LTA and LPS mediated activation of protein kinases in the regulation of inflammatory cytokines expression in macrophages

Background: Lipoteichoic acid (LTA) and lipopolysaccharide (LPS), the toxicants from bacteria, are potent inducers of inflammatory cytokines, such as tumor necrosis factor-α (TNF) and interleukin-1β (IL-1). Although LTA is much less reported than that on LPS, LTA is regarded as the gram-positive equivalent to LPS in some aspects. We investigated the LTA-induced signal transduction and biological effects, as well as to compare the effect of LTA with that of LPS. Methods: Kinase assay, ELISA and RT-PCR were performed to delineate LTA and LPS signaling as well as to determine the secretion and RNA expression of TNF and IL-1. Results: Src, Lyn and MAPKs are involved in LTA and LPS signaling in murine macrophages. Additionally, blockades of PKC, PI3K and p38, respectively, caused significant inhibition of both LTA- and LPS-induced proIL-1/IL-1 and TNF expression. ERK inactivation moderately reduced LTA- and LPS-induced proIL-1/IL-1, but considerably reduced TNF expression. Inhibition of JNK engendered super-induction of IL-1 secretion, but diminished TNF secretion. Strikingly, both IL-1 and TNF protein induction were declined by overexpression of dominant negative form of JNK. Conclusions: The results clarify the similarity and difference between LTA- and LPS-mediated signal transduction and induction of inflammatory cytokines in macrophages.