Calmodulin-dependent protein kinase kinase-β is an alternative upstream kinase for AMP-activated protein kinase

Abstract

The AMP-activated protein kinase (AMPK) is a critical regulator of energy balance at both the cellular and whole-body levels. Two upstream kinases have been reported to activate AMPK in cell-free assays, i.e., the tumor suppressor LKB1 and calmodulin-dependent protein kinase kinase. However, evidence that this is physiologically relevant currently only exists for LKB1. We now report that there is a significant basal activity and phosphorylation of AMPK in LKB1-deficient cells that can be stimulated by Ca2+ ionophores, and studies using the CaMKK inhibitor STO-609 and isoform-specific siRNAs show that CaMKKbeta is required for this effect. CaMKKbeta also activates AMPK much more rapidly than CaMKKalpha in cell-free assays. K(+)-induced depolarization in rat cerebrocortical slices, which increases intracellular Ca2+ without disturbing cellular adenine nucleotide levels, activates AMPK, and this is blocked by STO-609. Our results suggest a potential Ca(2+)-dependent neuroprotective pathway involving phosphorylation and activation of AMPK by CaMKKbeta.

Vagal nerve stimulation improves mitochondrial dynamics via an M3 receptor/CaMKKβ/AMPK pathway in isoproterenol‐induced myocardial ischaemia

“…Furthermore, inhibition of AMPK by Compound C mitigated the protective effect of VNS, suggesting that AMPK was indeed involved in VNS‐mediated protection of mitochondrial dynamics and function. In mammalian cells, CaMKKβ and LKB1 are thought to be the two major upstream kinases of AMPK 63, 64. This study found that VNS activation of AMPK was accompanied by increased CaMKKβ, but not LKB1, phosphorylation, which may be explained by the change in cytosolic Ca 2+ level 65, moreover, it should be noted that CaMKKβ is directly regulated by Ca 2+ .…”

Oxidative Stress in the Hypothalamus: the Importance of Calcium Signaling and Mitochondrial ROS in Body Weight Regulation

“…Recently neuronal over-expression of the Ca 2+ /calmodulin dependent protein kinase (CaMKK) was shown to protect mice from high fat diet-induced weight gain, insulin resistance and glucose homeostasis. CaMKK is activated by the change of the intracellular Ca 2+ [62-64] and acts as an upstream activator of AMPK, independent of AMP levels. In hypothalamic neurons, CaMKK regulates orexigenic NPY production [65, 66].…”

Kinase activity-independent suppression of p73α by AMP-activated kinase α (AMPKα)

“…Surprisingly, the AMPKa-mediated repression of p73a activity was independent of its kinase activity as shown using AICAR, a known agonist of AMPK, and various AMPKa2 mutants (D157A and K45R, dominant negatives; T172A, inactive; and T174D, constitutively active). It was recently suggested that AMPK can be activated by Ca 2 þ /CaM-dependent protein kinase kinase independently of AMP (Hawley et al, 2005;Hurley et al, 2005;Woods et al, 2005). Similar to AICAR, STO-609, a selective inhibitor of Ca 2 þ /CaMdependent protein kinase kinase, was not effective in the repression of p73a by AMPKa (data not shown).…”

“…AMPK has been primarily described as a metabolic sensor that responds to intracellular ATP depletion induced by various metabolic stresses, and it is directly activated by increases in the AMP:ATP ratio (Hardie et al, 1998(Hardie et al, , 1999Kemp et al, 1999). Recent studies suggest that it can also be activated by upstream AMPK kinases such as the serine/threonine kinase LKB1, which phosphorylates the a subunit of AMPK at Thr 174 (at Thr 172 for a2) (Woods et al, 2003;Lizcano et al, 2004;Shaw et al, 2004), and possibly by Ca 2 þ /CaMdependent protein kinase kinase, which functions independently of AMP but phosphorylates the same residue in AMPK (Hawley et al, 2005;Hurley et al, 2005;Woods et al, 2005). Once activated, AMPK phosphorylates several target proteins, which are mostly cytoplasmic enzymes involved in glucose and lipid metabolism.…”