Metastasis represents the major cause of mortality in cancer patients. The unique ability to breach the basement membrane of epithelial barriers and migrate is believed to distinguish non-metastatic from metastatic tumor cells. According to the three-step hypothesis of metastasis, adhesion, proteolysis, and motility are the keys steps involved at the cellular level in the traversal of basement membrane barriers. Angiogenesis is crucial in metastasis because it supplies the necessary nutrients for tumor growth and in particular, the mechanism for dissemination of the metastatic cells once the basement membrane of the endothelium has been breached. Tumor and host cells contribute in a highly interactive process to the three steps necessary to breach epithelial barriers. Macrophages, in particular, are believed necessary for enhancing the motility of tumor cells, proteolysis, and angiogenesis in the primary tumor. The tumor cells themselves contribute to invasion by exhibiting amoeboid chemotaxis, the crawling of cells toward a source of chemotactic hormone. This is a problem because normal cells also exhibit this ability during cellular mediated immunity, wound healing and embryogenesis. This makes the development of drugs specific for the inhibition of only tumor cell chemotaxis difficult to design. The Condeelis lab is focused, in particular, on defining the signaling pathways from tyrosine-kinase receptors to the actin cytoskeleton in carcinoma cells, macrophages and endothelial cells and how these pathways distinguish and regulate motility in these cell types. Recently, the EGF-receptor and its ligands have been implicated in the metastasis of adenocarcinomas of breast and prostate. This receptor pathway stimulates tumor cell motility and chemotaxis by stimulating actin polymerization and localized protein synthesis to cause a change in cell polarity.

The actin cytoskeleton is the primary organelle that determines how cell surface receptors regulate cell polarity in chemotactic cells. Key actin binding proteins determine the flow of information within the actin cytoskeleton and determine the location of protein synthesis. Our approach is to identify these key actin binding proteins and map their functional and regulatory domains. This information is used to create mutant cells by homologous recombination and RNA directed techniques that are altered in their expression of these proteins. The chemotactic phenotype of the mutant cells is then analyzed in detail by quantitative computer driven light microscopy to determine the function of the protein and, potentially, each domain in vivo. The goal of these studies is to identify the major proteins and pathways involved in amoeboid chemotaxis and the motility of tumor cells.

Students can select projects which involve (1) the preparation of animal models of breast cancer that allow interactions between tumor cells and macrophages to be measured in vivo (2) expression and domain analysis of key proteins in the EGF-signaling pathway to the actin cytoskeleton (3) preparation of caged molecules that can be used to test strategies for drug design to prevent tumor cell chemotaxis (4) imaging-based phenotype analysis of tumor cells in vitro and in vivo that have been genetically or drug manipulated to measure the effects of the agents on chemotaxis. Imaging is performed in the Analytical Imaging Facility of which Dr. Condeelis is the scientific director. The two types of organisms used in these studies are transgenic mouse models of cancer, and cell lines from human and rat/mouse tumors. Both laser confocal and multiphoton imaging are used with live animals.