Post‐receptor occupancy events in leukocytes during β1 integrin‐ligand interactions

Abstract

Leukocyte adhesion to and subsequent spreading on the endothelium are the initial steps in the migration of these cells to the surrounding tissues. We have investigated the participation of different VLA heterodimers in cell spreading by using the anti-beta 1 TS2/16 monoclonal antibody (mAb) which induces a conformational change of different VLA integrin receptors, enabling a high-affinity interaction with their ligands. Both VLA-4 and VLA-5 fibronectin (FN), as well as VLA-2 collagen (COL) receptors mediated cell spreading and morphological changes. The spreading of U-937 and alpha 4-transfected K-562 cells was induced in both FN and VCAM-1, suggesting that the morphological changes may be induced by cell-cell as well as cell-extracellular matrix (ECM) interactions. Furthermore, the beta 1-regulated cell spreading on VCAM-1 and COL took place independently of the VLA-5 FN receptor function. The enhancing effect on cell attachment induced by anti-beta 1 TS2/16 mAb was observed in the presence of different doses of cytochalasin D, whereas cell spreading was abolished. Signal transduction during beta 1-stimulated integrin-ligand interaction was also investigated. We have found the co-localization of beta 1 integrins and tyrosine-phosphorylated proteins during the spreading of U-937 and alpha 2- and alpha 4-transfected K-562 cells on both ECM (FN and COL) and cellular (VCAM-1) ligands. Kinetic studies showed that tyrosine phosphorylation was almost coincident with cellular spreading. The tyrosine phosphorylation of polypeptides of 130 kDa and 77 kDa was triggered in U-937 cells by the interaction of FN with the VLA-5 receptor in a high-affinity conformation. However, no signaling was observed by inducing the high-affinity state of receptor in the absence of appropriate ligand. These data suggest that tyrosine kinase activation is a post-receptor occupancy event that might be critical in regulating the adhesive properties of integrins.

CD44/chondroitin sulfate proteoglycan and alpha 2 beta 1 integrin mediate human melanoma cell migration on type IV collagen and invasion of basement membranes.

“…Such mechanisms could include interactions between the ectodomain of the integrin and CD44/CSPG, whereby both receptors may influence either ligand binding and/or clustering shown to be important for signal generation by both types of receptors (Miyamoto et al, 1995;Perschl et al, 1995). Alternatively, such mechanisms may also involve signaling through changes in the cytoskeleton or other signaling pathways that have been shown to be modified by CD44 (Jacobson et al, 1984;Tarone et al, 1984;Lacy and Underhill, 1987;Carter and Wayner, 1988;Kalomiris and Bourguignon, 1988;Geppert and Lipsky, 1991;Bourguignon et al, 1992) or a2f31 integrin (Kapron-Bras et al, 1993;Leavesley et al, 1993;Sanchez-Mateos et al, 1993).…”

Coordinated expression of the vitronectin receptor and the urokinase-type plasminogen activator receptor in metastatic melanoma cells.

“…integrins such as av,/5 and av/3 cannot be entirely ruled out. It should be noted however, that FACS® analyses with mAb IA9 to subunit /5 (36) Antibody-or ligand-mediated cross-linking of integrins has been shown to trigger signal transduction mechanisms leading to protein tyrosine phosphorylation (37), changes in calcium influx (38), gene transcription (39), and altered cell growth.…”

Integrin alpha v beta 3 differentially regulates adhesive and phagocytic functions of the fibronectin receptor alpha 5 beta 1.

“…8). Incubation of K562 with "activating" mAb which recognized the integrin 131 chain (4,5,54) induced efficient Fn-mediated phagocytosis in both control and C~v/33-expressing K562 in the absence of Mn ++ (Fig. 8 A).…”