Abstract

Prostate cancer (PCa) is a disease that typically affects middle-aged men. PCa is often thought of as a “silent” type of cancer because it is usually asymptomatic until it progresses to late stages. If early detection methods are not used to identify the disease while it remains localized in the prostate, PCa can metastasize to secondary sites in the body.

During metastasis of PCa, secondary tumors form in the bone approximately 90% of the time. While effective therapy is currently available for the localized form of the disease, advanced stages prove much more difficult to treat and are essentially incurable. During PCa metastasis, movement of cells through the remodeling of the ECM is a critical step. MMPs are a family of zinc-dependent enzymes which play a major role in the degradation of the ECM during the processes of angiogenesis, invasion, and metastasis of cancer. Considerable evidence has shown that MMPs are upregulated consistently in many different types of cancer, including PCa. The ECM is made up of several proteins that can be digested by MMPs. A major component of the ECM is perlecan, a large proteoglycan. Perlecan can be degraded into fragments, creating a subset of functionalities through its catabolism. MMPs expressed by PCa cells can cleave intact perlecan to produce limit peptides. Additionally, loss of perlecan in the basement membrane has been associated with the dissolution of the barrier that normally separates epithelia and stroma, which is a hallmark of tumor invasion. A better understanding of the molecular events involved in the production of these limit peptides is necessary in order to prevent the degradation that precedes tumor migration.

I hypothesized that proteolysis, specifically by MMPs produced by PCa cells, degrades the ECM component, perlecan, during cell invasion, tumor growth, and metastasis of PCa. To test this hypothesis, I utilized a colon adenocarcinoma cell line, WiDr, which secretes perlecan as essentially the only proteoglycan the cells make. Perlecan was purified from crude WiDr media in milligram quantities using ion-exchange and size exclusion column chromatography. Perlecan then was digested using several different MMPs to derive limit peptides similar to those found at sites of tumor activity in the body. Analysis of these limit peptides revealed the true sites of fragmentation that are present in perlecan. These data provide evidence that the degradation of perlecan by MMPs produces limit peptides that may be involved in the progression of PCa.