Cho Young-Wook, Hong Teresa, Hong Sunhwa, Guo Hong, Yu Hong, Kim Doyeob, Guszczynski Tad, Dressler Gregory R, Copeland Terry D, Kalkum Markus, Ge Kai
Nuclear Receptor Biology Section, Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Biol Chem. 2007 Jul 13;282(28):20395-406. doi: 10.1074/jbc.M701574200. Epub 2007 May 11.
PTIP, a protein with tandem BRCT domains, has been implicated in DNA damage response. However, its normal cellular functions remain unclear. Here we show that while ectopically expressed PTIP is capable of interacting with DNA damage response proteins including 53BP1, endogenous PTIP, and a novel protein PA1 are both components of a Set1-like histone methyltransferase (HMT) complex that also contains ASH2L, RBBP5, WDR5, hDPY-30, NCOA6, SET domain-containing HMTs MLL3 and MLL4, and substoichiometric amount of JmjC domain-containing putative histone demethylase UTX. PTIP complex carries robust HMT activity and specifically methylates lysine 4 (K4) on histone H3. Furthermore, PA1 binds PTIP directly and requires PTIP for interaction with the rest of the complex. Moreover, we show that hDPY-30 binds ASH2L directly. The evolutionarily conserved hDPY-30, ASH2L, RBBP5, and WDR5 likely constitute a subcomplex that is shared by all human Set1-like HMT complexes. In contrast, PTIP, PA1, and UTX specifically associate with the PTIP complex. Thus, in cells without DNA damage agent treatment, the endogenous PTIP associates with a Set1-like HMT complex of unique subunit composition. As histone H3 K4 methylation associates with active genes, our study suggests a potential role of PTIP in the regulation of gene expression.
PTIP是一种具有串联BRCT结构域的蛋白质，与DNA损伤反应有关。然而，其正常的细胞功能仍不清楚。在这里，我们表明，虽然异位表达的PTIP能够与包括53BP1在内的DNA损伤反应蛋白相互作用，但内源性PTIP和一种新蛋白PA1都是Set1样组蛋白甲基转移酶（HMT）复合物的组成成分，该复合物还包含ASH2L、RBBP5、WDR5、hDPY-30、NCOA6、含SET结构域的HMTs MLL3和MLL4，以及亚化学计量的含JmjC结构域的假定组蛋白去甲基化酶UTX。PTIP复合物具有强大的HMT活性，并特异性地使组蛋白H3上的赖氨酸4（K4）甲基化。此外，PA1直接结合PTIP，并需要PTIP与复合物的其他部分相互作用。而且，我们表明hDPY-30直接结合ASH2L。进化上保守的hDPY-30、ASH2L、RBBP5和WDR5可能构成一个所有人类Set1样HMT复合物共有的亚复合物。相比之下，PTIP、PA1和UTX特异性地与PTIP复合物相关联。因此，在没有DNA损伤剂处理的细胞中，内源性PTIP与具有独特亚基组成的Set1样HMT复合物相关联。由于组蛋白H3 K4甲基化与活跃基因相关，我们的研究表明PTIP在基因表达调控中具有潜在作用。
