Protection of Renal Epithelial Cells against Oxidative Injury by Endoplasmic Reticulum Stress Preconditioning Is Mediated by ERK1/2 Activation

Abstract

We investigated the role of the endoplasmic reticulum (ER) stress response in intracellular Ca 2؉ regulation, MAPK activation, and cytoprotection in LLC-PK 1 renal epithelial cells in an attempt to identify the mechanisms of protection afforded by ER stress. Cells preconditioned with trans-4,5-dihydroxy-1,2-dithiane, tunicamycin, thapsigargin, or A23187 expressed ER stress proteins and were resistant to subsequent H 2 O 2 -induced cell injury. In addition, ER stress preconditioning prevented the increase in intracellular Ca 2؉ concentration that normally follows H 2 O 2 exposure. Stable transfection of cells with antisense RNA targeted against GRP78 (pkASgrp78 cells) prevented GRP78 induction, disabled the ER stress response, sensitized cells to H 2 O 2 -induced injury, and prevented the development of tolerance to H 2 O 2 that normally occurs with preconditioning. ERK and JNK were transiently (30 -60 min) phosphorylated in response to H 2 O 2 . ER stress-preconditioned cells had more ERK and less JNK phosphorylation than control cells in response to H 2 O 2 exposure. Preincubation with a specific inhibitor of JNK activation or adenoviral infection with a construct that encodes constitutively active MEK1, the upstream activator of ERKs, also protected cells against H 2 O 2 toxicity. In contrast, the pkASgrp78 cells had less ERK and more JNK phosphorylation upon H 2 O 2 exposure. Expression of constitutively active ERK also conferred protection on native as well as pkASgrp78 cells. These results indicate that GRP78 plays an important role in the ER stress response and cytoprotection. ER stress preconditioning attenuates H 2 O 2 -induced cell injury in LLC-PK 1 cells by preventing an increase in intracellular Ca 2؉ concentration, potentiating ERK activation, and decreasing JNK activation. Thus, the ER stress response modulates the balance between ERK and JNK signaling pathways to prevent cell death after oxidative injury. Furthermore, ERK activation is an important downstream effector mechanism for cellular protection by ER stress.

ERK and p38 upregulation versus Bcl-6 downregulation in rat kidney epithelial cells exposed to prolonged hypoxia

“…As shown in our previous work and those of others, 18,47,52,53 the balance between the ERK1/2 and p38 signals is critical for cell survival under hypoxic stresses. Based on our observations on neurons, ERK1/2 functions as a survival signal under hypoxic conditions and there is a "yin-yang" pattern between ERK1/2 and p38 in neuronal injury and protection under hypoxia.…”

“…For example, most studies suggested that p38 is a mediator in the production of pro-inflammatory cytokines 15 and in pro-apoptotic signaling, 16,17 whereas ERK1/2 is a survival modulator under hypoxic stress. [18][19][20] However, reports have also suggested that kidney hypoxic injury can be combated by the inhibition of the ERK1/2 pathway. 21,22 The roles of p38 under hypoxic conditions are also controversial, similar to ERK1/2.…”

Enhanced selenium effect on growth arrest by BiP/GRP78 knockdown in p53-null human prostate cancer cells

“…The above finding implies that selenium may favor survival response in normal cells, but facilitates apoptotic response in cancer cells. Indeed, the protective role of pre-conditioned ER stress response against cytotoxicity has been reported in normal cells (Hung et al, 2003;Bednard et al, 2004). Many factors may impact on ER stress response to selenium.…”

Endoplasmic reticulum calcium release potentiates the ER stress and cell death caused by an oxidative stress in MCF-7 cells

“…It has long been known that disruption of intracellular calcium homeostasis is one of the primary processes in the early development of cell injury [1][2][3] [19,[24][25][26][27][28]. In summary, ER homeostasis is a fragile equilibrium, which can be modulated by dysregulation of calcium or oxidative/reductive balance, features previously associated with oxidative stress.…”