Kedar Vishram, McDonough Holly, Arya Ranjana, Li Hui-Hua, Rockman Howard A, Patterson Cam
Carolina Cardiovascular Biology Center, University of North Carolina, Chapel Hill, NC 27599-7126, USA.
Proc Natl Acad Sci U S A. 2004 Dec 28;101(52):18135-40. doi: 10.1073/pnas.0404341102. Epub 2004 Dec 15.
Muscle-specific RING finger protein 1 (MuRF1) is a sarcomere-associated protein that is restricted to cardiac and skeletal muscle. In skeletal muscle, MuRF1 is up-regulated by conditions that provoke atrophy, but its function in the heart is not known. The presence of a RING finger in MuRF1 raises the possibility that it is a component of the ubiquitin-proteasome system of protein degradation. We performed a yeast two-hybrid screen to search for interaction partners of MuRF1 in the heart that might be targets of its putative ubiquitin ligase activity. This screen identified troponin I as a MuRF1 partner protein. MuRF1 and troponin I were found to associate both in vitro and in vivo in cultured cardiomyocytes. MuRF1 reduced steady-state troponin I levels when coexpressed in COS-7 cells and increased degradation of endogenous troponin I protein in cardiomyocytes. The degradation of troponin I in cardiomyocytes was associated with the accumulation of ubiquitylated intermediates of troponin I and was proteasome-dependent. In vitro, MuRF1 functioned as a ubiquitin ligase to catalyze ubiquitylation of troponin I through a RING finger-dependent mechanism. In isolated cardiomyocytes, MuRF1 reduced indices of contractility. In cardiomyocytes, these processes may determine the balance between hypertrophic and antihypertrophic signals and the regulation of myocyte contractile responses in the setting of heart failure.
肌肉特异性E3泛素连接酶1（MuRF1）是一种与肌节相关的蛋白质，仅存在于心肌和骨骼肌中。在骨骼肌中，MuRF1在引发萎缩的条件下会上调，但其在心脏中的功能尚不清楚。MuRF1中存在一个E3泛素连接酶环指结构域，这增加了它是蛋白质降解泛素-蛋白酶体系统组成部分的可能性。我们进行了酵母双杂交筛选，以寻找MuRF1在心脏中的相互作用伙伴，这些伙伴可能是其假定的泛素连接酶活性的靶点。该筛选确定肌钙蛋白I是MuRF1的伙伴蛋白。在体外和培养的心肌细胞体内均发现MuRF1与肌钙蛋白I相互关联。当在COS-7细胞中共表达时，MuRF1降低了肌钙蛋白I的稳态水平，并增加了心肌细胞中内源性肌钙蛋白I蛋白的降解。心肌细胞中肌钙蛋白I的降解与肌钙蛋白I泛素化中间体的积累有关，并且是蛋白酶体依赖性的。在体外，MuRF1作为泛素连接酶，通过依赖于E3泛素连接酶环指结构域的机制催化肌钙蛋白I的泛素化。在分离的心肌细胞中，MuRF1降低了收缩性指标。在心肌细胞中，这些过程可能决定肥厚和抗肥厚信号之间的平衡以及心力衰竭时心肌收缩反应的调节。
