PT-1 selectively activates AMPK-{gamma}1 complexes in mouse skeletal muscle, but activates all three {gamma} subunit complexes in cultured human cells by inhibiting the respiratory chain

We report that the AMPK activator PT-1 selectively increased the activity of γ1- but not γ3-containing complexes in incubated mouse muscle. PT-1 increased the AMPK-dependent phosphorylation of the autophagy-regulating kinase ULK1 on Ser555, but not proposed AMPK-γ3 substrates such as Ser231 on TBC1D1 or Ser212 on ACC2, nor did it stimulate glucose transport. Surprisingly, however, in HEK-293 cells expressing human γ1, γ2 or γ3, PT-1 activated all three complexes equally. We were unable to reproduce previous findings suggesting that PT-1 activates AMPK by direct binding between the kinase and auto-inhibitory domains of the α subunit. We show instead that PT-1 activates AMPK indirectly by inhibiting the respiratory chain and increasing cellular AMP:ATP and/or ADP:ATP ratios. Consistent with this mechanism, PT-1 failed to activate AMPK in HEK-293 cells expressing an AMP-insensitive R299G mutant of AMPK-γ1. We propose that the failure of PT-1 to activate γ3-containing complexes in muscle is not an intrinsic feature of such complexes, but is because PT-1 does not increase cellular AMP:ATP ratios in the specific subcellular compartment(s) in which γ3 complexes are located.

Source: BJ Signal - February 19, 2015 Category: Biochemistry Authors: T Elbenhardt Jensen, F A Ross, M Kleinert, L Sylow, J R. Knudsen, G J. Gowans, D Grahame Hardie, E A. Richter Tags: BJ Signal Source Type: research