title: Post-translational stabilization of thiopurine S-methyltransferase by S-adenosyl-L-methionine reveals regulation of TPMT*1 and *3C allozymes.
abstract: Thiopurine S-methyltransferase (TPMT; EC 2.1.1.67) plays a pivotal role in thiopurine treatment outcomes. However, little has been known about its intracellular regulation. Here, we describe the effect of fluctuations in physiological levels of S-adenosyl-L-methionine (SAM) and related metabolites on TPMT activity levels in cell lines and erythrocytes from healthy donors. We determined higher TPMT activity in wild-type TPMT*1/*1 individuals with high SAM concentrations (n=96) compared to the low SAM level group (n=19; P<0.001). These findings confirm the results of our in vitro studies, which demonstrated that the restriction of L-methionine (Met) in cell growth media reversibly decreased TPMT activity and protein levels. Selective inhibition of distinct components of Met metabolism was used to demonstrate that SAM is implicitly responsible for direct post-translational TPMT stabilization. The greatest effect of SAM-mediated TPMT stabilization was observed in the case of wild-type TPMT*1 and variant *3C allozymes. In addition to TPMT genotyping, SAM may serve as an important biochemical marker in individualization of thiopurine therapy.
authors.affiliation: Department of Clinical Biochemistry, Faculty of Pharmacy, Askerceva 7, SI-1000, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Miha
authors.initials: M
authors.lastname: Milek
authors.forename: Alenka
authors.initials: A
authors.lastname: Smid
authors.forename: Riin
authors.initials: R
authors.lastname: Tamm
authors.forename: Natasa Karas
authors.initials: NK
authors.lastname: Kuzelicki
authors.forename: Andres
authors.initials: A
authors.lastname: Metspalu
authors.forename: Irena
authors.initials: I
authors.lastname: Mlinaric-Rascan
mesh_terms: D018929:Cell Culture Techniques; D003470:Culture Media; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000201:enzymology; D005492:Folic Acid / Q000378:metabolism / Q000494:pharmacology; D005838:Genotype; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D007527:Isoenzymes; D008715:Methionine / Q000378:metabolism / Q000494:pharmacology; D008716:Methionine Adenosyltransferase / Q000378:metabolism / Q000494:pharmacology; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D012436:S-Adenosylmethionine / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D003470:Culture Media; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D012436:S-Adenosylmethionine; D005492:Folic Acid; D008715:Methionine; D008780:Methyltransferases; C022745:thiopurine methyltransferase; D008716:Methionine Adenosyltransferase