Metformin activates AMP-activated protein kinase by promoting formation of the αβγ heterotrimeric complex.

Metformin is the most widely prescribed oral anti-diabetic agent. Recently, we have shown that low metformin concentrations found in the portal vein suppress glucose production in hepatocytes through activation of AMPK. Moreover, low concentrations of metformin were found to activate AMPK by increasing the phosphorylation of AMPKα at Thr-172. However, the mechanism underlying the increase in AMPKα phosphorylation at Thr-172 and activation by metformin remains unknown. In the current study, we find that low concentrations of metformin promote the formation of the AMPK αβγ complex, resulting in an increase in net phosphorylation of the AMPK α catalytic subunit at Thr-172 by augmenting phosphorylation by LKB1 and antagonizing dephosphorylation by PP2C.