- Professor , Cell and Developmental Biology(615) 322-1412 (lab)
The Wnt pathway is an evolutionarily conserved signaling pathway present in all metazoans. During development, Wnt signaling coordinate the formation of tissues, organs, and limbs, and its misregulation leads to a variety of human disease states such Alzheimer’s disease and cancer. My laboratory is interested in understanding the basic mechanism by which a Wnt signal is propagated and how this information can be used in regenerative medicine and in the treatment of cancer.
A major experimental approach in my laboratory involves the use of Xenopus extracts and purified proteins to biochemically reconstitute Wnt signaling in vitro. Genome-scale screens, cultured mammalian cells, Xenopus embryos, Drosophila genetics (in collaboration with Dr. Laura Lee), and mouse studies are employed to compliment and extend our biochemical findings.
Mechanism of Wnt signal transduction
One of the major mysteries of this pathway is how a Wnt signal is propagated from the cell surface. My laboratory has recently developed an in vitro system to study the mechanism of Wnt signal transduction from the plasma membrane. Towards this end, we have focused on understanding the mechanism of signaling from the coreceptor, LRP6, and the potential role of the membrane associated heterotrimeric G protein family members in Wnt signal transduction. Many components of the Wnt pathway are regulated by ubiquitin-mediated proteolysis. Recently, we have taken a genome-scale screen to identify deubiquitinating enzyme (DUBs) and ubiquitin ligases (E3s) that regulate the Wnt pathway. Several “hits” have been identified from these screens, and current efforts are directed towards validating their roles in Wnt signaling.
Regenerative medicine and cancer
In regenerative medicine, the healing process is manipulated to repair damaged tissues. Modern regenerative medicine is a field in which stem cells are manipulated to treat a variety of human diseases. Wnt signaling is one of a handful of molecular pathways critical to stem cells. Thus, agents that target Wnt signaling would be potentially useful for the treatment of cardiovascular disease, diabetes, neurodegeneration, and other disorders that may benefit from regenerative medicine.
Cancer stem cells (CSC) are fundamental to the initiation and maintenance of tumors. Failure to eradicate CSC (as is typical with conventional therapy) leaves behind a small reservoir of cells that drives relapse. Wnt inhibitors would be expected to specifically target this resistant CSC population. Using our Xenopus biochemical system, we have found several compounds that potently inhibit the Wnt pathway. One of these, VU-WS30, inhibits the viability of a variety of cancer cell lines that are highly dependent on Wnt signaling for growth and proliferation. Current efforts are directed towards identifying the molecular targets of VU-WS30 and other Wnt inhibitors identified in our screen.
Post Doctoral Fellows
- Research Assistant III, Cell and Developmental Biology
For any general lab questions please contact me
My personal microscopy website can be found here: http://www.sawyermicroscopy.wordpress.com
U-4200 MRB3(615) 322-1412 (lab)
Currently, I am working on multiple projects for the Lee lab. These include; studies of the drug Pyruvinium and it's affects on localization of Pygopus in cells, expression and turnover assays of NOTCH in the presence of XIAP and creation of fluorescent constructs that will tell us more about the interaction between beta-catenin and TCF4 via fluorescence microscopy.
- PhD student , Cell and Developmental BiologyU-4200 MRB3(615) 322-1412 (lab)
Studies in our lab support a role for heterotrimeric Gβγ in the regulation of the canonical Wnt pathway. In this model, Gβγ promotes the phosphorylation of LRP6 by membrane recruitment of GSK3. Our lab and others have demonstrated that Gαo can also regulate Wnt signaling, although a detailed mechanism as to how this occurs is lacking. Regulators of G protein signaling (RGS) proteins are a family of proteins that promote GTP hydrolysis by G proteins, thereby inhibiting signaling initiated by G protein coupled receptors. Axin contains an RGS domain that has been shown to bind APC and Gαo. A model has been proposed in which Gαo disrupts Axin-GSK3, thus inhibiting β-catenin phosphorylation and degradation. These studies were performed in cultured mammalian cells and cellular extracts. The goal of my study is to biochemically probe the interaction between Gαo and Axin using purified components, and to provide mechanistic insight into how Gαo-Axin binding leads to inhibition of β-catenin phosphorylation and degradation.