Lomonosova Iu N, Turtikova O V, Shenkman B S
Ross Fiziol Zh Im I M Sechenova. 2015 Jan;101(1):64-73.
Ubiquitin-proteasomal proteolytic pathway is one of the key signaling pathways determining protein degradation in muscle fibers. Among the E3 ubiquitin ligases, rate limiting enzymes of the ubiquitin-proteasomal pathway, the most interesting ones are the MuRF isoforms: MuRF-1 and MuRF-2. There are some pieces of evidence that these enzymes are also involved in the regulation of gene expression in skeletal muscle under some specific conditions (i. e. muscle disuse). We supposed that it was disuse that brought about to altered localization of MuRFs in postural muscle fibers and their translocation to nuclei. In the study using the conventional simulation model of the gravitational unloading (rat hindlimb suspension according to Ilyin and Novikov modified by Morey-Holton) we found that from the 3rd day till 14th day of unloading the content of MuRF-1 and MuRF-2 in the nuclear fraction 4-5 fold increased in unloaded soleus as compared to the control values. These data obtained by means of electrophoresis and western blot of the nuclear fraction of rat soleus were confirmed in the immunohistochemical study of co-localization of MuRF-1 and MuRF-2 antibodies and DAPI nuclear stain on transverse frozen sections of soleus muscle. Thus in the present study we observed the phenomenon of MuRF isoforms accumulation in nuclei of soleus muscle fibers during simulated gravitational unloading.
泛素-蛋白酶体蛋白水解途径是决定肌纤维中蛋白质降解的关键信号通路之一。在E3泛素连接酶（泛素-蛋白酶体途径的限速酶）中，最受关注的是MuRF亚型：MuRF-1和MuRF-2。有一些证据表明，在某些特定条件下（如肌肉废用），这些酶也参与骨骼肌基因表达的调控。我们推测，正是废用导致了MuRFs在姿势性肌纤维中的定位改变及其向细胞核的转位。在使用传统重力卸载模拟模型（根据Ilyin和Novikov并经Morey-Holton修改的大鼠后肢悬吊模型）的研究中，我们发现，与对照值相比，在卸载的第3天至第14天，卸载的比目鱼肌中核组分中MuRF-1和MuRF-2的含量增加了4至5倍。通过对大鼠比目鱼肌核组分进行电泳和蛋白质免疫印迹获得的数据，在比目鱼肌横向冰冻切片上对MuRF-1和MuRF-2抗体与DAPI核染色进行共定位的免疫组织化学研究中得到了证实。因此，在本研究中，我们观察到在模拟重力卸载过程中，比目鱼肌纤维细胞核中MuRF亚型的积累现象。
