title: Fbx7 functions in the SCF complex regulating Cdk1-cyclin B-phosphorylated hepatoma up-regulated protein (HURP) proteolysis by a proline-rich region.
abstract: F-box proteins, components of SCF ubiquitin-ligase complexes, are believed to be responsible for substrate recognition and recruitment in SCF-mediated proteolysis. F-box proteins that have been identified to function in the SCF complexes to date mostly have substrate-binding motifs, such as WD repeats or leucine-rich repeats in their C termini. However, many F-box proteins lack recognizable substrate-binding modules; whether they can function in the SCF complexes remains unclear. We show here that Fbx7, an F-box protein without WD repeats and leucine-rich repeats, is required for the proteasome-mediated proteolysis of the hepatoma up-regulated protein (HURP). Depletion of Fbx7 by small interfering RNA leads to depression of HURP ubiquitination and accumulation of HURP abundance. In the SCF(Fbx7) complex, Fbx7 recruits HURP through its C-terminal proline-rich region in a Cdk1-cyclin B-phosphorylation dependent manner. Mutation of the multiple Cdk1-cyclin B phosphorylation sites on HURP or the proline-rich region of Fbx7 abolishes the association between Fbx7 and HURP. Thus, Fbx7 is a functional adaptor of the SCF complex with a proline-rich region as the substrate-binding module. In addition to Fbx7, data base analyses reveal two putative mammalian proline-rich region-containing F-box proteins, KIAA1783 and RIKEN cDNA 2410015K21. Taken together, these findings further expound the diverse substrate-recognition abilities of the SCF complexes.
authors.affiliation: Division of Molecular and Genomic Medicine, National Health Research Institutes, Taipei 115, Taiwan.
authors.forename: Jung-Mao
authors.initials: JM
authors.lastname: Hsu
authors.forename: Yuan-Chii G
authors.initials: YC
authors.lastname: Lee
authors.forename: Chang-Tze R
authors.initials: CT
authors.lastname: Yu
authors.forename: Chi-Ying F
authors.initials: CY
authors.lastname: Huang
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002453:Cell Cycle; D002460:Cell Line; D019926:Cyclin B / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D019992:Databases as Topic; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044783:F-Box Proteins / Q000378:metabolism / Q000502:physiology*; D005822:Genetic Vectors; D006801:Humans; D008856:Microscopy, Fluorescence; D008938:Mitosis; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism*; D015739:Nocodazole / Q000494:pharmacology; D010750:Phosphoproteins / Q000737:chemistry; D010766:Phosphorylation; D011233:Precipitin Tests; D011392:Proline / Q000737:chemistry; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D011995:Recombination, Genetic; D017386:Sequence Homology, Amino Acid; D019089:Stem Cell Factor / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature; D013997:Time Factors; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D019926:Cyclin B; C465041:DLGAP5 protein, human; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D044783:F-Box Proteins; C489149:FBXO7 protein, human; D009363:Neoplasm Proteins; D010750:Phosphoproteins; D011500:Protein Synthesis Inhibitors; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D019089:Stem Cell Factor; D025801:Ubiquitin; D003513:Cycloheximide; D011392:Proline; D016203:CDC2 Protein Kinase; D015739:Nocodazole