Adhesion to fibronectin promotes the activation of the p125FAK/Zap-70 complex in human T cells

The beta 1 integrins are a family of heterodimeric adhesion receptors involved in cell-to-cell contacts and cell-to-extracellular matrix interactions. Through their adhesive role, integrins participate in transduction of outside/inside signals and contribute to trigger a multitude of cellular events such as differentiation, cell activation, and motility. The fibronectin integrin receptors, alpha(4)beta(1) and alpha(5)beta(1), can function as costimulatory molecules in T-cell receptor (TCR)-dependent T-cell activation. In the current study the Jurkat T-cell line was used as a model system to investigate the TCR-independent role of cell adhesion to fibronectin in the activation of Zap-70, a central molecule in the signalling events in T cells. Upon adhesion to plastic immobilized fibronectin but not to bovine serum albumin (ESA) the phosphorylation of p125(FAK), a protein kinase that localizes to focal adhesion sites, was induced. Moreover, clustering of fibronectin receptors led to the detection of a p125(FAK)/Zap-70 complex. Finally, while the complex between fak-B, another protein kinase localized to focal adhesion sites, and Zap-70 was detected in cells plated either on BSA or on fibronectin, the formation of the p125(FAK)/Zap-70 complex appeared specifically induced following fibronectin-mediated integrin clustering. These data suggest the existence of a high degree of specificity when the members of the pi integrin family mediate signalling pathways in T cells.