title: Insulin and LiCl synergistically rescue myogenic differentiation of FoxO1 over-expressed myoblasts.
abstract: 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.
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Yi Ju
authors.initials: YJ
authors.lastname: Wu
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Yen Hsin
authors.initials: YH
authors.lastname: Fang
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Hsiang Cheng
authors.initials: HC
authors.lastname: Chi
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Li Chiung
authors.initials: LC
authors.lastname: Chang
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Shih Ying
authors.initials: SY
authors.lastname: Chung
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Wei Chieh
authors.initials: WC
authors.lastname: Huang
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Xiao Wen
authors.initials: XW
authors.lastname: Wang
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Kuan Wei
authors.initials: KW
authors.lastname: Lee
authors.affiliation: Department of Life Sciences, National Central University, Jhongli, Taiwan.
authors.forename: Shen Liang
authors.initials: SL
authors.lastname: Chen
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003470:Culture Media; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D007328:Insulin / Q000494:pharmacology*; D018021:Lithium Chloride / Q000494:pharmacology*; D051379:Mice; D024510:Muscle Development / Q000187:drug effects / Q000235:genetics; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D032446:Myoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018006:Myogenic Regulatory Factors / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D044967:Serum / Q000737:chemistry; D015398:Signal Transduction; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D003470:Culture Media; D005231:Fatty Acids, Unsaturated; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D007328:Insulin; D018006:Myogenic Regulatory Factors; D051153:Wnt Proteins; D018021:Lithium Chloride; C038753:leptomycin B