The long-term objective of this study is to understand the biological role and mechanism of action of the c-fps/Fes proto-oncogene. Fes encodes a cytoplasmic tyrosine kinase that is specifically expressed in myeloid cells. We have obtained evidence that Fes is involved in signaling through a specialized class of surface receptors during cell- cell and cell-matrix interactions, and suggests a possible role of Fes in mediating the release of inflammatory cytokines during macrophage activation. We found that VLA-4 integrin engagement in macrophages, a process that induces the release of inflammatory mediators, results in the activation of Fes kinase. We have also identified a number of macrophage specific substrates of Fes, which are involved in cell adhesion and regulation of inflammatory cytokines. One of the substrates phosphorylated by Fes is the crk-associated substrates (Cas) and another is a new 130 kDa protein (P130). Cas is an adapter protein involved in integrin signalling. P130 is a protein expressed only in hematopoietic cells and has been implicated in release of inflammatory cytokines. We hypothesize that Fes is involved in a novel integrin- dependent pathway that regulates the release of inflammatory mediators. In this proposal we will study the mechanism by which integrin engagement results in activation of Fes kinase, and how phosphorylation of its specific substrates regulates the inflammatory response of macrophages. The macrophage adhesion receptor VLA-4 will be engaged by cross-linking with specific antibodies and by adhesions to fibronectin, and the functional interactions between Fes and the integrin cascade will be examined. Using a combination of genetic and biochemical approaches we will elucidate the mechanisms involved in Fes kinase activation, characterize the Fes substrates, identify its downstream targets, and analyze the role of Fes in the adhesion-dependent macrophage inflammatory response. Finally, we will identify the transcriptional regulators activated by Fes and map the Fes-responsive elements in the promoters of genes under Fes control. Macrophages are a central player in the immune response to microorganisms, in tumoricidal activity, and in pathological conditions such as atherosclerosis. The proposed investigation will bring to light a previously unknown regulatory cascade involved in inflammatory response of macrophage. This will have an impact on the rational design of therapies aimed at preventing the inappropriate activation of macrophages, a biomedical problem of paramount importance.