title: MARCH-XI, a novel transmembrane ubiquitin ligase implicated in ubiquitin-dependent protein sorting in developing spermatids.
abstract: A mechanism by which ubiquitinated cargo proteins are sorted into multivesicular bodies (MVBs) from plasma and trans-Golgi network (TGN) membranes is well established in yeast and mammalian somatic cells. However, the ubiquitin-dependent sorting pathway has not been clearly defined in germ cells. In this study we identified a novel member of the transmembrane RING-finger family of proteins, termed membrane-associated RING-CH (MARCH)-XI, that is expressed predominantly in developing spermatids and weakly in brain and pituitary. MARCH-XI possesses an E3 ubiquitin ligase activity that targets CD4 for ubiquitination. Immunoelectron microscopy of rat round spermatids showed that MARCH-XI is localized to TGN-derived vesicles and MVBs. Fluorescence staining of rat round spermatids and immunoprecipitation of rat testis demonstrated that MARCH-XI forms complexes with the adaptor protein complex-1 and with fucose-containing glycoproteins including ubiquitinated forms. Furthermore, the C-terminal region of MARCH-XI mediates its interaction with mu1-adaptin and Veli through a tyrosine-based motif and a PDZ binding motif, respectively. Our data suggest that MARCH-XI acts as a ubiquitin ligase with a role in ubiquitin-mediated protein sorting in the TGN-MVB transport pathway, which may be involved in mammalian spermiogenesis.
authors.affiliation: Department of Biological Sciences, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Morokuma
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nakamura
authors.forename: Akira
authors.initials: A
authors.lastname: Kato
authors.forename: Michitaka
authors.initials: M
authors.lastname: Notoya
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Sakai
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Fukuda
authors.forename: Shohei
authors.initials: S
authors.lastname: Yamashina
authors.forename: Yukio
authors.initials: Y
authors.lastname: Hirata
authors.forename: Shigehisa
authors.initials: S
authors.lastname: Hirose
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D008297:Male; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D013087:Spermatids / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000502:physiology
chemical_list: D011994:Recombinant Proteins; D025801:Ubiquitin; C523315:Marchf11 protein, rat; D044767:Ubiquitin-Protein Ligases