Ganglioside GD3 is widely expressed in human malignant melanoma cell lines and tumors. Previously, we reported that GD3؉ cells show stronger tyrosine phosphorylation of focal adhesion kinase (FAK), p130Cas , and paxillin when treated with fetal calf serum than GD3؊ cells. In this study, we analyzed the changes in the signals mediated by the interaction between integrins and extracellular matrices (ECM) to clarify how GD3 enhances cell signals in the vicinity of the cell membrane. An adhesion assay with a real time cell electronic sensing system revealed that GD3؉ cells had stronger adhesion to all extracellular matrices examined. In particular, GD3؉ cells attached more strongly to collagen type I and type IV than controls. Correspondingly, they showed stronger tyrosine phosphorylation of FAK and paxillin during adhesion to collagen type I. In the floating pattern of detergent extracts, a high level of integrin ␤1 was found in glycolipid-enriched microdomain (GEM)/rafts in GD3؉ cells before adhesion, whereas a smaller amount of integrin ␤1 was detected in the GEM/rafts of controls. Some phosphorylated forms of FAK as well as total FAK were found in GEM/rafts during cell adhesion only in GD3؉ cells. Another signal consisting of integrin-linked kinase/Akt was also activated during adhesion more strongly in GD3؉ cells than in controls. In double stained GD3؉ cells, GD3 and integrin ␤1 colocalized at the focal adhesion with a punctate pattern. All these results suggested that integrins assembled and formed a cluster in GEM/rafts, leading to the enhanced signaling and malignant properties under GD3 expression.

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