PHF8 mediates histone demethylation events in cell cycle progression [expression]

While reversible histone modifications are linked to an ever-expanding range of biological functions, the demethylases for histone H4 lysine 20 and their potential regulatory roles remain unknown. Here, we report that the PHD and Jumonji C (JmjC) domain-containing protein, PHF8, while utilizing multiple substrates, including H3K9me1/2 and H3K27me2, also functions as an H4K20me1 demethylase. PHF8 is recruited to promoters by its PHD domain based on interaction with H3K4me2/3 and controls G1/S transition in conjunction with E2F1, HCF-1 and Set1A, at least in part, by removing the repressive H4K20me1 mark from a subset of E2F1-regulated gene promoters. Phosphorylation-dependent PHF8 dismissal from chromatin in prophase is apparently required for the accumulation of H4K20me1 during early mitosis, which might represent a component of the Condensin II loading process. Accordingly, the HEAT repeat clusters in two non-SMC Condensin II subunits, N-CAPD3 and N-CAPG2, are capable of recognizing H4K20me1, and ChIP-seq. analysis demonstrate a significant overlap of Condensin II and H4K20me1 sites in mitotic HeLa cells. Thus, the identification and characterization of an H4K20me1 demethylase, PHF8, has revealed an intimate link between this enzyme and two distinct events in cell cycle progression. Keywords: Expression profiling by array HeLa cells were transfected with either control or PHF8 siRNAs. Experiments were performed in biological duplicates. RNA were extracted and sujected to microarray analysis.

尽管可逆组蛋白修饰（reversible histone modifications）所关联的生物学功能正持续拓展，但组蛋白H4赖氨酸20位（histone H4 lysine 20, H4K20）的去甲基化酶（demethylase）及其潜在调控作用仍未被阐明。本研究报道，同时包含PHD结构域（PHD domain）与Jumonji C（JmjC）结构域的蛋白PHF8，除可利用H3K9me1/2、H3K27me2等多种底物外，还可作为H4K20me1去甲基化酶发挥功能。PHF8可通过其PHD结构域与H3K4me2/3结合，被招募至基因启动子区域；其至少可通过移除部分受E2F1调控的基因启动子上的抑制性H4K20me1修饰标记，与E2F1、HCF-1及Set1A协同调控G1/S期转换。有丝分裂前期依赖磷酸化的PHF8从染色质上解离，这一过程似乎是有丝分裂早期H4K20me1积累所必需的，而该过程可能是凝集素II（Condensin II）加载过程的组成部分。据此，两个不含SMC结构域的凝集素II亚基N-CAPD3与N-CAPG2中的HEAT重复序列簇（HEAT repeat clusters）可识别H4K20me1；染色质免疫共沉淀测序（ChIP-seq, chromatin immunoprecipitation sequencing）分析显示，有丝分裂期HeLa细胞中凝集素II结合位点与H4K20me1富集位点存在显著重叠。综上，本研究鉴定并表征了H4K20me1去甲基化酶PHF8，揭示了该酶与细胞周期进程中两个独立事件间的紧密关联。关键词：芯片表达谱分析（Expression profiling by array）；将HeLa细胞转染对照小干扰RNA（siRNA）或PHF8 siRNA，实验设置生物学重复；提取RNA并进行微阵列分析。