Mechanism of activation of dsRNA-dependent protein kinase (PKR) in muscle atrophy.
The role of Ca(2+) in the activation of PKR (double-stranded-RNA-dependent protein kinase), which leads to skeletal muscle atrophy, has been investigated in murine myotubes using the cell-permeable Ca(2+) chelator BAPTA/AM (1,2-bis (o-aminphenoxy) ethane-N,N,N',N'-tetraacetic acid tetra (acetoxymethyl) ester). BAPTA/AM effectively attenuated both the increase in total protein degradation, through the ubiquitin-proteasome pathway, and the depression of protein synthesis, induced by both proteolysis-inducing factor (PIF) and angiotensin II (Ang II). Since both protein synthesis and degradation were attenuated this suggests the involvement of PKR. Indeed BAPTA/AM attenuated both the activation (autophosphorylation) of PKR and the subsequent phosphorylation of eIF2alpha (eukaryotic initiation factor 2alpha) in the presence of PIF, suggesting the involvement of Ca(2+) in this process. PIF also induced an increase in the activity of both caspases-3 and -8, which was attenuated by BAPTA/AM. The increase in caspase-3 and -8 activity was shown to be responsible for the activation of PKR, since the latter was completely attenuated by the specific caspase-3 and -8 inhibitors. These results suggest that Ca(2+) is involved in the increase in protein degradation and decrease in protein synthesis by PIF and Ang II through activation of PKR by caspases-3 and -8.
Eley
H L
HL
Aston University, Birmingham, United Kingdom.
Russell
S T
ST
Tisdale
M J
MJ
D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D061945:Caspase Inhibitors; D002460:Cell Line; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology; D009133:Muscular Atrophy / Q000201:enzymology* / Q000473:pathology*; D010766:Phosphorylation / Q000187:drug effects; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D019892:eIF-2 Kinase / Q000378:metabolism*
D061945:Caspase Inhibitors; D015852:Eukaryotic Initiation Factor-2; D011480:Protease Inhibitors; D021122:Protein Subunits; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D019892:eIF-2 Kinase; D053148:Caspase 3; D053181:Caspase 8; D046988:Proteasome Endopeptidase Complex