Our aims are to understand the mechanisms of tumor cell adhesion and invasion and to define the metabolic pathways that regulate these processes. We have demonstrated that cis-polyunsaturated fatty acids stimulate adhesion of human breast tumor cells through a pathway that involves MAP kinases, protein kinases C, and beta-1 integrins. We have identified a MAP kinase, p38, as a specific protein that is phosphorylated during the activation of adhesion in these cells by the fatty acids. Furthermore, we have shown that two isozymes, protein kinases C epsilon and mu, are translocated to membrane fractions in response to exposure of breast tumor cells to a dietary fatty acid. The phosphorylation and proteolytic processing of PKCmu is critical for adhesion of breast tumor cells on type IV collagen. We have also shown that dietary fatty acids induce changes in the localization of key cytoskeletal proteins, such as filamentous actin, vinculin, and alpha-actinin, and increase the colocalization of beta-1 integrins with these proteins. We are currently working to identify other members of signal transduction pathways whose activity is regulated by these fatty acids and to determine how these signals lead to changes in the cytoskeleton and, ultimately, in cell behaviors such as migration and invasion. We have also developed a mouse model with human gastric carcinoma cells that shows an increase in tumor cell growth when the mice are fed diets high in linoleic acid. We have now shown that the metastatic variant of these human tumor cells have increased invasive potential that depends on PI-3-Kinase activity. We are examining these cells to determine whether inhibition of PI-3-K can block the increased tumor growth in mice on high fat diets. We are also examining the signal transduction pathways responsible for the increase in invasive behavior in response to linoleic acid.
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