Focal adhesion kinase pp125FAK and the β1 integrin subunit are constitutively complexed in HaCaT cells

Binding of integrins to the extracellular matrix (ECM) activates various signal transduction pathways and regulates gene expression in many cell types. Integrin-dependent cytoplasmic protein/protein interactions are necessary for activation of those signal transduction cascades. In our studies we investigated a possible association of pp125(FAK), an adhesion involved tyrosine kinase, with the integrin beta 1 subunit. Further we wanted to know to which extent protein tyrosine phosphorylation affects cell adhesion to the ECM and the possible beta 1 integrin/pp125(FAK) complex. We were able to show that in HaCaT cells (a human keratinocyte derived cell line) the integrin beta subunit is associated with tyrosine kinase pp125(FAK). This association was observed in ECM-adherent cells and nonadherent cells and is independent of tyrosine phosphorylation. However, cell adhesion of HaCaT cells to specific substrates requires tyrosine phosphorylation since genistein treatment that blocks phosphorylation of many cellular proteins as pp125(FAK) led to a reduced substrate adhesion. (C) 1998 Academic Press.