Differential activation of intra-S-phase checkpoint in response to tripchlorolide and its effects on DNA replication

DNA replication is tightly regulated during the S phase of the cell cycle, and the activation of the intra-S-phase checkpoint due to DNA damage usually results in arrest of DNA synthesis. However, the molecular details about the correlation between the checkpoint and regulation of DNA replication are still unclear. To investigate the connections between DNA replication and DNA damage checkpoint, a DNA-damage reagent, tripchlorolide, was applied to CHO (Chinese ovary hamster) cells at early- or middle-stages of the S phase. The early-S-phase treatment with TC significantly delayed the progression of the S phase and caused the phosphorylation of the Chkl checkpoint protein, whereas the middle-S-phase treatment only slightly slowed down the progression of the S phase. Furthermore, the analysis of DNA replication patterns revealed that replication pattern II was greatly prolonged in the cells treated with the drug during the early-S phase, whereas the late-replication patterns of these cells were hardly detected, suggesting that the activation of the intra-S-phase checkpoint inhibits the late-origin firing of DNA replication. We conclude that cells at different stages of the S phase are differentially sensitive to the DNA-damage reagent, and the activation of the intra-S phase checkpoint blocks the DNA replication progression in the late stage of S phase.

介入化疗对宫颈癌DNA含量、细胞周期时相的影响

目的 :探讨介入化疗对宫颈癌DNA含量和细胞周期时相的影响。方法 :取正常宫颈组、宫颈癌组介入化疗前和介入化疗后各 2 0例的宫颈组织标本 ,用流式细胞术测定其DNA含量 (DI)和S期细胞比率 (SPF)。结果 :(1)宫颈癌组介入化疗前和介入化疗后的DI分别为 (1.31± 0 .34,1.10± 0 .15 ) ,都明显高于正常宫颈组 (1.0 1± 0 .0 6 )(P <0 .0 1,P <0 .0 5 )。宫颈癌组介入化疗后的DI显著低于介入化疗前 (P <0 .0 5 )。宫颈癌II期与III、IV期间DI无显著性差异 (P >0 .0 5 )。 (2 )宫颈癌组介入化疗前DNA异倍体为 13例 ,介入化疗后为 6例 ,两者有显著性差异 (P <0 .0 5 )。 (3)宫颈癌组介入化疗前的SPF(2 4 .93± 9.4 6 % )、介入化疗后的SPF(14 .0 3± 6 .5 9% )均较正常宫颈组的SPF高 (6 .99± 4 .0 7% ,P <0 .0 0 1)。宫颈癌组介入化疗后的SPF低于介入化疗前 (P <0 .0 0 1)。III、IV期的SPF显著高于II期的SPF(P <0 .0 5 )。结论 :介入化疗能抑制宫颈癌组织DNA的复制、降低宫颈癌组织的S期细胞比率 。

真核细胞DNA复制叉稳定性维持机制的研究进展

DNA复制是细胞最基本的生命活动之一,是生物体生存和繁殖的基础。从原核生物到真核生物,DNA复制过程基本保守,分为复制起始和延伸两个阶段。复制叉是DNA复制的基本结构,它容易遭受多种内源或外源的DNA复制压力影响而停顿,导致基因组不稳定,引起细胞凋亡、癌变或细胞死亡等严重后果。为了维持复制叉的稳定,细胞进化出了一系列机制,其中最重要机制之一便是S期细胞周期检验点。就影响DNA复制叉稳定的内外因素、S期细胞周期检验点与复制叉稳定性的关系以及复制叉稳定性与相关疾病的发生、治疗等问题进行简要综述。