GENESIS AND CONSEQUENCES OF ABERRANT DNA METHYLATION

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DESCRIPTION: Dr. Vertino's overall research initiative is focused on understanding the molecular mechanisms underlying establishment of altered DNA methylation patterns and its contribution to human carcinogenesis. The aberran methylation of normally unmethylated CpG island-containing gene promoters is one such alteration that has recently been implicated in the inactivation tumo suppresser and other genes in human cancer. In human breast cancer, CpG island methylation is involved in the inactivation of several genes known to be important mediators of tumor cell growth and clinical outcome, including the estrogen receptor gene, the E-cadherin gene, and the p16/INK4A gene. Furthermore, increased expression of DNA (cytosine-5)-methyltransferase (DNA MTase), the enzyme responsible for DNA methylation in mammalian cells, is associated with the more aggressive estrogen receptor negative tumor phenotype Although there have been numerous studies correlating aberrant CpG island methylation with gene inactivity, few studies have addressed how previously unmethylated CpG island sequences become methylated de novo in adult somatic cells and whether this event plays a direct role in gene silencing. We have recently demonstrated that cells engineered to overexpress DNA MTase can be used to model the progression of CpG island methylation as it might occur during the early stages of tumorigenesis. To address the molecular mechanisms underlying aberrant promoter region methylation and the role of this event in human breast carcinogenesis, we propose to develop an in vitro model of de nov methylation in human breast epithelial cells. Specifically, we will determine whether increased expression of DNA MTase can drive the methylation of genes known to be silenced in association with CpG island methylation in human breas tumors. Secondly, we will determine whether locus-specific signals serve to direct the de novo methylation of CpG island promoters in breast epithelial cells. Lastly, we will determine whether de novo methylation of CpG island sequences is sufficient to initiate the gene silencing process by determining the downstream effects of DNA MTase-driven CpG island methylation on gene expression. A further understanding of the genesis and consequences of aberran de novo methylation during carcinogenesis will provide the basis for the futur development of novel demethylation strategies in the treatment of human breast cancer and other neoplastic diseases.