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Control of mammalian circadian rhythm by CKIepsilon-regulated proteasome-mediated PER2 degradation

Erik J Eide1, Margaret F Woolf, Heeseog Kang

  • 1Huntsman Cancer Institute, University of Utah, Salt Lake City, UT 84112, USA.

Molecular and Cellular Biology
|March 16, 2005
PubMed

Insights

Mammalian circadian clock proteins PER2 are degraded daily, a process vital for rhythm. Inhibiting this degradation, particularly via casein kinase Iepsilon (CKIepsilon), significantly lengthens circadian periods.

Area of Science:

  • Chronobiology
  • Molecular Biology
  • Biochemistry

Background:

  • Mammalian circadian rhythms rely on daily cycles of PER1 and PER2 protein accumulation, phosphorylation, and degradation.
  • The precise role of phosphorylation-regulated proteolysis in maintaining circadian rhythmicity has remained unclear.

Purpose of the Study:

  • To elucidate the biochemical mechanism and functional significance of PER2 phosphorylation-dependent degradation in mammalian circadian clocks.
  • To investigate the role of casein kinase Iepsilon (CKIepsilon) and beta-TrCP in regulating PER2 stability and circadian period.

Main Methods:

  • Development of a cell-based model to study PER2 degradation.
  • Utilizing calyculin A to induce hyperphosphorylation and subsequent proteasomal degradation of murine PER2 (mPER2).
  • Employing proteasome inhibitors and CKIepsilon inhibitors to assess their impact on circadian period and PER2 degradation. Investigating the interaction between CKIepsilon, beta-TrCP, and PER2.

Main Results:

  • Hyperphosphorylation of mPER2, induced by calyculin A, leads to ubiquitination and degradation by the 26S proteasome.
  • Proteasome inhibition significantly lengthens the circadian period in Rat-1 cells.
  • CKIepsilon inhibition lengthens circadian period and slows PER2 degradation, demonstrating its crucial role.
  • CKIepsilon-mediated phosphorylation facilitates beta-TrCP recruitment, which is essential for phosphorylation-dependent PER2 degradation.

Conclusions:

  • Established a biochemical mechanism for the PER2 phosphorylation-degradation cycle, linking it to circadian clock function.
  • Demonstrated the critical role of CKIepsilon and the ubiquitin-proteasome system in regulating PER2 stability and mammalian circadian rhythm.
  • Highlighted the utility of cell-based biochemical assays combined with rhythm measurements for understanding clock mechanisms.

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