The GPI-linked Ly-6 antigen E48 regulates expression levels of the FX enzyme and of E-selectin ligands on head and neck squamous carcinoma cells

By differential display we demonstrated that antibody-mediated ligation of the GPI-linked protein product of E48, a newly discovered human Ly-6 gene, upregulates the expression of the FX enzyme in 3 lines of head and neck squ amous carcinoma cells. FX is responsible for the last step in the synthesis of GDP-L-fucose, The up-regulation of FX was E48 ligand-specific. 22AWT he ad and neck squamous carcinoma cells expressing high levels of E48 expresse d significantly higher levels of FX than the E48 antisense transfected 22AW T cells (8-3 cells). The former cells also expressed higher levels of two m ajor fucosylated glycans (the selectin ligand, Sialyl Lewis a, and VIM-2) t han the E48 antisense transfectants, Conversely, transfection of cells from the 14CWT line expressing very low levels of E48 with E48 cDNA caused an u p-regulated expression of FX and of the two fucosylated glycans in the 14C- CMV16 transfectants, Moreover, the expression levels of Sialyl Lewis a was significantly up-regulated on HNSCC upon ligation of E48 by anti-E48 antibo dies. The functional significance of the E48-mediated up-regulation of Sial yl Lewis a was demonstrated in rolling experiments on E-selectin bearing su rfaces under physiological conditions of shear flow and on tumor necrosis f actor cu activated human umbilical venous endothelial cells. Only high E48/ FX/Sialyl Lewis a expressing 14C-CMV16 cells could roll on purified E-sele ctin or establish E-selectin dependent rolling on the activated human umbil ical venous endothelial cells. Low E48/FX/Sialyl Lewis a expressing 14CWT c ells did not roll. These results show that E48 controls the expression of t he FX enzyme and of certain fucosylated E-selectin ligands by HNSCC, E48 ma y thus function as a key regulator of the adhesiveness of these tumor cells to inflamed vessel walls expressing E-selectin.