title: Versatile function of the circadian protein CIPC as a regulator of Erk activation.
abstract: The CLOCK-interacting protein, Circadian (CIPC), has been identified as an additional negative-feedback regulator of the circadian clock. However, recent study on CIPC knockout mice has shown that CIPC is not critically required for basic circadian clock function, suggesting other unknown biological roles for CIPC. In this study, we focused on the cell cycle dependent nuclear-cytoplasmic shuttling function of CIPC and on identifying its binding proteins. Lys186 and 187 were identified as the essential amino acid residues within the nuclear localization signal (NLS) of CIPC. We identified CIPC-binding proteins such as the multifunctional enzyme CAD protein (carbamoyl-phosphate synthetase 2, aspartate transcarbamoylase, and dihydroorotase), which is a key enzyme for de novo pyrimidine synthesis. Compared to control cells, HEK293 cells overexpressing wild-type CIPC showed suppressed cell proliferation and retardation of cell cycle. We also found that PMA-induced Erk activation was inhibited with expression of wild-type CIPC. In contrast, the NLS mutant of CIPC, which reduced the ability of CIPC to translocate into the nucleus, did not exhibit these biological effects. Since CAD and Erk have significant roles in cell proliferation and cell cycle, CIPC may work as a cell cycle regulator by interacting with these binding proteins.
authors.affiliation: Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima 727-0023, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Matsunaga
authors.affiliation: Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima 727-0023, Japan.
authors.forename: Tasuku
authors.initials: T
authors.lastname: Nishino
authors.affiliation: Department of Molecular Endocrinology, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yokoyama
authors.affiliation: Biosignal Research Center, Kobe University, Kobe 657-8501, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Nakashima
authors.affiliation: Biosignal Research Center, Kobe University, Kobe 657-8501, Japan.
authors.forename: Ushio
authors.initials: U
authors.lastname: Kikkawa
authors.affiliation: Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima 727-0023, Japan. Electronic address: hkonishi@pu-hiroshima.ac.jp.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Konishi
mesh_terms: D000818:Animals; D001221:Aspartate Carbamoyltransferase / Q000378:metabolism*; D019556:COS Cells; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002522:Chlorocebus aethiops; D002940:Circadian Rhythm / Q000502:physiology*; D004080:Dihydroorotase / Q000378:metabolism*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D025461:Feedback, Physiological / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans
chemical_list: C033626:CAD trifunctional enzyme; C518934:CIPC protein, mouse; D002352:Carrier Proteins; D001221:Aspartate Carbamoyltransferase; D048049:Extracellular Signal-Regulated MAP Kinases; D004080:Dihydroorotase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)
keywords: CAD; Cell cycle; Erk; Erk-D domain; Nuclear localization