Osteopontin induces ubiquitin-dependent degradation of STAT1 in RAW264.7 murine macrophages
Osteopontin induces ubiquitin-dependent degradation of STAT1 in RAW264.7 murine macrophages
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DOI：
10.4049/jimmunol.178.3.1870
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发表时间：
2007-02-01
影响因子：
4.4
通讯作者：
Kuo, Paul C.
中科院分区：
文献类型：
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作者：
Gao, Chengjiang;Guo, Hongtao;Kuo, Paul C.
在由内毒素（LPS）诱导的全身炎症中，巨噬细胞产生大部分循环NO代谢物。然而，虽然在巨噬细胞中上调iNOS表达的分子途径已被广泛研究，但对抑制或抑制巨噬细胞iNOS表达的平行反调节途径知之甚少。使用内毒素（LPS）刺激的体内和体外Muirine模型，我们以前已经证明，NO反馈通过增加骨桥蛋白（OPN）的转录来抑制其自身的合成，骨桥蛋白是诱导型NO合酶表达的有效反式阻遏物。在目前的研究中，使用LPS处理的RAW 264.7巨噬细胞系统，我们继续证明OPN增加STAT 1泛素化和随后的26 s蛋白酶体介导的降解，以抑制STAT 1依赖的iNOS启动子活性，转录和蛋白表达。此外，我们确定STAT相互作用的LIM蛋白作为关键STAT泛素E3连接酶的关键STAT 1降解在这种情况下。OPN以前与STAT 1降解无关。STAT 1降解的这种调节是OPN作为iNOS基因转录抑制剂的作用的基础。这些都是新的发现，并将OPN定义为一种独特的，但尚未充分表征的，由泛素-蛋白酶体系统降解STAT 1的反式激活因子。
In systemic inflammation induced by endotoxin (LPS), the macrophage produces the majority of the circulating NO metabolites. However, while the molecular pathways which up-regulate iNOS expression have been extensively studied in the macrophage, little is known of the parallel counterregulatory pathways which repress or inhibit macrophage iNOS expression. Using both in vivo and in vitro muirine models of endotoxin (LPS) stimulation, we have previously demonstrated that NO feedback inhibits its own synthesis by increasing transcription of osteopontin (OPN), a potent transrepressor of inducible NO synthase expression. In this current study, using a system of LPS-treated RAW264.7 macrophages, we go on to demonstrate that OPN increases STAT1 ubiquitination and subsequent 26s proteasome-mediated degradation to inhibit STAT1 dependent iNOS promoter activity, transcription, and protein expression. In addition, we identify STAT-interacting LIM protein as the critical STAT ubiquitin E3 ligase critical for STAT1 degradation in this setting. OPN has not been linked previously to STAT1 degradation. This regulation of STAT1 degradation underlies OPN's effect as an inhibitor of iNOS gene transcription. These are novel findings and define OPN as a unique and as yet, poorly characterized, transactivator of STAT1 degradation by the ubiquitin-proteasome system.