Aston University, Birmingham, United Kingdom.
Cell Signal. 2010 May;22(5):783-90. doi: 10.1016/j.cellsig.2010.01.002. Epub 2010 Jan 13.
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.
钙（Ca2+）在蛋白激酶 R（双链 RNA 依赖性蛋白激酶）的激活中的作用已在使用细胞通透型 Ca2+螯合剂 BAPTA/AM（1,2-双（邻氨基苯氧基）乙烷-N,N,N',N'-四乙酸四（乙酰氧甲基）酯）的鼠肌管中进行了研究。BAPTA/AM 有效减弱了两种情况引起的总蛋白降解的增加，一种是通过泛素蛋白酶体途径，另一种是通过蛋白水解诱导因子（PIF）和血管紧张素 II（Ang II）引起的蛋白合成抑制。由于蛋白合成和降解都受到抑制，这表明 PKR 的参与。事实上，BAPTA/AM 减弱了 PIF 存在时 PKR 的激活（自身磷酸化）和随后的真核起始因子 2α（eIF2alpha）的磷酸化，表明 Ca2+ 在此过程中的参与。PIF 还诱导了 caspase-3 和 -8 的活性增加，BAPTA/AM 减弱了这种增加。caspase-3 和 -8 活性的增加被证明是 PKR 激活的原因，因为后者被特异性 caspase-3 和 -8 抑制剂完全抑制。这些结果表明，Ca2+ 通过 caspase-3 和 -8 激活 PKR，参与 PIF 和 Ang II 引起的蛋白降解增加和蛋白合成减少。
