Mechanisms of Paradoxical Activation of AMPK by the Kinase Inhibitors SU6656 and Sorafenib

SU6656, a Src kinase inhibitor, was reported to increase fat oxidation and reduce body weight in mice, with proposed mechanisms involving AMP-activated protein kinase (AMPK) activation via inhibition of phosphorylation of either LKB1 or AMPK by the Src kinase, Fyn. However, we report that AMPK activation by SU6656 is independent of Src kinases or tyrosine phosphorylation of LKB1 or AMPK and is not due to decreased cellular energy status or binding at the ADaM site on AMPK. SU6656 is a potent AMPK inhibitor, yet binding at the catalytic site paradoxically promotes phosphorylation of Thr172 by LKB1. This would enhance phosphorylation of downstream targets provided the lifetime of Thr172 phosphorylation was sufficient to allow dissociation of the inhibitor and subsequent catalysis prior to its dephosphorylation. By contrast, sorafenib, a kinase inhibitor in clinical use, activates AMPK indirectly by inhibiting mitochondrial metabolism and increasing cellular AMP:ADP and/or ADP:ATP ratios. [Display omitted] •SU6656 activates AMPK independently of the Src kinases Src, Yes, and Fyn•SU6656 acutely inhibits AMPK by competing with ATP at the active site•SU6656 paradoxically activates AMPK by enhancing phosphorylation by LKB1•By contrast, sorafenib activates AMPK indirectly by increasing cellular AMP/ADP The kinase inhibitors SU6656 and sorafenib paradoxically activate AMPK. Ross et al. show that SU6656 inhibits AMPK by binding directly at the catalytic site, yet promotes phosphorylation and activation by LKB1, while sorafenib activates AMPK indirectly by inhibiting mitochondrial function.