Hijikata Takao, Nakamura Akio, Isokawa Keitaro, Imamura Michihiro, Yuasa Katsutoshi, Ishikawa Ryoki, Kohama Kazuhiro, Takeda Shinichi, Yorifuji Hiroshi
Department of Anatomy and Cell Biology, Faculty of Pharmacy, Research Institute of Pharmaceutical Sciences, Musashino University, Tokyo, Japan.
J Cell Sci. 2008 Jun 15;121(Pt 12):2062-74. doi: 10.1242/jcs.021634. Epub 2008 May 27.
In skeletal muscles, the sarcolemma is possibly stabilized and protected against contraction-imposed stress by intermediate filaments (IFs) tethered to costameric sarcolemma. Although there is emerging evidence that plectin links IFs to costameres through dystrophin-glycoprotein complexes (DGC), the molecular organization from plectin to costameres still remains unclear. Here, we show that plectin 1, a plectin isoform expressed in skeletal muscle, can interact with beta-synemin, actin and a DGC component, alpha-dystrobrevin, in vitro. Ultrastructurally, beta-synemin molecules appear to be incorporated into costameric dense plaques, where they seem to serve as actin-associated proteins rather than IF proteins. In fact, they can bind actin and alpha-dystrobrevin in vitro. Moreover, in vivo immunoprecipitation analyses demonstrated that beta-synemin- and plectin-immune complexes from lysates of muscle light microsomes contained alpha-dystrobrevin, dystrophin, nonmuscle actin, metavinculin, plectin and beta-synemin. These findings suggest a model in which plectin 1 interacts with DGC and integrin complexes directly, or indirectly through nonmuscle actin and beta-synemin within costameres. The DGC and integrin complexes would cooperate to stabilize and fortify the sarcolemma by linking the basement membrane to IFs through plectin 1, beta-synemin and actin. Besides, the two complexes, together with plectin and IFs, might have their own functions as platforms for distinct signal transduction.
在骨骼肌中，肌膜可能通过与肌节膜相连的中间丝（IFs）来稳定并抵御收缩产生的应力。尽管越来越多的证据表明，网蛋白通过肌营养不良蛋白-糖蛋白复合物（DGC）将IFs与肌节相连，但从网蛋白到肌节的分子组织仍不清楚。在这里，我们表明，网蛋白1，一种在骨骼肌中表达的网蛋白异构体，在体外可与β-联丝蛋白、肌动蛋白和一种DGC成分α-肌营养不良蛋白短链相互作用。在超微结构上，β-联丝蛋白分子似乎被纳入肌节致密斑，在那里它们似乎作为肌动蛋白相关蛋白而非IF蛋白发挥作用。事实上，它们在体外能结合肌动蛋白和α-肌营养不良蛋白短链。此外，体内免疫沉淀分析表明，来自肌肉轻微粒体裂解物的β-联丝蛋白免疫复合物和网蛋白免疫复合物含有α-肌营养不良蛋白短链、肌营养不良蛋白、非肌肉肌动蛋白、间线蛋白、网蛋白和β-联丝蛋白。这些发现提示了一种模型，即网蛋白1直接或通过肌节内的非肌肉肌动蛋白和β-联丝蛋白间接与DGC和整合素复合物相互作用。DGC和整合素复合物将通过网蛋白1、β-联丝蛋白和肌动蛋白将基底膜与IFs相连，从而协同稳定和强化肌膜。此外，这两种复合物与网蛋白和IFs一起，可能作为不同信号转导平台发挥各自的功能。
