Matsumoto Yuji, Hayashi Takeharu, Inagaki Natsuko, Takahashi Megumi, Hiroi Shitoshi, Nakamura Takeyuki, Arimura Takuro, Nakamura Kazufumi, Ashizawa Naoto, Yasunami Michio, Ohe Toru, Yano Katsusuke, Kimura Akinori
Department of Molecular Pathogenesis, Medical Research Institute, Tokyo Medical and Dental University, 2-3-10 Kandasurugadai, Chiyoda-Ku, 101-0062, Tokyo , Japan.
J Muscle Res Cell Motil. 2005;26(6-8):367-74. doi: 10.1007/s10974-005-9018-5.
Hypertrophic cardiomyopathy and dilated cardiomyopathy are two major clinical phenotypes of "idiopathic" cardiomyopathy. Recent molecular genetic analyses have now revealed that "idiopathic" cardiomyopathy is caused by mutations in genes for sarcomere components. We have recently reported several mutations in titin/connectin gene found in patients with hypertrophic cardiomyopathy or dilated cardiomyopathy. A hypertrophic cardiomyopathy-associated titin/connectin mutation (Arg740Leu) was found to increase the binding to actinin, while other dilated cardiomyopathy-associated titin/connectin mutations (Ala743Val and Val54Met) decreased the binding to actinin and Tcap/telethonin, respectively. We also reported several other mutations in the N2-B region of titin/connectin found in hypertrophic cardiomyopathy and dilated cardiomyopathy. Since the N2-B region expresses only in the heart, it was speculated that functional alterations due to the mutations cause cardiomyopathies. In this study, we investigated the functional changes caused by the N2-B region mutations by using yeast-two-hybrid assays. It was revealed that a hypertrophic cardiomyopathy-associated mutation (Ser3799Tyr) increased the binding to FHL2 protein, whereas a dilated cardiomyopathy-associated mutation (Gln4053ter) decreased the binding. In addition, another TTN mutation (Arg25618Gln) at the is2 region was found in familial DCM. Because FHL2 protein is known to tether metabolic enzymes to N2-B and is2 regions of titin/connectin, these observations suggest that altered recruitment of metabolic enzymes to the sarcomere may play a role in the pathogenesis of cardiomyopathies.
肥厚型心肌病和扩张型心肌病是“特发性”心肌病的两种主要临床表型。最近的分子遗传学分析现已表明，“特发性”心肌病是由肌节成分基因的突变引起的。我们最近报道了在肥厚型心肌病或扩张型心肌病患者中发现的肌联蛋白/伴肌动蛋白基因的几种突变。发现一种与肥厚型心肌病相关的肌联蛋白/伴肌动蛋白突变（Arg740Leu）增加了与辅肌动蛋白的结合，而其他与扩张型心肌病相关的肌联蛋白/伴肌动蛋白突变（Ala743Val和Val54Met）分别降低了与辅肌动蛋白和肌联蛋白结合蛋白/T-钙黏蛋白的结合。我们还报道了在肥厚型心肌病和扩张型心肌病中发现的肌联蛋白/伴肌动蛋白N2-B区域的其他几种突变。由于N2-B区域仅在心脏中表达，推测这些突变引起的功能改变导致心肌病。在本研究中，我们通过酵母双杂交试验研究了N2-B区域突变引起的功能变化。结果显示，一种与肥厚型心肌病相关的突变（Ser3799Tyr）增加了与FHL2蛋白的结合，而一种与扩张型心肌病相关的突变（Gln4053ter）降低了结合。此外，在家族性扩张型心肌病中发现了位于is2区域的另一种TTN突变（Arg25618Gln）。由于已知FHL2蛋白将代谢酶与肌联蛋白/伴肌动蛋白的N2-B和is2区域相连，这些观察结果表明，代谢酶向肌节的募集改变可能在心肌病的发病机制中起作用。
