Insulin and LiCl synergistically rescue myogenic differentiation of FoxO1 over-expressed myoblasts

• Published in: PloS one Vol. 9; no. 2; p. e88450
• Main Authors: Wu, Yi Ju, Fang, Yen Hsin, Chi, Hsiang Cheng, Chang, Li Chiung, Chung, Shih Ying, Huang, Wei Chieh, Wang, Xiao Wen, Lee, Kuan Wei, Chen, Shen Liang
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 13.02.2014; Public Library of Science (PLoS)
• Subjects: Accumulation; Active Transport, Cell Nucleus - drug effects; Animals; Autophagy; Biology; Cell cycle; Cell Differentiation - drug effects; Cell Line; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Culture Media; Cytosol - drug effects; Cytosol - metabolism; Deprivation; Differentiation; Endocrinology; Fatty Acids, Unsaturated - pharmacology; Forkhead Box Protein O1; Forkhead Transcription Factors - genetics; Forkhead Transcription Factors - metabolism; FOXO1 protein; Gene Expression Regulation; Gene silencing; Glucose; Hypertrophy; Insulin; Insulin - pharmacology; Kinases; Leptomycin B; Life sciences; Lithium chloride; Lithium Chloride - pharmacology; Mammals; Mice; Muscle Development - drug effects; Muscle Development - genetics; Muscle Fibers, Skeletal - cytology; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Musculoskeletal system; Myoblasts; Myoblasts - cytology; Myoblasts - drug effects; Myoblasts - metabolism; Myogenesis; Myogenic Regulatory Factors - genetics; Myogenic Regulatory Factors - metabolism; Myotubes; Nuclear transport; Overexpression; Phosphorylation; Promoter Regions, Genetic; Proteins; Rodents; Serum - chemistry; Signal Transduction; Signaling; Transcription factors; Wnt protein; Wnt Proteins - genetics; Wnt Proteins - metabolism
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0088450

Most recent studies reported that FoxO1 transcription factor was a negative regulator of myogenesis under serum withdrawal condition, a situation not actually found in vivo. Therefore, the role of FoxO1 in myogenesis should be re-examined under more physiologically relevant conditions. Here we found that FoxO1 was preferentially localized to nucleus in proliferating (PMB) and confluent myoblasts (CMB) and its nuclear exclusion was a prerequisite for formation of multinucleated myotubes (MT). The nuclear shuttling of FoxO1 in PMB could be prevented by leptomycin B and we further found that cytoplasmic accumulation of FoxO1 in myotubes was caused by the blockade of its nuclear import. Although over-expression of wildtype FoxO1 in C2C12 myoblasts significantly blocked their myogenic differentiation under serum withdrawal condition, application of insulin and LiCl, an activator of Wnt signaling pathway, to these cells successfully rescued their myogenic differentiation and generated myotubes with larger diameters. Interestingly, insulin treatment significantly reduced FoxO1 level and also delayed nuclear re-accumulation of FoxO1 triggered by mitogen deprivation. We further found that FoxO1 directly repressed the promoter activity of myogenic genes and this repression can be relieved by insulin and LiCl treatment. These results suggest that FoxO1 inhibits myogenesis in serum withdrawal condition but turns into a hypertrophy potentiator when other myogenic signals, such as Wnt and insulin, are available.