Glycosphingolipids (GSLs) at the cell surface membrane are associated or complexed with signal transducers (Src family kinases and small G-proteins), tetraspanins, growth factor receptors, and integrins. Such organizational framework, defining GSL-modulated or -dependent cell adhesion, motility, and growth, is termed "glycosynapse" (Hakomori, S., and Handa, K.

Ganglioside GM2 complexed with tetraspanin CD82 in glycosynaptic microdomain of HCV29 and other epithelial cells inhibits hepatocyte growth factor-induced cMet tyrosine kinase. In addition, adhesion of HCV29 cells to extracellular matrix proteins also activates cMet kinase through ''cross-talk '' of integrins with cMet, leading to inhibition of cell motility and growth. Present studies indicate that cell motility and growth are greatly influenced by expression of GM2, GM3, or GM2/GM3 complexes, which affect cMet kinase activity of various types of cells, based on the following series of observations: (i) Cells expressing CD82, cultured with GM2 and GM3 cocoated on silica nanospheres, displayed stronger and more consistent motility inhibition than those cultured with GM2 or GM3 alone or with other glycosphingolipids. (ii) GM2-GM3, in the presence of Ca 2؉ form a heterodimer, as evidenced by electrospray ionization (ESI) mass spectrometry and by specific reactivity with mAb 8E11, directed to GM2/GM3 dimer structure. (iii) Cells expressing cMet and CD82 were characterized by enhanced motility associated with HGF-induced cMet activation. Both cMet and motility were strongly inhibited by culturing cells with GM2/GM3 dimer coated on nanospheres. (iv) Adhesion of HCV29 or YTS-1/CD82 cells to laminin-5-coated plate activated cMet kinase in the absence of HGF, whereas GM2/GM3 dimer inhibited adhesioninduced cMet kinase activity and inhibited cell motility. (v) Inhibited cell motility as in i, iii, and iv was restored to normal level by addition of mAb 8E11, which blocks interaction of GM2/GM3 dimer with CD82. Signaling through Src and MAP kinases is activated or inhibited in close association with cMet kinase, in response to GM2/GM3 dimer interaction with CD82. Thus, a previously uncharacterized GM2/GM3 heterodimer complexed with CD82 inhibits cell motility through CD82-cMet or integrin-cMet pathway.glycosphingolipid ͉ growth factor receptor ͉ ldlD cells ͉ tyrosine kinase G lycosphingolipids (GSLs), including gangliosides, interact with specific membrane proteins, such as growth factor receptors, integrins, tetraspanins (TSPs), and nonreceptor cytoplasmic kinases (e.g., Src family kinases and small G proteins), to form glycosynaptic microdomains controlling GSL-dependent or -modulated cell adhesion, growth, and motility (for review, see refs. 1-3).Our previous studies indicate the following: (i) Ganglioside the GM3/TSP CD9 complex interacts with integrin ␣3␤1 or ␣5␤1 and inhibits motility of CD9-expressing tumor cells (4, 5). (ii) The GM3/CD9/CD81 complex inhibits tyrosine kinase associated with fibroblast growth factor receptor (FGFR) (6) and blocks functional interaction of integrins with FGFR (7). (iii) Enhancement of GM3 or CD9 level in bladder cancer cell line YTS-1 causes reversion to normal phenotype, whereby Src kinase activity is strongly inhibited (8).In contrast to these previous studies, focused on GM3-CD9 interaction that inhibits tumor cell motility, our recent studies (9) addressed the functional role of t...