CHARACTERIZING THE FUNCTION AND REGULATORY MECHANISMS OF THE HISTONE DEMETHYLASE KDM5B: INSIGHTS INTO THE COMPLEXITY OF EPIGENETIC REGULATION

Abstract

<p>KDM5b acts as a transcriptional repressor through its ability to demethylate tri-methylated lysine (K) 4 on histone H3 (H3K4me3). Demethylation of this histone modification leads to transcriptional repression and downstream biological effects on gene expression. KDM5b is involved in the regulation of differentiation and can exert an oncogenic and a tumour suppressive role depending on cellular context, making it an attractive future target for pharmaceutical intervention. Work from our group has shown that KDM5b expression is linked to differentiation, and that recruitment of the enzyme does not always result in an alteration of H3K4me3. Additionally, work from our group, as well as others, has failed to observe H3K4me3 demethylation by KDM5b in nucleosomal preparations. We therefore hypothesized that KDM5b may exert its demethylase potential on alternative histone targets and that KDM5b requires enzymatic co-factors to demethylate nucleosomes, similar to what is observed for other histone-modifying proteins. In this thesis, we describe KDM5b as having an alternate histone target, di-methylated histone H2B lysine 43 (H2BK43me2). We show that this methyl mark is the primary target for KDM5b, and that the expression level of H2BK43me2 is directly related to the process of differentiation. We additionally present a novel co-factor for KDM5b, the co-repressor TLE4 of the Groucho/TLE family. The presence of TLE4 is required and sufficient to confer nucleosomal demethylase activity to KDM5b, a novel discovery for any of the KDM5 family members. Overall, this work has described both an additional KDM5b target, and detailed requirements for KDM5b nucleosomal demethylation, advancing our understanding of how this enzyme is regulated <em>in vivo</em>. The novel aspects of KDM5b regulation presented within this thesis provide a framework from which future studies can be designed. This work contributes to our overall understanding of epigenetic regulation and will potentially aid in the development of novel anti-cancer therapeutic strategies.</p>