title: Stem cell factor presentation to c-Kit. Identification of a basolateral targeting domain.
abstract: Stem cell factor (also known as mast cell growth factor and kit-ligand) is a transmembrane growth factor with a highly conserved cytoplasmic domain. Basolateral membrane expression in epithelia and persistent cell surface exposure of stem cell factor are required for complete biological activity in pigmentation, fertility, learning, and hematopoiesis. Here we show by site-directed mutagenesis that the cytoplasmic domain of stem cell factor contains a monomeric leucine-dependent basolateral targeting signal. N-terminal to this motif, a cluster of acidic amino acids serves to increase the efficiency of basolateral sorting mediated by the leucine residue. Hence, basolateral targeting of stem cell factor requires a mono-leucine determinant assisted by a cluster of acidic amino acids. This mono-leucine determinant is functionally conserved in colony-stimulating factor-1, a transmembrane growth factor related to stem cell factor. Furthermore, this leucine motif is not capable of inducing endocytosis, allowing for persistent cell surface expression of stem cell factor. In contrast, the mutated cytoplasmic tail found in the stem cell factor mutant Mgf(Sl17H) induces constitutive endocytosis by a motif that is related to signals for endocytosis and lysosomal targeting. Our findings therefore present mono-leucines as a novel type of protein sorting motif for transmembrane growth factors.
authors.affiliation: Department of Pathology, Centre Medical Universitaire, 1 Rue Michel-Servet, 1211 Geneva 4, Switzerland. Bernhard.Wehrle-Haller@medecine.unige.ch
authors.forename: B
authors.initials: B
authors.lastname: Wehrle-Haller
authors.forename: B A
authors.initials: BA
authors.lastname: Imhof
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002645:Chickens; D016384:Consensus Sequence; D004285:Dogs; D004705:Endocytosis; D049452:Green Fluorescent Proteins; D007930:Leucine; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics; D008247:Lysosomes / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection; D014562:Caudata
chemical_list: D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D019089:Stem Cell Factor; D049452:Green Fluorescent Proteins; D019009:Proto-Oncogene Proteins c-kit; D007930:Leucine