We are studying the regulation and role of adhesion-linked tyrosine kinases during cell transformation and cancer progression. Specifically, the mechanisms by which the Src family kinases, and their functional partner focal adhesion kinase (FAK), control the dynamic regulation of the adhesion/de-adhesion cycle and cell motility are being elucidated. In addition, we are addressing whether tyrosine kinase modulation during tumour development is causally linked to the cancer phenotype. We are investigating the mode of intracellular targeting of Src to integrin-linked focal adhesions in fibroblasts. For this we use temperature-dependent mutants of v-Src and have defined the SH3 domain as a critical determinant of targeting, mediated by its role in linking Src to the actin cytoskeleton. Src¿s catalytic activity at peripheral adhesions induces tyrosine phosphorylation of FAK, and other integrin adhesion components. In turn, this results in adhesion turnover that facilitates cell migration. Src tyrosine kinase activity at cell-matrix adhesions stimulates intracellular signal transduction, including phosphatidyl inositol (PI) 3-kinase and protein kinase B (PKB or Akt), as well as the ERK/MAP kinase pathway. Via these effector pathways, Src (and possibly FAK) activity also control proliferation and cell survival. Our recent results indicate a key role for Src-induced modulation of the calpain/calpastatin proteolysis system during both adhesion turnover and cell cycle progression. In epithelial cells, the cell type from which the major clinically relevant cancers are derived, Src's protein interaction domains mediate incorporation of the tyrosine kinase into cadherin-dependent inter-cellular adhesions. Src's kinase activity at these membrane sites stimulates adhesion disruption, although the mechanism is not known. However, Src expression and/or activity is often raised during human epithelial tumour progression and may contribute to invasion via weakening of cadherin-dependent adhesion. Future projects We aim to define how Src kinases target to the cell periphery and the particular role of individual cytoskeletal networks in this process. We are elucidating the way in which tyrosine phosphorylation of key substrates induces dynamic re-modelling of cellular adhesions, leading to cell migration and cancer cell spread. In particular, the regulation and role of cellular proteases are being studied. In addition, Src's substrates in cancer cells are being identified by proteomics. Ultimately, we seek to understand how non-receptor tyrosine kinases control cancer spread and to identify new targets for intervention.