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CKIepsilon/delta-dependent phosphorylation is a temperature-insensitive, period-determining process in the mammalian

Yasushi Isojima1, Masato Nakajima, Hideki Ukai

  • 1Comparative Systems Biology Team, Genomic Science Center, RIKEN, 1-7-22, Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan.

Proceedings of the National Academy of Sciences of the United States of America
|October 7, 2009
PubMed

Insights

The mammalian circadian clock

Area of Science:

  • Biochemistry
  • Chronobiology
  • Molecular Biology

Background:

  • The circadian clock exhibits flexible yet robust responses to environmental changes.
  • Understanding the biochemical mechanisms behind this adaptability is crucial for chronobiology.
  • The mammalian circadian clock's period-determining processes remain incompletely understood.

Purpose of the Study:

  • To investigate the biochemical basis of the circadian clock's flexible and robust nature.
  • To identify compounds that modulate the mammalian circadian clock's period.
  • To elucidate the role of casein kinase I (CKI) phosphorylation in circadian rhythm regulation.

Main Methods:

  • Screening of 1,260 pharmacologically active compounds in mouse and human clock cell lines.
  • Assessing the effect of identified compounds on circadian period length in vitro and in vivo.
  • Investigating the impact of compounds on casein kinase Iepsilon (CKIepsilon) and CKIdelta phosphorylation of the PER2 protein.
  • Analyzing the temperature-dependence of PER2 degradation and CKIepsilon/delta-dependent phosphorylation.

Main Results:

  • Compounds significantly lengthening the circadian clock period were identified.
  • Most effective compounds inhibited CKIepsilon/delta phosphorylation of PER2.
  • Chemical perturbation of CKIepsilon/delta-dependent phosphorylation altered the mammalian clock period from 24 to 48 hours.
  • PER2 degradation rate was temperature-insensitive in cells but sensitive to chemical perturbation.
  • CKIepsilon/delta-dependent phosphorylation of a synthetic peptide in vitro was temperature-insensitive.

Conclusions:

  • CKIepsilon/delta-dependent phosphorylation is a key temperature-insensitive process determining the mammalian circadian clock's period.
  • The circadian clock is highly sensitive to chemical perturbations affecting CKIepsilon/delta activity.
  • This study reveals a critical molecular mechanism underlying circadian clock robustness and flexibility.

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