title: The tumour-associated antigen L6 (L6-Ag) is recruited to the tetraspanin-enriched microdomains: implication for tumour cell motility.
abstract: Tumour-associated antigen L6 (L6-Ag, also known as TM4SF1) regulates tumour cell motility and invasiveness. We found that L6-Ag is abundant on the plasma membrane and on intracellular vesicles, on which it is co-localised with the markers for late endosomal/lysosomal compartments, including Lamp1/Lamp2 proteins and LBPA. Antibody internalisation and live-imaging experiments suggested that L6-Ag is targeted to late endocytic organelles (LEO) predominantly via a biosynthetic pathway. Mapping experiments showed that the presence of transmembrane regions is sufficient for directing L6-Ag to LEO. On the plasma membrane, L6-Ag is associated with tetraspanin-enriched microdomains (TERM). All three predicted cytoplasmic regions of L6-Ag are crucial for the effective recruitment of the protein to TERM. Recruitment to TERM correlated with the pro-migratory activity of L6-Ag. Depletion of L6-Ag with siRNA has a selective effect on the surface expression of tetraspanins CD63 and CD82. By contrast, the expression levels of other tetraspanins and beta1 integrins was not affected. We found that L6-Ag is ubiquitylated and that ubiquitylation is essential for its function in cell migration. These data suggest that L6-Ag influences cell motility via TERM by regulating the surface presentation and endocytosis of some of their components.
authors.affiliation: Cancer Research UK Institute for Cancer Studies, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
authors.forename: Tamara
authors.initials: T
authors.lastname: Lekishvili
authors.forename: Elisa
authors.initials: E
authors.lastname: Fromm
authors.forename: Michelle
authors.initials: M
authors.lastname: Mujoomdar
authors.forename: Fedor
authors.initials: F
authors.lastname: Berditchevski
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002448:Cell Adhesion / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D002522:Chlorocebus aethiops; D015536:Down-Regulation / Q000235:genetics; D004705:Endocytosis / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D051861:Kangai-1 Protein / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism*; D009361:Neoplasm Invasiveness / Q000503:physiopathology*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D034741:RNA, Small Interfering / Q000378:metabolism; D060149:Tetraspanin 30; D022161:Transport Vesicles / Q000378:metabolism; D054875:Ubiquitination / Q000502:physiology
chemical_list: D015703:Antigens, CD; D000954:Antigens, Surface; C554586:CD63 protein, human; C497688:CD82 protein, human; D051861:Kangai-1 Protein; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D010980:Platelet Membrane Glycoproteins; D034741:RNA, Small Interfering; D060149:Tetraspanin 30; C074075:TM4SF1 protein, human