The JNK pathway modulates expression and phosphorylation of 4E‐BP1 in MIN6 pancreatic β‐cells under oxidative stress conditions

Abstract

Stress-mediated apoptosis may play a crucial role in loss of pancreatic beta-cell mass, contributing to the development of diabetes. We have recently identified that translational control involving the translational suppressor eIF4E binding protein-1 (4E-BP1) which is important for beta-cell survival under endoplasmic reticulum (ER) stress. The Eif4ebp1 gene, encoding 4E-BP1, is a direct target of a transcription factor activating transcription factor-4 (ATF4), a master regulator of gene expression in stress responses. In the current study, we investigated 4E-BP1 expression in mouse insulinoma line 6 (MIN6) cells treated with arsenite, an inducer of oxidative stress which is another contributor of beta-cell loss. We found that arsenite-induced 4E-BP1 expression level was lower than that induced by thapsigargin, an ER stress inducer, although ATF4 was similarly induced by these agents. The ratio of the dephosphorylated form of 4E-BP1, which has the highest activity, to phosphorylated forms was, however, greater in MIN6 cells treated with arsenite as compared to that in thapsigargin-treated cells. Arsenite-induced 4E-BP1 mRNA and protein expressions were augmented by simultaneous treatment with a c-Jun N-terminal kinase (JNK) specific inhibitor, SP600125. The agent also suppressed the level of the dephosphrylated form of 4E-BP1 in arsenite-treated MIN6 cells. Thus, JNK activated by oxidative stress is involved in the modulation of 4E-BP1 expression and phosphorylation in MIN6 cells, which may contribute to fine tuning of translational control under stress conditions.