title: Dimerization of Kit-ligand and efficient cell-surface presentation requires a conserved Ser-Gly-Gly-Tyr motif in its transmembrane domain.
abstract: Kit-ligand (Kitl), also known as stem cell factor, is a membrane-anchored, noncovalently bound dimer signaling via the c-kit receptor tyrosine kinase, required for migration, survival, and proliferation of hematopoietic stem and germ cells, melanocytes, and mastocytes. Despite its fundamental role in morphogenesis and stem cell biology, the mechanisms that regulate Kitl dimerization are not well understood. By employing cell-permeable cross-linker and quantitative bimolecular fluorescence complementation of wild-type and truncated forms of Kitl, we determined that Kitl dimerization is initiated in the endoplasmic reticulum and mediated to similar levels by the transmembrane and the extracellular growth factor domain. Further biochemical and mutational analysis revealed a conserved Ser-Gly-Gly-Tyr-containing motif that is required for transmembrane domain dimerization and efficient cell-surface expression of Kitl. A novel intracellular capture assay with the Kitl transmembrane domain as bait revealed specific interactions with Kitl, but not with unrelated transmembrane proteins. During evolution, the transmembrane dimerization motif appeared in Kitl at the transition from teleosts to tetrapods, which correlates with the emergence of Kitl as a supporter of stem cell populations. Thus, transmembrane-mediated association of membrane-anchored growth factors consists of a novel mechanism to improve paracrine signaling and morphogenesis.
authors.affiliation: Department of Cellular Physiology and Metabolism, Centre Médical Universitaire, University of Geneva, Geneva, Switzerland.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Paulhe
authors.forename: Monique
authors.initials: M
authors.lastname: Wehrle-Haller
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Jacquier
authors.forename: Beat A
authors.initials: BA
authors.lastname: Imhof
authors.forename: Séverine
authors.initials: S
authors.lastname: Tabone-Eglinger
authors.forename: Bernhard
authors.initials: B
authors.lastname: Wehrle-Haller
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D004285:Dogs; D008565:Membrane Proteins / Q000737:chemistry; D051379:Mice; D055503:Protein Multimerization; D019089:Stem Cell Factor / Q000737:chemistry*
chemical_list: D008565:Membrane Proteins; D019089:Stem Cell Factor