Halappanavar Sabina S, Shah Girish M
Laboratory for Skin Cancer Research, CHUL Research Center (CHUQ), Faculty of Medicine, Laval University, Sainte-Foy, Quebec, Canada.
Cell Cycle. 2004 Mar;3(3):335-42. Epub 2004 Mar 1.
Poly(ADP-ribose) polymerase-1 (PARP), a DNA damage-responsive nuclear enzyme present in higher eukaryotes, is well-known for its roles in protecting the genome after DNA damage. However, even without exogenous DNA damage, PARP may play a role in stabilizing the genome because cells or mice deficient in PARP exhibit various signs of genomic instability, such as tetraploidy, aneuploidy, chromosomal abnormalities and susceptibility to spontaneous carcinogenesis. Normally, cell cycle checkpoints ensure elimination of cells with genomic abnormalities. Therefore, we examined efficiency of mitotic and post-mitotic checkpoints in PARP-/- and PARP+/+ mouse embryonic fibroblasts treated with mitotic spindle disrupting agent colcemid. PARP+/+ cells, like most mammalian cells, eventually escaped from spindle disruption-induced mitotic checkpoint arrest by 60 h. In contrast, PARP-/- cells rapidly escaped from mitotic arrest within 24 h by downregulation of cyclin B1/CDK-1 kinase activity. After escaping from mitotic arrest; both the PARP genotypes arrive in G1 tetraploid state, where they face post-mitotic checkpoints which either induce apoptosis or prevent DNA endoreduplication. While all the G1 tetraploid PARP+/+ cells were eliminated by apoptosis, the majority of the G1 tetraploid PARP-/- cells became polyploid by resisting apoptosis and carrying out DNA endoreduplication. Introduction of PARP in PARP-/- fibroblasts partially increased the stringency of mitotic checkpoint arrest and fully restored susceptibility to G1 tetraploidy checkpoint-induced apoptosis; and thus prevented formation of polyploid cells. Our results suggest that PARP may serve as a guardian angel of the genome even without exogenous DNA damage through its role in mitotic and post-mitotic G1 tetraploidy checkpoints.
聚（ADP - 核糖）聚合酶 -1（PARP）是一种存在于高等真核生物中的DNA损伤反应性核酶，因其在DNA损伤后保护基因组的作用而闻名。然而，即使没有外源性DNA损伤，PARP也可能在稳定基因组方面发挥作用，因为PARP缺陷的细胞或小鼠表现出各种基因组不稳定的迹象，如四倍体、非整倍体、染色体异常以及对自发致癌的易感性。正常情况下，细胞周期检查点可确保清除具有基因组异常的细胞。因此，我们检测了用有丝分裂纺锤体破坏剂秋水仙酰胺处理的PARP - / - 和PARP + / +小鼠胚胎成纤维细胞中有丝分裂和有丝分裂后检查点的效率。PARP + / +细胞与大多数哺乳动物细胞一样，最终在60小时内从纺锤体破坏诱导的有丝分裂检查点停滞中逃脱。相比之下，PARP - / - 细胞通过下调细胞周期蛋白B1/CDK - 1激酶活性在24小时内迅速从有丝分裂停滞中逃脱。从有丝分裂停滞中逃脱后，两种PARP基因型的细胞都进入G1四倍体状态，在那里它们面临有丝分裂后检查点，该检查点要么诱导细胞凋亡，要么阻止DNA核内复制。虽然所有G1四倍体PARP + / +细胞都通过凋亡被清除，但大多数G1四倍体PARP - / - 细胞通过抵抗凋亡并进行DNA核内复制而变成多倍体。在PARP - / - 成纤维细胞中引入PARP部分增加了有丝分裂检查点停滞的严格性，并完全恢复了对G1四倍体检查点诱导凋亡的敏感性，从而防止了多倍体细胞的形成。我们的结果表明，即使没有外源性DNA损伤，PARP也可能通过其在有丝分裂和有丝分裂后G1四倍体检查点中的作用，充当基因组的守护天使。
