Proteolytic Mechanisms of Tumor Cell Invasion Investigators:

Investigators

• Robert W. Mason PhD.

Background

When cancer cells become invasive, they spread to adjacent and distant normal organs and become much more difficult to treat. New treatment possibilities are now being explored that target the mechanisms of tumor cell invasion in order to stop the cancer from invading. Proteases are recognized as major mediators of the invasive process, and this project is aimed at defining mechanisms by which one family of proteases, called cathepsins, contribute to the invasive process. Correlative studies have already implicated cathepsins in tumor cell growth and invasion, but mechanisms by which these proteases become active against extracellular proteins are poorly understood. In this project, techniques to identify active proteases will be further improved and used to demonstrate the critical cellular locations of the cathepsins while the cancer cells are invading. These techniques will be used to identify tumors that are more likely to respond to inhibitors of cathepsins. The eventual goal is to treat cancers that demonstrably use cathepsins to invade normal organs with specific inhibitors of the cathepsins.

What We're Doing

It is clear that proteases perform a number of key roles in the invasive process of tumor cells. Identifying the critical proteases in any given type of cancer will aid the design of specific treatments to inhibit the invasive properties of cancers that use the proteases to invade normal tissues. Matrix metalloproteases (MMPs) have emerged as one set of proteases important in tumor cell invasion. We hypothesize that cathepsins are a second group of proteases that make a significant contribution to the invasive process. Moreover, we hypothesize that regulation of the dynamic equilibrium of cathepsins between different cellular compartments will influence the ability of these proteases to facilitate invasion of tumor cells. In normal cells, 95% of the cathepsins are located in lysosomes, so redistribution of even a small portion of these proteases will have a major effect on the amount of cathepsin in the secondary location. Thus, aberrant regulation of the subcellular distribution of the cathepsins in cancer cells may result in delivery of these proteases to the extracellular milieu where they can destroy normal cellular matrices and enhance invasion. The key to examining the effects of such redistributions is the development of techniques that selectively identify cathepsins at the secondary sites. We have developed techniques using fluorescent molecules that bind with high specificity to the active sites of cathepsins to identify the active proteases in cells. To prove our hypothesis we propose to determine the effect of cathepsin inhibitors on tumor cell invasion, examine the cellular distribution of active cathepsins during the invasive process, and to experimentally manipulate the distribution of the cathepsins to modulate the invasive process. As a model system, we will focus on proteases in neuroblastoma cell lines and determine the relative contribution of MMPs and cathepsins to the invasive process.