Different lengths of a polymorphic repeat sequence in the thymidylate synthase gene affect translational efficiency but not its gene expression

Clin Cancer Res. 2001 Dec;7(12):4096-101.


Purpose: Thymidylate synthase (TS) is a target enzyme of 5-fluorouracil. Recently, the TS gene has been shown to contain a polymorphic tandem repeat sequence. The aim of this study was to determine whether differences in the number of tandem repeats could affect gene expression or mRNA translation.

Experimental design: We quantified TS mRNA isolated from 130 colorectal cancer tissues by real-time reverse transcription-PCR and TS protein in 92 available samples by the fluoro-dUMP binding assay. These values were compared with TS genotypes of the samples determined by a PCR assay.

Results: There was no relation between TS genotype and mRNA expression level. On the other hand, cancer tissues with the 3R/3R genotype had a significantly higher TS protein expression level than did those with the 2R/3R genotype. These results suggest that the efficiency of TS mRNA translation is responsible for the genotype-dependent difference in TS protein expression. Further analysis using TS 5'-untranslated region-luciferase reporter constructs showed that the RNA with the three-repeat sequence was translated three to four times more efficiently than that with two-repeat sequence.

Conclusions: From the results of both in vitro and in vivo study, we conclude that TS mRNA with a three-repeat sequence has greater translation efficiency than that with the two-repeat sequence. The results provide the rationale for comprehensive usage of TS genotyping with quantitation of TS mRNA or TS protein to predict the patient's response to 5-fluorouracil-based chemotherapy.

MeSH terms

  • 5' Untranslated Regions / genetics
  • Animals
  • Coleoptera
  • Colorectal Neoplasms / enzymology
  • Colorectal Neoplasms / genetics*
  • Gene Expression Regulation, Enzymologic*
  • Gene Expression Regulation, Neoplastic*
  • Genes, Reporter
  • Genotype
  • Humans
  • Luciferases / genetics
  • Phenotype
  • Polymorphism, Genetic*
  • Protein Biosynthesis*
  • RNA, Messenger / genetics
  • RNA, Messenger / isolation & purification
  • Repetitive Sequences, Nucleic Acid*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Thymidylate Synthase / genetics*
  • Transcription, Genetic


  • 5' Untranslated Regions
  • RNA, Messenger
  • Luciferases
  • Thymidylate Synthase