Metabolic Regulation of Cellular Signaling

Using the biochemically tractable Xenopus oocyte model system, we have previously characterized a novel metabolic regulation of cell death. We found that glucose-6-phosphate (G6P) via the pentose phosphate pathway leads to increased nicotinamide adenine dinucleotide phosphate (NADPH) levels, a subsequent increase in cytosolic acetyl-coenzyme A and activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII). We recently identified coenzyme A (CoA), derived from the breakdown of acetyl-CoA, as the key metabolic signal that mediates a novel mechanism of calmodulindependent activation of CaMKII. CoA binds directly to the calmodulin (CaM) binding domain (CaMBD) of CaMKII resulting in its activation and downstream inhibitory phosphorylation of caspase-2, suppressing apoptosis. In this dissertation, we questioned whether there are other CaMBD containing proteins metabolically regulated by CoA. In an unbiased approach, CaM binding proteins were first isolated from Xenopus extract using a CaM-Sepharose column. Purified CaM binding proteins were then incubated with CoA-Sepharose in a second purification step and resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining. The results indicate the presence of numerous CaM-binding proteins that also bind CoA and are thus potentially metabolically regulated. In a targeted approach, we tested the ability of aberrant glucose signaling to regulate the CaM-binding protein PI3K. We found that addition of G6P, mimicking aberrant glucose metabolism, or CoA to X. laevis egg extracts activated Akt in a phosphatidylinositol 3-kinase (PI3K), phosphoinositidedependent protein kinase 1(PDPK1)-dependent manner. Additionally, we show that CoA binds directly to and activates PI3K. These findings uncover a novel mechanism of PI3K activation by aberrant glucose metabolism and suggest a potentially unknown constitutive activation pathway of PI3K/Akt by aberrant glucose signaling

Metabolic activation of CaMKII by coenzyme A

Active metabolism regulates oocyte cell death via calcium/calmodulin-dependent protein kinase II (CaMKII)-mediated phosphorylation of caspase-2, but the link between metabolic activity and CaMKII is poorly understood. Here we identify coenzyme A (CoA) as the key metabolic signal that inhibits Xenopus laevis oocyte apoptosis by directly activating CaMKII. We found that CoA directly binds to the CaMKII regulatory domain in the absence of Ca(2+) to activate CaMKII in a calmodulin-dependent manner. Furthermore, we show that CoA inhibits apoptosis not only in X. laevis oocytes but also in Murine oocytes. These findings uncover a direct mechanism of CaMKII regulation by metabolism and further highlight the importance of metabolism in preserving oocyte viability