Role of retinoblastoma protein and E2F-1 transcription factor in the acquisition of 5-fluorouracil resistance by colon cancer cells.
5-fluorouracil (5-FU) is an important antineoplastic agent that has proven to be effective in the treatment of colorectal cancer. However, one of the main obstacles to the clinical use of 5-FU is the acquisition of resistance to the drug by cancer cells. In vitro studies have demonstrated that the resistance to 5-FU is correlated with increased activity of thymidylate synthase (TS), whose gene has a E2F binding site in its promoter region. To understand the mechanisms through which cancer cells acquire resistance to 5-FU, human colon cancer-derived cell line DLD-1 and its subcloned cell line DLD-1/5-FU, which has acquired resistance to 5-FU, were compared by assessing their phosphorylation of retinoblastoma protein (pRb) and E2F-1 transcriptional activity. The level of pRb phosphorylation in the DLD-1/5-FU cells was higher than in the parental DLD-1cells. In parallel with the increased phosphorylation of pRb, E2F-1 transcriptional activity, which has been shown to be a result of E2F-1 dissociation from hyperphosphorylated pRb, was increased in the DLD-1/5-FU cells. Examination of the effect of E2F-1 decoy oligodeoxynucleotides (ODNs) on the proliferation of DLD-1/5-FU cells in the presence of 5-FU to confirm the importance of E2F-1 in the mechanisms of the acquisition of 5-FU resistance showed that DLD-1/5-FU cells transfected with E2F-1 decoy ODNs recovered their sensitivity to 5-FU. These results suggested that pRb and E2F-1 play important roles in the acquisition of 5-FU resistance by cancer cells and that cancer therapy targeting transcription factor E2F might be effective.
Department of Surgery, Tazuke Kofukai Medical Research Institute and Kitano Hospital, Osaka 530-8480, Japan.
Kazutaka
K
Obama
Michiyuki
M
Kanai
Yasuhiro
Y
Kawai
Masakazu
M
Fukushima
Arimichi
A
Takabayashi
D000964:Antimetabolites, Antineoplastic / Q000627:therapeutic use*; D015153:Blotting, Western; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D004268:DNA-Binding Proteins; D019008:Drug Resistance, Neoplasm; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D024202:Electrophoretic Mobility Shift Assay; D005472:Fluorouracil / Q000627:therapeutic use*; D005786:Gene Expression Regulation; D006801:Humans; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D016160:Retinoblastoma Protein / Q000378:metabolism*; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D000964:Antimetabolites, Antineoplastic; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D009838:Oligodeoxyribonucleotides; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D013940:Thymidylate Synthase; D005472:Fluorouracil