Permissive roles of phosphatidyl inositol 3-kinase and Akt in skeletal myocyte maturation
Permissive roles of phosphatidyl inositol 3-kinase and Akt in skeletal myocyte maturation
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DOI：
10.1091/mbc.e03-05-0351
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发表时间：
2004-02-01
影响因子：
3.3
通讯作者：
Rotwein, P
中科院分区：
文献类型：
--
作者：
Wilson, EM;Tureckova, J;Rotwein, P
骨骼肌分化、成熟和再生受激素和生长因子激活的信号通路与肌源性转录因子（包括MyoD和肌细胞增强因子2（MEF 2）家族成员）控制的内在遗传程序之间的相互作用调节。胰岛素样生长因子（IGFs）在胚胎的肌肉发育中起着关键作用，在成人成熟肌肉的维持和肥大中起着关键作用，但负责这些作用的精确信号通路仍然不完全确定。为了研究IGF在肌肉中的作用机制，我们开发了一种小鼠成肌细胞系C2BP 5，该细胞系依赖于IGF-I受体和磷脂酰肌醇3-激酶（PI 3-激酶）-Akt通路的激活来启动分化。在这里，我们表明，C2BP 5成肌细胞的分化可以诱导在IGF作用的情况下，由重组腺病毒表达MyoD或肌细胞生成素，但它是可逆性受损的PI 3激酶抑制剂LY 294002。使用显性阴性形式的Akt（PI 3-激酶信号传导的关键下游组分）观察到类似的结果，并且在C3 H 10 T1/2成纤维细胞中也观察到。PI 3激酶的抑制并不能阻止肌肉分化特异性蛋白（肌细胞生成素、肌钙蛋白T或肌球蛋白重链）的积累，也不能阻断MyoD或肌细胞生成素对含有肌肉报告基因的E-box的转录激活，也不能抑制内源性MEF 2C或MEF 213的表达或功能。编码活性Akt的腺病毒可以部分恢复MyoD表达和LY 294002处理的成肌细胞的终末分化，但所得的肌纤维含有较少的细胞核，比正常的更小，更薄，这表明除了Akt之外，还需要另一种PI 3激酶刺激的途径来实现完全的肌细胞成熟。我们的研究结果支持这样的想法，IGF调节的PI 3-激酶通路的功能下游或平行于MyoD，肌细胞生成素，和MEF 2在肌肉发育中，以管理分化的后期步骤，导致多核肌管。
Skeletal muscle differentiation, maturation, and regeneration are regulated by interactions between signaling pathways activated by hormones and growth factors, and intrinsic genetic programs controlled by myogenic transcription factors, including members of the MyoD and myocyte enhancer factor 2 (MEF2) families. Insulin-like growth factors (IGFs) play key roles in muscle development in the embryo, and in the maintenance and hypertrophy of mature muscle in the adult, but the precise signaling pathways responsible for these effects remain incompletely defined. To study mechanisms of IGF action in muscle, we have developed a mouse myoblast cell line termed C2BP5 that is dependent on activation of the IGF-I receptor and the phosphatidyl inositol 3-kinase (PI3-kinase)-Akt pathway for initiation of differentiation. Here, we show that differentiation of C2BP5 myoblasts could be induced in the absence of IGF action by recombinant adenoviruses expressing MyoD or myogenin, but it was reversibly impaired by the PI3-kinase inhibitor LY294002. Similar results were observed using a dominant-negative version of Akt, a key downstream component of PI3-kinase signaling, and also were seen in C3H 10T1/2 fibroblasts. Inhibition of PI3-kinase did not prevent accumulation of muscle differentiation-specific proteins (myogenin, troponin T, or myosin heavy chain), did not block transcriptional activation of E-box containing muscle reporter genes by MyoD or myogenin, and did not inhibit the expression or function of endogenous MEF2C or MEF213. An adenovirus encoding active Akt could partially restore terminal differentiation of MyoD-expressing and LY294002-treated myoblasts, but the resultant myofibers contained fewer nuclei and were smaller and thinner than normal, indicating that another PI3-kinase-stimulated pathway in addition to Akt is required for full myocyte maturation. Our results support the idea that an IGF-regulated PI3-kinase pathway functions downstream of or in parallel with MyoD, myogenin, and MEF2 in muscle development to govern the late steps of differentiation that lead to multinucleated myotubes.