The decrease of the cytoskeleton tubulin follows the decrease of the associating molecular chaperone αB-crystallin in unloaded soleus muscle atrophy without stretch
The decrease of the cytoskeleton tubulin follows the decrease of the associating molecular chaperone αB-crystallin in unloaded soleus muscle atrophy without stretch
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DOI：
10.1096/fj.04-3060fje
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发表时间：
2005-05-01
期刊：
影响因子：
4.8
通讯作者：
Atomi, Y
中科院分区：
文献类型：
--
作者：
Sakurai, T;Fujita, Y;Atomi, Y
细胞骨架成分微管蛋白/微管通常允许细胞对环境做出机械反应。游离微管蛋白二聚体的浓度是在微管蛋白的游离二聚体和多聚体之间的平衡中自动调节的，具有“动态不稳定性”的内在属性，并通过共翻译的β-微管蛋白信使其降解。最近，我们已经证明了αB-晶体蛋白是肌肉萎缩的关键分子，因为αB-晶体蛋白具有伴侣样活性，在体外可以抑制微管蛋白聚集，保护MT不受钙离子和去多聚肌醇生物碱的影响。大多数小分子热休克蛋白(SHsps)，包括αB-晶体蛋白，都在骨骼肌中表达。然而，到目前为止，还没有关于微管蛋白/MT在肌肉适应过程中的变化的报道。在这里，我们研究了后肢悬吊(HS)后和恢复后大鼠比目鱼肌微管蛋白含量的变化。HS导致比目鱼肌质量迅速下降，大部分HSPs(αB-晶体蛋白、Hsp90、Hsp70、Hsp27和p20)和微管蛋白含量下降，而热休克同源70 kDa蛋白(Hsc70)没有减少。被动拉伸维持比目鱼肌质量、大部分热休克蛋白和微管蛋白。恢复5天后，微管蛋白和HSPs水平恢复到对照水平，而Hsc70水平无明显变化。用抗α-微管蛋白抗体和紫杉醇依赖的MT组装免疫沉淀法观察α-B-晶状体蛋白和微管蛋白/MT的相互作用。其他sHsps也与α-B-晶体蛋白和MT相关，而Hsp90和Hsp70不与它们共沉淀。这些数据表明，在肌肉组织中，αB-晶体蛋白与微管蛋白/MTS之间存在相互作用和密切关系。随着肌肉萎缩程度的加重，αB-晶状体蛋白的基因表达水平逐渐降低，而βI-微管蛋白的基因表达水平保持不变。这意味着微管蛋白/MT系统的转录后调节在肌肉适应中起着重要作用，而αB-晶体蛋白和大多数sHsps是在转录水平上调节的。在C2C12成肌细胞培养细胞中，αB-晶状体蛋白的表达降低或增加，研究了在肌管形成过程中αB-晶状体蛋白对微管/MTS的额外功能贡献。提示α-B-晶体蛋白在微管重组过程中的必要性。综上所述，微管蛋白/MTS是比目鱼肌早期萎缩的原因，提示αB-晶状体蛋白对细胞骨架的伴侣作用可能也是肌肉细胞内动态调节的，是肌肉适应和保护萎缩以及肌肉分化的关键机制。
The cytoskeletal component tubulin/microtubule commonly allows the cell to respond mechanically to the environment. The concentration of free tubulin dimer is autoregulated in the balance of free dimer and polymeric forms of microtubule (MT) protein, having an intrinsic property of "dynamic instability", and through cotranslational beta-tubulin mRNA degradation. Recently, we have demonstrated that alpha B-crystallin is a key molecule of muscle atrophy, since alpha B-crystallin has a chaperone-like-activity that suppresses tubulin aggregation and protects the MT disassembly against both Ca2+ and depolymelizing alkaloid in vitro. Most of the small heat-shock proteins (sHsps), including alpha B-crystallin, are expressed in skeletal muscle. However, no report to date has studied the changes of tubulin/MT during muscle adaptation. Here, we examined changes in tubulin content in rat soleus muscles after hindlimb suspension (HS) with/without passive stretch and the recovery. HS induced rapid decreases of soleus muscle mass, most Hsps ( alpha B-crystallin, Hsp90, Hsp70, Hsp27, and p20) and tubulin contents in soleus muscle, while heat-shock cognate 70-kDa protein (Hsc70) did not decrease. Soleus muscle mass, most Hsps, and tubulin were maintained with passive stretch. After 5 days' recovery, the levels of tubulin and Hsps, but not Hsc70, were restored to control levels. The interactions of alpha B-crystallin and tubulin/MT were observed with immunoprecipitation with an anti-alpha-tubulin antibody and taxol-dependent MT assembly. Other sHsps were also associated with alpha B-crystallin and MT, whereas Hsp90 and Hsp70 did not co-precipitate with them. These data imply an interaction and close relationship between alpha B-crystallin and tubulin/MTs in muscle tissues. The amount of mRNA of alpha B-crystallin decreased with the muscle atrophy level, whereas the gene expression level of beta I-tubulin was maintained during HS. This means a significant role of post-transcriptional regulation in tubulin/MT system in muscle adaptation, whereas alpha B-crystallin and most sHsps are regulated at the transcriptional level. Additional functional contribution of alpha B-crystallin to tubulin/MTs during myotube formation was examined using C2C12 myoblast cultured cells, the alpha B-crystallin expression of which was decreased or increased. It indicated the necessity of alpha B-crystallin during microtubule reorganization. In conclusion, tubulin/MTs were revealed to be early soleus muscle atrophy suggest that the chaperone effect of alpha B-crystallin on the cytoskeleton, which may be also dynamically regulated in the muscle cell, is a key mechanism for muscle adaptation and protection of the atrophy and also muscle differentiation.