title: Suprachiasmatic nucleus circadian oscillatory protein, a novel binding partner of K-Ras in the membrane rafts, negatively regulates MAPK pathway.
abstract: Suprachiasmatic nucleus circadian oscillatory protein (SCOP) is a member of the leucine-rich repeat (LRR)-containing protein family. In addition to circadian expression in the rat hypothalamic suprachiasmatic nucleus, SCOP is constitutively expressed in neurons throughout the rat brain. Here we found that a substantial amount of SCOP was localized in the brain membrane rafts, in which only K-Ras was abundant among Ras isoforms. SCOP interacted directly through its LRR domain with a subset of K-Ras in the guanine nucleotide-free form that was present in the raft fraction. This interaction interfered with the binding of added guanine nucleotide to K-Ras in vitro. A negative regulatory role of SCOP for K-Ras function was examined in PC12 cell lines stably overexpressing SCOP or its deletion mutants. Overexpression of full-length SCOP markedly down-regulated ERK1/ERK2 activation induced by depolarization or phorbol ester stimulation, and this inhibitory effect of overexpressed SCOP was dependent on its LRR domain. These results strongly suggest that SCOP negatively regulates K-Ras signaling in the membrane rafts, identifying a novel mechanism for regulation of the Ras-MAPK pathway.
authors.affiliation: Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Kimiko
authors.initials: K
authors.lastname: Shimizu
authors.forename: Masato
authors.initials: M
authors.lastname: Okada
authors.forename: Katsuya
authors.initials: K
authors.lastname: Nagai
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Fukada
mesh_terms: D000818:Animals; D015536:Down-Regulation; D006160:Guanosine Triphosphate / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008297:Male; D021962:Membrane Microdomains / Q000737:chemistry*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D016716:PC12 Cells; D010749:Phosphoprotein Phosphatases; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D009687:Nuclear Proteins; D006160:Guanosine Triphosphate; D020928:Mitogen-Activated Protein Kinases; C553451:PHLPP1 protein, rat; D010749:Phosphoprotein Phosphatases; D018631:ras Proteins