The endothelium contributes to the pathophysiology of adverse effects caused by conventional (genotoxic) anticancer therapeutics (cAT). The relevance of structurally different types of cAT-induced DNA lesions for eliciting selected endothelial stress responses is largely unknown. Here, we analyzed the cAT-induced formation of DNA double-strand breaks (DSB), transcription blockage and DNA damage response (DDR) in time kinetic analyses employing a monolayer of primary human endothelial cells (HUVEC). We observed that the degree of cAT-induced transcription blockage, the number of DSB and activation of DDR-related factors diverge. For instance, ionizing radiation caused the formation of numerous DSB and triggerd a substantial activation of ATM/Chk2 signaling, which however were not accompanied by a significant transcription inhibition. By contrast, the DNA cross-linking cAT cisplatin triggered a rapid and substantial blockage of transcription, which yet was not reflected by an appreciable number of DSB or increased levels of pATM/pChk2. In general, cAT-stimulated ATM-dependent phosphorylation of Kap1 (Ser824) and p53 (Ser15) reflected best cAT-induced transcription blockage. In conclusion, cAT-induced formation of DSB and profound activation of prototypical DDR factors is independent of the inhibition of RNA polymerase II-regulated transcription in an endothelial monolayer. We suggest that DSB formed directly or indirectly following cAT-treatment do not act as comprehensive triggers of superior signaling pathways shutting-down transcription while, at the same time, causing an appreciable stimulation of the DDR. Rather, it appears that distinct cAT-induced DNA lesions elicit diverging signaling pathways, which separately control transcription vs. DDR activity in the endothelium.
Keywords: DNA adduct; DNA damage response; Genotoxins; Non-replicating endothelial cells; Transcription.
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