title: Dissimilar effects of β-lapachone- and hydroxyurea-induced DNA replication stress in root meristem cells of Allium cepa.
abstract: Two anticancer drugs, β-lapachone (β-lap, a naphthoquinone) and hydroxyurea (HU, an inhibitor of ribonucleotide reductase), differently affect nuclear morphology and cell cycle control mechanisms in root meristem cells of Allium cepa. The 18 h treatment with 100 μM β-lap results in a lowered number of M-phase cells, increased occurrence of mitotic abnormalities, including over-condensation of chromosomes, their enhanced stickiness, formation of anaphase bridges, micronucleation and reduced mitotic spindles. Following prolonged incubations using high doses of β-lap, cell nuclei reveal dark-red fluorescence evenly distributed in chromatin surrounding the unstained regions of nucleoli. Both drugs generate H2O2 and induce DNA double strand breaks, which is correlated with γ-phoshorylation of H2AX histones. However, the extent of H2AX phosphorylation (including the frequency of γ-H2AX foci and the relative number cells creating phospho-H2AX domains) is considerably reduced in root meristem cells treated jointly with the β-lap/HU mixture. Furthermore, various effects of caffeine (an inhibitor of ATM/ATR cell cycle checkpoint kinases) on β-lap- and HU-induced γ-phoshorylation of H2AX histones and the protective activity of HU against β-lap suggest that their genotoxic activities are largely dissimilar. β-Lap treatment results in the induction of apoptosis-like programmed cell death, while HU treatment leads to cell adaptation to replication stress and promotion of abnormal nuclear divisions with biphasic interphase/mitotic states of chromatin condensation.
authors.affiliation: Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236 Łódź, Poland. Electronic address: zabkka@poczta.onet.pl.
authors.forename: Aneta
authors.initials: A
authors.lastname: Zabka
authors.forename: Paweł
authors.initials: P
authors.lastname: Trzaskoma
authors.forename: Janusz
authors.initials: J
authors.lastname: Maszewski
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D059447:Cell Cycle Checkpoints; D002455:Cell Division / Q000187:drug effects*; D002843:Chromatin / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects*; D018744:DNA, Plant / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D006918:Hydroxyurea / Q000009:adverse effects*; D018519:Meristem / Q000187:drug effects* / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects; D009153:Mutagens / Q000009:adverse effects; D009285:Naphthoquinones / Q000009:adverse effects*; D019697:Onions / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D010936:Plant Extracts / Q000009:adverse effects; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D013312:Stress, Physiological; D029663:Tabebuia / Q000737:chemistry
chemical_list: D002843:Chromatin; D018744:DNA, Plant; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D009153:Mutagens; D009285:Naphthoquinones; D010936:Plant Extracts; C014638:beta-lapachone; D006861:Hydrogen Peroxide; D006918:Hydroxyurea
keywords: Cell cycle checkpoints; DNA damage; Hydrogen peroxide; Hydroxyurea; β-Lapachone; γ-H2AX histones