TY - JOUR
T1 - Human thiopurine S-methyltransferase pharmacogenetics
T2 - Variant allozyme misfolding and aggresome formation
AU - Wang, Liewei
AU - Nguyen, Tien V.
AU - McLaughlin, Richard W.
AU - Sikkink, Laura A.
AU - Ramirez-Alvarado, Marina
AU - Weinshilboum, Richard M.
PY - 2005/6/28
Y1 - 2005/6/28
N2 - Thiopurine S-methyltransferase (TPMT) catalyzes the S-methylation of thiopurine drugs. TPMT genetic polymorphisms represent a striking example of the potential clinical value of pharmacogenetics. Subjects homozygous for TPMT*3A, the most common variant allele for low activity, an allele that encodes a protein with two changes in amino acid sequence, are at greatly increased risk for life-threatening toxicity when treated with standard doses of thiopurines. These subjects have virtually undetectable levels of TPMT protein. In this study, we tested the hypothesis that TPMT*3A might result in protein misfolding and aggregation. We observed that TPMT*3A forms aggresomes in cultured cells and that it aggregates in vitro, functional mechanisms not previously described in pharmacogenetics. Furthermore, there was a correlation among TPMT half-life values in rabbit reticulocyte lysate, aggresome formation in COS-1 cells, and protein aggregation in vitro for the three variant allozymes encoded by alleles that include the two TPMT*3A single-nucleotide polymorphisms. These observations were compatible with a common structural explanation for all of these effects, a conclusion supported by size-exclusion chromatography and CD spectroscopy. The results of these experiments provide insight into a unique pharmacogenetic mechanism by which common polymorphisms affect TPMT protein function and, as a result, therapeutic response to thiopurine drugs.
AB - Thiopurine S-methyltransferase (TPMT) catalyzes the S-methylation of thiopurine drugs. TPMT genetic polymorphisms represent a striking example of the potential clinical value of pharmacogenetics. Subjects homozygous for TPMT*3A, the most common variant allele for low activity, an allele that encodes a protein with two changes in amino acid sequence, are at greatly increased risk for life-threatening toxicity when treated with standard doses of thiopurines. These subjects have virtually undetectable levels of TPMT protein. In this study, we tested the hypothesis that TPMT*3A might result in protein misfolding and aggregation. We observed that TPMT*3A forms aggresomes in cultured cells and that it aggregates in vitro, functional mechanisms not previously described in pharmacogenetics. Furthermore, there was a correlation among TPMT half-life values in rabbit reticulocyte lysate, aggresome formation in COS-1 cells, and protein aggregation in vitro for the three variant allozymes encoded by alleles that include the two TPMT*3A single-nucleotide polymorphisms. These observations were compatible with a common structural explanation for all of these effects, a conclusion supported by size-exclusion chromatography and CD spectroscopy. The results of these experiments provide insight into a unique pharmacogenetic mechanism by which common polymorphisms affect TPMT protein function and, as a result, therapeutic response to thiopurine drugs.
KW - Pharmacogenomics
KW - Protein aggregation
KW - Protein degradation
KW - Thiopurine toxicity
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U2 - 10.1073/pnas.0502352102
DO - 10.1073/pnas.0502352102
M3 - Article
C2 - 15967990
AN - SCOPUS:21544457479
SN - 0027-8424
VL - 102
SP - 9394
EP - 9399
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 26
ER -