INTEGRIN VLA-2 (ALPHA(2)BETA(1)) FUNCTION IN POSTEXTRAVASATION MOVEMENT OF HUMAN RHABDOMYOSARCOMA RD CELLS IN THE LIVER

It is now known that members of the selectin and integrin families are critical in the initial interaction of cells in circulation with endo thelial surfaces. Also, platelet/endothelial cell adhesion molecule-1 has been shown to be involved in transendothelial migration of extrava sating cells. Little is known about adhesion molecules involved in sub sequent postex-travasation events. In this study, the significance of VLA-2 (alpha(2) beta(1)) integrin in the movement of human rhabdomyosa rcoma RD cells in the liver was characterized by in vivo videomicrosco py. Results show that after extravasation, the mock-transfected RDpF c ells were able to migrate to the subcapsular region of the liver. Alth ough the RDX2C2 transfectant expressing VLA-2 integrin extravasated eq ually well, a majority of RDX2C2 cells remained in close proximity to blood vessels and failed to reach the subcapsular region. The function al involvement of VLA-2 in affecting the ability of RD cells to reach the subcapsular region was verified by the preparation of an RD transf ectant [RDX2C2(I-)] expressing a nonfunctional variant of VLA-2 lackin g the inserted (I)-domain of alpha 2 subunit. In vivo microscopy showe d that RDX2C2(I-) cells migrated in a maimer similar to control RDpF c ells. To demonstrate that RDX2C2 cells that remained in close proximit y to blood vessels were due to VLA-2 function, a blocking monoclonal a ntibody against VLA-2 (BHA2.1) was prepared. Mice were injected with B HA2.1 or control monoclonal antibody P3 at the time when RDX2C2 cells completed their extravasation. Treatment with BHA2.1 increased the num ber of RDX2C2 cells that reached the subcapsular region and subsequent ly formed tumor foci. Therefore, VLA-2 integrin expression has major r oles in postextravasation movement and affects tumor foci formation at the liver surface.