Phosphatidylinositol 3-kinase p110α mediates phosphorylation of AMP-activated protein kinase in myoblasts.

AMP-activated protein kinase (AMPK) is a serine/threonine kinase that functions as a sensor of intracellular energy. Activation of AMPK is associated with increased phosphorylation of the α-subunit at threonine 172 (T172) and decreased phosphorylation at serine 485 in AMPKα1 and serine 491 in AMPKα2 (S485/491). One potential mediator of AMPK phosphorylation is phosphatidylinositol 3-kinase (PI3K); however, the mechanism and the identities of the specific PI3K isoforms that regulate AMPK activation are not known. To determine whether PI3K p110α regulated AMPK activation in muscle cells, C2C12 myoblasts were subjected to pharmacological inhibition of p110α, siRNA directed against p110α, or overexpression of constitutively-active or dominant negative p110α. Chemical inhibition, siRNA, and expression of dominant-negative p110α were all associated with increased AMPK T172 phosphorylation, whereas expression of constitutively-active p110α reduced T172 phosphorylation. Conversely, pharmacological inhibition of p110α reduced AMPK S485/491 phosphorylation, while constitutively-active p110α increased AMPK S485/491 phosphorylation. This p110α-mediated increase in AMPK S485/491 phosphorylation was eliminated in the presence of the Akt inhibitor MK2206, suggesting that p110α-mediated phosphorylation of AMPKα at S485/491 is Akt-dependent. In response to oligomycin or serum-starvation, AMPK T172 phosphorylation was elevated in p110α-deficient myoblasts compared to control myoblasts. Overall, our findings identify PI3K p110α as a mediator of AMPK phosphorylation in myoblasts.