|Our laboratory employs biochemical and structural methods
(primarily X-ray crystallography) to define the molecular interactions that
underlie cytoplasmic signal transduction. We are especially interested in
determining the structure of signaling complexes that underlie cancer, and
in using structural approaches to facilitate development of anti-cancer
drugs. Active areas of investigation include: 1) the structural biology
of integrins, focal adhesion kinase (FAK), and Src-family kinases in the
regulation of cytoskeletal rearrangements, 2) the cytoplasmic signaling
interactions that control antigen-dependent T-cell activation, and 3) the
interactions of the transcription factor Tcf4 with beta-catenin, a driving
force in the development of colon cancer.
Src and focal adhesion kinase are activated by growth factor receptors and by integrin-mediated cell adhesion. FAK signaling is critical for changes in cell morphology and migration, and thus may be an important driving force in the invasiveness of human tumors. FAK is known to associate with the cytoplasmic domain of a subset of integrin receptors via its N-terminal region, which contains a FERM domain. In order to understand FAK regulation, we are determining the structure of relevant regions of FAK in complex with integrin tails and with Src-family kinases, which phosphorylate and activate FAK.
In T-cell activation, we are studying the Src-family kinases Lck and Fyn, as well as Zap-70, SAP, and c-Cbl. We have recently determined structures of the N-terminal domain of Lck in complex with the cytoplasmic tails of T-cell co-receptors CD4 and CD8 using multi-dimensional NMR methods. In our structural studies of these molecules and their component domains, alone and in multi-molecular complexes, we address the following general themes: (1) How is specificity achieved in molecular recognition? (2) How do these modular domains regulate their associated catalytic subunits? (3) How does phosphorylation regulate the activity and interactions of these molecules? and (4) How can our structural results be used for design of immunomodulatory drugs?
The multifunctional protein beta-catenin acts in cell adhesion by binding cadherins and in the wnt signal transduction pathway through its interactions with the Adenomatous polyposis coli (APC) protein and TCF/Lef family transcription factors. Mutations in APC or in beta-catenin are estimated to drive formation over 90% of all colon cancers. In colonic epithelia these mutations produce elevated levels of Tcf4/beta-catenin which stimulates a transcriptional response that initiates polyp formation and eventually malignant growth. Thus disruption of Tcf4/beta-catenin interaction may be an attractive target for therapeutic intervention. We have determined the crystal structure of a human Tcf4/beta-catenin complex, and are working with pharmaceutical collaborators to develop inhibitors of the interaction.