Necdin Enhances Myoblasts Survival by Facilitating the Degradation of the Mediator of Apoptosis CCAR1/CARP1

Regeneration of muscle fibers, lost during pathological muscle degeneration or after injuries, is sustained by the production of new myofibers by means of the satellite cells. Survival of the satellite cells is a critical requirement for efficient muscle reconstitution. Necdin, a member of the MAGE proteins family, is expressed in satellite cell-derived myogenic precursors during perinatal growth and in the adult upon activation during muscle regeneration, where it plays an important role both in myoblast differentiation and survival. We show here that necdin exerts its pro-survival activity by counteracting the action of the pro-apoptotic protein Cell Cycle Apoptosis Regulatory Protein (CCAR1/CARP1) that we have identified as a new molecular interactor of necdin by two-hybrid screening. Necdin is responsible for the maintenance of CCAR1 protein levels, by implementing its ubiquitination and degradation through the proteasome. Taken together, these data shed new light on the molecular mechanism of necdin anti-apoptotic activity in myogenesis.

病理肌肉变性或损伤后丢失的肌纤维（myofibers），其再生过程需依赖卫星细胞（satellite cells）生成新肌纤维来维持。卫星细胞的存活是高效实现肌肉重构的关键前提。作为黑色素瘤相关抗原（MAGE）蛋白家族成员的尼克丁蛋白（Necdin），在围产期生长阶段的卫星细胞源性成肌前体细胞（myogenic precursors）中表达，并在成年个体发生肌肉再生且卫星细胞被激活时表达；其在成肌细胞（myoblast）分化与存活过程中均发挥重要作用。本研究证实，尼克丁蛋白可通过拮抗促凋亡蛋白细胞周期凋亡调控蛋白（Cell Cycle Apoptosis Regulatory Protein, CCAR1/CARP1）的活性发挥促存活作用；我们通过酵母双杂交筛选（two-hybrid screening）鉴定出该蛋白是尼克丁蛋白的新型分子互作靶点。尼克丁蛋白可介导CCAR1蛋白经蛋白酶体（proteasome）途径发生泛素化修饰并降解，从而维持CCAR1蛋白的稳态水平。综上，本研究数据为阐明尼克丁蛋白在肌发生（myogenesis）过程中的抗凋亡活性分子机制提供了全新视角。