The ubiquitin‐proteasome system is a major protein degradation pathway in the cell. Proteasomes produce several peptides that are rapidly degraded to free amino acids by intracellular aminopeptidases. Our previous studies reported that proteolysis via proteasomes and aminopeptidases is required for myoblast proliferation and differentiation. However, the role of intracellular aminopeptidases in myoblast proliferation and differentiation had not been clarified. In this study, we investigated the effects of puromycin‐sensitive aminopeptidase (PSA) on C2C12 myoblast proliferation and differentiation by knocking down PSA. Aminopeptidase enzymatic activity was reduced in PSA‐knockdown myoblasts. Knockdown of PSA induced impaired cell cycle progression in C2C12 myoblasts and accumulation of cells at the G2/M phase. Additionally, after the induction of myogenic differentiation in PSA‐knockdown myoblasts, multinucleated circular‐shaped myotubes with impaired cell polarity were frequently identified. Cell division cycle 42 (CDC42) knockdown in myoblasts resulted in a loss of cell polarity and the formation of multinucleated circular‐shaped myotubes, which were similar to PSA‐knockdown myoblasts. These data suggest that PSA is required for the proliferation of myoblasts in the growth phase and for the determination of cell polarity and elongation of myotubes in the differentiation phase.

中文翻译：

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C2C12 成肌细胞增殖和分化需要嘌呤霉素敏感的氨肽酶

泛素-蛋白酶体系统是细胞中主要的蛋白质降解途径。蛋白酶体产生几种肽，这些肽会被细胞内氨肽酶迅速降解为游离氨基酸。我们之前的研究报告称，成肌细胞增殖和分化需要通过蛋白酶体和氨肽酶进行蛋白水解。然而，细胞内氨肽酶在成肌细胞增殖和分化中的作用尚未阐明。在这项研究中，我们通过敲低 PSA 研究了嘌呤霉素敏感性氨肽酶 (PSA) 对 C2C12 成肌细胞增殖和分化的影响。抑制 PSA 的成肌细胞中的氨肽酶活性降低。PSA 的敲除会导致 C2C12 成肌细胞中细胞周期进程受损以及 G2/M 期细胞的积累。此外，在 PSA 抑制的成肌细胞中诱导肌源性分化后，经常发现细胞极性受损的多核圆形肌管。成肌细胞中的细胞分裂周期 42 (CDC42) 敲低导致细胞极性的丧失和多核圆形肌管的形成，这与 PSA 敲低的成肌细胞相似。这些数据表明 PSA 是生长期成肌细胞增殖和确定细胞极性和分化阶段肌管伸长所必需的。成肌细胞中的细胞分裂周期 42 (CDC42) 敲低导致细胞极性的丧失和多核圆形肌管的形成，这与 PSA 敲低的成肌细胞相似。这些数据表明 PSA 是生长期成肌细胞增殖和确定细胞极性和分化阶段肌管伸长所必需的。成肌细胞中的细胞分裂周期 42 (CDC42) 敲低导致细胞极性的丧失和多核圆形肌管的形成，这与 PSA 敲低的成肌细胞相似。这些数据表明 PSA 是生长期成肌细胞增殖和确定细胞极性和分化阶段肌管伸长所必需的。