A di-leucine motif mediates endocytosis and basolateral sorting of macrophage IgG Fc receptors in MDCK cells.
An important function of the low affinity IgG Fc receptor FcRII-B2 (FcR) on macrophages is the internalization of soluble antigen-antibody complexes for lysosomal degradation. Most endocytic receptors possess tyrosine-containing cytoplasmic determinants required for endocytosis. In many proteins, signals which overlap with the endocytosis determinant and share the same critical tyrosine residue also mediate basolateral sorting in the trans-Golgi network of epithelial cells. Despite the presence of two tyrosine residues in the FcR cytosolic domain, neither one is absolutely required for coated pit localization or basolateral targeting. Nevertheless, a short domain of 13 residues containing one of the non-critical tyrosine residues mediates endocytosis and basolateral delivery. Alanine scan mutagenesis of this region now revealed a critical role of a leucine-leucine motif in both events. These findings suggest that endocytosis and basolateral sorting can be mediated by both tyrosine- and di-leucine-based signals and confirm the close relationship between the two determinants already observed for 'classical' tyrosine-dependent motifs.
Institute of Biochemistry, University of Lausanne, Epalinges, Switzerland.
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Hunziker
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Fumey
D000595:Amino Acid Sequence; D000936:Antigen-Antibody Complex / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D006056:Golgi Apparatus / Q000378:metabolism; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D007074:Immunoglobulin G / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000502:physiology*; D008264:Macrophages / Q000166:cytology / Q000502:physiology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017452:Receptors, IgG / Q000235:genetics / Q000502:physiology*
D000936:Antigen-Antibody Complex; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D017452:Receptors, IgG; D007930:Leucine