Cell cycle regulation.  The cell division cycle in eukaryotic organisms is a complex series of strictly regulated events that ensures 1) that the genome is replicated accurately and 2) that complete copies of the genome are faithfully distributed to the daughter cells. Cancer ultimately results from loss of control over the cell division cycle, and therefore a clear understanding of the molecular processes that dictate cell cycle progression is essential to a fundamental understanding of carcinogenesis. In all eukaryotic cells the sequential stages of the cell cycle are regulated by two important post-translational mechanisms:  reversible protein phosphorylation, and ubiquitin-dependent proteolysis. These processes are interdependent, and together they drive the cell cycle forward with the proper order and timing.

The anaphase-promoting complex (APC). Our lab is interested in how ubiquitin-dependent proteolysis directed by the anaphase-promoting complex (APC) is used to regulate cell division in the budding yeast, Saccharomyces cerevisiae. Budding yeast are easy to work with and manipulate genetically, and therefore make a highly attractive and suitable model organism for studying the evolutionarily conserved cell cycle and understanding its relationship to cancer in humans. The APC is a large, highly conserved, multisubunit enzyme that catalyzes the polyubiquitylation of specific substrate proteins at specific points during the cell cycle. The polyubiquitin tags serve as markers for substrates to be destroyed by the proteasome. By the selective and irreversible elimination of inhibitory proteins, the cell cycle can progress from one stage to the next. Understanding how APC activity is regulated and how it recognizes its substrates are important questions that we are currently addressing.

APC co-activators. Although the APC is constitutively present during the cell cycle, its activity is tightly regulated. A major target of APC regulation is the co-activator proteins Cdh1 and Cdc20, which are not stable components of the APC but instead interact with it at specific times to promote activity. We are interested in studying how phosphorylation and protein binding partners regulate interaction of the co-activators with the APC and its substrates, and thereby control APC activity during the cell cycle. In particular, we have identified and are characterizing a protein called Acm1, which is a specific inhibitor of Cdh1 and acts by mimicking an APC substrate (called “pseudosubstrate inhibition”). Pseudosubstrate inhibition appears to be a commonly evolved mechanism for controlling APC activity. Studying pseudosubstrate inhibitors may also help us understand the structural determinants of substrate recognition by the APC and its co-activators.

Mass spectrometry as a research tool.  In all of our research areas, we use mass spectrometry as a powerful research tool for the discovery, quantification, and characterization of protein-protein interactions and post-translational modifications. We complement our mass spectrometric analyses with a wide array of biochemical, molecular and cell biological, and genetic approaches in a comprehensive effort to understand the function and regulation of the APC. In addition to the specific application of mass spectrometric techniques to our APC research projects, we are using and developing methods that are also of more general utility in the fields of proteomics and phosphoproteomics.