Sussman M A, Baqué S, Uhm C S, Daniels M P, Price R L, Simpson D, Terracio L, Kedes L
Department of Biochemistry and Molecular Biology and the Institute for Genetic Medicine, University of Southern California School of Medicine, Los Angeles, USA.
Circ Res. 1998;82(1):94-105. doi: 10.1161/01.res.82.1.94.
Tropomodulin is a tropomyosin-binding protein that terminates "pointed-end" actin filament polymerization. To test the hypothesis that regulation of tropomodulin:actin filament stoichiometry is critical for maintenance of actin filament length, tropomodulin levels were altered in cells by infection with recombinant adenoviral expression vectors, which produce either sense or antisense tropomodulin mRNA. Neonatal rat cardiomyocytes were infected, and sarcomeric actin filament organization was examined. Confocal microscopy indicated that overexpression of tropomodulin protein shortened actin filaments and caused myofibril degeneration. In contrast, decreased tropomodulin content resulted in the formation of abnormally long actin filament bundles. Despite changes in myofibril structure caused by altered tropomodulin expression, total protein turnover of the cardiomyocytes was unaffected. Biochemical analyses of infected cardiomyocytes indicated that changes in actin distribution, rather than altered actin content, accounted for myofibril reorganization. Ultrastructural analysis showed thin-filament disarray and revealed the presence of leptomeres after tropomodulin overexpression. Tropomodulin-mediated effects constitute a novel mechanism to control actin filaments, and our findings demonstrate that regulated tropomodulin expression is necessary to maintain stabilized actin filament structures in cardiac muscle cells.
原肌球蛋白调节蛋白是一种与原肌球蛋白结合的蛋白质，可终止“尖端”肌动蛋白丝的聚合。为了验证原肌球蛋白调节蛋白：肌动蛋白丝化学计量的调节对于维持肌动蛋白丝长度至关重要这一假设，通过用产生有义或反义原肌球蛋白调节蛋白mRNA的重组腺病毒表达载体感染细胞，改变细胞中原肌球蛋白调节蛋白的水平。感染新生大鼠心肌细胞，并检查肌节肌动蛋白丝的组织情况。共聚焦显微镜检查表明，原肌球蛋白调节蛋白的过表达缩短了肌动蛋白丝并导致肌原纤维变性。相反，原肌球蛋白调节蛋白含量的降低导致形成异常长的肌动蛋白丝束。尽管原肌球蛋白调节蛋白表达改变导致肌原纤维结构发生变化，但心肌细胞的总蛋白质周转率未受影响。对感染的心肌细胞进行生化分析表明，肌动蛋白分布的变化而非肌动蛋白含量的改变是肌原纤维重组的原因。超微结构分析显示细肌丝排列紊乱，并揭示了原肌球蛋白调节蛋白过表达后存在细肌丝节段。原肌球蛋白调节蛋白介导的效应构成了一种控制肌动蛋白丝的新机制，我们的研究结果表明，调节原肌球蛋白调节蛋白的表达对于维持心肌细胞中稳定的肌动蛋白丝结构是必要的。
