The L1 Adhesion Molecule Supports αvβ3-Mediated Migration of Human Tumor Cells and Activated T Lymphocytes

The L1 adhesion molecule is a member of the immunoglobulin superfamily which is expressed by neural and hematopoietic cells. L1 is primarily a cell surface molecule but in its released form it becomes embedded in the extracellular matrix. In addition to the established L1-L1 homotypic interaction, L1 can bind to αvβ3 in the human. The 6th Ig-like domain is critical for this function. We now demonstrate that a fusion protein containing the 6th Ig-like domain of L1 (6.L1-Fc) can support the migration of human MED-B1 (αvβ3+) but not of Nalm-6 cells (α5β1+). The migration was blocked in the presence of a mab to αvβ3 and was not seen on a 6.L1-Fc in which the RGD site was mutated. Activation of human T lymphocytes in the presence of PHA and PMA led to the induction of αvβ3 and αvβ5 expression and concomitantly induced migration of the cells on 6.L1-Fc. The migration was blocked by mabs to αvβ3 but not to αvβ5. Our results suggest that L1 exposed at the cell surface or as a matrix constituent can serve as a potent substrate for αvβ3 mediated cell migration.