Alisi A, Spaziani A, Anticoli S, Ghidinelli M, Balsano C
Laboratory of Molecular Virology and Oncology, Fondazione A. Cesalpino, University of Rome La Sapienza, Policlinico Umberti I, Viale del Policlinico no. 155, Rome, Italy.
Cell Signal. 2008 Mar;20(3):534-42. doi: 10.1016/j.cellsig.2007.11.006. Epub 2007 Nov 26.
Myogenic differentiation is a highly orchestrated multistep process controlled by extracellular growth factors that modulate largely unknown signals into the cell affecting the muscle-transcription program. P38MAPK-dependent signalling, as well as PI3K/Akt pathway, has a key role in the control of muscle gene expression at different stages during the myogenic process. P38MAPK affects the activities of transcription factors, such as MyoD and myogenin, and contributes, together with PI3K/Akt pathway, to control the early and late steps of myogenic differentiation. The aim of our work was to better define the role of PKR, a dsRNA-activated protein kinase, as potential component in the differentiation program of C2C12 murine myogenic cells and to correlate its activity with p38MAPK and PI3K/Akt myogenic regulatory pathways. Here, we demonstrate that PKR is an essential component of the muscle development machinery and forms a functional complex with p38MAPK and/or Akt, contributing to muscle differentiation of committed myogenic cells in vitro. Inhibition of endogenous PKR activity by a specific (si)RNA and a PKR dominant-negative interferes with the myogenic program of C2C12 cells, causing a delay in activation of myogenic specific genes and inducing the formation of thinner myofibers. In addition, the construction of three PKR mutants allowed us to demonstrate that both N and C-terminal regions of PKR are critical for the interaction with p38MAPK and Akt. The novel discovered complex permits PKR to timely regulate the inhibition/activation of p38MAPK and Akt, controlling in this way the different steps characterizing skeletal muscle differentiation.
成肌分化是一个高度协调的多步骤过程，由细胞外生长因子控制，这些因子将 largely 未知的信号调节到细胞中，影响肌肉转录程序。P38MAPK 依赖性信号通路以及 PI3K/Akt 途径在成肌过程的不同阶段对肌肉基因表达的控制中起关键作用。P38MAPK 影响转录因子如 MyoD 和肌细胞生成素的活性，并与 PI3K/Akt 途径一起，有助于控制成肌分化的早期和晚期步骤。我们工作的目的是更好地确定 PKR（一种双链 RNA 激活的蛋白激酶）作为 C2C12 小鼠成肌细胞分化程序中潜在成分的作用，并将其活性与 p38MAPK 和 PI3K/Akt 成肌调节途径相关联。在这里，我们证明 PKR 是肌肉发育机制的重要组成部分，并与 p38MAPK 和/或 Akt 形成功能复合物，有助于体外定向成肌细胞的肌肉分化。通过特异性（si）RNA 和 PKR 显性负性抑制内源性 PKR 活性会干扰 C2C12 细胞的成肌程序，导致成肌特异性基因激活延迟并诱导形成更细的肌纤维。此外，构建三种 PKR 突变体使我们能够证明 PKR 的 N 端和 C 端区域对于与 p38MAPK 和 Akt 的相互作用都至关重要。新发现的复合物使 PKR 能够及时调节 p38MAPK 和 Akt 的抑制/激活，从而控制骨骼肌分化的不同步骤。
