||Forkhead box O (FoxO) transcription factors could regulate many cellular functions, including cell cycle, glucose metabolism, stress response, cell differentiation, cell death and survival. FoxO6, one of the forkhead family, was discovered in 2003. It was different from other FoxO factor because FoxO6 remained mostly nuclear due to its impaired shuttling ability . It lacked the conserved C-terminal PKB motif, which was the cause of the shuttling impairment. Although FoxO6 is majorly expressed in developing brain, it is also expressed in muscle and its function in skeletal muscle was unknown. PGC-1 alpha??was a transtcription coactivator that interacted with PPAR-gamma?and?played a key role in mitochondrial metabolism. When PGC-1 alpha?was?overexpressed in muscle, it transformed type2 myofiber into type1 myofiber. Our study had discovered that C2C12-mFoxO6 cell line could decrease the number and size of myotube compared with C2C12-control. We supposed that FoxO6 may be interfere with cell cycle to inhibit myogenic differentiation. However in flow cytometer assay, confluent C2C12-mFoxO6 myoblast also could majorly stay at G0/G1 phase during cell cycle, it meaned that C2C12-mFoxO6 myoblast also had normal cell cycle exit. We also found that overexpression of FoxO6 inhibited expression of PGC-1 alpha gene in confluent C2C12 myoblast. Thus, we supposed that FoxO6 may regulate PGC-1 alpha promoter activity. By using reporter assay we demonstrated that FoxO6 could inhibit the PGC-1?alpha?promoter activity. Then, we supposed FoxO6 may bind directly to PGC-1?alpha promoter. By EMSA and footprinting we demonstrated that FoxO6 really could bind to PGC-1?alpha?promoter. In the future, we hope to confirm the binding site by chromatin immunoprecipitation assy.|
||1. Pourquie O, et al. (1996) Lateral and axial signals involved in avian somite patterning: a role for BMP4. Cell 84:461-471|
2. Tonegawa A, Funayama N, Ueno N, & Takahashi Y (1997) Mesodermal subdivision along the mediolateral axis in chicken controlled by different concentrations of BMP-4. Development 124:1975-1984.
3. Johnson RL, Laufer E, Riddle RD, & Tabin C (1994) Ectopic expression of Sonic hedgehog alters dorsal-ventral patterning of somites. Cell 79:1165-1173.
4. Fan CM & Tessier-Lavigne M (1994) Patterning of mammalian somites by surface ectoderm and notochord: evidence for sclerotome induction by a hedgehog homolog. Cell 79:1175-1186.
5. Brill G, et al. (1995) Epithelial-mesenchymal conversion of dermatome progenitors requires neural tube-derived signals: characterization of the role of Neurotrophin-3. Development 121:2583-2594.
6. Ikeya M & Takada S (1998) Wnt signaling from the dorsal neural tube is required for the formation of the medial dermomyotome. Development 125:4969-4976.
7. Stern HM, Brown AM, & Hauschka SD (1995) Myogenesis in paraxial mesoderm: preferential induction by dorsal neural tube and by cells expressing Wnt-1. Development 121:3675-3686.
8. Munsterberg AE & Lassar AB (1995) Combinatorial signals from the neural tube, floor plate and notochord induce myogenic bHLH gene expression in the somite. Development 121:651-660.
9. Dietrich S, Schubert FR, Healy C, Sharpe PT, & Lumsden A (1998) Specification of the hypaxial musculature. Development 125:2235-2249.
10. Cossu G, Tajbakhsh S, & Buckingham M (1996) How is myogenesis initiated in the embryo? Trends Genet 12:218-223.
11. Pownall ME, Gustafsson MK, & Emerson CP, Jr. (2002) Myogenic regulatory factors and the specification of muscle progenitors in vertebrate embryos. Annu Rev Cell Dev Biol 18:747-783.
12. Tajbakhsh S, Rocancourt D, Cossu G, & Buckingham M (1997) Redefining the genetic hierarchies controlling skeletal myogenesis: Pax-3 and Myf-5 act upstream of MyoD. Cell 89:127-138.
13. Maroto M, et al. (1997) Ectopic Pax-3 activates MyoD and Myf-5 expression in embryonic mesoderm and neural tissue. Cell 89:139-148.
14. Boettiger D, et al. (1995) Regulation of integrin alpha 5 beta 1 affinity during myogenic differentiation. Dev Biol 169:261-272.
15. Yagami-Hiromasa T, et al. A metalloprotease-disintegrin participating in myoblast fusion. Nature 377:652-656.
16. Bergstrom DA & Tapscott SJ (2001) Molecular Distinction between Specification and Differentiation in the Myogenic Basic Helix-Loop-Helix Transcription Factor Family. Mol. Cell. Biol. 21:2404-2412.
17. Horsley V, Jansen KM, Mills ST, & Pavlath GK (2003) IL-4 Acts as a Myoblast Recruitment Factor during Mammalian Muscle Growth. Cell 113:483-494.
18. Lehmann OJ, Sowden JC, Carlsson P, Jordan T, & Bhattacharya SS (2003) Fox's in development and disease. Trends in Genetics 19:339-344.
19. Accili D & Arden KC (2004) FoxOs at the Crossroads of Cellular Metabolism, Differentiation, and Transformation. Cell 117:421-426.
20. Greer EL & Brunet A (2005) FOXO transcription factors at the interface between longevity and tumor suppression. Oncogene 24:7410-7425.
21. Nakae J, Oki M, & Cao Y (2008) The FoxO transcription factors and metabolic regulation. FEBS Letters 582:54-67.
22. Barthel A, Schmoll D, & Unterman TG (2005) FoxO proteins in insulin action and metabolism. Trends Endocrinol Metab 16:183-189.
23. Kaestner KH, Knochel W, & Martinez DE (2000) Unified nomenclature for the winged helix/forkhead transcription factors. Genes Dev 14:142-146.
24. Nakae J, Park BC, & Accili D (1999) Insulin stimulates phosphorylation of the forkhead transcription factor FKHR on serine 253 through a Wortmannin-sensitive pathway. J Biol Chem 274:15982-15985.
25. Rena G, et al. (2002) Two novel phosphorylation sites on FKHR that are critical for its nuclear exclusion. EMBO J 21:2263-2271.
26. Woods YL, et al. (2001) The kinase DYRK1A phosphorylates the transcription factor FKHR at Ser329 in vitro, a novel in vivo phosphorylation site. Biochem J 355:597-607.
27. Matsuzaki H, Daitoku H, Hatta M, Tanaka K, & Fukamizu A (2003) Insulin-induced phosphorylation of FKHR (Foxo1) targets to proteasomal degradation. Proc Natl Acad Sci U S A 100:11285-11290.
28. Kops GJ, et al. (1999) Direct control of the Forkhead transcription factor AFX by protein kinase B. Nature 398:630-634.
29. Matsuzaki H, et al. (2005) Acetylation of Foxo1 alters its DNA-binding ability and sensitivity to phosphorylation. Proc Natl Acad Sci U S A 102:11278-11283.
30. van der Heide LP, Jacobs FM, Burbach JP, Hoekman MF, & Smidt MP (2005) FoxO6 transcriptional activity is regulated by Thr26 and Ser184, independent of nucleo-cytoplasmic shuttling. Biochem J 391:623-629.
31. Jacobs FM, et al. (2003) FoxO6, a novel member of the FoxO class of transcription factors with distinct shuttling dynamics. J Biol Chem 278:35959-35967.
32. Tureckova J, Wilson EM, Cappalonga JL, & Rotwein P (2001) Insulin-like growth factor-mediated muscle differentiation: collaboration between phosphatidylinositol 3-kinase-Akt-signaling pathways and myogenin. J Biol Chem 276:39264-39270.
33. Bodine SC, et al. (2001) Identification of ubiquitin ligases required for skeletal muscle atrophy. Science 294:1704-1708.
34. Kamei Y, et al. (2004) Skeletal muscle FOXO1 (FKHR) transgenic mice have less skeletal muscle mass, down-regulated Type I (slow twitch/red muscle) fiber genes, and impaired glycemic control. J Biol Chem 279:41114-41123.
35. Kitamura T, et al. (2007) A Foxo/Notch pathway controls myogenic differentiation and fiber type specification. J Clin Invest 117:2477-2485.
36. Suzuki N, et al. (2007) NO production results in suspension-induced muscle atrophy through dislocation of neuronal NOS. J Clin Invest 117:2468-2476.
37. Lara-Pezzi E, et al. (2007) A naturally occurring calcineurin variant inhibits FoxO activity and enhances skeletal muscle regeneration. J Cell Biol 179:1205-1218.
38. Finck BN & Kelly DP (2006) PGC-1 coactivators: inducible regulators of energy metabolism in health and disease. J Clin Invest 116:615-622.
39. Sadana P & Park EA (2007) Characterization of the transactivation domain in the peroxisome-proliferator-activated receptor gamma co-activator (PGC-1). Biochem J 403:511-518.
40. Andersson U & Scarpulla RC (2001) Pgc-1-related coactivator, a novel, serum-inducible coactivator of nuclear respiratory factor 1-dependent transcription in mammalian cells. Mol Cell Biol 21:3738-3749.
41. Handschin C, Rhee J, Lin J, Tarr PT, & Spiegelman BM (2003) An autoregulatory loop controls peroxisome proliferator-activated receptor gamma coactivator 1alpha expression in muscle. Proc Natl Acad Sci U S A 100:7111-7116.
42. Lin J, et al. (2002) Transcriptional co-activator PGC-1 alpha drives the formation of slow-twitch muscle fibres. Nature 418:797-801.
43. Leone TC, et al. (2005) PGC-1alpha deficiency causes multi-system energy metabolic derangements: muscle dysfunction, abnormal weight control and hepatic steatosis. PLoS Biol 3:e101.
44. Daitoku H, Yamagata K, Matsuzaki H, Hatta M, & Fukamizu A (2003) Regulation of PGC-1 promoter activity by protein kinase B and the forkhead transcription factor FKHR. Diabetes 52:642-649.
45. Sandri M, et al. (2006) PGC-1alpha protects skeletal muscle from atrophy by suppressing FoxO3 action and atrophy-specific gene transcription. Proc Natl Acad Sci U S A 103:16260-16265.
46. Brault JJ, Jespersen JG, & Goldberg AL (2010) Peroxisome proliferator-activated receptor gamma coactivator 1alpha or 1beta overexpression inhibits muscle protein degradation, induction of ubiquitin ligases, and disuse atrophy. J Biol Chem 285:19460-19471.
47. Schmidt M, et al. (2002) Cell cycle inhibition by FoxO forkhead transcription factors involves downregulation of cyclin D. Mol Cell Biol 22:7842-7852.
48. Kops GJ, et al. (2002) Control of cell cycle exit and entry by protein kinase B-regulated forkhead transcription factors. Mol Cell Biol 22:2025-2036.