Mode of SUV420H2 heterochromatin localization through multiple HP1 binding motifs in the heterochromatic targeting module

Constitutive heterochromatin is transcriptionally repressed and densely packed chromatin, typically harboring histone H3 Lys9 trimethylation (H3K9me3) and heterochromatin protein 1 (HP1). SUV420H2, a histone H4 Lys20 methyltransferase, is recruited to heterochromatin by binding to HP1 through its Heterochromatic Targeting Module (HTM). Here, we have identified three HP1 binding motifs within the HTM. Both the full-length HTM and its N-terminal region (HTM-N), which contains the first and second motifs, stabilized HP1 on heterochromatin. The intervening region between the first and second HP1 binding motifs in HTM-N was also crucial for HP1 binding. In contrast, the C-terminal region of HTM (HTM-C), containing the third motif, destabilized HP1 on chromatin. An HTM V374D mutant, featuring a Val374 to Asp substitution in the second HP1 binding motif, localizes to heterochromatin without affecting HP1 stability. These data suggest that the second HP1 binding motif in the SUV420H2 HTM is critical for locking HP1 on H3K9me3-enriched heterochromatin. HTM V374D, tagged with a fluorescent protein, can serve as a live-cell probe to visualize HP1-bound heterochromatin.

Histone Methyltransferases as a New Target for Epigenetic Action of Vorinostat

Epigenetic genome regulation during malignant cell transformation is characterized by the aberrant methylation and acetylation of histones. Vorinostat (SAHA) is an epigenetic modulator actively used in clinical oncology. The antitumor activity of vorinostat is commonly believed to be associated with the inhibition of histone deacetylases, while the impact of this drug on histone methylation has been poorly studied. Using HeLa TI cells as a test system allowing evaluation of the effect of epigenetically active compounds from the expression of the GFP reporter gene and gene knockdown by small interfering RNAs, we showed that vorinostat not only suppressed HDAC1, but also reduced the activity of EZH2, SUV39H1, SUV39H2, and SUV420H1. The ability of vorinostat to suppress expression of EZH2, SUV39H1/2, SUV420H1 was confirmed by Western blotting. Vorinostat also downregulated expression of SUV420H2 and DOT1L enzymes. The data obtained expand our understanding of the epigenetic effects of vorinostat and demonstrate the need for a large-scale analysis of its activity toward other enzymes involved in the epigenetic genome regulation. Elucidation of the mechanism underlying the epigenetic action of vorinostat will contribute to its more proper use in the treatment of tumors with an aberrant epigenetic profile.

Epigenetic regulation of DHRS2 by SUV420H2 inhibits cell apoptosis in renal cell carcinoma

Renal cell carcinoma (RCC), also known as kidney cancer, is a common malignant tumor of the urinary system. While surgical treatment is essential, novel therapeutic targets and corresponding drugs for RCC are still needed due to the high relapse rate and low five-year survival rate. In this study, we found that SUV420H2 is overexpressed in renal cancers and that high SUV420H2 expression is associated with a poor prognosis, as evidenced by RCC RNA-seq results derived from the TCGA. SUV420H2 knockdown using siRNA led to growth suppression and cell apoptosis in the A498 cell line. Furthermore, we identified DHRS2 as a direct target of SUV420H2 in the apoptosis process through a ChIP assay with a histone 4 lysine 20 (H4K20) trimethylation antibody. Rescue experiments showed that cotreatment with siSUV420H2 and siDHRS2 attenuated cell growth suppression induced by SUV420H2 knockdown only. Additionally, treatment with the SUV420H2 inhibitor A-196 induced cell apoptosis via upregulation of DHRS2. Taken together, our findings suggest that SUV420H2 may be a potential therapeutic target for the treatment of renal cancer.

H4K20me3 methyltransferase SUV420H2 shapes the chromatin landscape of pluripotent embryonic stem cells

Heterochromatin, a densely packed chromatin state that is transcriptionally silent, is a critical regulator of gene expression. However, it is unclear how the repressive histone modification H4K20me3 or the histone methyltransferase SUV420H2 regulates embryonic stem (ES) cell fate by patterning the epigenetic landscape. Here, we report that depletion of SUV420H2 leads to a near-complete loss of H4K20me3 genome wide, dysregulated gene expression and delayed ES cell differentiation. SUV420H2-bound regions are enriched with repetitive DNA elements, which are de-repressed in SUV420H2 knockout ES cells. Moreover, SUV420H2 regulation of H4K20me3-marked heterochromatin controls chromatin architecture, including fine-scale chromatin interactions in pluripotent ES cells. Our results indicate that SUV420H2 plays a crucial role in stabilizing the three-dimensional chromatin landscape of ES cells, as loss of SUV420H2 resulted in A/B compartment switching, perturbed chromatin insulation, and altered chromatin interactions of pericentric heterochromatin and surrounding regions, indicative of localized decondensation. In addition, depletion of SUV420H2 resulted in compromised interactions between H4K20me3 and gene-regulatory regions. Together, these findings describe a new role for SUV420H2 in regulating the chromatin landscape of ES cells.

Impact of histone methyltransferase SUV420H2 in breast cancer

Breast cancer is the most common type of cancer in women worldwide. Triple methylation of H4 lysine 20 (H4K20me3), a key component of epigenetic regulation of genomic integrity, is catalyzed by the methyltransferase, SUV420H2. Data on the expression status of SUV420H2 in breast cancer are limited. In the present study, the influence of SUV420H2 suppression on the proliferation of breast cancer cells was experimentally investigated. Subsequently, SUV420H2 expression was assessed in resectable breast cancer along with H4K20me3 status. SUV420H2 expression was knocked down in breast cells using small interfering RNA oligonucleotides. SUV420H2 expression was determined semi-quantitatively at the mRNA level. H4K20me3 was measured on extracted histone proteins using an approach similar to ELISA. Suppression of the SUV420H2 gene resulted in increased cell proliferation. Although the median SUV420H2 expression values were similar in tumor tissues and non-cancerous regions in the entire cohort (0.0022 and 0.0015, respectively; P=0.46), there was a notable difference in expression between tumor tissues and the adjacent non-cancerous region in the majority of patients. Increased SUV420H2 expression in tumors compared with healthy tissue was predominantly observed in patients with early-stage breast cancer, whereas reduced SUV420H2 expression was observed in tumors more frequently in patients with advanced stage diseases. There was no association between SUV420H2 expression and the tissue levels of H4K20me3. The results showed that SUV420H2 exhibited anti-proliferative activity in vitro, and exhibits a heterogeneous expression pattern in breast cancer tissues.

SUV420H2 suppresses breast cancer cell invasion through down regulation of the SH2 domain-containing focal adhesion protein tensin-3

The genome-wide loss of histone H4 lysine 20 tri-methylation (H4K20me3) is observed in multiple types of cancer, including breast tumors. Since H4K20me3 is preferentially targeted to repetitive elements in the pericentromeric and telomeric heterochromatin and plays a role in chromatin integrity, the pathological effects of disrupted H4K20me3 in tumors have been attributed to genomic instability. However, in this report, we show that loss of H4K20me3 modulates gene expression profiles, leading to increased cell invasion. Reduced H4K20me3 levels in tumor cells are often accompanied by a decrease in the expression of the H4K20-specific methyltransferase, SUV420H2. Exogenous delivery of SUV420H2 into MDA-MB-231 human breast cancer cells induced selective and specific changes in the expression of cancer-related genes. One of the most downregulated genes in response to SUV420H2 expression was the Src substrate, tensin-3, a focal adhesion protein that contributes to cancer cell migration. Depletion of tensin-3 suppressed breast cancer cell invasiveness. Furthermore, silencing of tensin-3 was associated with enrichment of H4K20me3 immediately upstream of the tensin-3 transcription start site, suggesting that the loss of H4K20me3 in tumor cells induced the expression of cancer-promoting genes. These findings connect the loss of H4K20me3 with tumor progression, through the transcriptional activation of cancer-promoting genes.

A dual role for the histone methyltransferase PR-SET7/SETD8 and histone H4 lysine 20 monomethylation in the local regulation of RNA polymerase II pausing

RNA polymerase II (Pol II) promoter-proximal pausing plays a critical role in postinitiation transcriptional regulation at many metazoan genes. We showed recently that histone H4 lysine 16 acetylation (H4K16Ac), mediated by the MSL complex, facilitates the release of paused Pol II. In contrast, H4 lysine 20 trimethylation (H4K20me3), mediated by SUV420H2, enforces Pol II pausing by inhibiting MSL recruitment. However, how the balance between H4K16Ac and H4K20me3 is locally regulated remains unclear. Here, we demonstrate that PR-SET7/SETD8, which monomethylates histone H4 lysine 20 (H4K20me1), controls both H4K16Ac and H4K20me3 and in doing so, regulates Pol II pausing dynamics. We find that PR-SET7-mediated H4K20me1 is necessary for the recruitment of the MSL complex, subsequent H4K16Ac, and release of Pol II into active elongation. Although dispensable for SUV420H2 recruitment, PR-SET7-mediated H4K20me1 is required for H4K20me3. Although depletion of SUV420H2 is sufficient to deplete H4K20me3 and relieve an H4K20me3-induced pause, pausing is maintained in the absence of PR-SET7 despite H4K20me3 depletion because of an inability to recruit the MSL complex in the absence of H4K20me1. These findings highlight the requirement for PR-SET7 and H4K20me1 in establishing both the H4K16Ac and H4K20me3 marks and point to a dual role in the local regulation of Pol II pausing.

Cracking the survival code: autophagy-related histone modifications

Modifications of histones, the chief protein components of the chromatin, have emerged as critical regulators of life and death. While the "apoptotic histone code" came to light a few years ago, accumulating evidence indicates that autophagy, a cell survival pathway, is also heavily regulated by histone-modifying proteins. In this review we describe the emerging "autophagic histone code" and the role of histone modifications in the cellular life vs. death decision.