Hypomethylation of urokinase (uPA) promoter in hormone-dependent malignancies : prognostic and therapeutic implications

Urokinase plasminogen activator (uPA) promotes tumor invasion and metastasis in several malignancies including breast and prostate cancer. High levels of uPA are associated with invasive and metastatic characteristics of cancer. I examined the differential regulation of uPA expression by DNA methylation in normal, hormone responsive and hormone insensitive human breast and prostate cancer cell lines. Lack of uPA expression in normal and hormone responsive cells is due to methylation of uPA promoter. Treatment of these cells with a demethylating agent resulted in induction of uPA, higher invasive capacity of the cells, and significant increase in tumor volume. These studies demonstrated that DNA methylation is the molecular mechanism responsible for uPA gene silencing in normal and hormone responsive cancer cells. Since levels of uPA production is already a reliable prognostic marker of disease progression, determination of uPA promoter methylation status can potentially serve as a reliable early marker for induction of uPA and thus progression of cancer into metastatic stages. I therefore examined the methylation status of uPA promoter in surgical biopsy samples from patients with breast cancer of different grades and found that hypomethylation of uPA promoter is in fact associated with induction of uPA expression and poor grade in these patients. Determination of uPA promoter methylation status can therefore serve as an early reliable indicator of uPA production in breast cancer patients. Since uPA expression and its hypomethylated state is strongly correlated with the malignant phenotype, I utilized uPA gene in the highly invasive human breast cancer cells as a model system to test the hypothesis that pharmacological reversal of the uPA hypomethylation can result in its silencing and inhibition of metastasis. I found that treatment of these cells with the methylating agent SAM significantly inhibits uPA expression, tumor cell invasion,