Role in translation of a triple tandemly repeated sequence in the 5′-untranslated region of human thymidylate synthase mRNA

Abstract

A triple tandem repeat (TTR) consisting of 90 nucleotides exists immediately upstream of the ATG initiator codon in human thymidylate synthase (TS) cDNA (pcHTS-1). To investigate the role of the TTR in the expression of the TS cDNA, we used pcHTS-1 to construct mutant cDNA clones in which part of the TTR was deleted or an additional element was inserted. The mutant cDNA plasmid was introduced into murine TS-negative mutant cells and the relative translation efficiencies of the mutant cDNAs were determined by measuring the transient expression of TS activity and the amount of TS mRNA transcribed. The translation efficiency in transient expression of the mutants was increased by deletions covering all the first two repeated elements, and the part of the third closest to the ATG initiator codon, but was not affected by deletions of only parts of the first two repeated elements at the 5' end. The translation efficiency was also not affected by insertion of an additional repeated element into the TTR. These results suggest that the first two repeated elements at the 5' end both have inhibitory effects on translation of the TS mRNA, probably due to the unique structural feature of this element.

Prognostic Value of Tumoral Thymidylate Synthase and p53 in Metastatic Colorectal Cancer Patients Receiving Fluorouracil-Based Chemotherapy: Phenotypic and Genotypic Analyses

“…tein, [5][6][7] present results clearly demonstrate that TS genotype cannot serve as a substitute for TS activity in order to predict FU responsiveness. Besides, although TS activity in metastasis is correlated to TS activity in primary tumor, the latter is not predictive of FU efficacy on liver metastasis, in line with data from Aschele et al 37 Considering the tumoral evolution from initial tumor to distant metastasis, it is not surprising that measurement at the target level is the most relevant approach.…”

“…Importantly, the TS promoter enhancer region is polymorphic, and this polymorphism influences the translation efficiency of TS mRNA. [5][6][7] TS promoter comprises 28-base pair sequences, usually presented as a double-tandem repeat (2R) or a triple-tandem repeat (3R), and it was demonstrated that homozygous 3R/3R cells overexpressed TS mRNA as compared with homozygous 2R/2R cells. 6,7 Numerous investigators have demonstrated that a low tumoral TS expression in colorectal cancer patients receiving FU-based chemotherapy was related to clinical responsiveness as well as to longer survival.…”

Identification of a novel single nucleotide polymorphism in the first tandem repeat sequence of the thymidylate synthase 2R allele

“…The first of these is a variable number of tandem repeat (VNTR) polymorphism consisting of multiple repeats of a 28-bp sequence. 5 Although there have been reports of up to 9 copies of the VNTR in certain populations, 6-8 the majority of TYMS alleles contain only 2 or 3 repeats, and have been designated 2R or 3R, respectively. The frequency of these alleles differs with ethnicity, and Caucasians demonstrate a higher frequency of 2R (0.40) compared to Chinese (0.18).…”

Genomic studies of GVHD—lessons learned thus far

“…Individuals with a homozygous threerepeat genotype, TSER 3R/3R, exhibit enhanced mRNA transcription of TS compared to individuals homozygous for only two repeats, TSER 2R/2R. 20 This may result in enhanced enzyme expression, which could increase the rate of DNA transcription and, thus, cell proliferation. Studies have shown that a donor TSER haplotype 3R/2R is associated with a higher risk of aGVHD.…”