Cell adherence to fibronectin and the aggregation of the high affinity immunoglobulin E receptor synergistically regulate tyrosine phosphorylation of 105-115-kDa proteins.

Adherence of cells to extracellular matrix components modulates cellular responses. Here we compared the array of tyrosine phosphorylated proteins induced by the aggregation of the high affinity receptor for IgE (Fc epsilon RI) in fibronectin-adherent and in nonadherent rat basophilic leukemia (RBL-2H3) cells. Adherence to fibronectin in the absence of Fc epsilon RI aggregation induced tyrosine phosphorylation of 105-115-kDa proteins. This phosphorylation was reversed by EDTA and by a synthetic peptide containing the sequence Arg-Gly-Asp, demonstrating a requirement for fibronectin-integrin interaction. Aggregation of Fc epsilon RI in fibronectin-adherent cells markedly enhanced the tyrosine phosphorylation of the same 105-115-kDa proteins. There were minimal differences in tyrosine phosphorylation of other proteins induced by the aggregation of Fc epsilon RI in nonadherent and in fibronectin-adherent cells. Direct activation of protein kinase C and/or increase in calcium influx induced the phosphorylation of the 105-115-kDa proteins only in fibronectin-adherent cells. The magnitude of the phosphorylation of the 105-115-kDa proteins induced by the aggregation of Fc epsilon RI in fibronectin-adherent cells was substantially greater than the sum of that due to adherence to fibronectin and the aggregation of Fc epsilon RI in nonadherent cells. Therefore, cell adherence and the aggregation of Fc epsilon RI synergistically regulate tyrosine phosphorylation of the 105-115 kDa proteins.