Department of Pathology, Metabolic Diseases Institute, University of Cincinnati, Cincinnati, OH 45237, USA.
J Hepatol. 2012 Jan;56(1):192-8. doi: 10.1016/j.jhep.2011.03.019. Epub 2011 May 18.
BACKGROUND & AIMS: Saturated free fatty acid (SFA)-stimulated c-Jun NH(2)-terminal kinase (JNK) activation is associated with the pathogenesis of non-alcoholic fatty liver disease (NAFLD). However, the mechanisms responsible for the effects of SFA are incompletely understood. The goal of this study was to determine the molecular mechanisms by which SFA induce JNK activation in hepatocytes.
We used siRNA-mediated knockdown in Hepa1c1c7 and AML12 cell lines, as well as primary mouse hepatocytes for these studies.
The current model for JNK activation by SFA involves endoplasmic reticulum (ER) stress, which induces JNK activation through an inositol requiring enzyme 1 (IRE1α) Apoptosis Regulating Kinase 1 (ASK1)-dependent mechanism. Here, we find that SFA-induced JNK activation is not inhibited in the absence of IRE1α and ASK1. Instead we show that activation of the small GTP-binding proteins Cdc42 and Rac1 is required for SFA-stimulated MLK3-dependent activation of JNK in hepatocytes. In addition, we demonstrate that SFA-induced cell death in hepatocytes is independent of IRE1α, but dependent on Cdc42, Rac1, and MLK3.
Our results demonstrate that Cdc42 and Rac1, rather than ER stress, are important components of a SFA-stimulated signaling pathway that regulates MLK3-dependent activation of JNK in hepatocytes.
饱和游离脂肪酸（SFA）刺激 c-Jun NH（2）-末端激酶（JNK）的激活与非酒精性脂肪性肝病（NAFLD）的发病机制有关。然而，导致 SFA 作用的机制尚不完全清楚。本研究的目的是确定 SFA 诱导肝细胞 JNK 激活的分子机制。
我们使用 Hepa1c1c7 和 AML12 细胞系以及原代小鼠肝细胞中的 siRNA 介导的敲低来进行这些研究。
目前认为 SFA 通过内质网（ER）应激激活 JNK，通过肌醇需求酶 1（IRE1α）凋亡调节激酶 1（ASK1）依赖性机制诱导 JNK 激活。在这里，我们发现 SFA 诱导的 JNK 激活在没有 IRE1α 和 ASK1 的情况下不受抑制。相反，我们表明，小 GTP 结合蛋白 Cdc42 和 Rac1 的激活是 SFA 刺激 MLK3 依赖性 JNK 在肝细胞中激活所必需的。此外，我们证明 SFA 诱导的肝细胞死亡不依赖于 IRE1α，但依赖于 Cdc42、Rac1 和 MLK3。
我们的结果表明，Cdc42 和 Rac1 而不是 ER 应激是 SFA 刺激信号通路的重要组成部分，该信号通路调节 MLK3 依赖性 JNK 在肝细胞中的激活。
