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Regulation of ubiquitinated protein sorting at multivesicular endosomes
Author(s) -
Piper Robert Charles,
Ren Jihui,
Pashkova Natasha,
Winistorfer Stanley
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.628.3
Subject(s) - endosome , ubiquitin , microbiology and biotechnology , signal transducing adaptor protein , escrt , vacuolar protein sorting , tsg101 , deubiquitinating enzyme , lysosome , nedd4 , ubiquitin ligase , biology , chemistry , biochemistry , signal transduction , gene , microrna , microvesicles , intracellular , enzyme
Ubiquitinated membrane proteins are transported into the interior of the lysosome for degradation. This sorting pathway involves incorporation of cargo proteins into endosomal intralumenal vesicles, which accumulate to form a multivesicular endosome/body (MVB). The apparatus that recognizes ubiquitinated membrane cargo proteins in yeast includes Vps27 and Hse1, which are orthologous to Hrs and STAM in animal cells. We find that the Vps27‐Hse1 ubiquitin‐sorting complex associates with a variety of factors that help regulate the fate of ubiquitinated cargo. Recently, we discovered that Ufd3/Doa1 directly binds the SH3 domain of Hse1. Doa1 associates with the AAA ATPase Cdc48, which is involved in processing a number of ubiquitinated substrates. We find that Doa1 possesses 3 distinct ubiquitin binding domains, and a novel SH3 ligand motif required for Hse1 binding. We also found that Doa1 can partially localize to endosomes. Unlike doa1 null mutants, Doa1 mutants lacking the SH3 binding motif for Hse1 have normal levels of ubiquitin and display no growth defects; however, these Doa1 mutants are defective in sorting particular MVB cargo proteins. We also find that the novel Cdc48 cofactor Ubx3 also plays a role at the endosome similar to Doa1 and that ubx3 null mutants are defective in aspects of MVB sorting. These results point to a novel role for a Cdc48‐Doa1‐Ubx3 complex on endosomes that may foster proper processing of ubiquitinated MVB cargo.