Doherty Katherine R, Demonbreun Alexis R, Wallace Gregory Q, Cave Andrew, Posey Avery D, Heretis Konstantina, Pytel Peter, McNally Elizabeth M
Department of Molecular Genetics and Cell Biology, Committee on Developmental Biology, The University of Chicago, Chicago, IL 60637, USA.
J Biol Chem. 2008 Jul 18;283(29):20252-60. doi: 10.1074/jbc.M802306200. Epub 2008 May 23.
Skeletal muscle is a multinucleated syncytium that develops and is maintained by the fusion of myoblasts to the syncytium. Myoblast fusion involves the regulated coalescence of two apposed membranes. Myoferlin is a membrane-anchored, multiple C2 domain-containing protein that is highly expressed in fusing myoblasts and required for efficient myoblast fusion to myotubes. We found that myoferlin binds directly to the eps15 homology domain protein, EHD2. Members of the EHD family have been previously implicated in endocytosis as well as endocytic recycling, a process where membrane proteins internalized by endocytosis are returned to the plasma membrane. EHD2 binds directly to the second C2 domain of myoferlin, and EHD2 is reduced in myoferlin null myoblasts. In contrast to normal myoblasts, myoferlin null myoblasts accumulate labeled transferrin and have delayed recycling. Introduction of dominant negative EHD2 into myoblasts leads to the sequestration of myoferlin and inhibition of myoblast fusion. The interaction of myoferlin with EHD2 identifies molecular overlap between the endocytic recycling pathway and the machinery that regulates myoblast membrane fusion.
骨骼肌是一种多核的合胞体，它通过成肌细胞与合胞体的融合而发育并得以维持。成肌细胞融合涉及两个相对膜的有序融合。肌铁蛋白是一种膜锚定的、含有多个C2结构域的蛋白质，在融合的成肌细胞中高度表达，是成肌细胞有效融合形成肌管所必需的。我们发现肌铁蛋白直接与eps15同源结构域蛋白EHD2结合。EHD家族成员先前已被证明与内吞作用以及内吞循环有关，内吞循环是一个通过内吞作用内化的膜蛋白返回质膜的过程。EHD2直接与肌铁蛋白的第二个C2结构域结合，并且在缺乏肌铁蛋白的成肌细胞中EHD2减少。与正常成肌细胞相比，缺乏肌铁蛋白的成肌细胞积累标记的转铁蛋白并且循环延迟。将显性负性EHD2导入成肌细胞会导致肌铁蛋白的隔离并抑制成肌细胞融合。肌铁蛋白与EHD2的相互作用确定了内吞循环途径与调节成肌细胞膜融合的机制之间的分子重叠。
