title: Hrs recognizes a hydrophobic amino acid cluster in cytokine receptors during ubiquitin-independent endosomal sorting.
abstract: Hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) is a component of the ESCRT-0 protein complex that captures ubiquitylated cargo proteins and sorts them to the lysosomal pathway. Although Hrs acts as a key transporter for ubiquitin-dependent endosomal sorting, we previously reported that Hrs is also involved in ubiquitin-independent endosomal sorting of interleukin-2 receptor β (IL-2Rβ). Here, we show direct interactions between bacterially expressed Hrs and interleukin-4 receptor α (IL-4Rα), indicating that their binding is not required for ubiquitylation of the receptors, similar to the case for IL-2Rβ. Examinations of the Hrs binding regions of the receptors reveal that a hydrophobic amino acid cluster in both IL-2Rβ and IL-4Rα is essential for the binding. Whereas the wild-type receptors are delivered to LAMP1-positive late endosomes, mutant receptors lacking the hydrophobic amino acid cluster are sorted to lysobisphosphatidic acid-positive late endosomes rather than LAMP1-positive late endosomes. We also show that the degradation of these mutant receptors is attenuated. Accordingly, Hrs functions during ubiquitin-independent endosomal sorting of the receptors by recognizing the hydrophobic amino acid cluster. These findings suggest the existence of a group of cargo proteins that have this hydrophobic amino acid cluster as a ubiquitin-independent sorting signal.
authors.affiliation: Department of Microbiology and Immunology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Amano
authors.forename: Yuki
authors.initials: Y
authors.lastname: Yamashita
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kojima
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Yoshino
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Tanaka
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sugamura
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Takeshita
mesh_terms: D021542:Amino Acids, Neutral / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D018121:Receptors, Cytokine / Q000378:metabolism*; D019948:Receptors, Interleukin-4 / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D021542:Amino Acids, Neutral; D056827:Endosomal Sorting Complexes Required for Transport; D010750:Phosphoproteins; D018121:Receptors, Cytokine; D019948:Receptors, Interleukin-4; D025801:Ubiquitin; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate