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ORIGINAL RESEARCH ARTICLE

c-Jun Inhibits Thapsigargin-Induced ER Stress Through Up-Regulation of DSCR1/Adapt78

Peng Zhao^*,, Xiaoyan Xiao, Agnes S. Kim, M. Fatima Leite^||, Jinxia Xu, Xinglei Zhu^*, Jun Ren and Ji Li^,,1

^* Department of Cardiology, Shandong Provincial Hospital, Shandong University, Jinan, Shandong 250021, China; Department of Pharmaceutical Sciences & Center for Cardiovascular Research and Alternative Medicine, Dept 3375, School of Pharmacy, University of Wyoming, Laramie, Wyoming 82071; Department of Endocrinology, Qilu Hospital, Shandong University, Jinan, Shandong 250012, China; Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520; and ^|| Department of Physiology and Biophysics, Universidade Federal de Minas Gerais, CEP 30310-100, Belo Horizonte, Brazil

To whom requests for reprints should be addressed at ¹ School of Pharmacy, University of Wyoming, 1000 E. University Ave., Dept 3375, Laramie, WY 82071. E-mail: jli6{at}uwyo.edu

The endoplasmic reticulum (ER) is exquisitely sensitive to changes in its internal environment. Various conditions, collectively termed "ER stress", can perturb ER function, leading to the activation of a complex response known as the unfolded protein response (UPR). Although c-Jun N-terminal kinase (JNK) activation is nearly always associated with cell death by various stimuli, the functional role of JNK in ER stress-induced cell death remains unclear. JNK regulates gene expression through the phosphorylation and activation of transcription factors, such as c-Jun. Here, we investigated the role of c-Jun in the regulation of ER stress-related genes. c-Jun expression levels determined the response of mouse fibroblasts to ER stress induced by thapsigargin (TG, an inhibitor of sarco/endoplasmic reticulum Ca²⁺ ATPase). c-jun^–/– mouse fibroblast cells were more sensitive to TG-induced cell death compared to wild-type mouse fibroblasts, while reconstitution of c-Jun expression in c-jun^–/– cells (c-Jun Re) enhanced resistance to TG-induced cell death. The expression levels of ER chaperones Grp78 and Gadd153 induced by TG were lower in c-Jun Re than in c-jun^–/– cells. Moreover, TG treatment significantly increased calcineurin activity in c-jun^–/– cells, but not in c-Jun Re cells. In c-Jun Re cells, TG induced the expression of Adapt78, also known as the Down syndrome critical region 1 (DSCR1), which is known to block calcineurin activity. Taken together, our findings suggest that c-Jun, a transcription factor downstream of the JNK signaling pathway, up-regulates Adapt78 expression in response to TG-induced ER stress and contributes to protection against TG-induced cell death.

Key Words: c-Jun • thapsigargin • ER stress • calcineurin • Adapt78 • apoptosis • caspase-12