title: Control of WHITE COLLAR localization by phosphorylation is a critical step in the circadian negative feedback process.
abstract: Reversible protein phosphorylation has critical functions in the eukaryotic circadian negative feedback loops. In Neurospora, the FREQUENCY protein closes the circadian negative feedback loop by promoting the phosphorylation of its transcription activator, the WHITE COLLAR complex (WCC) and consequently inhibiting WCC activity. Here we show that protein phosphatase 4 is a novel component of the Neurospora clock by regulating both processes of the circadian negative feedback loop. The disruption of pp4 results in short period rhythms with low amplitude. In addition to its role in regulating FRQ phosphorylation and stability, PP4 also dephosphorylates and activates WCC. In contrast to PP2A, another phosphatase that activates WCC, PP4 has a major function in promoting nuclear entry of WCC. PKA, a WC kinase, inhibits WC nuclear localization. Furthermore, the FRQ-dependent WC phosphorylation promotes WCC cytosolic localization. Together, these results revealed WCC nucleocytoplasmic shuttling as an important step in the circadian negative feedback process and delineated the FRQ-dependent WCC inhibition as a two-step process: the inhibition of WCC DNA-binding activity followed by sequestration of WCC into the cytoplasm.
authors.affiliation: Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA.
authors.forename: Joonseok
authors.initials: J
authors.lastname: Cha
authors.forename: Shwu-Shin
authors.initials: SS
authors.lastname: Chang
authors.forename: Guocun
authors.initials: G
authors.lastname: Huang
authors.forename: Ping
authors.initials: P
authors.lastname: Cheng
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
mesh_terms: D002467:Cell Nucleus / Q000737:chemistry; D003593:Cytoplasm; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D017353:Gene Deletion; D009492:Neurospora crassa / Q000235:genetics / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D014157:Transcription Factors; C103772:white collar 2 protein, Neurospora; D010749:Phosphoprotein Phosphatases; C080406:protein phosphatase 4