Department of Pathology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Gut. 2011 May;60(5):648-57. doi: 10.1136/gut.2010.223891. Epub 2011 Jan 3.
Radiotherapy for neoplastic disease is associated with significant adverse enteric effects associated with excessive cell death. Ionising radiation induces cell death by a mechanism that is dependent on JNK (c-jun N-terminal kinase) pathway signalling. Additionally, it is known that cells exposed to extracellular bacterial products such as flagellin, pleiotropically activate a number of innate immune pathways, including that of JNK. The JNK pathway controls its own activity by inducing the transcription of mitogen-activated protein kinase phosphatase-7 (MKP-7) which directly targets phosphorylated JNK, thus functioning as a negative feedback loop. Previously, it has been shown that flagellin limits ionising radiation-induced mortality in mice, but the cellular mechanism of protection remained unknown.
Wild-type C57BL/6 or tlr5(-/-) C57BL/6 were injected with flagellin 2 h before exposure to irradiation, and their intestines were examined for apoptosis. Candidate proteins mediating cytoprotection from irradiation were identified by expression profiling. One of these candidates, MKP-7, was cloned and packaged into adenovirus particles, used to infect cultured cells, and examined for the extent to which its activity reduced cellular apoptosis by flow cytometry or immunoblot analysis.
Flagellin pretreatment protected mice from radiation-induced intestinal mucosal injury and apoptosis via a Toll-like receptor 5 (TLR5)-dependent mechanism. Expression profiling of flagellin-treated mice showed upregulation of MKP-7, an inducible repressor of the JNK pathway. MKP-7 expression reached a maximum at 2 h after flagellin treatment, coinciding with suppression of phosphorylated JNK and JNK pathway inhibition. Furthermore, constitutive MKP-7 expression protected cultured cells from radiation-induced apoptosis.
Flagellin is a promising adjuvant for suppressing ionising radiation-induced injury. MKP-7 activity exhibits cytoprotective effects, and is thus a candidate cellular molecule for limiting the damaging effect of radiotherapy on the gastreointestinal system.
针对肿瘤疾病的放射疗法与过量细胞死亡相关的严重肠道不良影响有关。电离辐射通过依赖于 JNK（c-jun N-末端激酶）途径信号的机制诱导细胞死亡。此外，已知暴露于细胞外细菌产物（如鞭毛蛋白）的细胞会多效性地激活许多先天免疫途径，包括 JNK 途径。JNK 途径通过诱导丝裂原激活蛋白激酶磷酸酶-7（MKP-7）的转录来控制自身的活性，MKP-7 直接靶向磷酸化的 JNK，从而作为负反馈环起作用。先前已经表明，鞭毛蛋白可限制小鼠中电离辐射诱导的死亡率，但保护的细胞机制仍不清楚。
在暴露于照射前 2 小时给野生型 C57BL/6 或 tlr5(-/-) C57BL/6 注射鞭毛蛋白，并检查其肠道的凋亡情况。通过表达谱鉴定介导对辐射保护的候选蛋白。这些候选蛋白之一，MKP-7，被克隆并包装成腺病毒颗粒，用于感染培养的细胞，并通过流式细胞术或免疫印迹分析检查其活性降低细胞凋亡的程度。
鞭毛蛋白预处理通过 Toll 样受体 5（TLR5）依赖性机制保护小鼠免受辐射诱导的肠道黏膜损伤和凋亡。鞭毛蛋白处理小鼠的表达谱分析显示 MKP-7 的上调，MKP-7 是 JNK 途径的诱导抑制剂。MKP-7 的表达在鞭毛蛋白处理后 2 小时达到最大值，此时与抑制磷酸化 JNK 和 JNK 途径抑制同时发生。此外，MKP-7 的组成型表达可保护培养的细胞免受辐射诱导的凋亡。
鞭毛蛋白是一种有前途的佐剂，可抑制电离辐射诱导的损伤。MKP-7 活性具有细胞保护作用，因此是限制放疗对胃肠道系统破坏性影响的候选细胞分子。
