title: Fas ligand is targeted to secretory lysosomes via a proline-rich domain in its cytoplasmic tail.
abstract: Fas ligand (FasL) induces apoptosis through its cell surface receptor Fas. T lymphocytes and natural killer cells sort newly synthesised FasL to secretory lysosomes but, in cell types with conventional lysosomes, FasL appears directly on the plasma membrane. Here, we define a proline-rich domain (PRD) in the cytoplasmic tail of FasL that is responsible for sorting FasL to secretory lysosomes. Deletion of this PRD results in cell surface expression of FasL in cells with secretory lysosomes. Positively charged residues flanking the PRD are crucial to the sorting motif and changing the charge of these residues causes mis-sorting to the plasma membrane. In cells with conventional lysosomes, this motif is not recognised and FasL is expressed at the plasma membrane. The FasL PRD is not required for endocytosis in any cell type, as deletion mutants lacking this motif are endocytosed efficiently to the lysosomal compartment. Endogenous FasL cannot internalise extracellular antibody, demonstrating that FasL does not transit the plasma membrane en route to the secretory lysosomes. We propose that an interaction of the PRD of FasL with an SH3-domain-containing protein, enables direct sorting of FasL from the Golgi to secretory lysosomes.
authors.affiliation: Sir William Dunn School of Pathology, Oxford University, South Parks Rd, Oxford, OX1 3RE, UK.
authors.forename: E J
authors.initials: EJ
authors.lastname: Blott
authors.forename: G
authors.initials: G
authors.lastname: Bossi
authors.forename: R
authors.initials: R
authors.lastname: Clark
authors.forename: M
authors.initials: M
authors.lastname: Zvelebil
authors.forename: G M
authors.initials: GM
authors.lastname: Griffiths
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis; D053222:Fas Ligand Protein; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000502:physiology; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D011392:Proline; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D018909:src Homology Domains
chemical_list: C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D011392:Proline