The L1 adhesion molecule is a cellular ligand for VLA-5

Area of Science:

• Immunology
• Cell Biology
• Neuroscience

Background:

• The L1 adhesion molecule, part of the immunoglobulin superfamily, is found on neural and immune cells.
• L1 mediates homophilic cell binding in the nervous system.
• Integrins are key mediators of cell-cell and cell-extracellular matrix interactions.

Purpose of the Study:

• To investigate the potential interaction between the L1 adhesion molecule and integrins on leukocytes.
• To elucidate the role of L1 in leukocyte adhesion and aggregation.

Main Methods:

• Utilized cell aggregation assays with murine ESb-MP cells expressing L1 and VLA-5.
• Employed monoclonal antibodies (mAbs) against L1 and VLA-5 to block interactions.
• Performed heterotypic binding assays using mouse bone marrow cells and platelets.
• Used purified L1 coated on beads and RGD-containing peptides for binding studies.
• Demonstrated direct protein-protein interaction between L1 and VLA-5.

Main Results:

• VLA-5 (an RGD-specific fibronectin receptor) binds to murine L1.
• L1 and VLA-5 expression on ESb-MP cells enabled aggregation induced by anti-CD24 mAbs.
• Aggregation was inhibited by mAbs to L1, VLA-5, and an L1-derived RGD peptide.
• L1-dependent adhesion of bone marrow cells to platelets expressing VLA-5 was observed.
• Thymocytes and Nalm-6 cells expressing VLA-5 adhered to L1, enhanced by Mn(2+) ions and blocked by anti-VLA-5 mAbs.

Conclusions:

• A novel binding pathway exists where VLA-5 integrin binds to L1 on adjacent cells.
• L1-VLA-5 interaction is critical for leukocyte-platelet and leukocyte-leukocyte adhesion.
• L1's downregulation on lymphocytes suggests its role in activation-regulated cell-cell interactions.