Frisan Teresa, Cortes-Bratti Ximena, Chaves-Olarte Esteban, Stenerlöw Bo, Thelestam Monica
Microbiology and Tumorbiology Center, Karolinska Institutet, Box 280, S-171 77 Stockholm, Sweden.
Cell Microbiol. 2003 Oct;5(10):695-707. doi: 10.1046/j.1462-5822.2003.00311.x.
Among bacterial protein toxins, the cytolethal distending toxins (CDTs) are unique in their ability to activate the DNA damage checkpoint responses, causing cell cycle arrest or apoptosis in intoxicated cells. We provide direct evidence that natural intoxication of cells with the Haemophilus ducreyi CDT (HdCDT) holotoxin induces DNA double-strand breaks similarly to ionizing radiation. Upon DNA damage, epithelial cells and fibroblasts promote the formation of actin stress fibres via activation of the small GTPase RhoA. This phenomenon is not toxin specific, but is part of the ATM-induced cellular responses to genotoxic stresses, including ionizing radiation. Activation of RhoA is associated with prolonged cell survival, as HdCDT-treated epithelial cells expressing a dominant-negative form of RhoA detach and consequently die faster than cells expressing a functional RhoA. Our data highlight several novel aspects of CDT biology: (i) we show that a member of the CDT family causes DNA double-strand breaks in naturally intoxicated cells, acting as a true genotoxic agent; and (ii) we disclose the existence of a novel signalling pathway for intracellularly triggered activation of the RhoA GTPase via the ATM kinase in response to DNA damage, possibly required to prolong cell survival.
在细菌蛋白毒素中，细胞致死性膨胀毒素（CDTs）在激活DNA损伤检查点反应的能力方面独具特色，可导致中毒细胞的细胞周期停滞或凋亡。我们提供了直接证据，表明用杜克雷嗜血杆菌CDT（HdCDT）全毒素对细胞进行自然中毒会诱导DNA双链断裂，这与电离辐射类似。DNA损伤后，上皮细胞和成纤维细胞通过激活小GTP酶RhoA促进肌动蛋白应激纤维的形成。这种现象并非毒素特异性的，而是ATM诱导的细胞对包括电离辐射在内的基因毒性应激反应的一部分。RhoA的激活与细胞存活时间延长相关，因为用HdCDT处理的表达RhoA显性阴性形式的上皮细胞会脱离，因此比表达功能性RhoA的细胞死亡更快。我们的数据突出了CDT生物学的几个新方面：（i）我们表明CDT家族的一个成员在自然中毒的细胞中导致DNA双链断裂，作为一种真正的基因毒性剂；（ii）我们揭示了存在一种新的信号通路，即细胞内通过ATM激酶触发RhoA GTP酶的激活以响应DNA损伤，这可能是延长细胞存活所必需的。
