zeta expression and that the high levels of I kappa B zeta expression in ATF3-/- cells disrupts Kdo(2)-Lipid A-mediated signaling pathways.