Skeletal muscle cells and adipocytes differ in their reliance on TC10 and Rac for insulin-induced actin remodeling
Skeletal muscle cells and adipocytes differ in their reliance on TC10 and Rac for insulin-induced actin remodeling
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DOI：
10.1210/me.2003-0294
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发表时间：
2004-02-01
影响因子：
--
通讯作者：
Klip, A
中科院分区：
文献类型：
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作者：
Jebailey, L;Rudich, A;Klip, A
胰岛素引起肌肉和脂肪细胞中明显的皮质肌动蛋白重塑，并且干扰肌动蛋白动力学阻止葡萄糖转运蛋白4（GLUT 4）易位到膜。磷脂酰肌醇3-激酶（PI 3-K）和小G蛋白Rac控制肌细胞肌动蛋白重塑，而TC 10 α在Cbl相关蛋白（CAP）和Cbl下游促进脂肪细胞肌动蛋白动力学，独立于PI 3-K。鉴于胰岛素作用在两种细胞类型中的重要性，确定信号通路和肌动蛋白表现是否具有细胞类型特异性至关重要。我们发现CAP表达和胰岛素介导的Cbl磷酸化在分化的肌管，但不是在成肌细胞。与脂肪细胞不同，Cbl在肌管中在Y 774和Y 731上磷酸化。TC 10 α和β-转录本在肌细胞中通过RT-PCR扩增，但内源性蛋白质使用两种不相关的抗体几乎检测不到。尽管缺乏CAP表达和Cbl磷酸化，但转染成肌细胞的TC 10 α被胰岛素激活。此外，显性失活TC 10 α突变体不能阻止成肌细胞或肌管中胰岛素诱导的肌动蛋白重塑，也不能干扰胰岛素介导的c-myc表位标记的GLUT 4向细胞表面的募集。与TC 10 α相反，内源性Rac在肌肉细胞和脂肪细胞中均容易检测到，并以PI 3-K依赖性方式在胰岛素后结合GTP。这些数据表明，虽然CAP到TC 10通路的单个组分受胰岛素调节，但导致肌动蛋白重塑和GLUT 4易位的功能性TC 10依赖性信号通路可能不像在脂肪细胞中那样在肌细胞中起作用。
Insulin causes distinct cortical actin remodeling in muscle and fat cells, and interfering with actin dynamics halts glucose transporter 4 ( GLUT4) translocation to the membrane. Phosphatidylinositol 3-kinase (PI3-K) and the small G protein Rac govern myocyte actin remodeling, whereas TC10alpha contributes to adipocyte actin dynamics downstream of Cbl-associated protein (CAP) and Cbl, independently of PI3-K. Given the importance of insulin action in both cell types, it is paramount to determine whether signaling pathways and actin manifestations are cell type specific. We found CAP expression and insulin-mediated Cbl phosphorylation in differentiated myotubes but not in myoblasts. Unlike adipocytes, Cbl is phosphorylated on Y774 and Y731 in myotubes. TC10alpha and beta-transcripts are amplified by RT-PCR in muscle cells, but the endogenous proteins are barely detectable using two unrelated antibodies. TC10alpha transfected into myoblasts is activated by insulin despite the lack of CAP expression and Cbl phosphorylation. Moreover, dominant-negative TC10alpha mutants do not prevent insulin- induced actin remodeling in either myoblasts or myotubes and do not interfere with insulin- mediated recruitment of c-myc epitope-tagged GLUT4 to the cell surface. In contrast to TC10alpha, endogenous Rac is readily detectable in both muscle cells and adipocytes and binds GTP after insulin in a PI3-K-dependent manner. These data suggest that whereas individual components of the CAP to TC10 pathway are regulated by insulin, a functional TC10-dependent signaling pathway leading to actin remodeling and GLUT4 translocation may not operate in myocytes, as it does in adipocytes.