Decrease in beta cell mass by apoptosis represents the key turning point in the manifestation of both type 1 and type 2 diabetes. The molecular basis of beta cell death is not well understood and remains an intense area of research. While several independent triggers can initiate the death pathway, activation of the stress kinase JNK is required in most cases for apoptosis of beta cells. At the same time, the inhibition of anti-apoptotic Akt kinase and other prosurvival pathways is also required for the acceleration of apoptosis. In beta cells the stress kinase pathway is executed in a three-tiered module consisting of MAPKKK, MAPKK, and JNK. The existence of multiple MAPKKKs belonging to distinct families has obscured our understanding of how a variety of stimuli including cytokines, oxidative stress, DNA and UV damage lead to highly specific responses by the engagement of specific MKKKs. Furthermore, the high level of complexity and redundancy in apoptosis pathways has made identification of downstream effectors of the JNK pathway far more challenging. In such a situation, identifying the key initiator kinase/s that activate/s beta cell apoptosis would provide clear and attractive targets for therapeutic intervention. We have recently found that cytokines upregulate the expression mixed lineage kinases (MLKs) in pancreatic beta cells.
The specific aims to be addressed in this grant include 1) Demonstration of a causal role for MLKs in induction of beta cell apoptosis using animal models of type 1 and type 2 diabetes. 2) Examine downstream molecular mechanisms by which mixed lineage kinases regulate beta cell death. 3) Examination of post-translational mechanisms that regulate the activation of MLKs in the pancreatic beta cell.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Cellular Aspects of Diabetes and Obesity Study Section (CADO)
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Abraham, Kristin M
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University of California San Diego
Schools of Medicine
La Jolla
United States
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Humphrey, Rohan K; Ray, Anamika; Gonuguntla, Sumati et al. (2014) Loss of TRB3 alters dynamics of MLK3-JNK signaling and inhibits cytokine-activated pancreatic beta cell death. J Biol Chem 289:29994-30004
Humphrey, Rohan K; Yu, Shu Mei A; Bellary, Aditi et al. (2013) Lysine 63-linked ubiquitination modulates mixed lineage kinase-3 interaction with JIP1 scaffold protein in cytokine-induced pancreatic ? cell death. J Biol Chem 288:2428-40
Humphrey, Rohan K; Newcomb, Christina J; Yu, Shu-Mei A et al. (2010) Mixed lineage kinase-3 stabilizes and functionally cooperates with TRIBBLES-3 to compromise mitochondrial integrity in cytokine-induced death of pancreatic beta cells. J Biol Chem 285:22426-36
Humphrey, Rohan K; Yu, Shu-Mei; Flores, Luis E et al. (2010) Glucose regulates steady-state levels of PDX1 via the reciprocal actions of GSK3 and AKT kinases. J Biol Chem 285:3406-16