Clinical Biochemistry

Major Research Interests

Our laboratory focuses on the biological roles of intracellular proteases, with particular emphasis on enzymes called cathepsins that are found in the endosomal-lysosomal system. Originally, these proteases were discovered as enzymes with broad specificities that degrade proteins down to small peptides and amino acids. The amino acids produced can then be re-used for new protein synthesis. The majority of the cathepsins were found in lysosomes, intracellular organelles that contain an array of hydrolytic enzymes. These organelles were viewed as terminal degradative compartments. This suggested that this group of enzymes were designed to be "the garbage disposal unit" of cells and at best could be viewed as "recycling centers." In recent years, we and others have begun to challenge these views. Gene knock-outs of individual cathepsins do not block bulk protein turnover, but result in defective processing of unique proteins. It is now clear that the lysosomal proteases play critical roles in antigen processing and presentation, tumor cell invasion, and bone remodeling. One project in the laboratory is to design novel inhibitor probes that target proteases in discreet intracellular compartments. We have designed inhibitors that can identify active proteases in living cells, allowing us to measure intracellular concentrations of active proteases without manipulating assay conditions. More selective inhibitors have been synthesized by conjugating reagents to proteins that specifically target the endosomal compartments of cells. These inhibitors are being evaluated in more applied projects as potential agents that can selectively impair the immune response, tumor cell invasion and bone turnover. A second project has arisen from early studies that showed that rodent placentae express a unique set of proteins that interact with synthetic protease inhibitors. Genome-wide searches have enabled us to discover a new family of cathepsins that are uniquely expressed in placenta. Molecular modeling of these enzymes shows that each has evolved to provide a distinctive substrate binding site that is likely to yield an enzyme with a very restricted specificity. It is our working hypothesis that these enzymes perform important functions in implantation and hormone processing and we plan to express each of these enzymes in order to determine their biological functions.

Current Projects

• Evolution of Placental Proteases
• Proteolytic Mechanisms of Tumor Cell Invasion

Current Research Group

Guizhen Lu, BS - Guizhen Lu gained her B.S. degree in Peking, China, before coming to the USA and obtaining extensive experience in molecular biology, enzymology and biochemistry at Oklahoma State University and the University of Pennsylvania.

Robert W. Mason, PhD