Knudsen K A
J Cell Biol. 1985 Sep;101(3):891-7. doi: 10.1083/jcb.101.3.891.
Presumptive myoblasts from explants of chick embryo pectoral muscle proliferate, differentiate, and fuse to form multinucleate myotubes. One event critical to multinucleate cell formation is the specific adhesion of myoblasts before union of their membranes. In the studies reported here five known inhibitors of myotube formation--trifluoperazine, sodium butyrate, chloroquine, 1,10 phenanthroline, and tunicamycin--were tested for their effect on the Ca++-dependent myoblast adhesion step. The first four inhibitors of myotube formation do not perturb myoblast adhesion but rather block fusion of aggregated cells, which suggests that these agents perturb molecular events required for the union of the lipid bilayers. By contrast, tunicamycin exerts its effect by inhibiting the myoblast adhesion step, thereby blocking myotube formation. The effect of tunicamycin can be blocked by a protease inhibitor, however, which implies that the carbohydrate residues protect the glycoproteins from proteolytic degradation rather than participate directly in cell-cell adhesion. Whereas trypsin treatment of myoblasts in the absence of Ca++ destroys the cells' ability to exhibit Ca++-dependent adhesion, the presence of Ca++ during trypsin treatment inhibits the enzyme's effect, which suggests that myoblast adhesion is mediated by a glycoprotein(s) that has a conformation affected by Ca++. Finally, myoblast adhesion is inhibited by an antiserum raised against fusion-competent myoblasts. The effect of the antiserum is blocked by a fraction from the detergent extract of pectoral muscle that binds to immobilized wheat germ agglutinin, which again suggests that glycoproteins mediate Ca++-dependent myoblast adhesion.
来自鸡胚胸肌外植体的推定成肌细胞会增殖、分化并融合形成多核肌管。对多核细胞形成至关重要的一个事件是成肌细胞在细胞膜结合之前的特异性黏附。在本文报道的研究中,测试了五种已知的肌管形成抑制剂——三氟拉嗪、丁酸钠、氯喹、1,10-菲咯啉和衣霉素——对钙离子依赖性成肌细胞黏附步骤的影响。前四种肌管形成抑制剂不会干扰成肌细胞的黏附,而是阻止聚集细胞的融合,这表明这些试剂干扰了脂质双层结合所需的分子事件。相比之下,衣霉素通过抑制成肌细胞黏附步骤发挥作用,从而阻止肌管形成。然而,衣霉素的作用可以被一种蛋白酶抑制剂阻断,这意味着碳水化合物残基保护糖蛋白免受蛋白水解降解,而不是直接参与细胞间黏附。在没有钙离子的情况下用胰蛋白酶处理成肌细胞会破坏细胞表现出钙离子依赖性黏附的能力,而在胰蛋白酶处理期间存在钙离子会抑制该酶的作用,这表明成肌细胞黏附是由一种其构象受钙离子影响的糖蛋白介导的。最后,抗血清抑制了针对具有融合能力的成肌细胞产生的抗血清对成肌细胞黏附的作用。该抗血清的作用被胸肌去污剂提取物中与固定化麦胚凝集素结合的部分阻断,这再次表明糖蛋白介导钙离子依赖性成肌细胞黏附。