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First published online 12 February 2008
doi: 10.1242/jcs.020347

Journal of Cell Science 121, 685-694 (2008)
Published by The Company of Biologists 2008
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Research Article

The tumour-associated antigen L6 (L6-Ag) is recruited to the tetraspanin-enriched microdomains: implication for tumour cell motility

Tamara Lekishvili, Elisa Fromm, Michelle Mujoomdar and Fedor Berditchevski*

Cancer Research UK Institute for Cancer Studies, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

* Author for correspondence (e-mail: f.berditchevski{at}bham.ac.uk)

Accepted 21 November 2007

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 β1 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.

Key words: L6 antigen, Tetraspan, Late endosomes, Migration, Tetraspanin






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