title: The leucine-based motif DDQxxLI is recognized both for internalization and basolateral sorting of invariant chain in MDCK cells.
abstract: The major histocompatibility complex (MHC) class II-associated invariant chain (Ii) contains signals for transport to endocytic compartments where the class II molecules bind antigenic peptides for presentation to CD4+ T cells. Two leucine-based signals in the Ii cytoplasmic tail can be independently recognized for endosomal sorting of Ii, and we have recently shown that each signal is sufficient for basolateral sorting and internalization of Ii in polarized Madine Darby Canine Kidney (MDCK) II cells. The recognition motif for endosomal sorting is complex and consists of two critical leucine-like residues as well as surrounding amino acids. Here, we have analyzed the importance of residues surrounding the membrane-distal leucine-based signal in basolateral sorting and internalization of Ii in MDCK II cells. We find that the DDQxxLI motif is involved in both sorting events indicating the presence of similar signal recognition components both at the TGN and at the plasma membrane. The identical motif is required for endosomal localization and internalization of Ii also in simian COS cells and the human HeLa and M1 cells.
authors.affiliation: Department of Biology, University of Oslo, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Simonsen
authors.forename: B
authors.initials: B
authors.lastname: Bremnes
authors.forename: T W
authors.initials: TW
authors.lastname: Nordeng
authors.forename: O
authors.initials: O
authors.lastname: Bakke
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D016764:Cell Polarity; D004285:Dogs; D006367:HeLa Cells; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid; D007930:Leucine / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D012694:Serine / Q000378:metabolism
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D000949:Histocompatibility Antigens Class II; C045084:invariant chain; D012694:Serine; D007930:Leucine