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Evaluation of Substrate Ubiquitylation by E3 Ubiquitin-ligase in Mammalian Cell Lysates
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The ETS protein MEF is regulated by phosphorylation-dependent proteolysis via the protein-ubiquitin ligase SCFSkp2

Yan Liu1, Cyrus V Hedvat, Shifeng Mao

  • 1Division of Hematologic Oncology, Department of Medicine, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, Box 575, New York, NY 10021, USA.

Molecular and Cellular Biology
|April 4, 2006
PubMed

Insights

MEF (ELF4) is a cell cycle-regulated transcription factor crucial for immune cell development. Its rapid degradation in S phase, controlled by specific phosphorylation and ubiquitination, ensures proper cell proliferation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Immunology

Background:

  • MEF (ELF4) is an ETS-related transcription factor impacting hematopoietic stem cell behavior and NK/NKT cell development.
  • MEF gene expression is regulated by oncogenic fusion proteins and retroviral insertions.
  • Previous work indicated MEF activity is restricted to G1 phase by cyclin A-dependent phosphorylation.

Purpose of the Study:

  • To investigate the cell cycle regulation of MEF protein stability and its underlying molecular mechanisms.
  • To determine how MEF protein levels are controlled throughout the cell cycle and impact cell proliferation.

Main Methods:

  • Mutagenesis studies to identify key phosphorylation sites.
  • Analysis of MEF protein turnover using ubiquitination and proteolysis assays.
  • Cell cycle analysis and proliferation assays upon MEF overexpression.

Main Results:

  • MEF is a short-lived protein with peak expression in late G1 phase.
  • Rapid MEF turnover in S phase is mediated by cdk2 phosphorylation at T643/S648 and SCF(Skp2) ubiquitination.
  • MEF overexpression accelerates the G1/S transition and promotes cell proliferation.

Conclusions:

  • Tight cell cycle regulation of MEF protein levels is critical for controlling cell cycle entry and proliferation.
  • The identified phosphorylation and ubiquitination pathway provides a mechanism for MEF degradation.
  • Understanding MEF regulation offers insights into immune cell development and cancer biology.

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