Effects of chromatin decondensation on alternative NHEJ.
In cells of higher eukaryotes, repair of DNA double strand breaks (DSBs) utilizes different forms of potentially error-prone non-homologous end joining (NHEJ): canonical DNA-PK-dependent (C-NHEJ) and alternative backup pathways (A-NHEJ). In contrast to C-NHEJ, A-NHEJ shows pronounced efficiency fluctuations throughout the cell cycle and is severely compromised as cells cease proliferating and enter the plateau phase (Windhofer et al., 2007 [23]). The molecular mechanisms underpinning this response remain unknown but changes in chromatin structure are prime candidate-A-NHEJ-modulators. Since parameters beyond chromatin acetylation appear to determine A-NHEJ efficiency (Manova et al., 2012 [42,76]), we study here the role of chromatin decondensation mediated either by treatment with 5'-aza-2'-deoxycytidine (AzadC) or growth in hypotonic conditions, on A-NHEJ. We report that both treatments have no detectable effect on C-NHEJ but provoke, specifically for A-NHEJ, cell-growth-dependent effects. These results uncover for the first time a link between A-NHEJ and chromatin organization and provide means for understanding the regulatory mechanisms underpinning the growth-state dependency of A-NHEJ. A-NHEJ is implicated in the formation of chromosomal translocations and in chromosome fusions that underlie genomic instability and carcinogenesis. The observations reported here may therefore contribute to the development of drug-based A-NHEJ suppression-strategies aiming at optimizing cancer treatment outcomes and possibly also at suppressing carcinogenesis.
Institute of Medical Radiation Biology, University of Duisburg-Essen, Hufelandstrasse 55, 45122 Essen, Germany.
Mario
M
Moscariello
George
G
Iliakis
D000818:Animals; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002843:Chromatin / Q000737:chemistry / Q000235:genetics*; D043171:Chromosomal Instability; D003596:Cytosine / Q000032:analysis; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D000077209:Decitabine; D005786:Gene Expression Regulation; D006801:Humans; D007038:Hypotonic Solutions; D051379:Mice; D014178:Translocation, Genetic
D002843:Chromatin; D007038:Hypotonic Solutions; D000077209:Decitabine; D003596:Cytosine; D011088:DNA Ligases; D001374:Azacitidine
4′,6-diamidino-2-phenylindole; 5-meC; 5-methyl-cytosine; 5′-aza-2′-deoxycytidine; AzadC; Backup NHEJ; Chromatin condensation; DAPI; DNA double strand breaks (DSBs); DNA methylation; FBS; HDAC; HRR; Ionizing radiation (IR); NHEJ; Non-homologous end-joining; Osm; fetal bovine serum; histone deacetylase; homologous recombination repair; non-homologous end-joining; osmolality