Zhang S Y, Liu S C, Johnson D G, Klein-Szanto A J
Department of Pathology, For Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Cancer Res. 2000 Nov 1;60(21):5972-6.
The transcription factor E2F-1, a downstream regulator of the p16-cyclinD-Rb pathway, is required for cell cycle progression. Evidence shows that overexpression of E2F-1 can either promote or inhibit development of tumors, depending on tissue or experimental conditions. To study whether the E2F-1 gene plays a role in tumor progression, the expression of E2F-1 protein was evaluated in 10 human head and neck squamous cell carcinoma cell lines using Western blot analysis. In addition, the invasive ability of these cell lines was determined by evaluating the penetration of cell lines into the tracheal wall in an in vivo invasion assay using deepithelialized tracheas transplanted into the s.c. tissue of Scid mice. This study showed that the aggressive cell lines had higher expression of E2F-1 than the less invasive cell lines. To evaluate the hypothesis that E2F-1 enhances invasiveness, we selected two cell lines, SCC9 and SCC12, for a gene transfer experiment. These cell lines exhibited low invasive ability with low expression of E2F-1. Two stable clones with overexpression of transfected E2F-1 gene and two clones with their respective vector-alone control were selected from each cell line for in vivo invasion evaluation. The clones containing the transfected E2F-1 gene had significantly higher invasive ability than their respective vector-alone clones. Flow cytometry showed that parental, transfected E2F-1, and vector-alone cells had a similar proliferation pattern under normal culture conditions. Nevertheless, transfected E2F-1 cells exhibited a higher portion of cells in S phase than the control cells after serum-starvation and refeeding. The results indicated that overexpression of E2F-1 plays a positive role in cell cycle reentry from quiescence and is associated with increased in vivo invasiveness.
转录因子E2F-1是p16-细胞周期蛋白D-Rb通路的下游调节因子，是细胞周期进程所必需的。有证据表明，E2F-1的过表达可促进或抑制肿瘤发展，这取决于组织或实验条件。为了研究E2F-1基因在肿瘤进展中是否发挥作用，我们使用蛋白质免疫印迹分析评估了10种人头颈部鳞状细胞癌细胞系中E2F-1蛋白的表达。此外，通过在体内侵袭试验中评估细胞系对移植到Scid小鼠皮下组织的去上皮气管壁的穿透能力，来确定这些细胞系的侵袭能力。这项研究表明，侵袭性强的细胞系比侵袭性弱的细胞系具有更高的E2F-1表达。为了评估E2F-1增强侵袭性的假说，我们选择了两种细胞系SCC9和SCC12进行基因转移实验。这些细胞系侵袭能力低，E2F-1表达也低。从每个细胞系中选择两个转染E2F-1基因过表达的稳定克隆和两个各自单独载体对照的克隆进行体内侵袭评估。含有转染E2F-1基因的克隆比各自单独载体克隆具有显著更高的侵袭能力。流式细胞术显示，亲本细胞、转染E2F-1的细胞和单独载体细胞在正常培养条件下具有相似的增殖模式。然而，血清饥饿和再喂养后，转染E2F-1基因的细胞在S期的细胞比例高于对照细胞。结果表明，E2F-1的过表达在细胞从静止期重新进入细胞周期中起积极作用，并与体内侵袭性增加有关。
