Cell adhesion via murine alpha4 human beta1 integrin chimera on transfected K562 cells to endothelial cells

To evaluate the property of binding activity of alpha4beta1 integrin in cell-cell interaction, we newly established a cell line, alpha4mK562, by transfecting cDNA of murine integrin alpha4 subunit into human erythroleukemic K562 cells. alpha4mK562 transfectant expressed both murine alpha4 and human beta1 subunit, which generated a functional heterodimer. alpha4mK562 cells more efficiently bound to murine endothelial cell lines and recombinant human TNFalpha (rhTNF)-treated human umbilical vein endothelial cells (HUVEC) than the parental K562 cells. These adhesion resulted from the interaction between alpha4beta1 and VCAM-1. Interestingly, treatment with mAb against human beta1 (4B4 clone), which has been known as inhibitory mAb, enhanced binding of alpha4mK562 cells to rhTNF-treated HUVEC but not to murine endothelial cells. This increase in binding induced by 4B4 mAb was completely inhibited by another mAb against human beta1 (mAb13), but only partially by anti-alpha4 mAb (PSsolidus2). The increase in binding induced by 4B4 mAb was also abolished by metabolic inhibitors, indicating that the increased binding is energy dependent. These observations suggest that the binding of 4B4 mAb to the chimeric alpha4beta1 induces an unique outside-in signaling and enhances the specific binding of alpha4mK562 cells to rhTNF-treated HUVEC.