Negative control of circadian clock regulator E4BP4 by casein kinase Iepsilon-mediated phosphorylation.
Light-dependent transcriptional regulation of clock genes is a crucial step in the entrainment of the circadian clock. E4bp4 is a light-inducible gene in the chick pineal gland, and it encodes a bZIP protein that represses transcription of cPer2, a chick pineal clock gene. Here, we demonstrate that prolonged light period-dependent accumulation of E4BP4 protein is temporally coordinated with a delay of the rising phase of cPer2 in the morning. E4BP4 was phosphorylated progressively and then disappeared in parallel with induced cPer2 expression. Characterization of E4BP4 revealed Ser182, a phosphoacceptor site located at the amino-terminal border of the Ser/Thr cluster, which forms the phosphorylation motifs for casein kinase 1epsilon (CK1epsilon). CK1epsilon physically associated with E4BP4 and phosphorylated it. CK1epsilon-catalyzed phosphorylation of E4BP4 resulted in proteasomal proteolysis-dependent decrease of E4BP4 levels, while E4BP4 nuclear accumulation was attenuated by CK1epsilon in a kinase activity-independent manner. CK1epsilon-mediated posttranslational regulation was accompanied by reduction of the transcriptional repression executed by E4BP4. These results not only demonstrate a phosphorylation-dependent regulatory mechanism for E4BP4 function but also highlight the role of CK1epsilon as a negative regulator for E4BP4-mediated repression of cPer2.
Doi
Masao
M
Department of Biophysics and Biochemistry, Graduate School of Science, Univeristy of Tokyo, Japan.
Okano
Toshiyuki
T
Yujnovsky
Irene
I
Sassone-Corsi
Paolo
P
Fukada
Yoshitaka
Y
D000595:Amino Acid Sequence; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors; D001683:Biological Clocks / Q000502:physiology*; D047388:Casein Kinases; D002645:Chickens; D002940:Circadian Rhythm / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism* / Q000502:physiology; D051790:G-Box Binding Factors; D005786:Gene Expression Regulation; D015151:Immunoblotting; D008027:Light; D008156:Luciferases; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010870:Pineal Gland / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011233:Precipitin Tests; D011494:Protein Kinases / Q000378:metabolism*; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D051790:G-Box Binding Factors; D014157:Transcription Factors; D008156:Luciferases; D011494:Protein Kinases; D047388:Casein Kinases