Study of the Regulatory Mechanisms of Macrophage Apoptosis Induced by Lipopolysaccharides

点击翻译按钮获取中文摘要

Continuation of phosphorylation but not the activation itself of p38 MAP kinase was shown to be one of the most important factors for the induction of macrophage apoptosis induced by lipopolysaccharide (LPS) in the presence of cycloheximide. Although it has widely been believed that phosphorylation of the kinase corresponds to the activation of this enzyme, we showed that SB202190, a potent and specific inhibitor of p38 MAP kinase, induced apototic cell death of macrophages in the presence of LPS, with complete inhibition of the kinase activity but with sustained phosphorylation of the kinase. These results suggest that LPS-induced (nacrophage apoptosis is closely linked to the regulation of phosphorylation of p38 MAP kinase, not through activation of the down-stream kinase cascades but rather through prolonged phosphorylation of the kinase and the presence of the phosphorylated kinase in the nucleus.Another important result is the dissociation of the signaling pathways between apoptotic and activated macrophages. Refined procedures with pulse exposure of LPS to the macrophages in the presence or absence of serum and subsequent washing and reincubation of the cells revealed that as short as I min is enough to transduce the signals for the both apototic and activation processes of the macrophages, and that TLR4 and CD14 are involved in these processes, although later incubation than 30 min after LPS addition distinguish the signaling pathways either to the apoptosis or to the activation ; the former requires sustained phosphorylation of p38 MAP kinase by addition of cycloheximide or SB202190, as described above. Besides, the extents of CD14 expression was suggested to regulate the initial steps of the signal transduction.