Characterization of Nuclear Localization Signal in the N Terminus of CUL4B and Its Essential Role in Cyclin E Degradation and Cell Cycle Progression
Characterization of Nuclear Localization Signal in the N Terminus of CUL4B and Its Essential Role in Cyclin E Degradation and Cell Cycle Progression
复制标题
CUL4B N 末端核定位信号的表征及其在细胞周期蛋白 E 降解和细胞周期进展中的重要作用
DOI：
10.1074/jbc.m109.050427
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发表时间：
2009-11-27
影响因子：
4.8
通讯作者：
Gong, Yaoqin
中科院分区：
文献类型：
--
作者：
Zou, Yongxin;Mi, Jun;Gong, Yaoqin
CUL4A 和 CUL4B 源自同一祖先 CUL4，编码组织 cullin-RING 泛素连接酶 (E3) 复合物的支架蛋白。最近的遗传学研究表明，CUL4B 种系突变可导致人类智力低下、身材矮小和其他异常。尽管尚未报道人类 CUL4A 发生种系突变，但观察到 CUL4A 在乳腺癌和肝细胞癌中过度表达。尽管已知 CUL4A 参与许多细胞过程，包括 DNA 修复和细胞周期调节，但人们对 CUL4B 是否具有类似功能知之甚少。在本报告中，我们测试了 CUL4B 在细胞增殖中的功能重要性，并表征了对其功能至关重要的核定位信号 (NLS)。我们发现，CUL4B 的 RNA 干扰沉默导致细胞增殖抑制和 S 期延长，这是由于细胞周期蛋白 E（CUL4B 泛素化的靶向底物）过度积累所致。我们发现，与 CUL4A 和其他在 C 末端携带 NLS 的 cullin 不同，CUL4B 中的 NLS 位于其 N 末端，位于氨基酸 37 和 40 之间，KKRK。该NLS可以结合输入蛋白α1、α3和α5。NLS缺失的CUL4B分布在细胞质中，不能促进细胞增殖。因此，NLS介导的CUL4B的核定位对于其在细胞增殖中的正常功能至关重要。
CUL4A and CUL4B, which are derived from the same ancestor, CUL4, encode scaffold proteins that organize cullin-RING ubiquitin ligase (E3) complexes. Recent genetic studies have shown that germ line mutation in CUL4B can cause mental retardation, short stature, and other abnormalities in humans. CUL4A was observed to be overexpressed in breast and hepatocellular cancers, although no germ line mutation in human CUL4A has been reported. Although CUL4A has been known to be involved in a number of cellular processes, including DNA repair and cell cycle regulation, little is known about whether CUL4B has similar functions. In this report, we tested the functional importance of CUL4B in cell proliferation and characterized the nuclear localization signal (NLS) that is essential for its function. We found that RNA interference silencing of CUL4B led to an inhibition of cell proliferation and a prolonged S phase, due to the overaccumulation of cyclin E, a substrate targeted by CUL4B for ubiquitination. We showed that, unlike CUL4A and other cullins that carry their NLS in their C termini, NLS in CUL4B is located in its N terminus, between amino acid 37 and 40, KKRK. This NLS could bind to importin alpha 1, alpha 3, and alpha 5. NLS-deleted CUL4B was distributed in cytoplasm and failed to promote cell proliferation. Therefore, the nuclear localization of CUL4B mediated by NLS is critical for its normal function in cell proliferation.