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Mirk/dyrk1B kinase destabilizes cyclin D1 by phosphorylation at threonine 288

Yonglong Zou1, Daina Z Ewton, Xiaobing Deng

  • 1Department of Pathology, Upstate Medical University, Syracuse, New York 13210, USA.

The Journal of Biological Chemistry
|April 13, 2004
PubMed

Insights

The protein kinase Mirk phosphorylates cyclin D1 at threonine 288, promoting its degradation and aiding cell cycle arrest. This adds to glycogen synthase kinase 3beta

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Phosphorylation of cyclin D1 at threonine 286 by GSK3beta targets it for ubiquitination, nuclear export, and proteasomal degradation.
  • Mutation at threonine 288 to alanine reduces cyclin D1 ubiquitination, suggesting its phosphorylation also promotes degradation.

Purpose of the Study:

  • To investigate the role of Mirk/dyrk1B in cyclin D1 phosphorylation and stability.
  • To determine Mirk's function in regulating the cell cycle, specifically G(0)/G(1) arrest.

Main Methods:

  • Demonstrated Mirk binding and in vivo phosphorylation of cyclin D1 at threonine 288.
  • Utilized cyclin D1-T288A constructs to assess protein stability.
  • Employed transient overexpression and RNA interference in Mv1Lu cells to study Mirk's effects on cyclin D1 levels and cell cycle progression.
  • Performed in vitro phosphorylation assays with Mirk and GSK3beta.

Main Results:

  • Mirk phosphorylates cyclin D1 at threonine 288, leading to increased protein stability (cyclin D1-T288A construct).
  • Mirk overexpression caused G(0)/G(1) cell cycle arrest, while Mirk depletion increased cyclin D1 protein levels.
  • Mirk destabilizes cyclin D1 protein, decreasing its half-life and correlating with increased Mirk expression and blocked cell migration.
  • Mirk and GSK3beta phosphorylate cyclin D1 in an additive manner in vitro.

Conclusions:

  • Mirk/dyrk1B phosphorylates cyclin D1 at threonine 288, contributing to its destabilization and degradation.
  • Mirk, along with GSK3beta, may cooperate to induce cell arrest in the G(0)/G(1) phase by destabilizing cyclin D1.
  • Mirk plays a significant role in regulating cyclin D1 protein levels and cell cycle progression.

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