PHF8 is a histone H3K9me2 demethylase regulating rRNA synthesis

Abstract

Dimethylation of histone H3 lysine 9 (H3K9me2) is an important epigenetic mark associated with transcription repression. Here, we identified PHF8, a JmjC-domain-containing protein, as a histone demethylase specific for this repressing mark. Recombinant full-length wild type protein could remove methylation from H3K9me2, but mutation of a conserved histidine to alanine H247A abolished the demethylase activity. Overexpressed exogenous PHF8 was colocalized with B23 staining. Endogenous PHF8 was also colocalized with B23 and fibrillarin, two well-established nucleolus proteins, suggesting that PHF8 is localized in the nucleolus and may regulate rRNA transcription. Indeed, PHF8 bound to the promoter region of the rDNA gene. Knockdown of PHF8 reduced the expression of rRNA, and overexpression of the gene resulted in upregulation of rRNA transcript. Concomitantly, H3K9me2 level was elevated in the promoter region of the rDNA gene in PHF8 knockdown cells and reduced significantly when the wild type but not the catalytically inactive H247A mutant PHF8 was overexpressed. Thus, our study identified a histone demethylase for H3K9me2 that regulates rRNA transcription.

Systematic knockdown of epigenetic enzymes identifies a novel histone demethylase PHF8 overexpressed in prostate cancer with an impact on cell proliferation, migration and invasion

“…Interestingly, no adverse events were observed in 273 PrCa's with low/negative PHF8 expression, whereas the PHF8-high patients had an overall 81% survival (240 months). PHF8 protein was located in the nucleoli, in accordance with previous studies in vitro (Feng et al, 2010;Zhu et al, 2010). …”

“…As PHF8 has been previously linked to rRNA synthesis and assigned a putative function in cell cycle progression (Feng et al, 2010;Liu et al, 2010;Zhu et al, 2010), we set out to validate these effects in PrCa cell lines. PHF8 silencing significantly (Po0.001) reduced cell proliferation of the most rapidly proliferating PrCa cell lines (LNCaP, 22rV-1, DU-145 and PC-3), and least affected the nontransformed normal primary prostate epithelial and premalignant RWPE-1 cells ( Figure 6).…”

The Epigenetic Pathways to Ribosomal DNA Silencing

“…In contrast, JMJD2b, which demethylates H3K9me2/3 in the pericentromeric heterochromatin, is found enriched on both rDNA promoters and the 28S rRNA coding sequence in colon and prostate cancer cells, implying that JMJD2b has a role in disrupting rDNA silencing (85). Human PHF8 also negatively regulates rDNA silencing by binding to the promoter of the rRNA gene and specifically demethylating H3K9me2 (86,87).…”

The G2/M Regulator Histone Demethylase PHF8 Is Targeted for Degradation by the Anaphase-Promoting Complex Containing CDC20

“…PHF8 activates gene transcription primarily by demethylating H3K9me1 and H4K20me1 (7,9). At ribosomal DNA (rDNA) loci, however, PHF8 preferentially demethylates H3K9me2 (11,12). The importance of enzymatic demethylation mediated by PHF8 is underscored by the discovery of the link between PHF8 mutations that disrupt its enzymatic activity and X-linked intellectual disability (XLID) and craniofacial deformities (13)(14)(15).…”