Zani B M, Molinaro M
Prog Clin Biol Res. 1982;85 Pt B:403-14.
When differentiated, multinucleated cultured myotubes are treated with PMA (Phorbol-12-myristate-13-acetate), they display drastic morphological alterations and undergo inhibition of the expression of differentiative traits, without being induced to reenter the cell cycle. Differentiated myotubes, obtained after cytochalasin B treatment of primary chick embryo myoblast cultures, were treated with 1.6 x 10(7) M PMA for different times, labelled with 35S-methionine and different fractions of cell extracts were analysed by SDS-PAGE followed by fluorography. The data presented here indicate that PMA treatment induces in myotubes increased synthesis of a 31.000 Mr polypeptide (31 K) within 4 hr of treatment, while the inhibition of the synthesis of contractile proteins, such as myosin and actin, occurs only after 8 hr of treatment. Morphological alterations of myotubes require longer incubation with PMA (15-20 hr). The reported effects of PMA are not induced by non tumor promotor analogs of the drug, and pulse chase experiments indicate that 31 K stimulation is not the result of increased protein degradation induced by PMA. In addition the stimulation of 31K does not occur in cultured fibroblast indicating that this is a specific early response of differentiated myogenic cells preceeding the dedifferentiative effect of this tumor promotor.
当分化的多核培养肌管用佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA）处理时，它们会表现出剧烈的形态学改变，并受到分化特性表达的抑制，且不会被诱导重新进入细胞周期。对原代鸡胚成肌细胞培养物用细胞松弛素B处理后获得的分化肌管，用1.6×10⁻⁷M的PMA处理不同时间，用³⁵S-甲硫氨酸标记，细胞提取物的不同组分通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）后进行荧光自显影分析。此处呈现的数据表明，PMA处理在处理后4小时内诱导肌管中一种31000道尔顿分子量（31K）的多肽合成增加，而收缩蛋白如肌球蛋白和肌动蛋白的合成抑制仅在处理8小时后发生。肌管的形态学改变需要用PMA孵育更长时间（15 - 20小时）。PMA的上述作用不是由该药物的非肿瘤促进剂类似物诱导的，脉冲追踪实验表明31K的刺激不是由PMA诱导的蛋白质降解增加所致。此外，在培养的成纤维细胞中未发生31K的刺激，这表明这是分化的成肌细胞在该肿瘤促进剂的去分化作用之前的一种特异性早期反应。
