Moraczewski J, Piekarska E, Bonavaud S, Wosinska K, Chazaud B, Barlovatz-Meimon G
Faculty of Biology, University of Warsaw, Poland.
C R Acad Sci III. 1996 Aug;319(8):681-6.
Calpains are intracellular calcium-dependent cystein proteases active at neutral pH. There have been found in human adult myogenic cells (i.e. satellite cells) 2 forms of calpains requiring either micromolar Ca2+: mu-calpain, or millimolar Ca2+: m-calpain. Calpains could be involved in both intracellular proteolysis and cytoskeleton reorganization required for myogenic cell fusion. We showed significant differences in calpains distribution during differentiation of myogenic cells. Using mono- and polyclonal antibodies against both types of calpains, we localized mu-calpain and m-calpain in cultured human satellite cells. mu-calpain was detected in the nuclei of myoblasts and in the cytoplasm of myotubes. m-calpain was only present in the cytoplasm, and was concentrated near the nuclear envelope. Biochemical assays for calpain activities showed that the amounts of these proteinases were modulated during cell growth and differentiation. m-calpain activity was high at the proliferation phase (day 4 of culture) and reached a maximum with the beginning of fusion (day 8) and decreased slightly when the number of myotubes increased (day 12). This activity profile suggests that m-calpain could play a role in the initiation of fusion of satellite cells. The activity of mu-calpain increased regularly with cell growth, the maximum being reached when the cells differentiate, i.e. when its intracellular localization shifted from the nucleus to the cytoplasm. We conclude that the activity and the intracellular localization of the 2 forms of calpains differ with the state of differentiation of myogenic cells.
钙蛋白酶是在中性pH值下具有活性的细胞内钙依赖性半胱氨酸蛋白酶。在人类成年肌原性细胞（即卫星细胞）中发现了两种形式的钙蛋白酶，一种需要微摩尔浓度的Ca2+：μ-钙蛋白酶，另一种需要毫摩尔浓度的Ca2+：m-钙蛋白酶。钙蛋白酶可能参与肌原性细胞融合所需的细胞内蛋白水解和细胞骨架重组。我们发现肌原性细胞分化过程中钙蛋白酶的分布存在显著差异。使用针对两种类型钙蛋白酶的单克隆和多克隆抗体，我们在培养的人类卫星细胞中定位了μ-钙蛋白酶和m-钙蛋白酶。在成肌细胞的细胞核和肌管的细胞质中检测到了μ-钙蛋白酶。m-钙蛋白酶仅存在于细胞质中，并集中在核膜附近。钙蛋白酶活性的生化分析表明，这些蛋白酶的量在细胞生长和分化过程中受到调节。m-钙蛋白酶活性在增殖期（培养第4天）较高，在融合开始时（第8天）达到最大值，当肌管数量增加时（第12天）略有下降。这种活性谱表明m-钙蛋白酶可能在卫星细胞融合的起始过程中发挥作用。μ-钙蛋白酶的活性随着细胞生长而有规律地增加，在细胞分化时达到最大值，即当其细胞内定位从细胞核转移到细胞质时。我们得出结论，两种形式的钙蛋白酶的活性和细胞内定位随肌原性细胞的分化状态而不同。
