A specific endoplasmic reticulum export signal drives transport of stem cell factor (Kitl) to the cell surface.
Stem cell factor, also known as Kit ligand (Kitl), belongs to the family of dimeric transmembrane growth factors. Efficient cell surface presentation of Kitl is essential for the migration, proliferation, and survival of melanocytes, germ cells, hemopoietic stem cells, and mastocytes. Here we demonstrate that intracellular transport of Kitl to the cell surface is driven by a motif in the cytoplasmic tail that acts independently of the previously described basolateral sorting signal. Transport of Kitl to the cell surface is controlled at the level of the endoplasmic reticulum (ER) and requires a C-terminal valine residue positioned at a distance of 19-36 amino acids from the border between the transmembrane and cytoplasmic domains. Deletion or substitution of the valine with other hydrophobic amino acids results in ER accumulation and reduced cell surface transport of Kitl at physiological expression levels. When these mutant proteins are overexpressed in the ER, they are transported by bulk flow to the cell surface albeit at lower efficiency. A fusion construct between Kitl and the green fluorescent protein-labeled extracellular domain of a temperature-sensitive mutant of vesicular stomatitis virus G protein revealed the valine-dependent recruitment into coat protein complex II-coated ER exit sites and vesicular ER to Golgi transport in living cells. Thus the C-terminal valine defines a specific ER export signal in Kitl. It is responsible for the capture of Kitl at coat protein complex II-coated ER exit sites, leading to subsequent cell surface transport under physiological conditions.
Department of Pathology and Immunology, Centre Medical Universitaire, 1 rue Michel Servet, 1211 Geneva 4, Switzerland.
Frédérique
F
Paulhe
Beat A
BA
Imhof
Bernhard
B
Wehrle-Haller
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001360:Avidin / Q000737:chemistry; D001692:Biological Transport; D019921:Biotinylation; D015153:Blotting, Western; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D049109:Cell Proliferation; D002470:Cell Survival; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000737:chemistry* / Q000378:metabolism; D005434:Flow Cytometry; D017353:Gene Deletion; D006026:Glycoside Hydrolases / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008544:Melanocytes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D014162:Transfection; D014633:Valine / Q000737:chemistry; D014759:Viral Envelope Proteins / Q000737:chemistry
C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D019089:Stem Cell Factor; D014759:Viral Envelope Proteins; D001360:Avidin; D049452:Green Fluorescent Proteins; D006026:Glycoside Hydrolases; D014633:Valine