Activation status and function of the VLA-4 (α4β1) integrin expressed on human melanoma cell lines

We have examined the functional status of the VLA-4/alpha4beta1 integrin in a panel of human melanoma cell lines, focusing on the ability of cells expressing alpha4beta1 to mediate adhesion to the alpha4-specific ligands CS-1 peptide and VCAM-1. All melanoma cells expressing alpha4pbeta1 (8 of 10 lines examined) were capable of adhering to these specific ligands in adhesion assays, whereas 2 cell lines (HMB2 and VUP) which lacked surface alpha4 were unable to do so. Adherence of different melanoma cell lines to VCAM-1 was relatively uniform and not susceptible to upregulation with known integrin-activating factors, such as manganese ions, phorbol ester and activating monoclonal antibody (mAb) TS2/16. Cell adhesion to CS-1 peptide, however, varied according to cell surface receptor density and, in some cases, could be up-regulated by integrin-activating factors. Adhesion of SK23 cells to CS-1 peptide was increased by all 3 activating stimuli, whereas for all other melanoma cells an increase was obtained only by the use of TS2/16 mAb. Our data indicate not only an unusually low activation state of alpha4beta1 in SK23 cells but also heterogeneity in the activating capacity of the various stimuli. Moreover, a protein kinase C-dependent role in alpha4beta1 activity was suggested by adhesion assays carried out in the presence of the protein kinase C inhibitor calphostin C, which considerably reduced adhesion to CS-1 peptide.