Schild-Poulter C, Pope L, Giffin W, Kochan J C, Ngsee J K, Traykova-Andonova M, Haché R J
Department of Medicine, The Loeb Health Research Institute at the Ottawa Hospital, University of Ottawa, Ottawa, Ontario K1Y 4E9, Canada.
J Biol Chem. 2001 May 18;276(20):16848-56. doi: 10.1074/jbc.M100768200. Epub 2001 Feb 20.
The Ku antigen (70- and 80-kDa subunits) is a regulatory subunit of DNA-dependent protein kinase (DNA-PK) that promotes the recruitment of the catalytic subunit of DNA-PK (DNA-PKcs) to DNA ends and to specific DNA sequences from which the kinase is activated. Ku and DNA-PKcs plays essential roles in double-stranded DNA break repair and V(D)J recombination and have been implicated in the regulation of specific gene transcription. In a yeast two-hybrid screen of a Jurkat T cell cDNA library, we have identified a specific interaction between the 70-kDa subunit of Ku heterodimer and the homeodomain of HOXC4, a homeodomain protein expressed in the hematopoietic system. Unexpectedly, a similar interaction with Ku was observed for several additional homeodomain proteins including octamer transcription factors 1 and 2 and Dlx2, suggesting that specific binding to Ku may be a property shared by many homeodomain proteins. Ku-homeodomain binding was mediated through the extreme C terminus of Ku70 and was abrogated by amino acid substitutions at Lys595/Lys596. Ku binding allowed the recruitment of the homeodomain to DNA ends and dramatically enhanced the phosphorylation of homeodomain-containing proteins by DNA-PK. These results suggest that Ku functions as a substrate docking protein for signaling by DNA-PK to homeodomain proteins from DNA ends.
Ku抗原（70 kDa和80 kDa亚基）是DNA依赖性蛋白激酶（DNA-PK）的调节亚基，可促进DNA-PK催化亚基（DNA-PKcs）募集至DNA末端以及激酶被激活的特定DNA序列。Ku和DNA-PKcs在双链DNA断裂修复和V(D)J重组中发挥重要作用，并与特定基因转录的调控有关。在对Jurkat T细胞cDNA文库进行的酵母双杂交筛选中，我们鉴定出Ku异二聚体的70 kDa亚基与HOXC4的同源结构域之间存在特异性相互作用，HOXC4是一种在造血系统中表达的同源结构域蛋白。出乎意料的是，在包括八聚体转录因子1和2以及Dlx2在内的其他几种同源结构域蛋白中也观察到了与Ku的类似相互作用，这表明与Ku的特异性结合可能是许多同源结构域蛋白共有的特性。Ku-同源结构域结合是通过Ku70的极端C末端介导的，并被Lys595/Lys596处的氨基酸取代所消除。Ku结合可使同源结构域募集至DNA末端，并显著增强DNA-PK对含同源结构域蛋白的磷酸化作用。这些结果表明，Ku作为一种底物对接蛋白，通过DNA-PK从DNA末端向同源结构域蛋白传递信号。
