A Characterization of the Role of Post-translational Modification in Transcriptional Regulation by the Histone Variant H2A.Z

H2A.Z is an essential histone variant that has multiple chromosomal functions. One such role is transcriptional regulation. However, its role in this process is complex since it has been reported to function both as a repressor and activator. Earlier work in our lab showed that H2A.Z can be post-translationally modified with monoubiquitin (H2A.Zub1) and this form of H2A.Z is linked to transcriptional silencing. We further predicted that changes in the H2A.Z ubiquitylation status directly modulated its function in transcription. Furthermore, H2A.Z-containing nucleosomes possess a unique set of post-translational modifications (PTMs), compared to H2A nucleosomes, many of which are linked to transcriptional activation. The central aim of this thesis was to characterize the role of PTMs on H2A.Z nucleosomes in transcriptional regulation. To this end, I have provided the first evidence linking H2A.Z deubiquitylation to transcriptional activation. I demonstrated that ubiquitin specific protease 10 (USP10) is a deubiquitylase that targets H2A.Z in vitro and in vivo. Moreover, I found that both H2A.Z and USP10 are required for activation of androgen-receptor (AR)-regulated genes, and that USP10 regulates the levels of H2A.Zub1 at these genes. To understand how H2A.Z engages downstream effector proteins, in the nucleosome context, we used a mass spectrometry approach to identify H2A.Z-nucleosome-interacting proteins. Many of the identified proteins contained conserved structural motifs that bind post-translationally modified histones. For example, we found that Brd2 contains tandem bromodomains that engage H2A.Z nucleosomes through acetylated H4 residues. To investigate the biological relevance of this interaction, I present evidence that Brd2 is recruited to AR-regulated genes in a manner dependent on H2A.Z and the bromodomains of Brd2. Consistent with this observation, chemical inhibition of Brd2 recruitment greatly inhibited AR-regulated gene expression. Collectively, these studies have defined how H2A.Z mediates transcriptional regulation through multiple mechanisms and pathways.Ph