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Actin binding to WH2 domains regulates nuclear import of the multifunctional actin regulator JMY

J Bradley Zuchero1, Brittany Belin, R Dyche Mullins

  • 1Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158, USA.

Molecular Biology of the Cell
|January 21, 2012
PubMed

Insights

Junction-mediating and regulatory protein (JMY) controls its nuclear import via actin binding. DNA damage triggers actin assembly, reducing JMY nuclear entry and promoting apoptosis.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Junction-mediating and regulatory protein (JMY) regulates transcription and actin filament assembly.
  • JMY accumulates in the nucleus upon DNA damage, initiating p53-dependent apoptosis.
  • JMY possesses three actin-binding Wiskott-Aldrich syndrome protein homology 2 (WH2) domains crucial for actin nucleation.

Purpose of the Study:

  • To investigate the mechanism regulating JMY's subcellular localization, particularly its nuclear import.
  • To determine how actin binding influences JMY's nuclear localization and function.
  • To elucidate the role of JMY's WH2 domains in its localization and response to DNA damage.

Main Methods:

  • Site-directed mutagenesis to alter actin-binding affinity of WH2 domains.
  • Cellular fractionation and Western blotting to assess JMY localization.
  • Immunofluorescence microscopy to visualize JMY and actin distribution.
  • Treatment with DNA-damaging agents and actin polymerization inhibitors.

Main Results:

  • The WH2 domain cluster in JMY overlaps a bipartite nuclear localization sequence (NLS).
  • Actin monomer binding to WH2 domains inhibits importin binding to the NLS, preventing nuclear import.
  • Mutations disrupting actin binding or conditions favoring actin polymerization lead to JMY nuclear accumulation.
  • DNA damage induces cytoplasmic actin polymerization and requires the WH2/NLS region and importin β for JMY nuclear import.

Conclusions:

  • Actin assembly dynamically regulates JMY's nuclear import.
  • The WH2/NLS region acts as a sensor for cytoplasmic actin levels, controlling JMY localization.
  • This mechanism links actin dynamics to JMY's role in DNA damage response and apoptosis.

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