Forces required to initiate membrane tether extrusion from cell surface depend on cell type but not on the surface molecule.

When a cell adhered to another cell or substratum via surface proteins is forced to detach, lipid membrane tethers are often extruded from the cell surface before the protein bond dissociates. For example, during the inflammatory reaction leukocytes roll on the surface of activated endothelial cells. The rolling adhesion is mediated by interactions of selectins with their ligands, e.g., P-selectin glycoprotein ligand (PSGL)-1, which extrudes membrane tethers from the surfaces of both leukocytes and endothelial cells. Membrane tether extrusion has been suggested to regulate leukocyte rolling. Here we examine several factors that may affect forces required to initiate membrane tethers, or initial tether force. It was found that initial tether forces were similar regardless of the presence or absence of the cytoplasmic tail of P-selectin and regardless of whether the tethers were extruded via binding to PSGL-1 or Fcy receptors. Initial tether forces were found to depend on the cell types tested and were greatly reduced by treatment of latrunculin A, which inhibits actin polymerization. These data provide additional insights to the control of membrane tether extrusion, which should be taken into account when cellular functions such as rolling where tether extrusion plays a regulatory role are compared using different cell types expressing the same molecule.