Hypomethylation of Urokinase (uPA) Promoter in Breast and Prostate Cancer: Prognostic and Therapeutic Implications

Methylation of CpG islands of tumor suppressor genes, growth factors, and hormone receptors among other genes causes epigenetic changes in chromatin structure without altering DNA sequence to regulate transcription of these genes. This epigenetic regulation of gene expression plays an important role in the process of tumor invasion, growth and metastasis in malignancies. In hormone dependent malignancies such as breast and prostate cancer, sex steroids play an important role in the process of tumor initiation and progression. These malignancies are often initiated as a less aggressive hormone-responsive type that gradually progresses to become highly invasive and hormone-insensitive. At the early stages, cells lose a functional hormone receptor due to mutations, blockage of signaling pathway or hormone receptor gene silencing. This transition of cancer cells causes them to become refractory to the standard hormone therapies. In later stages, important factors like growth factors, cytokines and proteases promote tumor growth, invasion and metastases. The most commonly implicated protease in these processes is urokinase type plasminogen activator (uPA), which is known to be expressed in a number of malignancies including breast and prostate cancer and is directly associated with the higher invasive and metastatic potential of malignancies. In this chapter, we will review DNA methylation as the underlying molecular mechanism regulating uPA gene expression and its potential diagnostic, prognostic and therapeutic implication.