DESCRIPTION: (Applicant's Description) The long-term goal of this project is to improve our ability to diagnose and block the most lethal phase of human cancer, acquisition of the invasive state. Little is known about the molecular mechanisms of cell invasion because no powerful model systems have been developed for analyzing this process. We have used Drosophila genetics to develop egg chamber morphogenesis as a powerful cell and tissue model for dissecting the molecular mechanisms of cell invasion. Egg chambers are exceptional for analyzing cell invasion because their simple architecture provides an easy to score assay. This proposal focuses on the role of the conserved tumor suppressor Discs-large (Dlg) in suppressing cell invasion. The human Dlg homolog SAP97 binds to APC, the most commonly mutated gene in colorectal cancer, while another human Dig homolog, ZO-1, is specifically lost in the majority of invasive breast tumors. Dlg, SAP97, and ZO-1 are scaffolding proteins have three PDZ domains, an SH3 domain, and a GuK domain. The PDZ domains are crucial for suppressing cell invasion in Drosophila, and directly bind to proteins that are specifically involved in suppressing cell invasion in both Drosophila and human tissues, including the cell adhesion molecules FasII/NCAM and the Egf receptor (EgfR). Another conserved molecule, Kekkonl (Keki), binds to both Dlg PDZ and EgfR, but it role in cell invasion remains to be established. These results suggest that D1g organizes and regulates a large assembly of proteins in controlling normal cell migration and suppressing tumor cell invasion. The following specific aims utilize a combination of molecular genetics, cell biology, and biochemistry to obtain insight into how the D1g family of proteins organize and regulate a supramolecular assembly to prevent cell invasion. Aim 1 is to determine the role of individual Dig domains in blocking cell invasion. Aim 2 is to determine how PDZ-binding proteins FasII and Kek1 cooperate with Dlg to block cell invasion. Aim 3 is to determine critical interactions between Dlg and the EgfR signaling pathway. Aim 4 is to determine the cellular routes by which Dlg invasive cells bypass normal migration pathways. Aim 5 is characterize additional candidate D1g PDZ-binding proteins. This model system is strong because both key molecules and a cellular process that resembles human disease have been identified. The ability to analyze conserved tumor suppressors and oncogenes in a powerful cell invasion assay will reveal the structure and function of a supramolecular assembly that blocks cell invasion. This work is likely to uncover cell and molecular targets to block tumor cell invasion as a means of cancer therapy.