title: Cytoskeletal protein ABP-280 directs the intracellular trafficking of furin and modulates proprotein processing in the endocytic pathway.
abstract: Furin catalyzes the proteolytic maturation of many proproteins within the trans-Golgi network (TGN)/endosomal system. Furin's cytosolic domain (cd) directs both the compartmentalization to and transit between its manifold processing compartments (i.e., TGN/biosynthetic pathway, cell surface, and endosomes). Here we report the identification of the first furin cd sorting protein, ABP-280 (nonmuscle filamin), an actin gelation protein. The furin cd was used as bait in a yeast two-hybrid screen to identify ABP-280 as a furin-binding protein. Binding analyses in vitro and coimmunoprecipitation studies in vivo showed that furin and ABP-280 interact directly and that ABP-280 tethers furin molecules to the cell surface. Quantitative analysis of both ABP-280-deficient and genetically replete cells showed that ABP-280 modulates the rate of internalization of furin but not of the transferrin receptor, a cycling receptor. However, although ABP-280 directs the rate of furin internalization, the efficiency of sorting of the endoprotease from the cell surface to early endosomes is independent of expression of ABP-280. By contrast, efficient sorting of furin from early endosomes to the TGN requires expression of ABP-280. In addition, ABP-280 is also required for the correct localization of late endosomes (dextran bead uptake) and lysosomes (LAMP-1 staining), demonstrating a pleiotropic role for this actin binding protein in the organization of cellular compartments and directing protein traffic. Finally, and consistent with the trafficking studies on furin, we showed that ABP-280 modulates the processing of furin substrates in the endocytic but not the biosynthetic pathways. The novel roles of ABP-280 and the cytoskeleton in the sorting of furin in the TGN/ endosomal system and the formation of proprotein processing compartments are discussed.
authors.affiliation: Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201, USA.
authors.forename: G
authors.initials: G
authors.lastname: Liu
authors.forename: L
authors.initials: L
authors.lastname: Thomas
authors.forename: R A
authors.initials: RA
authors.lastname: Warren
authors.forename: C A
authors.initials: CA
authors.lastname: Enns
authors.forename: C C
authors.initials: CC
authors.lastname: Cunningham
authors.forename: J H
authors.initials: JH
authors.lastname: Hartwig
authors.forename: G
authors.initials: G
authors.lastname: Thomas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D002451:Cell Compartmentation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D003285:Contractile Proteins / Q000378:metabolism*; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D064448:Filamins; D045683:Furin; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011990:Receptors, Transferrin / Q000378:metabolism; D013381:Subtilisins / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D003285:Contractile Proteins; D064448:Filamins; D008840:Microfilament Proteins; D011498:Protein Precursors; D011990:Receptors, Transferrin; D013381:Subtilisins; D045683:Furin