Overview of Epigenetics: Dna Methylation and Histone Modifications

Classically, the development of cancer in humans has been viewed as a progressive, multistep process of transformation of normal cells into malignant cells driven by genetic alterations [1, 2]. However, a wealth of data in the past decade indicates that human cancer cells, in addition to a large number of genetic alterations, exhibit prominent epigenetic abnormalities, e.g. aberrant DNA methylation and histone modifications. This knowledge has largely changed the view on cancer as being a solely genetic disease [3]. Currently, cancer is recognized as a disease associated with both genetic and epigenetic alterations, and both of these components cooperate and complement each other to promote cancer progression [4]. Recognition of the fundamental role of epigenetic alterations in cancer progression has resulted in the identification of a number of epigenetic abnormalities in cancer that can be used as diagnostic and therapeutic targets for cancer management. While the role of epigenetic changes in cancer has been studied extensively [3, 5, 6], the contribution of epigenetic alterations to the mechanism of neoplastic cell transformation has remained relatively unexplored, despite the fact that the involvement of epigenetic events in cancer initiation has been proposed for forty years [7]. This review summarizes the significance of epigenetic changes in cancer cells and the role of epigenetic dysregulation in carcinogenesis.