Modulation of the transactivation function of nuclear factor-kappaB by lipopolysaccharide in RAW264.7 macrophages

In macrophages, nuclear factor kappa B (NF-kappaB) activation has important roles for the regulation of an inducible nitric oxide synthase (iNOS), several pro-inflammatory cytokines, and anti-apoptotic proteins. In order to analyze the transactivation process of NF-kappaB by lipopolysaccharide (LPS), we used the GAL4-NF-kappaB-p65 fusion protein. This chimeric NF-kappaB is activated transcriptionally only if NF-kappaB transactivation domain is active. With this system, we found that LPS can enhance the transactivation of GAL-NF-kappaB-p65 subunit independent of DNA binding ability and inhibitor of kappaB (IkappaB) regulation. Interestingly, this transactivation by LPS was eliminated with the treatment of U0126, specific inhibitor of mitogen-activated protein kinase (MAPK) kinases (MEKs) 1/2 which has little effect on NF-kappaB activation. We also investigated the effect of inhibitors of apoptosis (IAPs), which might be involved in LPS responses and c-Jun amino terminal kinase (JNKs) activation, on the transactivation of GAL-NF-kappaB-p65. The cIAP1, cIAP2 and XIAP could enhance the NF-kappaB transcription and the chimeric NF-kappaB-p65 transactivation. However, survivin decreased the NF-kappaB transcription and did not influence significantly the chimeric NF-kappaB-p65 transactivation. Taken together, LPS-dependent NF-kappaB transactivation may be involved in extracellular signal-regulated kinase (ERK) pathway and IAPs.