Diabetes is a major public health problem in the United States and the world, with a huge societal cost in both human and financial terms. Phosphoinositide 3-kinases (PI 3-kinases) are lipid kinases that play an essential role in insulin action. While the function of p85/p110 PI 3-kinases in insulin responsive cells is well documented, the Class III PI 3-kinase, hVps34, also plays an significant role in insulin action. In this application, exciting new evidence is presented that links hVps34 to two nutrient sensing systems in mammalian cells: the AMP-activated Protein Kinase (AMPK), which regulates the utilization of alternative energy sources under low-nutrient conditions, and p70 S6-kinase (S6K), an key regulator of insulin- stimulated protein synthesis. Data presented in this application show that overexpression of hVps34 activates S6K, and that inhibition of hVps34 blocks insulin stimulation of S6K. In addition, hVps34 is inhibited by either glucose or amino acid starvation, conditions that also inhibit S6K. Finally, it is shown that hVps34 is inhibited by activation of AMPK. These novel data suggest that hVps34 plays an important role in nutrient sensing in mammalian cells;this is explored in four specific aims.
Aim 1 examines the regulation of hVps34 by amino acids and glucose starvation, and will identify changes in hVps34 phosphorylation (using mass spectrometry-based methods) and in hVps34-associated proteins that occurs in starved cells.
Aim 2 studies the role of AMPK in the inhibition of hVps34 in glucose-starved cells, and the mechanism of hVps34 regulation by AMPK.
Aim 3 explores potential mechanisms of hVps34 signaling to S6K, including interactions with mTOR, Cdc42, and CISK. Finally, Aim 4 examines the function of the hVps34-associated protein beclin- 1. These studies explore the mechanism of beclin-1-hVps34 association, and the role of beclin-1 in hVps34- dependent vesicular trafficking and activation of S6K. Overall, these studies will have important implications for our understanding of the function and regulation of hVps34, and its role in insulin action and diabetes.
