Bcl-2/Bax protein ratio predicts 5-fluorouracil sensitivity independently of p53 status

Br J Cancer. 2000 Nov;83(10):1380-6. doi: 10.1054/bjoc.2000.1455.


p53 tumour-suppressor gene is involved in cell growth control, arrest and apoptosis. Nevertheless cell cycle arrest and apoptosis induction can be observed in p53-defective cells after exposure to DNA-damaging agents such as 5-fluorouracil (5-FU) suggesting the importance of alternative pathways via p53-independent mechanisms. In order to establish relationship between p53 status, cell cycle arrest, Bcl-2/Bax regulation and 5-FU sensitivity, we examined p53 mRNA and protein expression and p53 protein functionality in wild-type (wt) and mutant (mt) p53 cell lines. p53 mRNA and p53 protein expression were determined before and after exposure to equitoxic 5-FU concentration in six human carcinoma cell lines differing in p53 status and displaying marked differences in 5-FU sensitivity, with IC(50)values ranging from 0.2-22.6 mM. 5-FU induced a rise in p53 mRNA expression in mt p53 cell lines and in human papilloma virus positive wt p53 cell line, whereas significant decrease in p53 mRNA expression was found in wt p53 cell line. Whatever p53 status, 5-FU altered p53 transcriptional and translational regulation leading to up-regulation of p53 protein. In relation with p53 functionality, but independently of p53 mutational status, after exposure to 5-FU equitoxic concentration, all cell lines were able to arrest in G1. No relationship was evidenced between G1 accumulation ability and 5-FU sensitivity. Moreover, after 5-FU exposure, Bax and Bcl-2 proteins regulation was under p53 protein control and a statistically significant relationship (r = 0.880, P = 0.0097) was observed between Bcl-2/Bax ratio and 5-FU sensitivity. In conclusion, whatever p53 status, Bcl-2 or Bax induction and Bcl-2/Bax protein ratio were correlated to 5-FU sensitivity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenocarcinoma / genetics*
  • Adenocarcinoma / pathology
  • Apoptosis / drug effects*
  • Breast Neoplasms / genetics*
  • Breast Neoplasms / pathology
  • Carcinoma / genetics*
  • Carcinoma / pathology
  • Cell Cycle
  • Dose-Response Relationship, Drug
  • Female
  • Fluorouracil / pharmacology*
  • Gene Expression Regulation, Neoplastic
  • Genes, p53 / genetics*
  • Head and Neck Neoplasms / genetics*
  • Head and Neck Neoplasms / pathology
  • Humans
  • Pancreatic Neoplasms / genetics*
  • Pancreatic Neoplasms / pathology
  • Proto-Oncogene Proteins / analysis*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins c-bcl-2 / analysis*
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • RNA, Messenger / biosynthesis
  • Tumor Cells, Cultured / drug effects
  • Up-Regulation
  • bcl-2-Associated X Protein


  • BAX protein, human
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • RNA, Messenger
  • bcl-2-Associated X Protein
  • Fluorouracil