TNFα-induced DLK activation contributes to apoptosis in the beta-cell line HIT

Abstract

Reduction in beta-cell mass and function contributes to the pathogenesis of diabetes mellitus type 2. The proinflammatory cytokines tumor necrosis factor (TNF)α and interleukin (IL)-1β have been implicated in the pathogenesis of this disease. Overexpression of the dual leucine zipper kinase (DLK) inhibits beta-cell function and induces apoptosis in the beta-cell line HIT. In the present study, it was investigated whether TNFα or IL-1β stimulates DLK enzymatic activity. Immunoblot analysis, transient transfection with luciferase reporter gene assays, and immunofluorescence were used. In contrast to IL-1β, TNFα stimulated DLK kinase activity, which was dependent on the c-Jun N-terminal kinase (JNK). Furthermore, DLK contributed to TNFα-induced JNK phosphorylation. The phosphorylation of DLK on Ser-302 within the activation loop was required for DLK to stimulate JNK and to inhibit CREB-dependent gene transcription. TNFα induced apoptosis in a time- and concentration-dependent manner and inhibited CREB-directed gene transcription in HIT cells. The reduction of endogenous DLK by small interfering or small hairpin RNA attenuated TNFα's effects on apoptosis and CREB-dependent transcription. These data suggest that TNFα induces beta-cell apoptosis through activation of DLK thereby inhibiting the beta-cell protective transcription factor CREB. Furthermore, activation of DLK by a well-known diabetic risk factor supports the role of DLK in the pathogenesis of diabetes mellitus. Thus, the inhibition of DLK might prevent or retard the pathogenesis of diabetes mellitus type 2.

The role of dual leucine zipper kinase (DLK) in β-cell apoptosis: a potential target for the prevention and treatment of type 2 diabetes?

“…With their paper published in the current issue of NaunynSchmiedeberg's Archives of Pharmacology, Börchers et al 2017 support the inflammation hypothesis and provide important insight into the mechanism of cytokine-induced apoptosis of β-cells. Specifically, the study investigated the role of the dual leucine zipper kinase (DLK) in TNF-α-induced apoptosis of HIT cells.…”

“…In summary, the data by Börchers et al 2017 demonstrate an important role of DLK in the pathogenesis of type 2 diabetes and elucidate a signaling pathway with the players DLK, JNK and CREB which appears to be critical for β-cell survival and apoptosis. The data represent an important contribution to our understanding of the pathogenesis of diabetes and have identified a potential target for the prevention of type 2 diabetes which should further be explored.…”

“…Based on their data, Börchers et al 2017 suggest that inhibition of DLK could be a promising strategy for the prevention of type 2 diabetes. However, there are few limitations of the study which require further experiments, before a search for specific inhibitors of DLK is initiated: Firstly, the data were obtained solely by in vitro studies and need confirmation by in vivo experiments in mammals, preferably diabetic mouse models.…”

“…However, there are few limitations of the study which require further experiments, before a search for specific inhibitors of DLK is initiated: Firstly, the data were obtained solely by in vitro studies and need confirmation by in vivo experiments in mammals, preferably diabetic mouse models. Secondly, the experimental model employed by Börchers et al 2017 is a tumor cell line. Consequently, it cannot fully be excluded that induction of apoptosis is regulated differently in primary β-cells and that DLK plays a minor role.…”

Multitasking: Dual Leucine Zipper–Bearing Kinases in Neuronal Development and Stress Management

“…Surprisingly, the pancreatic islet β-cells in C57BL6/J mice that were fed with high-fat diet and developed a prediabetic condition showed an accumulation of DLK in the nuclei (Wallbach et al 2016). HIT cells treated with either TNFα or IL-1β also showed nuclear localization of DLK (Borchers et al 2017). A bipartite nuclear localization signal in mouse DLK was located at aa 185 to aa 200, the exact region of ATP binding (Figure 1).…”