Tyrosine kinase-dependent assembly of actin plaques linking Fc epsilon R1 cross-linking to increased cell substrate adhesion in RBL-2H3 tumor mast cells.

RBL-2H3 rat tumor mast cells form monolayers on various surfaces without assembling specialized adhesion structures at the cell substrate interface. Incubation of RBL-2H3 cells with Ag that cross-link the high affinity IgE receptor, Fc epsilon R1, activates at least two receptor-associated protein tyrosine kinases, Syk and Lyn, and elicits secretion and F-actin assembly, membrane ruffling, and increased spreading and adhesion. Herein, we report that Fc epsilon R1 cross-linking also causes the assembly in cell monolayers of a network of F-actin-rich plaques that form footlike processes at contact sites between the plasma membrane and the underlying substratum. Sheets of F-actin-rich ventral plasma membrane-bearing actin plaques are left on the substrate when monolayers of activated cells are displaced by incubation with ZnCl2 followed by shearing in a stream of buffer; in contrast, most unstimulated cells are completely displaced or leave only fragile membrane fragments. These observations link actin plaque assembly to increased cell substrate adhesion. Actin plaques disassemble rapidly in the presence of monovalent hapten, indicating their dependence on continued Fc epsilon R1 cross-linking. They accumulate antibody to phosphotyrosine and disassemble rapidly in the presence of the protein tyrosine kinase inhibitor, piceatannol, indicating their additional dependence on tyrosine kinase activation. Structures resembling actin plaques form when RBL-2H3 cell monolayers are incubated with the protein tyrosine phosphatase inhibitor, vanadyl hydroperoxide, in the presence of PMA, which increases actin polymerization. It is likely that the tyrosine kinase-dependent assembly of actin plaques plays an important role in linking the activation of signaling receptors to adhesive responses in RBL-2H3 and other immune system cells.