JMJC domain-containing histone demethylase 2 (Jhd2): Bridging the gap between H3K4 trimethylation and H3 acetylation

Kayla M Harmeyer, Purdue University

Abstract

Gene expression has been shown to be regulated through epigenetic modifications to the N-terminal tail of histones. Among these modifications is methylation of lysine residues. The enzyme Jhd2 is a histone demethylase that functions to remove H3K4 methylation in S. cerevisiae. Jhd2 is a homologue of the human JARID1 family of histone demethylases, which has four members: JARID1A, B, C and D. JARID1B is of particular interest because it has been shown to be up regulated in 90 percent of primary breast cancers. Furthermore, JARID1A has been shown to be up regulated in gastric cancer. Therefore studying how these H3K4 histone demethylases function will give great insight into how JARID1 family members are missregulated during tumorigenesis and how they can be targeted by inhibitors. Studies have shown cross-talk between H3K4 methylation and H3K14 acetylation, two marks generally associated with active transcription. Our study shows H3K14 acetylation mediates this cross-talk with H3K4 trimethylation by modulating the interaction between the H3K4 demethylase Jhd2 and the H3 N-terminal tail and by affecting Jhd2's association with chromatin. By mutating H3K14, H3K4 trimethylation can be modulated in a Jhd2 dependent manner. Additionally, deletion of a histone acetyltransferase GCN5 results in a decrease in not only H3 acetylation but also in global and gene specific H3K4 trimethylation. This decrease in H3K4 trimethylation is dependent on Jhd2. We further demonstrate that deletion of GCN5 causes an increase in Jhd2 binding to chromatin. We also show the opposite phenotype, lower levels of Jhd2 at chromatin, when histone deacetylases are deleted. This indicates that the turnover of H3K14 acetylation affects H3K4 trimethylation through Jhd2. We were able to demonstrate that this mechanism may be conserved through humans and Drosophila melanogaster and that deletion of JHD2 partially rescues a gcn5Δ 6-AU sensitivity phenotype, elucidating to a role for this cross-talk mechanism in transcriptional elongation. Furthermore, we show that deletion of the histone deacetylase RPD3 results in an increase of H3K4 trimethylation, most significantly at the 3' regions of the genes analyzed. Though this increase in H3K4 trimethylation is observed, deletion of RPD3 does not alter the localization of either Set1, the sole H3K4 methyltransferase, or Jhd2 across the gene. This suggests a new mechanism in which histone acetylation affects the H3K4 trimethylation enrichment at actively transcribed genes. Altogether, these studies mechanistically describe how H3K14 acetylation modulates H3K4 trimethylation through the histone demethylase Jhd2 as well as present a new mechanism in which histone acetylation may play a role in the enrichment of H3K4 trimethylation throughout the open reading frame of actively transcribed genes.

Degree

Ph.D.

Advisors

Briggs, Purdue University.

Subject Area

Biochemistry

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