Qi Runzi, An Huazhang, Yu Yizhi, Zhang Minghui, Liu Shuxun, Xu Hongmei, Guo Zhenghong, Cheng Tao, Cao Xuetao
Institute of Immunology, Second Military Medical University, Shanghai, People's Republic of China.
Cancer Res. 2003 Dec 1;63(23):8323-9.
Notch signaling plays a critical role in maintaining the balance between cell proliferation, differentiation, and apoptosis; hence, perturbed Notch signaling may contribute to tumorigenesis. Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in Africa and Asia. The mechanisms that orchestrate the multiple oncogenic insults required for initiation and progression of HCC are not clear. We constitutively overexpressed active Notch1 in human HCC to explore the effects of Notch1 signaling on HCC cell growth and to investigate the underlying molecular mechanisms. We show here that overexpression of Notch1 was able to inhibit the growth of HCC cells in vitro and in vivo. Biochemical analysis revealed the involvement of cell cycle regulated proteins in Notch1-mediated G(0)/G(1) arrest of HCC cells. Compared with green fluorescent protein (GFP) control, transient transfection of Notch1 ICN decreased expression of cyclin A (3.5-fold), cyclin D1 (2-fold), cyclin E (4.5-fold), CDK2 (2.8-fold), and the phosphorylated form of retinoblastoma protein (3-fold). Up-regulation of p21(waf/cip1) protein expression was observed in SMMC7721-ICN cells stably expressing active Notch1 but not in SMMC7721-GFP cells, which only express GFP. Furthermore, a 12-fold increase in p53 expression and an increase (4.8-fold) in Jun-NH(2)-terminal kinase activation were induced in SMMC7721-ICN cells compared with SMMC7721-GFP cells. In contrast, expression of the antiapoptotic Bcl-2 protein could not be detected in SMMC7721-ICN cells. These findings suggest that Notch1 signaling may participate in the development of HCC cells, affecting multiple pathways that control both cell proliferation and apoptosis.
Notch信号通路在维持细胞增殖、分化和凋亡之间的平衡中起着关键作用；因此，Notch信号通路紊乱可能会促进肿瘤发生。肝细胞癌（HCC）是非洲和亚洲最常见的恶性肿瘤之一。引发和推动HCC起始和进展所需的多种致癌损伤的协调机制尚不清楚。我们在人HCC中组成性过表达活性Notch1，以探讨Notch1信号通路对HCC细胞生长的影响，并研究其潜在的分子机制。我们在此表明，Notch1的过表达能够在体外和体内抑制HCC细胞的生长。生化分析揭示了细胞周期调节蛋白参与Notch1介导的HCC细胞G(0)/G(1)期阻滞。与绿色荧光蛋白（GFP）对照相比，瞬时转染Notch1 ICN可使细胞周期蛋白A（3.5倍）、细胞周期蛋白D1（2倍）、细胞周期蛋白E（4.5倍）、细胞周期蛋白依赖性激酶2（CDK2，2.8倍）以及视网膜母细胞瘤蛋白的磷酸化形式（3倍）的表达降低。在稳定表达活性Notch1的SMMC7721-ICN细胞中观察到p21(waf/cip1)蛋白表达上调，而在仅表达GFP的SMMC7721-GFP细胞中未观察到。此外，与SMMC7721-GFP细胞相比，SMMC7721-ICN细胞中p53表达增加了12倍，Jun-NH(2)-末端激酶激活增加了4.8倍。相反，在SMMC7721-ICN细胞中未检测到抗凋亡Bcl-2蛋白的表达。这些发现表明，Notch1信号通路可能参与HCC细胞的发生发展，影响控制细胞增殖和凋亡的多种途径。
