Shuttling imbalance of MLF1 results in p53 instability and increases susceptibility to oncogenic transformation
Shuttling imbalance of MLF1 results in p53 instability and increases susceptibility to oncogenic transformation
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DOI：
10.1128/mcb.02335-06
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发表时间：
2008-01-01
影响因子：
5.3
通讯作者：
Kato, Jun-ya
中科院分区：
文献类型：
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作者：
Yoneda-Kato, Noriko;Kato, Jun-ya
髓系白血病因子1 （MLF1）通过COPS信号体的第三个组分（CSN3）抑制其E3泛素连接酶COP1，从而稳定肿瘤抑制因子p53的活性。然而，对于MLF1如何在CSN3-COP1-p53通路上游发挥作用，以及由t(3;5)（q25.1;q34）染色体易位产生融合蛋白核磷蛋白(NPM)-MLF1如何导致白血病发生，人们知之甚少。在这里，我们发现MLF1是一种细胞质核穿梭蛋白，其与NPM融合时的核核定位阻止了基因毒性和致癌细胞应激对p53的完全诱导。大多数MLF1位于细胞质中，但用leptomycin B处理细胞可迅速诱导MLF1的核积累。在MLF1序列中发现的核输出信号（NES）基序突变增强了MLF1的抗增殖活性。MLF1与NPM的融合将MLF1转移到核仁中，消除了其抑制生长的活性。将NPM-MLF1引入早期传代小鼠胚胎成纤维细胞，使细胞在明显更早的阶段摆脱细胞衰老，并与致癌形式的Ras协同诱导肿瘤转化。有趣的是，破坏mlf1衍生的NES序列完全消除了NPM-MLF1在小鼠成纤维细胞和造血细胞中的促生长活性。因此，我们的研究结果提供了重要的证据，证明MLF1的穿梭对细胞增殖的调节至关重要，而穿梭平衡的紊乱会增加细胞对致癌转化的易感性。
Myeloid leukemia factor 1 (MLF1) stabilizes the activity of the tumor suppressor p53 by suppressing its E3 ubiquitin ligase, COP1, through a third component of the COPS signalosome (CSN3). However, little is known about how MLF1 functions upstream of the CSN3-COP1-p53 pathway and how its deregulation by the formation of the fusion protein nucleophosmin (NPM)-MLF1, generated by t(3;5)(q25.1;q34) chromosomal translocation, leads to leukemogenesis. Here we show that MLF1 is a cytoplasmic-nuclear-shuttling protein and that its nucleolar localization on fusing with NPM prevents the full induction of p53 by both genotoxic and oncogenic cellular stress. The majority of MLF1 was located in the cytoplasm, but the treatment of cells with leptomycin B rapidly induced a nuclear accumulation of MLF1. A mutation of the nuclear export signal (NES) motif identified in the MLF1 sequence enhanced the antiproliferative activity of MLF1. The fusion of MLF1 with NPM translocated MLF1 to the nucleolus and abolished the growth-suppressing activity. The introduction of NPM-MLF1 into early-passage murine embryonic fibroblasts allowed the cells to escape from cellular senescence at a markedly earlier stage and induced neoplastic transformation in collaboration with the oncogenic form of Ras. Interestingly, disruption of the MLF1-derived NES sequence completely abolished the growth-promoting activity of NPM-MLF1 in murine fibroblasts and hematopoietic cells. Thus, our results provide important evidence that the shuttling of MLF1 is critical for the regulation of cell proliferation and a disturbance in the shuttling balance increases the cell's susceptibility to oncogenic transformation.