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Loss of Emi1-dependent anaphase-promoting complex/cyclosome inhibition deregulates E2F target expression and elicits

Emmy W Verschuren1, Kenneth H Ban, Marilyn A Masek

  • 1Department of Tumor Biology and Angiogenesis, Genentech Inc., 1 DNA way, South San Francisco, California 94080, USA.

Molecular and Cellular Biology
|September 19, 2007
PubMed

Insights

Emi1, an anaphase-promoting complex/cyclosome (APC/C) inhibitor, is vital for cell proliferation and DNA integrity. Its absence triggers cellular senescence due to DNA damage and replication stress.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Genetics

Background:

  • The anaphase-promoting complex/cyclosome (APC/C) is a crucial regulator of cell cycle progression.
  • Emi1 (early mitotic inhibitor 1) is a key inhibitor of the APC/C, essential for timely progression through mitosis.
  • Emi1's role in maintaining genomic stability and preventing cellular senescence is not fully understood.

Purpose of the Study:

  • To investigate the function of Emi1 in regulating cell cycle progression and preventing cellular senescence.
  • To elucidate the molecular mechanisms by which Emi1 depletion leads to DNA damage and senescence.
  • To determine the necessity of Emi1 for maintaining a positive-feedback loop crucial for cell cycle control.

Main Methods:

  • In vivo analysis of Emi1 expression in correlation with cellular proliferation.
  • Depletion of Emi1 using genetic methods and assessment of APC/C substrate and E2F target mRNA levels.
  • Measurement of cyclin E mRNA, protein levels, and associated kinase activities.
  • Analysis of DNA damage induction and cellular senescence.
  • Inhibition of ATM kinase to assess its role in Emi1 depletion-induced senescence.
  • Depletion of Emi1-stabilizing factors Evi5 and Pin1.

Main Results:

  • Emi1 expression inversely correlates with cellular proliferation and its absence induces cellular senescence.
  • Emi1 depletion causes decreased E2F target mRNA and APC/C substrate protein levels, but increased cyclin E mRNA, protein, and kinase activity.
  • Cells lacking Emi1 exhibit DNA damage, likely due to replication stress from deregulated cyclin E/A activity.
  • ATM kinase inhibition prevents senescence, indicating DNA damage as the cause.
  • Depletion of Evi5 or Pin1 does not induce significant senescence.

Conclusions:

  • Emi1 is essential for maintaining a positive-feedback circuit involving protein stabilization and mRNA expression, which is critical for cell cycle progression.
  • Accurate cell cycle progression, DNA integrity, and prevention of cellular senescence depend on Emi1-mediated feedback.
  • Emi1 plays a critical role in preventing DNA damage and subsequent cellular senescence.

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