Myogenic stage, sarcomere length, and protease activity modulate localization of muscle-specific calpain
Myogenic stage, sarcomere length, and protease activity modulate localization of muscle-specific calpain
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DOI：
10.1074/jbc.m610806200
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发表时间：
2007-05-11
影响因子：
4.8
通讯作者：
Sorimachi, Hiroyuki
中科院分区：
文献类型：
--
作者：
Ojima, Koichi;Ono, Yasuko;Sorimachi, Hiroyuki
P94/calain 3是一种钙离子结合的细胞内蛋白水解酶，主要在骨骼肌中表达。P94与连接素/肌动蛋白的N2A区和M线区结合，定位于Z带。遗传证据表明，p94蛋白分解活性受损会导致肌营养不良(肢带型2A型肌营养不良症)，表明p94功能在肌原纤维中的重要性。在这里，我们展示了一系列p94剪接变异体在肌肉分化后立即表达，并在肌纤维形成过程中差异地改变定位。我们发现p94的内源性N端(而不是C端)结构域不仅定位在Z带中，而且还直接与肌小节α-肌动蛋白结合。这些数据表明p94的蛋白水解性N-末端片段被掺入Z-带。在肌原纤维中，随着肌节长度的增加，外源表达的p94的定位从M线转移到N2a，与野生型和蛋白水解酶失活的p94分别为2.6和2.8微米相似。这些数据首次表明，p94蛋白水解酶活性参与了对肌肉状况的反应，这可能解释了为什么p94失活会导致肢体带状肌营养不良。
p94/calpain 3 is a Ca2+-binding intracellular protease predominantly expressed in skeletal muscles. p94 binds to the N2A and M-line regions of connectin/titin and localizes in the Z-bands. Genetic evidence showing that compromised p94 proteolytic activity leads to muscular dystrophy (limb-girdle muscular dystrophy type 2A) indicates the importance of p94 function in myofibrils. Here we show that a series of p94 splice variants is expressed immediately after muscle differentiation and differentially change localization during myofibrillogenesis. We found that the endogenous N-terminal ( but not C-terminal) domain of p94 was not only localized in the Z-bands but also directly bound to sarcomeric alpha-actinin. These data suggest the incorporation of proteolytic N-terminal fragments of p94 into the Z-bands. In myofibrils localization of exogenously expressed p94 shifted from the M-line to N2A as the sarcomere lengthens beyond similar to 2.6 and 2.8 mu m for wild-type and protease-inactive p94, respectively. These data demonstrate for the first time that p94 proteolytic activity is involved in responses to muscle conditions, which may explain why p94 inactivation causes limb-girdle muscular dystrophy.