Integrins are responsible for anchoring cells to the extracellular matrix and also can initiate intracellular signal pathways. The interaction between integrins and the extracellular matrix results in activation of PKC, PTKs, p21Ras, MAPK and PI3-kinase. The a4b1 integrins are expressed mainly on haematopoietic cells and also appear on several tumour types. The adhesion of a4b1 to VCAM-1 is an essential step for lymphocyte extravasation during the inflammatory response. Furthermore, the interaction of a4b1, expressed on tumour cells, with VCAM-1, might have a role in tumour cell extravasation. We examined the role of PI3-kinase activation in a4b1-mediated melanoma cell adhesion and migration. Inhibition of PI3-kinase did not have any effect on cell adhesion. However, the migration of HMB2-a4 and DX3 cells on fibronectin, but not VUP-a4, was inhibited by PI3-kinase inhibitor. avb3-mediated migration in VUP cells which had been transfected with b3 cDNA to create expression of the avb3, did not involve PI3-kinase activity, suggesting that this was not the case. On the other hand, VUP-a4 cells were found not to express p110a, a specific form of PI3-kinase, which may be involved in melanoma migration, whereas the HMB2-a4 cells expressed this isoform.

Integrins are responsible for anchoring cells to the extracellular matrix and also can initiate intracellular signal pathways. The interaction between integrins and the extracellular matrix results in activation of PKC, PTKs, p21Ras, MAPK and PI3-kinase. The a4b1 integrins are expressed mainly on haematopoietic cells and also appear on several tumour types. The adhesion of a4b1 to VCAM-1 is an essential step for lymphocyte extravasation during the inflammatory response. Furthermore, the interaction of a4b1, expressed on tumour cells, with VCAM-1, might have a role in tumour cell extravasation. We examined the role of PI3-kinase activation in a4b1-mediated melanoma cell adhesion and migration. Inhibition of PI3-kinase did not have any effect on cell adhesion. However, the migration of HMB2-a4 and DX3 cells on fibronectin, but not VUP-a4, was inhibited by PI3-kinase inhibitor. avb3-mediated migration in VUP cells which had been transfected with b3 cDNA to create expression of the avb3, did not involve PI3-kinase activity, suggesting that this was not the case. On the other hand, VUP-a4 cells were found not to express p110a, a specific form of PI3-kinase, which may be involved in melanoma migration, whereas the HMB2-a4 cells expressed this isoform.