Functional Analysis of the Role of the TPMT Gene Promoter VNTR Polymorphism in TPMT Gene Transcription

Abstract

Aims: Thiopurine S-methyltransferase (TPMT) activity is polymorphic, and a trimodal distribution has been demonstrated in Caucasians (low, intermediate and high methylator groups). The TPMT gene promoter contains a variable number of three GC-rich tandem repeats, namely A, B and C, ranging from three to nine in length in a A_nB_mC architecture. Materials & methods: Here, we investigated the influence of number and type of TPMT gene promoter tandem repeats on human TPMT gene transcription in K562 cells transiently transfected with reporter constructs bearing various variable number of tandem repeats (VNTR) and addressed the interaction of transcription factor binding to the VNTRs by electrophoretic mobility shift assays. Results: We found that the distribution patterns of VNTR alleles do not significantly differ among acute lymphoblastic leukemia patients, acute myeloid leukemia patients and normal individuals. We also demonstrated that the A repeat has a negative effect in TPMT gene transcription and that a positive regulatory element, identified immediately upstream to the VNTR region of the TPMT gene promoter, is indispensable for TPMT gene transcription. Our electrophoretic mobility shift assay analysis indicated that the Sp1 and Sp3 transcription factors bind to the VNTR repeats. Conclusion: Overall, our data underline that both the number and type of VNTRs, as well as the upstream regulatory region of the TPMT gene promoter, determine the overall level of TPMT gene transcription. It remains to be seen whether these VNTRs can be employed as pharmacogenetic markers to individualize thiopurine therapy.

KEYWORDS::

• 6-mercaptopurine
• 6-MP
• pharmacogenetics
• thiopurine S-methyltransferase
• TPMT
• transcription
• variable number tandem repeat
• VNTR

Financial & competing interests disclosure

This work has been partly funded by the Ministry of Science and Technology Development, Republic of Serbia grant No. 143051 to Sonja Pavlovic and from a Research Promotion Foundation (RPFΠΔΕ046_02) and European Commission grants to George P Patrinos. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Additional information

Funding

This work has been partly funded by the Ministry of Science and Technology Development, Republic of Serbia grant No. 143051 to Sonja Pavlovic and from a Research Promotion Foundation (RPFΠΔΕ046_02) and European Commission grants to George P Patrinos. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.