Phosphorylation and destabilization of human period I clock protein by human casein kinase I epsilon.
Period (PER), a central component of the circadian clock in Drosophila, undergoes daily oscillation in abundance and phosphorylation state. Here we report that human casein kinase I epsilon (hCKI epsilon) can phosphorylate human PER I (hPER I). Purified recombinant hCKI epsilon (but not a kinase negative mutant of hCKI epsilon, hCKI epsilon-K38R) phosphorylated hPER I in vitro. When co-transfected with wild-type hCKI epsilon, in 293T cells, hPER I showed a significant increase in phosphorylation as evidenced by a shift in molecular mass. Furthermore, phosphorylation of hPER I by hCKI epsilon caused a decrease in protein stability in hPER I. Whereas phosphorylated hPER I had a half-life of approximately 12 h, unphosphorylated hPER I remained stable in the cell for > 24 h. hPER I protein could also be co-immunoprecipitated with transfected hCKI epsilon as well as endogenous hCKI epsilon, indicating physical association between hPER I and hCKI epsilon proteins in vivo.
Keesler
G A
GA
Department of Neuroscience, Aventis Pharmaceuticals Inc., Bridgewater, NJ 08807, USA. george.keesler@aventis.com
Camacho
F
F
Guo
Y
Y
Virshup
D
D
Mondadori
C
C
Yao
Z
Z
D000818:Animals; D056926:CLOCK Proteins; D047388:Casein Kinases; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D002940:Circadian Rhythm / Q000502:physiology; D029721:Drosophila Proteins; D005333:Fetus; D005822:Genetic Vectors; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D056950:Period Circadian Proteins; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
D018797:Cell Cycle Proteins; C120526:Clk protein, Drosophila; D029721:Drosophila Proteins; D009687:Nuclear Proteins; C539022:PER1 protein, human; D056950:Period Circadian Proteins; D014157:Transcription Factors; D056926:CLOCK Proteins; D011494:Protein Kinases; D047388:Casein Kinases