A 6 bp polymorphism in the thymidylate synthase gene causes message instability and is associated with decreased intratumoral TS mRNA levels.
OBJECTIVE
A 6 bp deletion polymorphism in the thymidylate synthase (TS) gene was investigated in order to determine its function.


METHODS
A luciferase system was used to investigate the function of the 6 bp/1494 polymorphism in vitro. A group of 43 patients with colorectal carcinoma were evaluated for the 6 bp/1494 polymorphism and for intratumoral TS mRNA levels in vivo.


RESULTS
The 3'UTR of TS containing the +6 bp polymorphism resulted in an approximate 35% decrease in luciferase activity and mRNA levels, while the TS-3'UTR bearing the -6 bp deletion resulted in an approximate 70% decrease in luciferase activity and mRNA levels. The TS-3'UTR construct containing the -6 bp/1494 deletion also had a higher rate of message degradation compared to the +6 bp/1494 construct. Individuals homozygous for the insertion (+6 bp/+6 bp) had significantly higher TS mRNA levels compared to individuals that were homozygous for the deletion (-6 bp/-6 bp) (P < 0.007). We determined the frequency of the -6 bp/1494 deletion polymorphism to be 41% in non-Hispanic whites, 26% in Hispanic whites, 52% in African-Americans and 76% in Singapore Chinese.


CONCLUSIONS
These results suggest that the -6 bp/1494 deletion polymorphism in the 3'UTR of TS is associated with decreased mRNA stability in vitro and lower intratumoral TS expression in vivo. Further, the 6 bp/1494 polymorphism varies greatly within different ethnic populations and is in linkage disequilibrium with the TS 5' tandem repeat enhancer polymorphism. Taken together, these data suggest that the 6 bp/1494 polymorphism may be a useful screening tool in predicting TS mRNA expression.
Mandola
Michael V
MV
Department of Molecular Biology, The University of Medicine and Dentistry of New Jersey, School of Osteopathic Medicine, Stratford, New Jersey 08084, USA.
Stoehlmacher
Jan
J
Zhang
Wu
W
Groshen
Susan
S
Yu
Mimi C
MC
Iqbal
Syma
S
Lenz
Heinz-Josef
HJ
Ladner
Robert D
RD
D020413:3' Untranslated Regions; D001483:Base Sequence; D002460:Cell Line; D015179:Colorectal Neoplasms / Q000201:enzymology*; D017931:DNA Primers; D004742:Enhancer Elements, Genetic; D005006:Ethnicity / Q000235:genetics; D006801:Humans; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D020080:Tandem Repeat Sequences; D013940:Thymidylate Synthase / Q000235:genetics*
D020413:3' Untranslated Regions; D017931:DNA Primers; D012333:RNA, Messenger; D013940:Thymidylate Synthase