Translocation of Glycogen Synthase Kinase-3β (GSK-3β), a Trigger of Permeability Transition, Is Kinase Activity-dependent and Mediated by Interaction with Voltage-dependent Anion Channel 2 (VDAC2)
2014
Glycogen synthasekinase-3β (GSK-3β) is a major positive regulator of the
mitochondrial permeability transition pore(
mPTP), a principle trigger of cell death, under the condition of oxidative stress. However, the mechanism by which cytosolic GSK-3β translocates to mitochondria, promoting
mPTPopening, remains unclear. Here we addressed this issue by analyses of the effect of site-directed mutations in GSK-3β on mitochondrial translocation and protein/protein interactions upon oxidative stress. H9c2 cardiomyoblasts were transfected with GFP-tagged GSK-3β (WT), a mutant GSK-3β insensitive to inhibitory phosphorylation (S9A), or kinase-deficient GSK-3β (K85R). Time lapse observation revealed that WT and S9A translocated from the cytosol to the mitochondria more promptly than did K85R after exposure to oxidative stress. H2O2 increased the density of nine spots on
two-dimensional gel electrophoresisof anti-GSK-3β-immunoprecipitates by more than 3-fold. MALDI-TOF/MS analysis revealed that one of the spots contained
voltage-dependent anion channel2 (
VDAC2). Knockdown of
VDAC2, but not
VDAC1or
VDAC3, by siRNA attenuated both the mitochondrial translocation of GSK-3β and
mPTPopening under stress conditions. The mitochondrial translocation of GSK-3β was attenuated also when Lys-15, but not Arg-4 or Arg-6, in the N-terminal domain of GSK-3β was replaced with alanine. The oxidative stress-induced mitochondrial translocation of GSK-3β was associated with an increase in cell death, which was suppressed by
lithium chloride(LiCl), a GSK-3β inhibitor. These results demonstrate that GSK-3β translocates from the cytosol to mitochondria in a kinase activity- and
VDAC2-dependent manner in which an N-terminal domain of GSK-3β may function as a mitochondrial targeting sequence.
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