Department of Pharmacology, University of Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany.
Institute of Clinical Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246, Hamburg, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 2017 Aug;390(8):813-825. doi: 10.1007/s00210-017-1385-0. Epub 2017 May 27.
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.
胰岛β细胞数量和功能的减少是 2 型糖尿病发病的原因之一。促炎细胞因子肿瘤坏死因子（TNF）α和白细胞介素（IL）-1β已被认为与这种疾病的发病机制有关。双亮氨酸拉链激酶（DLK）的过表达抑制β细胞功能并诱导β细胞系 HIT 细胞凋亡。在本研究中，研究了 TNFα 或 IL-1β是否刺激 DLK 酶活性。使用免疫印迹分析、瞬时转染荧光素酶报告基因检测和免疫荧光法。与 IL-1β相反，TNFα刺激了依赖于 c-Jun N 端激酶（JNK）的 DLK 激酶活性。此外，DLK 有助于 TNFα诱导的 JNK 磷酸化。激活环内的 DLK 丝氨酸 302 磷酸化对于 DLK 刺激 JNK 和抑制 CREB 依赖性基因转录是必需的。TNFα 以时间和浓度依赖的方式诱导 HIT 细胞凋亡并抑制 CREB 指导的基因转录。通过小干扰或短发夹 RNA 减少内源性 DLK 可减弱 TNFα 对细胞凋亡和 CREB 依赖性转录的影响。这些数据表明，TNFα 通过激活 DLK 诱导β细胞凋亡，从而抑制β细胞保护转录因子 CREB。此外，糖尿病的危险因素激活 DLK 支持 DLK 在糖尿病发病机制中的作用。因此，抑制 DLK 可能预防或延缓 2 型糖尿病的发病。
