Cancer epigenetics: Linking basic mechanisms to therapy.

摘要

Due to the technology revolution in epigenetic profiling, the number of genes that contain epigenetic aberrations in disease is growing, emphasizing the critical role of epigenetics in disease states. The reversibility of epigenetic abnormalities upon pharmacological interventions has spurred interest in developing epigenetic therapy with the primary goal of restoring the expression of aberrantly silenced genes. The focus of this thesis was twofold: to elucidate the role of DNA methylation occurring at non-CpG island promoters and investigate mechanisms involved in therapeutic efficacy of a DNA methyltransferase inhibitor, 5-Aza-2'-deoxycytidine.;In the field of epigenetics, the significance of CpG island methylation in both normal and disease states, especially in cancer, has been well elucidated. However, the importance of DNA methylation occurring at non-CpG island promoters and its potential role in tumorigenesis are still controversial. Using LAMB3 and RUNX3 as examples, I have shown that DNA methylation directly silences genes containing non-CpGI promoters and their epigenetic signatures are almost identical to CpG island promoters, suggesting aberrant methylation patterns of non-CpG island promoters may also contribute to tumorigenesis and should therefore be included in analyses of cancer epigenetics.;The clinical efficacies of DNA methyltransferase inhibitors are irrefutable; however, mechanisms involved in therapeutic efficacy of these inhibitors are not completely understood. By investigating genome-wide changes in DNA methylation and gene expression at various time points after transient exposure to 5-Aza-CdR, I revealed that different genomic regions have different rate of remethylation upon drug withdrawal. In general, promoters remethylate much slower than gene bodies, resulting in sustained DNA demethylation and subsequent gene reactivation, which may potentially responsible for the less tumorigenic phenotype of cancer cells produced by transient exposure to 5-Aza-CdR. Elucidating the therapeutic efficacy of 5-Aza-CdR helps pave the way for developing combinatorial therapies to target multiple aberrant epigenetic modifiers. I also demonstrated the efficacy of combining 5-Aza-CdR with clorgyline, a lysine specific demethylase inhibitor, in enhancing the degree and prolonging the duration of gene reactivation. Taken together, this thesis presents the role of non-CpG island methylation and the therapeutic mechanism of 5-Aza-CdR, thus aiding in developing new epigenetic therapies, extending the application of and improving the efficacies of current therapies.