目的　探讨细胞内基本p2 1水平和被应急反应诱导的p2 1,在大肠肿瘤细胞DLD1对化学治疗、放射治疗和基因治疗所诱发的细胞凋亡中的作用和机制。方法　建立受IPTG控制表达p2 1大肠肿瘤细胞系DLD1 p2 1,用阿霉素、X射线和暂时性转染p5 3基因的方法处理表达和不表达p2 1的两种DLD1细胞 ,观察其细胞形态、DNA片段化和测定细胞的生存率 ;并用放射性同位素标记进入S期细胞来显示细胞周期和凋亡间的关系。结果　 (1)p2 1不仅能以p5 3依赖性方式产生 ,而且还能以p5 3非依赖性方式产生。 (2 )细胞内基本的p2 1在抗细胞凋亡中发挥着主要作用 ,而相反 ,应急产生的p2 1几乎不在抗细胞凋亡中发挥作用。凋亡细胞数分别为 9%对 5 5 %、12 %对 6 5 %和 7%对 5 9%。结论　在抗细胞凋亡作用中 ,基本的p2 1比应急产生的p2 1起着更为重要作用 Objective To investigate the role of basic cellular p21 levels and p21, induced by emergency response, in the induction of apoptosis by DLD1 in chemotherapy, radiotherapy and gene therapy. Methods Two DLD1 cells with and without p21 expression were treated with IPTG-controlled expression of the p21 colorectal tumor cell line DLD1 p2 1, adriamycin, X-rays, and transient transfection of the p53 gene. , DNA fragmentation and determination of cell survival; and radioisotope labeled into the S phase cells to show the relationship between cell cycle and apoptosis. Results (1) p21 can be produced not only in a p53-dependent manner but also in a p53 independent manner. (2) The basic p21 in cells plays a major role in anti-apoptosis, but conversely, the p2 1 produced in the emergency does not play a role in anti-apoptosis. The number of apoptotic cells was 9% vs. 55%, 12% vs. 65%, and 7% vs. 59%. Conclusion In the anti-apoptosis effect, the basic p21 plays a more important role than the emergent p21