Novy Michael, Pohn Regina, Andorfer Peter, Novy-Weiland Tina, Galos Barbara, Schwarzmayr Ludwig, Rotheneder Hans
Max F. Perutz Laboratories, Department of Medical Biochemistry, University Departments at the Vienna Biocenter, Medical University of Vienna, A-1030 Vienna, Austria.
Mol Biol Cell. 2005 May;16(5):2181-90. doi: 10.1091/mbc.e04-11-0975. Epub 2005 Feb 16.
E2F transcription factors play an essential role in cell proliferation and apoptosis and their activity is frequently deregulated in human cancers. In a yeast two-hybrid screen we identified a novel E2F-binding protein. Due to its strong phosphorylation we named it EAPP (e2F-associated phosphoprotein). EAPP is localized in the nucleus and interacts with E2F-1, E2F-2, and E2F-3, but not with E2F-4. Examination of a number of human cell lines revealed that EAPP levels are elevated in most transformed cells. Moreover, EAPP mRNA was detected in all investigated human tissues in varying amounts. EAPP is present throughout the cell cycle but disappears during mitosis. In transfection assays with reporters controlled by either an artificial E2F-dependent promoter or the murine thymidine kinase promoter, EAPP increased the activation caused by E2F-1 but not by E2F-4. Surprisingly, the promoter of the p14(ARF) gene, which was also activated by E2F-1, became repressed by EAPP. Overexpression of EAPP in U2OS cells resulted in a significant increase of cells in S-phase, whereas RNAi-mediated knock down of EAPP reduced the fraction of cells in S-phase. Taken together, these data suggest that EAPP modulates E2F-regulated transcription, stimulates proliferation, and may be involved in the malignant transformation of cells.
E2F转录因子在细胞增殖和凋亡中起着至关重要的作用，其活性在人类癌症中经常失调。在酵母双杂交筛选中，我们鉴定出一种新型的E2F结合蛋白。由于其强烈的磷酸化作用，我们将其命名为EAPP（E2F相关磷蛋白）。EAPP定位于细胞核内，并与E2F-1、E2F-2和E2F-3相互作用，但不与E2F-4相互作用。对多种人类细胞系的检测显示，大多数转化细胞中的EAPP水平升高。此外，在所有研究的人类组织中均检测到不同量的EAPP mRNA。EAPP在整个细胞周期中均存在，但在有丝分裂期间消失。在用人工E2F依赖性启动子或鼠胸苷激酶启动子控制的报告基因进行的转染实验中，EAPP增加了由E2F-1引起的激活，但未增加由E2F-4引起的激活。令人惊讶的是，同样被E2F-1激活的p14（ARF）基因的启动子被EAPP抑制。在U2OS细胞中过表达EAPP导致S期细胞显著增加，而RNAi介导的EAPP敲低则降低了S期细胞的比例。综上所述，这些数据表明EAPP调节E2F调控的转录，刺激细胞增殖，并可能参与细胞的恶性转化。
