Protein kinase A and casein kinases mediate sequential phosphorylation events in the circadian negative feedback loop

Guocun Huang, She Chen, Shaojie Li, Joonseok Cha, Chengzu Long, Lily Li, Qiyang He, Yi Liu

Research output: Contribution to journalArticle

85 Scopus citations

Abstract

Regulation of circadian clock components by phosphorylation plays essential roles in clock functions and is conserved from fungi to mammals. In the Neurospora circadian negative feedback loop, FREQUENCY (FRQ) protein inhibits WHITE COLLAR (WC) complex activity by recruiting the casein kinases CKI and CKII to phosphorylate the WC proteins, resulting in the repression of frq transcription. On the other hand, CKI and CKII progressively phosphorylate FRQ to promote FRQ degradation, a process that is a major determinant of circadian period length. Here, by using whole-cell isotope labeling and quantitative mass spectrometry methods, we show that the WC-1 phosphorylation events critical for the negative feedback process occur sequentially - first by a priming kinase, then by the FRQ-recruited casein kinases. We further show that the cyclic AMP-dependent protein kinase A (PKA) is essential for clock function and inhibits WC activity by serving as a priming kinase for the casein kinases. In addition, PKA also regulates FRQ phosphorylation, but unlike CKI and CKII, PKA stabilizes FRQ, similar to the stabilization of human PERIOD2 (hPER2) due to the phosphorylation at the familial advanced sleep phase syndrome (FASPS) site. Thus, PKA is a key clock component that regulates several critical processes in the circadian negative feedback loop.

Original languageEnglish (US)
Pages (from-to)3283-3295
Number of pages13
JournalGenes and Development
Volume21
Issue number24
DOIs
StatePublished - Dec 15 2007

Keywords

  • Casein kinase I
  • Circadian clock
  • Neurospora
  • Phosphorylation
  • Protein kinase A

ASJC Scopus subject areas

  • Genetics
  • Developmental Biology

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