Cancer cell attachment to distant tissues is fundamental to metastasis. We propose that signals within tumor cells interact with the cytoskeleton to modify the adhesiveness of cell surface receptors required for adhesion and metastasis. Based on preliminary data using established cell lines, a murine model, and primary cells from human colon cancers, we hypothesize that inside-out regulation of integrin receptors governs cancer cell adhesion. In particular, we have shown that increased extracellular pressure, such as may occur during passage through the venous or lymphatic system, during surgical procedures, or postoperatively due to increased intra-abdominal pressure, stimulates FAK-Src interaction and activates PI3-K together with the PI3-K substrate Akt. Preliminary studies suggest that these signals influence cancer cell adhesion in a manner that requires an intact actin cytoskeleton. We will now use pressure activation to further define the mechanisms of inside-out regulation of cancer cell adhesion. We will delineate the signals involved, explore the role of the cytoskeleton, and determine whether adhesiveness is regulated by changes in integrin affinity or avidity by measuring both integrin clustering and the bond strength of individual integrin-matrix bonds in cancer cells subjected to pressure. We will test our hypothesis in human primary cancer cells and in a mouse model, to establish its relevance to intact organisms. This work will elucidate a scientifically important paradigm for inside-out signaling that may explain why some circulating cancer cells may adhere while others do not. The signals we define will represent important targets for perioperative intervention to reduce iatrogenic tumor spread during surgery and perhaps new targets for cancer therapy to inhibit metastasis.