PHF8 is a histone H3K9me2 demethylase regulating rRNA synthesis

histone H3 离氨酸 9 的 Dimethylation (H3K9me2 ) 是与抄写压抑联系的一个重要 epigenetic 标记。这里，我们识别了 PHF8， JmjC-domain-containing 蛋白质，为这个镇压标记特定的 histone demethylase。Recombinant 全身的野类型蛋白质能把 methylation 从 H3K9me2 移开，但是到丙氨酸 H247A 的保存 histidine 的变化废除 demethylase 活动。Overexpressed 外长的 PHF8 是 colocalized， B23 染色。内长的 PHF8 也是有 B23 和 fibrillarin 的 colocalized，二生长得很好的核蛋白质，建议那 PHF8 在核是局部性的并且可以调整 rRNA 抄写。确实， PHF8 跳了到 rDNA 基因的倡导者区域。减少的 PHF8 击倒 rRNA 的表示，和基因的 overexpression 导致了 rRNA 的 upregulation 抄本。附随地， H3K9me2 水平在 PHF8 击倒的房间在 rDNA 基因的倡导者区域被提高并且当野类型然而并非催化地不活跃的 H247A 变异的 PHF8 是 overexpressed 时，显著地减少了。因此，我们的学习为调整 rRNA 抄写的 H3K9me2 识别了 histone demethylase。

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.