Barton Biology Lab

The two basic phenotypes that describe a cancer cell are simply the ability to proliferate uncontrolled and the ability to withstand normal regulatory mechanisms such as apoptosis.  Apoptosis is programmed cell death and is essential for multi-cellular organisms during development, wound repair, and tissue homeostasis.  The decision by a cell to undergo apoptosis is dictated by many cell signaling molecules and a complex pathway of regulation.  For example, when a cell is damaged or stressed, it must sense the damage and respond in an appropriate manner.  If the damage is repairable, then the cell will survive, but if the damage is irreparable, then the cell must sacrifice itself for the benefit of the larger organism.  That means there is a balance between pro-survival signals and pro-apoptotic signals antagonizing each other ultimately determining the outcome for the cell.  These signals can be controlled by synthesis, activation, and degradation.  Proteasomes, as the predominant cytosolic protease, are essential in determining the outcome of such apoptotic balancing acts by degrading proteins on one side or another and tipping the scales to favor survival or apoptosis.  Since proteasomes require proteasome activators, such as PA28g, to facilitate the substrate selection for these proteases, then the proteasome activators have key roles in controlling the apoptotic response to stress.  I am very interested in understanding how PA28g, a protein over expressed in several cancers, affects the outcome of a cell's life and death decision when stressed. 

Students examining these questions will learn research techniques including mammalian tissue culture, protein electrophoresis, immuno-detection methods, cell-based and enzyme-based high-throughput assays, and light and fluorescence microscopy.

Senescence, the aging of cells, is correlated with both proteasome function and oxidative stress.  In age-related degenerative disorders, such as Parkinson's Disease, where development of pathology is related to reduced proteasome activity, an accumulation of oxidatively damaged proteins are found. Furthermore, when many cancer cells are treated with proteasome inhibitors, such as bortezomib, an increase in the concentration of cellular reactive oxygen species (ROS) precedes apoptosis and is related to the effectiveness of these drugs' anti-tumor properties. Moreover when differentiated cells are exposed to oxidative stress, defined as an imbalance in the intracellular levels of free radicals and cellular defenses that disarm them, there is an increase in proteolysis, mediated largely by proteasomes, that is required for survival. Thus, the relationship between regulation of the proteasome system and oxidative stress is well documented, as is the ability to induce programmed cell death or apoptosis through proteasome inhibition and increases in cellular ROS. Because PA28γ is highly expressed in several forms of cancer, our improved understanding of the cell's ability to manage oxidative stress through the PA28γ-proteasome system will provide novel insight into the molecular mechanisms of cancer. I am intrigued by the possible link between oxidative stress, proteasome regulation by PA28γ and regulation of the cell cycle and apoptosis.

Students examining these questions will learn research techniques including mammalian tissue culture, protein electrophoresis, immuno-detection methods, cell-based  and enzyme-based high-throughput assays, and light and fluorescence microscopy.

How proteins are selected for degradation by proteasomes is still an area of active research.  It is now clear that the process of poly-ubiquitination is much more diverse than originally recognized.  Furthermore, ubiquitin-independent substrate selection by proteasomes is very poorly understood.  PA28g is a proteasome activator that can facilitate the degradation of specific proteins by proteasomes independently of ubiquitin and ATP in vitro.  The mechanism of substrate recognition remains completely unknown, while the list of proteins selectively degraded by PA28g continues to grow.  PA28g was originally thought to simply act as a "gatekeeper" for the proteasome core, however it is now clear that such a model is too simple.  I am very curious how PA28g recognizes substrates and the mechanism of physical interaction with proteasomes that translates into ATP-dependent protein degradation.

Students examining these questions will learn research techniques including mammalian tissue culture, protein electrophoresis, microscopy, immuno-detection methods, enzyme-based assays, yeast culture, yeast transformation, and protein purification.

Mammals are complex organisms with a complex physiology.  The physiology of mammals is not only dependent on the biology of mammalian cells, but also on the physiology of prokaryotic cells living in mutualistic relationships in and on the mammalian organism.  The complex interactions between microbes and mammals are dynamic and change over time and in response to several environmental cues.  Despite the dynamic relationship between microbes and host, these microbiome communities tend to be somewhat robust within individuals.  Alterations in the microbiome of the gut has been correlated with a number of human disease states.  Since PA28g affects several key areas of host biology at the interface between host and microbes (immunology, epithelial cell regeneration, gene expression, carcinogenic transformation), we believe that the community structure of the gut microbiome may be an effective mechanism to understand the biological relevance of PA28g expression in mammals.

Students examining these questions will learn research techniques including genomic DNA isolation and analysis, Polymerase Chain Reaction, animal husbandry, bacterial culture, and differential microbiology.