Molecular Dissection Of PLK1-AMPK Signaling Axis In Mitotic Progression

Cells constantly adapt their metabolism to meet their energy needs and respond to nutrient availability.Eukaryotes have evolved a very sophisticated system to sense low cellular ATP levels via the serine/threonine kinase AMP-activated protein kinase(AMPK)complex.AMPK is a heterotrim eric complex composed of a catalytic a subunit and two regulatory subunits,β and γ.Under conditions of low energy,AMPK phosphorylates specific enzymes/growth control nodes to increase ATP generation and decrease ATP consumption.This maintains cell homeostasis.In higher eukaryotes,AMPK has acquired the capacity to sense the amount of energy available in the cell by directly binding adenine nucleotides.The γ subunit enables AMPK to respond to changes in the ATP to AMP ratio by binding AMP directly.Binding of AMP further promotes the conformational changes of the AMPK complex and mediates its activation of AMPK by the upstream kinase LKB1.Meanwhile,recent studies have revealed that AMPK is able to sense glucose availability independently of changes in adenine nucleotides.In the past decade,studies about the function of AMPK in metabolism and its activation mechanism have received a great attention.Also,several groups found AMPK not only plays an important role in metabolism,but also plays an irreplaceable role in mitosis.Prolonged mitotic arrest will result in AMPK activation and mitophagy.AMPK phosphorylated PFKFB3 and switched oxidative respiration to glycolysis(Domenech et al.,2015).Moreover,another group from Pan and Zhang found Cellular ATP levels drop during early mitosis,and the mitochondrial Ca2+transients boost mitochondrial respiration to restore energy homeostasis.This is achieved through mitosis-specific MCU phosphorylation and activation by the mitochondrial translocation of energy sensor AMP-activated protein kinase(Zhao et al.,2019).However,the specific function of AMPK in mitosis and the activation mechanism of AMPK in mitosis are still unclear.Our study found that different from the activation mechanism under energy deperivation,activation of AMPK in mitosis is not dependent on its classical upstream kinase LKB1.At the same time,we also found that the activity of AMPK in mitosis is not regulated by other upstream kinase,CAMKKβ.In mitosis,activated AMPK is localized on the centrosome/midbody.Specifically inhibit PLK1 kinase in mitosis,we find the activity of AMPK is significantly abolished.In vitro biochemical experiments also confirmed that PLK1 can directly phosphorylate the active site of AMPK Thr172.Further studies find that the activation of AMPK by PLK1 requires another mitotic regulatory kinase CDK1 to phosphorylate the Thr485 of the C terminus of the AMPKα subunit.Phosphorylation of the AMPKa subunit at Thr485 promotes the binding of the PBD domain of PLK1 and the AMPKa subunit,which in turn leads to further phosphorylation of the AMPKα subunit Thr 172 by PLK1.Meanwhile,in vivo experiments have fond that activation of AMPK in mitosis is essential for normal mitosis progression.In summary,our study revealed a mechanism different from the classical AMPK activation mechanism of LKB1-AMPK in metabolism;the Thr485 of AMPK is pre-phosphorylated by CDK1 in mitosis.This phosphorylation of CDK1 will further increase the binding between PBD domain of PLK1 and AMPK.Thereby further promots the activation of AMPK by PLK1.PLK1-mediated activation of AMPK is essential for normal mitosis.