Apoptosis or senescence-like growth arrest: Influence of cell-cycle position, p53, p21 and bax in H2O2 response of normal human fibroblasts

Qin M. Chen, Juping Liu, Jessica B. Merrett

Research output: Contribution to journalArticlepeer-review

229 Scopus citations


Early-passage human diploid fibroblasts (HDFs) undergo senescence-like growth arrest in response to sublethal concentrations of H2O2. We determine here whether H2O2 can cause apoptosis in HDFs and the molecular changes that differ between apoptosis and senescence-like growth arrest. When exponentially growing early-passage IMR-90 cells were treated for 2 h with 50-200 μM (or 0.25-1 pmol/cell) H2O2, a fraction of cells detached at 16-32 h after the treatment. The cells remaining attached were growth-arrested and developed features of senescence in 1 week. The detached cells showed caspase-3 activation and typical morphological changes associated with apoptosis. Caspase-3 activation was H2O2 dose-dependent and preceded nuclear condensation or plasma membrane leakage. Apoptotic cells were mainly distributed in the S-phase of the cell cycle, while growth-arrested cells exhibited predominantly G1- and G2/M-phase distributions. H2O2 pretreatment induced G1 arrest and prohibited induction of apoptosis by a subsequent H2O2 challenge. The p53 protein showed an average 6.1-fold elevation in apoptotic cells and a 3.5-fold elevation in growth-arrested cells. Reduction of p53 levels with human papillomavirus E6 protein prohibited the activation of caspase-3 and decreased the proportion of apoptotic cells. Growth-arrested cells had elevated p21, while p21 was absent in apoptotic cells. Bcl-2 was elevated in both growth-arrested and apoptotic cells. Finally, although the overall level of bax did not change in growth-arrested or apoptotic cells, the solubility of bax protein increased in apoptotic cells. Our data suggest that in contrast with growth arrested cells, apoptotic cells show an S-phase cell cycle distribution, a higher degree of p53 elevation, an absence of p21 protein and increased solubility of bax protein.

Original languageEnglish (US)
Pages (from-to)543-551
Number of pages9
JournalBiochemical Journal
Issue number2
StatePublished - Apr 15 2000


  • Caspases
  • G1 arrest
  • Oxidants
  • S-phase

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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