|
||


§
* Vollum Institute and 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.
Department of Cell and Developmental Biology, Oregon Health Sciences University, Portland, Oregon
97201; and § Division of Experimental Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston,
Massachusetts 02115
This article has been cited by other articles:
|
|