PR‐Set7‐mediated monomethylation of histone H4 lysine 20 at specific genomic regions induces transcriptional repression

Abstract

Increasing evidence indicates that the post-translational modifications of the histone proteins play critical roles in all eukaryotic DNA-templated processes. To gain further biological insights into two of these modifications, the mono- and trimethylation of histone H4 lysine 20 (H4K20me1 and H4K20me3), ChIP-chip experiments were performed to identify the precise genomic regions on human chromosomes 21 and 22 occupied by these two modifications. Detailed analysis revealed that H4K20me1 was preferentially enriched within specific genes; most significantly between the first approximately 5% and 20% of gene bodies. In contrast, H4K20me3 was preferentially targeted to repetitive elements. Among genes enriched in H4K20me3, the modification was typically targeted to a small region approximately 1 kb upstream of transcription start. Our collective findings strongly suggest that H4K20me1 and H4K20me3 are both physically and functionally distinct. We next sought to determine the role of H4K20me1 in transcription since this has been controversial. Following the reduction of PR-Set7/Set8/KMT5a and H4K20me1 in cells by RNAi, all H4K20me1-associated genes analyzed displayed an approximately 2-fold increase in gene expression; H4K20me3-associated genes displayed no changes. Similar results were obtained using a catalytically dead dominant negative PR-Set7 indicating that H4K20me1, itself, is essential for the selective transcriptional repression of H4K20me1-associated genes. Furthermore, we determined that the H4K20me1-associated DNA sequences were sufficient to nucleate H4K20me1 and induce repression in vivo. Our findings reveal the molecular mechanisms of a mammalian transcriptional repressive pathway whereby the DNA sequences within specific gene bodies are sufficient to nucleate the monomethylation of H4K20 which, in turn, reduces gene expression by half.

Dynamic regulation of the PR-Set7 histone methyltransferase is required for normal cell cycle progression

“…During G2, we demonstrated that PR-Set7 is targeted primarily to specific heterochromatic regions of the genome, resulting in histone H4K20me1 (Congdon et al 2010). Importantly, PR-Set7-mediated H4K20me1 is required for cell cycle progression, as ablation of H4K20me1 results in a G2 arrest.…”

Broad chromosomal domains of histone modification patterns in C. elegans

“…On the other hand, H4K20me1 may be related to somatic dosage compensation, which starts in early embryos and is fully established in L3s. H4K20me1 has been implicated in gene repression in Drosophila and human cells and is known to be associated with X inactivation in mouse cells (Nishioka et al 2002;Kohlmaier et al 2004;Congdon et al 2010). In humans, both H3K27me1 and H4K20me1 are found on actively transcribed regions (Barski et al 2007).…”

Histone H4 Lysine 20 (H4K20) Methylation, Expanding the Signaling Potential of the Proteome One Methyl Moiety at a Time

“…However, RNAi-mediated reduction of SETD8 can increase the expression levels of specific target genes, and an increase in H4K20me1 levels by PHF8 knockdown reduces the mRNA levels of PHF8-bound genes (40,41,45). Additionally, tethering SETD8 to endogenous loci as well as to reporter genes results in mild repression of transcription (74). Finally, SETD8 depletion in flies is associated with position-effect variegation, a typical heterochromatin defect (75).…”