Induction of REDD1 <i>via</i> AP-1 prevents oxidative stress-mediated injury in hepatocytes

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Regulated in development and DNA damage responses 1 (REDD1) is an inducible gene in response to various stresses, which functions as a negative regulator of the mammalian target of rapamycin protein kinase in complex 1. In the present study, we identified the role of REDD1 under the oxidative stress-mediated hepatocyte injury and its regulatory mechanism. REDD1 protein was increased in H<SUB>2</SUB>O<SUB>2</SUB> or <I>tert</I>-butylhydroperoxide (t-BHP)-treated hepatocytes<SUB>·</SUB> H<SUB>2</SUB>O<SUB>2</SUB> also elevated REDD1 mRNA levels. This event was inhibited by antioxidants such as diphenyleneiodonium chloride, <I>N</I>-acetyl-<SMALL>L</SMALL>-cysteine, or butylated hydroxy anisole. Interestingly, we found that H<SUB>2</SUB>O<SUB>2</SUB>-mediated REDD1 induction was transcriptionally regulated by activator protein-1 (AP-1), and that overexpression of c-Jun increased REDD1 protein levels and REDD1 promoter-driven luciferase activity. Deletion of the putative AP-1 binding site in proximal region of the human <I>REDD1</I> promoter significantly abolished REDD1 transactivation by c-Jun. A NF-E2-related factor 2 activator, <I>tert</I>-butylhydroquinone treatment also elevated REDD1 levels, but it was independent on NF-E2-related factor 2 activation. Furthermore, we observed that REDD1 overexpression attenuated H<SUB>2</SUB>O<SUB>2</SUB> or t-BHP-derived reactive oxygen species formation as well as cytotoxicity. Conversely, siRNA against REDD1 aggravated t-BHP-induced reactive oxygen species generation and cell death. In addition, we showed that REDD1 was induced by <I>in vitro</I> or <I>in vivo</I> ischemia/reperfusion model. Our results demonstrate that REDD1 induction by oxidative stress is mainly transcriptionally regulated by AP-1, and protects oxidative stress-mediated hepatocyte injury. These findings suggest REDD1 as a novel molecule that reduced susceptibility to oxidant-induced liver injury.</P> <P><B>Highlights</B></P> <P> <UL> <LI> REDD1 was enhanced in response to oxidative stress. </LI> <LI> AP-1 site from − 644 to − 638 bp in human <I>REDD1</I> was critical for gene expression. </LI> <LI> REDD1 protects cells against ROS in hepatocytes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>