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Identification of Intracellular Signaling Events Induced in Viable Cells by Interaction with Neighboring Cells Undergoing Apoptotic Cell Death
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Phospho-ablated Id2 is growth suppressive and pro-apoptotic in proliferating myoblasts

David C Butler1, Satoshi Haramizu, David L Williamson

  • 1Laboratory of Muscle Biology and Sarcopenia, Department of Exercise Physiology, West Virginia University School of Medicine, Morgantown, West Virginia, United States of America.

Plos One
|July 18, 2009
PubMed

Insights

Inhibitor of differentiation protein-2 (Id2) phosphorylation at serine 5 impacts its cellular localization and role in skeletal muscle cells. Unphosphorylated Id2, localized in the cytosol, suppresses growth and promotes apoptosis.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Muscle Development

Background:

  • Inhibitor of differentiation protein-2 (Id2) is a helix-loop-helix (HLH) protein regulating cell proliferation.
  • Id2's N-terminal phosphorylation site at serine 5 (S5) is implicated in apoptosis in myeloid cells, but its role in skeletal muscle is unknown.

Purpose of the Study:

  • To investigate the effect of Id2 phosphorylation at S5 on its subcellular localization, proliferation, and apoptosis in C2C12 myoblasts.
  • To determine if altering Id2 phosphorylation affects its interaction with basic HLH proteins.

Main Methods:

  • Overexpression of wild-type Id2, phospho-ablated Id2 (S5A), and phospho-mimicking Id2 (S5D) in C2C12 myoblasts.
  • Assessment of MyoD protein expression, bromodeoxyuridine incorporation, subcellular localization, and apoptosis.
  • Analysis of Id2 binding to E47 and E12 basic HLH proteins.

Main Results:

  • Overexpression of wild-type Id2 decreased MyoD expression and increased proliferation, while S5A mutant decreased proliferation.
  • Phospho-ablated Id2 (S5A) showed decreased nuclear localization compared to wild-type and S5D mutants.
  • Decreased nuclear localization of S5A correlated with reduced proliferation and increased apoptosis.

Conclusions:

  • Id2 phosphorylation at serine 5 influences its subcellular localization and function in C2C12 myoblasts.
  • Unphosphorylated Id2 appears to be primarily cytosolic, mediating growth suppression and promoting apoptosis.
  • Modulating unphosphorylated Id2 levels may enhance myoblast proliferation and differentiation potential.

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