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Prolonged activation of S6K1 does not suppress IRS or PI-3 kinase signaling during muscle cell differentiation

Hamilton, D Lee, Philp, Andrew, MacKenzie, Matthew G and Baar, Keith 2010, Prolonged activation of S6K1 does not suppress IRS or PI-3 kinase signaling during muscle cell differentiation, BMC cell biology, vol. 11, pp. 1-10, doi: 10.1186/1471-2121-11-37.

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Title Prolonged activation of S6K1 does not suppress IRS or PI-3 kinase signaling during muscle cell differentiation
Author(s) Hamilton, D Lee
Philp, Andrew
MacKenzie, Matthew G
Baar, Keith
Journal name BMC cell biology
Volume number 11
Article ID 37
Start page 1
End page 10
Total pages 10
Publisher BioMed Central
Place of publication London, Eng.
Publication date 2010-05-27
ISSN 1471-2121
Keyword(s) Animals
Cell Line
Culture Media, Serum-Free
Extracellular Matrix Proteins
Feedback, Physiological
Insulin Receptor Substrate Proteins
Mice
Muscle Development
Muscle Fibers, Skeletal
Myoblasts
Phosphatidylinositol 3-Kinases
RNA, Small Interfering
Ribosomal Protein S6 Kinases, 90-kDa
Signal Transduction
Summary BACKGROUND: Myogenesis in C2C12 cells requires the activation of the PI3K/mTOR signaling pathways. Since mTOR signaling can feedback through S6K1 to inhibit the activation of PI3K, the aim of this work was to assess whether feedback from S6K1 played a role in myogenesis and determine whether siRNA mediated knockdown of S6K1 would lead to an increased rate of myotube formation.

RESULTS: S6K1 activity increased in a linear fashion following plating and was more than 3-fold higher after Day 3 of differentiation (subconfluent = 11.09 +/- 3.05, Day 3 = 29.34 +/- 3.58). IRS-1 levels tended to increase upon serum withdrawal but decreased approximately 2-fold (subconfluent = 0.88 +/- 0.10, Day 3 = 0.42 +/- 0.06) 3 days following differentiation whereas IRS-2 protein remained stable. IRS-1 associated p85 was significantly reduced upon serum withdrawal (subconfluent = 0.86 +/- 0.07, Day 0 = 0.31 +/- 0.05), remaining low through day 1. IRS-2 associated p85 decreased following serum withdrawal (subconfluent = 0.96 +/- 0.05, Day 1 = 0.56 +/- 0.08) and remained suppressed up to Day 3 following differentiation (0.56 +/- 0.05). Phospho-tyrosine associated p85 increased significantly from subconfluent to Day 0 and remained elevated throughout differentiation. siRNA directed against S6K1 and S6K2 did not result in changes in IRS-1 levels after either 48 or 96 hrs. Furthermore, neither 48 nor 96 hrs of S6K1 knockdown caused a change in myotube formation.

CONCLUSIONS: Even though S6K1 activity increases throughout muscle cell differentiation and IRS-1 levels decrease over this period, siRNA suggests that S6K1 is not mediating the decrease in IRS-1. The decrease in IRS-1/2 associated p85 together with the increase in phospho-tyrosine associated p85 suggests that PI3K associates primarily with scaffolds other than IRS-1/2 during muscle cell differentiation.
Language eng
DOI 10.1186/1471-2121-11-37
Field of Research 0601 Biochemistry And Cell Biology
HERDC Research category CN.1 Other journal article
Copyright notice ©2010, Hamilton et al.
Free to Read? Yes
Use Rights Creative Commons Attribution licence
Persistent URL http://hdl.handle.net/10536/DRO/DU:30112504

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