The MAPK kinase kinase-1 is essential for stress-induced pancreatic islet cell death

The aim of the present investigation was to characterize the role of the MAPK kinase kinase-1 (MEKK-1) in stress-induced cell death of insulin producing cells. We observed that transient overexpression of the wild type MEKK-1 protein in the insulin-producing cell lines RIN-5AH and betaTC-6 increased c-Jun N-terminal kinase (JNK) phosphorylation and augmented cell death induced by diethylenetriamine/nitroso-1-propylhydrazino)-1-propanamine (DETA/NO), streptozotocin (STZ), and hydrogen peroxide (H2O2). Furthermore, DETA/NO or STZ induced a rapid threonine phosphorylation of MEKK-1. Silencing of MEKK-1 gene expression in betaTC-6 and human dispersed islet cells, using in vitro-generated diced small interfering RNA, resulted in protection from DETA/NO, STZ, H2O2, and tunicamycin induced cell death. Moreover, in DETA/NO-treated cells diced small interfering RNA-mediated down-regulation of MEKK-1 resulted in decreased activation of JNK but not p38 and ERK. Inhibition of JNK by treatment with SP600125 partially protected against DETA/NO- or STZ-induced cell death. In summary, our results support an essential role for MEKK-1 in JNK activation and stress-induced beta-cell death. Increased understanding of the signaling pathways that augment or diminish beta-cell MEKK-1 activity may aid in the generation of novel therapeutic strategies in the treatment of type 1 diabetes.