Dissimilar effects of β-lapachone- and hydroxyurea-induced DNA replication stress in root meristem cells of Allium cepa

Plant Physiol Biochem. 2013 Dec:73:282-93. doi: 10.1016/j.plaphy.2013.10.001. Epub 2013 Oct 11.

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.

Keywords: Cell cycle checkpoints; DNA damage; Hydrogen peroxide; Hydroxyurea; β-Lapachone; γ-H2AX histones.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects
  • Cell Cycle Checkpoints
  • Cell Division / drug effects*
  • Chromatin / metabolism
  • DNA Breaks, Double-Stranded
  • DNA Damage*
  • DNA Replication / drug effects*
  • DNA, Plant / metabolism
  • DNA-Binding Proteins / metabolism
  • Histones / genetics
  • Histones / metabolism
  • Humans
  • Hydrogen Peroxide / metabolism
  • Hydroxyurea / adverse effects*
  • Meristem / drug effects*
  • Meristem / metabolism
  • Mitosis / drug effects
  • Mutagens / adverse effects
  • Naphthoquinones / adverse effects*
  • Onions / drug effects*
  • Onions / genetics
  • Onions / metabolism
  • Phosphorylation
  • Plant Extracts / adverse effects
  • Plant Roots / drug effects
  • Plant Roots / metabolism
  • Stress, Physiological
  • Tabebuia / chemistry

Substances

  • Chromatin
  • DNA, Plant
  • DNA-Binding Proteins
  • H2AX protein, human
  • Histones
  • Mutagens
  • Naphthoquinones
  • Plant Extracts
  • beta-lapachone
  • Hydrogen Peroxide
  • Hydroxyurea