Introduction

The AMP-activated protein kinase (AMPK) is a pivotal sensor for monitoring cellular nutrient supply and energy status, and plays crucial roles in adaptive responses to nutrient availability and falling energy levels.1,2,3,4,5 AMPK comprises a heterotrimeric complex of a catalytic α subunit and regulatory β and γ subunits. The γ subunit provides binding sites for the regulatory nucleotides AMP, ADP and ATP, whose occupancy depends upon the cellular AMP:ATP and ADP:ATP ratios.6,1c, followed by immunoblotting. h, i AMP/ATP and ADP/ATP ratios, acetyl-coA and malonyl-coA levels in livers from mice under starvation or hepatic ischemia. Mice were starved for 16 h or subjected to hepatic ischemia (for 10 min), followed by measurement of AMP/ATP and ADP/ATP ratios by CE-MS (h) or acetyl-coA and malonyl-coA levels by HPLC-MS (i). Results are mean ± SD; ***p < 0.001 by Student’s t-test (h), **p < 0.01, N.S., not significant by ANOVA (i), n = 6. j A schematic diagram showing the three fusion constructs of the β1 subunit (with modifications at the N-terminus) that allow AMPK to locate on lysosomal surface, mitochondrial outer membrane, or in cytosol. k ACC2 can only be phosphorylated by cytosol-localized and the mitochondrion-localized AMPK. AMPKβ-DKO HEK293T cells were infected with HA-tagged lyso-β1 (left panel), cyto-β1 (middle panel), and mito-β1 (right panel), respectively. Cells were then treated with 1 μM A-769662 for 2 h to allow full activation of AMPK, followed by fractionation and immunoblotting for analyzing p-AMPKα, or by immunoprecipitation and immunoblotting for analyzing p-ACC1 and p-ACC2. Experiments in a, c, d, e, g, and k were performed three times, and the others twice. See also Supplementary information, Figs. S3, S4