Different Lengths of a Polymorphic Repeat Sequence in the Thymidylate Synthase Gene Affect Translational Efficiency but Not Its Gene Expression

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....

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Bibliographic Details
Published in:Clinical cancer research 2001-12, Vol.7 (12), p.4096-4101
Main Authors: KAWAKAMI, Kazuyuki, SALONGA, Dennis, JI MIN PARK, DANENBERG, Kathleen D, UETAKE, Hiroyuki, BRABENDER, Jan, OMURA, Kenji, WATANABE, Go, DANENBERG, Peter V
Format: Article
Language:English
Subjects:
5' Untranslated Regions - genetics
Animals
Biological and medical sciences
Coleoptera
Colorectal Neoplasms - enzymology
Colorectal Neoplasms - genetics
Gastroenterology. Liver. Pancreas. Abdomen
Gene Expression Regulation, Enzymologic
Gene Expression Regulation, Neoplastic
Genes, Reporter
Genotype
Humans
Luciferases - genetics
Medical sciences
Phenotype
Polymorphism, Genetic
Protein Biosynthesis
Repetitive Sequences, Nucleic Acid
Reverse Transcriptase Polymerase Chain Reaction
RNA, Messenger - genetics
RNA, Messenger - isolation & purification
Stomach. Duodenum. Small intestine. Colon. Rectum. Anus
Thymidylate Synthase - genetics
Transcription, Genetic
Tumors
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Summary: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.
ISSN:1078-0432
1557-3265