ERK1/2‐dependent bestrophin‐3 (Best‐3) expression prevents ER‐stress‐induced cell death of renal epithelial cells by reducing CHOP

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Upon ER stress induction, cells endeavor to survive by engaging the adaptive stress response, known as the unfolded protein response, or by removing aggregated proteins. Chronic ER stress leads to apoptosis through induction of pro‐apoptotic CHOP. Here, we show that Best‐3, a Ca2+‐activated Cl−channel, is upregulated by the ER stressors, thapsigargin (TG, 3 μM), tunicamycin (TUN, 6 μM) and the toxic metal Cd2+ (25 μM). In cultured rat kidney proximal tubule cells, ER stress after 6 h by Cd2+, TG and TUN was downstream of reactive oxygen species formation and attenuated by Ca2+ chelator BAPTA‐AM (10 μM) or general antioxidant α‐tocopherol (100 μM). Immunofluorescence staining localized Best‐3 to the plasma membrane, nuclei and intracellularly, though not in the ER, in cultured cells and rat kidney cortex sections. ER stress augmented Best‐3 mRNA and was decreased by α‐tocopherol, BAPTA‐AM, calmodulin kinase inhibitor calmidazolium (40 μM), ERK1/2 inhibitor U0126 (10 μM), and ERK1/2 RNAi. Knockdown of Best‐3 resulted in decreased cell number consequentially of cell death, as determined by nuclear staining and PARP‐1 cleavage. Furthermore, Best‐3 overexpression reduced cell death by Cd2+, TG and TUN, attributed to diminished CHOP. From our novel data, we conclude that ERK1/2‐dependent Best‐3 activation regulates cell fate decisions during ER stress by suppressing CHOP induction and death.Funded by DFG TH345/10‐1