Zhou Ming, Liu Huaying, Xu Xiaojie, Zhou Houde, Li Xiaoling, Peng Cong, Shen Shourong, Xiong Wei, Ma Jian, Zeng Zhaoyang, Fang Songqing, Nie Xinmin, Yang Yixin, Zhou Jie, Xiang Juanjuan, Cao Li, Peng Shuping, Li Shufang, Li Guiyuan
Cancer Research Institute, Central South University Xiang-Ya School of Medicine, 110 Xiang-Ya Road, Changsha, Hunan 410078, China.
J Cell Biochem. 2006 Jul 1;98(4):920-30. doi: 10.1002/jcb.20788.
BRD7, a novel bromodomain gene, is identified to be associated with nasopharyngeal carcinoma (NPC). Decreased or loss of expression of BRD7 was detected in NPC biopsies and cell lines. Overexpression of BRD7 could inhibit NPC cell growth and arrest cells in cell cycle by transcriptionally regulating some important molecules involved in ras/MEK/ERK and Rb/E2F pathway, and downregulate the promoter activity of E2F3. In the present study, the subcellular localization of BRD7 was investigated. It was found that BRD7 was mainly localized in nucleus without distinct cell-specific difference between COS7 and HNE1. Furthermore, a functional nuclear localization signal (NLS) sequence ranging from amino acid 65 to 96 was identified and characterized. The NLS is composed of a cluster of four bipartite nuclear targeting sequences, which are tightly linked and extremely overlapped. We found that whether the entire NLS or the four bipartite nuclear targeting sequences could respectively determine the nuclear import of green fluorescent protein (GFP). The most important is that NLS-deleted BRD7 shifted the nuclear localization to be mostly in cytoplasm, and failed or reduced to negatively regulate the expression of cell cycle related molecules, cyclin D1 and E2F3, and cell cycle progression from G1 to S phase. In conclusion, NLS is an essential motif affecting BRD7 nuclear distribution, and the nuclear localization of BRD7 is critical for the expression of cell cycle related molecules and cell biological function.
BRD7是一种新发现的含溴结构域基因，已被证实与鼻咽癌（NPC）相关。在鼻咽癌活检组织和细胞系中检测到BRD7表达降低或缺失。BRD7的过表达可通过转录调控参与ras/MEK/ERK和Rb/E2F通路的一些重要分子来抑制鼻咽癌细胞生长并使细胞停滞于细胞周期，同时下调E2F3的启动子活性。在本研究中，对BRD7的亚细胞定位进行了研究。结果发现，BRD7主要定位于细胞核，在COS7和HNE1细胞之间无明显的细胞特异性差异。此外，还鉴定并表征了一个从氨基酸65至96的功能性核定位信号（NLS）序列。该NLS由一簇四个二分体核靶向序列组成，它们紧密相连且高度重叠。我们发现，无论是整个NLS还是四个二分体核靶向序列都能分别决定绿色荧光蛋白（GFP）的核输入。最重要的是，缺失NLS的BRD7的核定位大多转移至细胞质，并且无法或减少对细胞周期相关分子细胞周期蛋白D1和E2F3的负调控以及从G1期到S期的细胞周期进程。总之，NLS是影响BRD7核分布的必需基序，BRD7的核定位对于细胞周期相关分子的表达和细胞生物学功能至关重要。
