We study cell signaling and regulation of the actin cytoskeleton using structural and biochemical approaches. We seek to understand fundamental signaling mechanisms and principles by dissecting out and determining the structure of “regulatory modules” – multi-domain proteins or protein complexes that contain the necessary elements to both sense and change state in response to cellular events. Intimate understanding of the structure of such modules allows us to probe their biology in a cellular context. Particular areas of interest include kinases and their dysregulation in cancer and the control of actin assembly by formin proteins. Active projects include: 1) the regulation of focal adhesion kinase (FAK) and its interactions with integrins and Src-family kinases, 2) JAK-family kinases and their interactions with cytokine receptors, 3) lung cancer-derived mutations in the epidermal growth factor receptor (EGFR) and 4) mechanism of actin assembly by formin proteins.

Our work with FAK illustrates our general approach. FAK is a non-receptor tyrosine kinase that is activated by integrin-mediated cell adhesion. Its signaling is critical for changes in cell morphology and migration, and thus is thought to be a driving force in the invasiveness and metastasis of human tumors. FAK catalytic activity is regulated by its N-terminal region, which contains a “FERM” domain. We determined the structure of FAK in its autoinhibited conformation. This structure revealed that the FERM domain blocks the catalytic cleft of the kinase, and also “hides” key autophosphorylation sites to prevent inadvertent activation of the protein. Using the structure as a guide, we designed a FRET-based biosensor that allows direct visualization of FAK and its activation state in living cells. This work, in collaboration with Mike Schaller at UNC, led to our discovery that FAK is activated by binding to phosphoinositides at the membrane. We are now working to understand at a molecular level how phosphoinositide binding releases autoinhibition by the FERM domain.