Laboratory of Muscle Biology and Sarcopenia, Department of Exercise Physiology, and Center for Cardiovascular and Respiratory Sciences, Robert C. Byrd Health Sciences Center, West Virginia University School of Medicine, Morgantown, WV 26506, USA.
Cell Tissue Res. 2013 Jan;351(1):183-200. doi: 10.1007/s00441-012-1515-4. Epub 2012 Nov 9.
β-Catenin is essential for muscle development because it regulates both cadherin-mediated cell-cell adhesion and canonical Wingless and Int1 (Wnt) signaling. The phosphorylation of β-catenin by glycogen synthase kinase-3β (GSK-3β) at serine31/37/threonine41 regulates its stability and its role in canonical Wnt signaling. In this study, we have investigated whether the N-terminal phosphorylation of β-catenin is regulated by M-cadherin, and whether this regulation mediates the role of M-cadherin in myogenic differentiation. Our data show that the knockdown of M-cadherin expression by RNA interference (RNAi) in C2C12 myoblasts significantly increases the phosphorylation of β-catenin at Ser33/37/Thr41 and decreases the protein abundance of ser37/thr41-unphosphorylated active β-catenin. Furthermore, M-cadherin RNAi promotes TCF/LEF transcription activity but also blunts the initiation of the myogenic progress by Wnt pathway activator lithium chloride or Wnt-3a treatment. Knockdown of β-catenin expression by RNAi decreases myogenic induction in myoblasts. Forced expression of a phosphorylation-resistant β-catenin plasmid (S33Y-β-catenin) fails to enhance myogenic differentiation, but it partially rescues C2C12 cells from M-cadherin RNAi-induced apoptosis. These data show, for the first time, that M-cadherin-mediated signaling attenuates β-catenin phosphorylation at Ser31/37/Thr41 by GSK-3β, and that this regulation has a positive effect on myogenic differentiation induced by canonical Wnt signaling.
β-连环蛋白对于肌肉发育是必不可少的，因为它调节着钙黏蛋白介导的细胞间黏附以及经典的 Wingless 和 Int1（Wnt）信号通路。糖原合酶激酶-3β（GSK-3β）在丝氨酸 31/37/苏氨酸 41 位点对β-连环蛋白的磷酸化作用调节着其稳定性及其在经典 Wnt 信号通路中的作用。在本研究中，我们研究了β-连环蛋白的 N 端磷酸化是否受到 M 钙黏蛋白的调节，以及这种调节是否介导了 M 钙黏蛋白在成肌分化中的作用。我们的数据表明，用 RNA 干扰（RNAi）在 C2C12 成肌细胞中敲低 M 钙黏蛋白表达，显著增加了β-连环蛋白在 Ser33/37/Thr41 位点的磷酸化，并降低了丝氨酸 37/苏氨酸 41 未磷酸化的活性β-连环蛋白的蛋白丰度。此外，M 钙黏蛋白 RNAi 促进了 TCF/LEF 转录活性，但也抑制了 Wnt 通路激活剂氯化锂或 Wnt-3a 处理引起的成肌进程的启动。用 RNAi 敲低β-连环蛋白的表达降低了成肌细胞的成肌诱导。用磷酸化抗性β-连环蛋白质粒（S33Y-β-连环蛋白）强制表达不能增强成肌分化，但它部分挽救了 C2C12 细胞免受 M 钙黏蛋白 RNAi 诱导的细胞凋亡。这些数据首次表明，M 钙黏蛋白介导的信号通过 GSK-3β 抑制β-连环蛋白在 Ser31/37/Thr41 位点的磷酸化，并且这种调节对经典 Wnt 信号诱导的成肌分化有积极的影响。
