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INH, a negative regulator of MPF, is a form of protein phosphatase 2A

T H Lee1, M J Solomon, M C Mumby

  • 1Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.

Cell
|January 25, 1991
PubMed

Insights

Maturation promoting factor (MPF) drives cell cycle progression. This study identifies INH as protein phosphatase 2A, which inactivates MPF by dephosphorylating key subunits, opposing cell cycle activation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Maturation promoting factor (MPF) is crucial for the G2 to M phase transition in eukaryotic cells.
  • MPF activation involves dephosphorylation of p34cdc2, but its inactivation pathway remains unclear.
  • INH was identified as an inhibitor of pre-MPF activation in Xenopus oocytes.

Purpose of the Study:

  • To elucidate the molecular identity and function of INH in MPF regulation.
  • To investigate the role of INH in the inactivation of MPF.
  • To understand the mechanism by which INH opposes MPF activation.

Main Methods:

  • Purification of INH from Xenopus oocytes.
  • Biochemical assays to assess INH's phosphatase activity.
  • In vitro inactivation of isolated p34cdc2-cyclin complexes using INH and protein phosphatase 2A (PP2A).
  • Analysis of protein dephosphorylation on p34cdc2 and cyclin subunits.

Main Results:

  • INH was purified and identified as a form of protein phosphatase 2A.
  • Both INH and the catalytic subunit of PP2A directly inactivated isolated p34cdc2-cyclin complexes.
  • Inactivation correlated with the dephosphorylation of both cyclin and p34cdc2 subunits.
  • Dephosphorylation occurred at a specific site on p34cdc2, mirroring the critical activation step.

Conclusions:

  • INH functions as a protein phosphatase 2A, opposing MPF activation.
  • INH inactivates MPF by reversing the critical phosphorylation of p34cdc2.
  • This dephosphorylation mechanism is key to regulating the G2 to M phase transition.

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