Hubmann Rainer, Schwarzmeier Josef D, Shehata Medhat, Hilgarth Martin, Duechler Markus, Dettke Markus, Berger Rudolf
Department of Hematology, Clinic of Internal Medicine I, University of Vienna, Vienna, Austria.
Blood. 2002 May 15;99(10):3742-7. doi: 10.1182/blood.v99.10.3742.
Members of the Notch family encode transmembrane receptors that modulate differentiation, proliferation, and apoptotic programs of many precursor cells, including hematopoietic progenitors. Stimulation of Notch causes cleavage followed by translocation of the intracellular domain (NotchIC) to the nucleus, where it activates transcription of CBF1 responsive genes. The aim of this study was to elucidate the mechanisms leading to the overexpression of CD23, a striking feature of B-cell chronic lymphocytic leukemia (B-CLL) cells. By electrophoretic mobility shift assays, we identified a transcription factor complex (C1) that binds sequence specific to one known and 4 newly identified putative CBF1 recognition sites in the CD23a core promoter region. With the use of Epstein-Barr virus (EBV)-infected B cells as a model for CBF1 mediated CD23a expression, C1 was found to be EBV inducible. Supershift assays revealed that the nuclear form of Notch2 is a component of C1 in B-CLL cells, supporting a model in which NotchIC activates transcription by binding to CBF1 tethered to DNA. Transient transfection of REH pre-B cells with an activated form of Notch2 induced endogenous CD23a, confirming that CD23a is a target gene of Notch2 signaling. Finally, reverse transcription-polymerase chain reaction and kinetic analysis demonstrated that the Notch2 oncogene is not only overexpressed in B-CLL cells but might also be related to the failure of apoptosis characteristic for this disease. In conclusion, these data suggest that deregulation of Notch2 signaling is involved in the aberrant expression of CD23 in B-CLL.
Notch家族成员编码跨膜受体，可调节包括造血祖细胞在内的许多前体细胞的分化、增殖和凋亡程序。Notch的激活会导致裂解，随后细胞内结构域（NotchIC）易位至细胞核，在细胞核中它会激活CBF1反应性基因的转录。本研究的目的是阐明导致CD23过表达的机制，CD23过表达是B细胞慢性淋巴细胞白血病（B-CLL）细胞的一个显著特征。通过电泳迁移率变动分析，我们鉴定出一种转录因子复合物（C1），它能结合CD23a核心启动子区域中一个已知的和4个新鉴定的假定CBF1识别位点的序列特异性。以爱泼斯坦-巴尔病毒（EBV）感染的B细胞作为CBF1介导的CD23a表达的模型，发现C1是EBV可诱导的。超迁移分析显示，Notch2的核形式是B-CLL细胞中C1的一个组成部分，支持了NotchIC通过与拴系在DNA上的CBF1结合来激活转录的模型。用激活形式的Notch2瞬时转染REH前B细胞可诱导内源性CD23a，证实CD23a是Notch2信号的靶基因。最后，逆转录-聚合酶链反应和动力学分析表明，Notch2癌基因不仅在B-CLL细胞中过表达，而且可能与该疾病特有的凋亡失败有关。总之，这些数据表明Notch2信号失调与B-CLL中CD23的异常表达有关。
