Pagliara Valentina, Amodio Giuseppina, Vestuto Vincenzo, Franceschelli Silvia, Russo Nicola Antonino, Cirillo Vittorio, Mottola Giovanna, Remondelli Paolo, Moltedo Ornella
Department of Medicine, Surgery and Dentistry "Scuola Medica Salernitana", University of Salerno, Via Salvador Allende, 84081 Baronissi, Italy.
Department of Pharmacy, University of Salerno, Via Giovanni Paolo II, 84084 Fisciano, Italy.
Biomedicines. 2023 May 16;11(5):1457. doi: 10.3390/biomedicines11051457.
Activating transcription factor 6α (ATF6α) is an endoplasmic reticulum protein known to participate in unfolded protein response (UPR) during ER stress in mammals. Herein, we show that in mouse C2C12 myoblasts induced to differentiate, ATF6α is the only pathway of the UPR activated. ATF6α stimulation is p38 MAPK-dependent, as revealed by the use of the inhibitor SB203580, which halts myotube formation and, at the same time, impairs trafficking of ATF6α, which accumulates at the cis-Golgi without being processed in the p50 transcriptional active form. To further evaluate the role of ATF6α, we knocked out the ATF6α gene, thus inhibiting the C2C12 myoblast from undergoing myogenesis, and this occurred independently from p38 MAPK activity. The expression of exogenous ATF6α in knocked-out ATF6α cells recover myogenesis, whereas the expression of an ATF6α mutant in the p38 MAPK phosphorylation site (T166) was not able to regain myogenesis. Genetic ablation of ATF6α also prevents the exit from the cell cycle, which is essential for muscle differentiation. Furthermore, when we inhibited differentiation by the use of dexamethasone in C2C12 cells, we found inactivation of p38 MAPK and, consequently, loss of ATF6α activity. All these findings suggest that the p-p38 MAPK/ATF6α axis, in pathophysiological conditions, regulates myogenesis by promoting the exit from the cell cycle, an essential step to start myoblasts differentiation.
激活转录因子6α（ATF6α）是一种内质网蛋白，已知在哺乳动物内质网应激期间参与未折叠蛋白反应（UPR）。在此，我们表明，在诱导分化的小鼠C2C12成肌细胞中，ATF6α是被激活的UPR的唯一途径。ATF6α的刺激是p38丝裂原活化蛋白激酶（MAPK）依赖性的，这通过使用抑制剂SB203580得以揭示，该抑制剂会阻止肌管形成，同时损害ATF6α的运输，ATF6α在顺式高尔基体中积累，而未被加工成p50转录活性形式。为了进一步评估ATF6α的作用，我们敲除了ATF6α基因，从而抑制C2C12成肌细胞进行肌生成，且这一过程独立于p38 MAPK活性发生。在敲除ATF6α的细胞中外源表达ATF6α可恢复肌生成，而在p38 MAPK磷酸化位点（T166）的ATF6α突变体的表达则无法恢复肌生成。ATF6α的基因缺失也会阻止细胞周期退出，而这对于肌肉分化至关重要。此外，当我们在C2C12细胞中使用地塞米松抑制分化时，我们发现p38 MAPK失活，进而导致ATF6α活性丧失。所有这些发现表明，在病理生理条件下，p-p38 MAPK/ATF6α轴通过促进细胞周期退出调节肌生成，而细胞周期退出是启动成肌细胞分化的关键步骤。
