The transcription factor CHOP, a central component of the transcriptional regulatory network induced upon CCl4 intoxication in mouse liver, is not a critical mediator of hepatotoxicity
The transcription factor CHOP, a central component of the transcriptional regulatory network induced upon CCl4 intoxication in mouse liver, is not a critical mediator of hepatotoxicity
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DOI：
10.1007/s00204-014-1240-8
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发表时间：
2014-06-01
影响因子：
6.1
通讯作者：
Godoy, Patricio
中科院分区：
文献类型：
--
作者：
Campos, Gisela;Schmidt-Heck, Wolfgang;Godoy, Patricio
由于外源性物质通过肝脏进入生物体，肝细胞必须科普许多扰动，包括导致内质网应激（ER-应激）的蛋白质修饰。这触发了称为未折叠蛋白反应（UPR）的信号通路，其目的是恢复稳态或通过凋亡消除受干扰的肝细胞。在本研究中，我们使用了完善的CCl 4肝毒性模型在小鼠中，以解决的问题，CCl 4是否诱导ER应激，如果是这样的话，是否是众所周知的ER应激效应CHOP是负责CCl 4诱导的细胞凋亡。为此目的，我们用高剂量的CCl 4腹腔注射处理小鼠，并使用Affytron基因阵列分析随时间推移跟踪基因表达谱。这种时间分辨的基因表达分析允许鉴定具有三种最重要的ER应激诱导的转录因子CHOP、XBP 1和ATF 4的过度表达结合位点的基因簇。CCl 4诱导的XBP 1剪接、CHOP在mRNA和蛋白水平上的上调以及CHOP向细胞核的易位证实了这一结果。两个观察结果表明，CHOP可能是负责CCl 4诱导的细胞死亡：（1）CHOP的核转位只在肝细胞的中心周围部分观察到，在响应CCl 4和（2）CHOP调节的基因与先前报道的促凋亡功能，如GADD 34，TRB 3和ERO 1 L诱导中心周围区以及。因此，我们比较了CCl 4诱导的CHOP基因敲除小鼠与野生型小鼠的肝毒性。令人惊讶的是，CHOP的遗传耗竭并没有提供对CCl 4诱导的损伤的保护，如血清GOT和GPT以及死亡组织面积的定量所证明的。在几个时间点（8、24和72 h）和不同CCl 4剂量（1.6和0.132 g/kg）下获得阴性结果。总之，我们的结果表明，所有分支的UPR被激活后，四氯化碳处理小鼠肝脏。然而，CHOP在CCl 4诱导的细胞死亡中不起关键作用，不能被认为是与肝毒性严格相关的生物标志物。替代性UPR效应物如XBP 1的作用仍有待研究。
Since xenobiotics enter the organism via the liver, hepatocytes must cope with numerous perturbations, including modifications of proteins leading to endoplasmic reticulum stress (ER-stress). This triggers a signaling pathway termed unfolded protein response (UPR) that aims to restore homeostasis or to eliminate disturbed hepatocytes by apoptosis. In the present study, we used the well-established CCl4 hepatotoxicity model in mice to address the questions whether CCl4 induces ER-stress and, if so, whether the well-known ER-stress effector CHOP is responsible for CCl4-induced apoptosis. For this purpose, we treated mice with a high dose of CCl4 injected i.p. and followed gene expression profile over time using Affymetrix gene array analysis. This time resolved gene expression analysis allowed the identification of gene clusters with overrepresented binding sites for the three most important ER-stress induced transcription factors, CHOP, XBP1 and ATF4. Such result was confirmed by the demonstration of CCl4-induced XBP1 splicing, upregulation of CHOP at mRNA and protein levels, and translocation of CHOP to the nucleus. Two observations indicated that CHOP may be responsible for CCl4-induced cell death: (1) Nuclear translocation of CHOP was exclusively observed in the pericentral fraction of hepatocytes that deteriorate in response to CCl4 and (2) CHOP-regulated genes with previously reported pro-apoptotic function such as GADD34, TRB3 and ERO1L were induced in the pericentral zone as well. Therefore, we compared CCl4 induced hepatotoxicity in CHOP knockout versus wild-type mice. Surprisingly, genetic depletion of CHOP did not afford protection against CCl4-induced damage as evidenced by serum GOT and GPT as well as quantification of dead tissue areas. The negative result was obtained at several time points (8, 24 and 72 h) and different CCl4 doses (1.6 and 0.132 g/kg). Overall, our results demonstrate that all branches of the UPR are activated in mouse liver upon CCl4 treatment. However, CHOP does not play a critical role in CCl4-induced cell death and cannot be considered as a biomarker strictly linked to hepatotoxicity. The role of alternative UPR effectors such as XBP1 remains to be investigated.