Gambelli Federica, Di Peter, Niu Xiaomei, Friedman Mitchell, Hammond Timothy, Riches David W H, Ortiz Luis A
Division of Occupational Medicine, Department of Environmental and Occupational Health, University of Pittsburgh, A731 Crabtree Hall, 130 De Soto Street, Pittsburgh, PA 15261, USA.
J Biol Chem. 2004 Jan 16;279(3):2020-9. doi: 10.1074/jbc.M309763200. Epub 2003 Oct 21.
Macrophages play a fundamental role in silicosis in part by removing silica particles and producing inflammatory mediators in response to silica. Tumor necrosis factor alpha (TNFalpha) is a prominent mediator in silicosis. Silica induction of apoptosis in macrophages might be mediated by TNFalpha. However, TNFalpha also activates signal transduction pathways (NF-kappaB and AP-1) that rescue cells from apoptosis. Therefore, we studied the TNFalpha-mediated mechanisms that confer macrophage protection against the pro-apoptotic effects of silica. We will show that exposure to silica induced TNFalpha production by RAW 264.7 cells, but not by IC-21. Silica-induced activation of NF-kappaB and AP-1 was only observed in RAW 264.7 macrophages. ERK activation in response to silica exposure was only observed in RAW 264.7 macrophages, whereas activation of p38 phosphorylation was predominantly observed in IC-21 macrophages. No changes in JNK activity were observed in either cell line in response to silica exposure. Silica induced apoptosis in both macrophage cell lines, but the induction of apoptosis was significantly larger in IC-21 cells. Protection against apoptosis in RAW 264.7 cells in response to silica was mediated by enhanced NF-kappaB activation and ERK-mediated phosphorylation of the p55 TNFalpha receptor. Inhibition of these two protective mechanisms by specific pharmacological inhibitors or transfection of dominant negative mutants that inhibit IkappaBalpha or ERK phosphorylation significantly increased silica-induced apoptosis in RAW 264.7 macrophages. These data suggest that NF-kappaB activation and ERK-mediated phosphorylation of the p55 TNF receptor are important cell survival mechanisms in the macrophage response to silica exposure.
巨噬细胞在矽肺中发挥着重要作用，部分原因是通过清除二氧化硅颗粒并对二氧化硅产生炎症介质做出反应。肿瘤坏死因子α（TNFα）是矽肺中的一种重要介质。二氧化硅诱导巨噬细胞凋亡可能由TNFα介导。然而，TNFα也激活信号转导通路（NF-κB和AP-1），从而使细胞免于凋亡。因此，我们研究了TNFα介导的赋予巨噬细胞抵御二氧化硅促凋亡作用的机制。我们将表明，暴露于二氧化硅会诱导RAW 264.7细胞产生TNFα，但不会诱导IC-21细胞产生。仅在RAW 264.7巨噬细胞中观察到二氧化硅诱导的NF-κB和AP-1激活。仅在RAW 264.7巨噬细胞中观察到对二氧化硅暴露的ERK激活，而p38磷酸化的激活主要在IC-21巨噬细胞中观察到。在两种细胞系中，未观察到JNK活性因二氧化硅暴露而发生变化。二氧化硅在两种巨噬细胞系中均诱导凋亡，但IC-21细胞中的凋亡诱导明显更大。RAW 264.7细胞对二氧化硅诱导的凋亡的保护作用是由增强的NF-κB激活和ERK介导的p55 TNFα受体磷酸化介导的。通过特异性药理抑制剂或转染抑制IκBα或ERK磷酸化的显性负突变体来抑制这两种保护机制，可显著增加RAW 264.7巨噬细胞中二氧化硅诱导的凋亡。这些数据表明，NF-κB激活和ERK介导的p55 TNF受体磷酸化是巨噬细胞对二氧化硅暴露反应中的重要细胞存活机制。
