Sumi Koichiro, Higashi Seiichiro, Natsume Midori, Kawahata Keiko, Nakazato Koichi
a Food Science Research Laboratories, R&D Division, Meiji Co., Ltd. 540 Naruda, Odawara, 540 Naruda, Odawara, Kanagawa 250-0862, Japan.
Appl Physiol Nutr Metab. 2014 Aug;39(8):902-10. doi: 10.1139/apnm-2013-0431. Epub 2014 Feb 26.
Extracellular signal-regulated kinase (ERK) is required for clenbuterol (CB)-dependent fast-type myofibril enlargement; however, its contribution to translation control is unclear. ERK mediates translational regulation through mammalian target of rapamycin complex 1 (mTORC1) activation and (or) mTORC1-independent pathways. In this study, we aimed to investigate the role of ERK in translational control during CB-induced muscular hypertrophy by measuring time-dependent changes in the phosphorylation statuses of ERK, p70 ribosomal S6 kinase (p70S6K; an indicator of mTORC1 activity), 4E-binding protein 1 (4E-BP1), eukaryotic elongation factor 2 (eEF2), and other related signaling molecules in rat gastrocnemius muscles. Five-day administration of CB induced phenotypes associated with muscular hypertrophy (significant increases in wet weight and isometric ankle flexion torque in the gastrocnemius muscle), but was not accompanied by elevated ERK or p70S6K phosphorylation. One-day administration of CB caused significant increases in the phosphorylation of ERK, p70S6K, and 4E-BP1. In contrast, 3-day administration of CB caused significant increases in the phosphorylation of ERK and 4E-BP1, but not p70S6K. In addition, positive correlations were observed between ERK and 4E-BP1 on days 1 and 3, whereas a correlation between ERK and p70S6K was only observed on day 1. eEF2 phosphorylation was unchanged on both days 1 and 3. These findings suggest that ERK accelerates the initiation of translation, but does not support the involvement of ERK in translational elongation. Furthermore, ERK may play a major role in promoting translational initiation by mediating the phosphorylation of 4E-BP1, and may contribute to the initial activation of mTORC1 during CB administration.
细胞外信号调节激酶（ERK）是克伦特罗（CB）依赖性快肌纤维增大所必需的；然而，其对翻译控制的作用尚不清楚。ERK通过雷帕霉素复合物1（mTORC1）的激活和（或）不依赖mTORC1的途径介导翻译调控。在本研究中，我们旨在通过测量大鼠腓肠肌中ERK、p70核糖体S6激酶（p70S6K；mTORC1活性指标）、4E结合蛋白1（4E-BP1）、真核生物延伸因子2（eEF2）及其他相关信号分子磷酸化状态的时间依赖性变化，来研究ERK在CB诱导的肌肉肥大过程中对翻译控制的作用。连续5天给予CB可诱导出与肌肉肥大相关的表型（腓肠肌湿重和等长踝关节屈曲扭矩显著增加），但并未伴随ERK或p70S6K磷酸化水平升高。给予CB 1天可导致ERK、p70S6K和4E-BP1磷酸化显著增加。相比之下，给予CB 3天可导致ERK和4E-BP1磷酸化显著增加，但p70S6K未增加。此外，在第1天和第3天观察到ERK与4E-BP1之间呈正相关，而ERK与p70S6K之间的相关性仅在第1天观察到。在第1天和第3天，eEF2磷酸化均未改变。这些发现表明，ERK加速翻译起始，但不支持ERK参与翻译延伸。此外，ERK可能通过介导4E-BP1的磷酸化在促进翻译起始中起主要作用，并且可能在给予CB期间对mTORC1的初始激活有贡献。
