Hilenski L L, Terracio L, Haas A L, Borg T K
Department of Pathology (LLH,TKB), University of South Carolina, Columbia.
J Histochem Cytochem. 1992 Jul;40(7):1037-42. doi: 10.1177/40.7.1318894.
Ubiquitin, a highly conserved 76-residue protein found in all eukaryotic cells, can be covalently bound to a wide variety of proteins in the nucleus, cytosol, cytoskeleton, and plasmalemma. This diversity of target proteins reflects a diversity of functions for ubiquitin conjugation. Previous studies have showed enhanced localization of ubiquitin conjugates to Z-bands of normal skeletal muscle and increased ubiquitination in atrophic muscles. These results have implicated a ubiquitin-mediated pathway in protein turnover and degradation in striated muscle. To investigate whether such a pathway might also exist in cardiac striated muscle, we used an affinity-purified polyclonal antibody (conjugate specific) and indirect immunofluorescence to localize ubiquitin conjugates in neonatal and adult rat cardiac myocytes both in vitro and in vivo. In both cultured myocytes and heart tissue, fluorescent ubiquitin conjugates were found in the nucleus as aggregates, in the cytoplasm in a striated pattern indicative of Z-bands, and in intercellular junctions at the intercalated discs between myocytes. Although the acceptor proteins and the physiological significance of ubiquitination at these locations are unknown, the targeting of ubiquitin to specific sites within the nucleus, myofibrils, and sarcolemma could provide a means for selective processing of individual components within these larger macromolecular assemblies, thus implying a regulatory role for ubiquitin conjugation in turnover or stability of proteins in the heart.
泛素是一种在所有真核细胞中都能找到的高度保守的由76个氨基酸组成的蛋白质，它可以共价结合到细胞核、细胞质、细胞骨架和质膜中的多种蛋白质上。靶蛋白的这种多样性反映了泛素缀合的多种功能。先前的研究表明，泛素缀合物在正常骨骼肌的Z带处定位增强，而在萎缩肌肉中泛素化增加。这些结果表明，泛素介导的途径参与了横纹肌中的蛋白质周转和降解。为了研究这种途径是否也存在于心脏横纹肌中，我们使用了亲和纯化的多克隆抗体（缀合物特异性）和间接免疫荧光法，在体外和体内定位新生大鼠和成年大鼠心肌细胞中的泛素缀合物。在培养的心肌细胞和心脏组织中，荧光泛素缀合物在细胞核中以聚集体形式存在，在细胞质中呈指示Z带的条纹状，并且在心肌细胞间闰盘处的细胞间连接中也有发现。尽管这些位置上的受体蛋白和泛素化的生理意义尚不清楚，但泛素靶向细胞核、肌原纤维和肌膜内的特定位点，可能为这些较大的大分子组装体中单个成分的选择性加工提供一种方式，从而暗示泛素缀合在心脏蛋白质周转或稳定性方面具有调节作用。
