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Published on: March 28, 2017
Interactions between human UGT1A1, UGT1A4, and UGT1A6 affect their enzymatic activities
Ryoichi Fujiwara1, Miki Nakajima, Hiroyuki Yamanaka
1Drug Metabolism and Toxicology, Division of Pharmaceutical Sciences, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-1192, Japan.
Summary
Human UDP-glucuronosyltransferase (UGT) 1A1, UGT1A4, and UGT1A6 isoforms interact, potentially through heterodimerization. These protein-protein interactions significantly alter their enzymatic activities in complex ways, depending on the specific UGT isoforms and substrates involved.
Area of Science:
- Biochemistry
- Pharmacology
- Molecular Biology
Background:
- Human UDP-glucuronosyltransferases (UGTs) are crucial enzymes for drug and xenobiotic metabolism.
- Understanding the interactions between UGT isoforms is essential for predicting drug efficacy and toxicity.
- Previous studies have suggested potential interactions, but the specific effects on enzymatic activity remain largely uncharacterized.
Purpose of the Study:
- To investigate protein-protein interactions among human UDP-glucuronosyltransferase (UGT) 1A1, UGT1A4, and UGT1A6.
- To determine the impact of coexpressing these UGT isoforms on their individual substrate-specific enzymatic activities.
- To elucidate the potential mechanisms underlying these interactions, such as heterodimerization.
Main Methods:
- Utilized double expression systems in HEK293 cells to coexpress pairs of UGT1A isoforms (UGT1A1/UGT1A4, UGT1A1/UGT1A6, UGT1A4/UGT1A6).
- Assessed the effects of coexpression on enzymatic kinetics (S50, Km, Vmax) using isoform-specific substrates (estradiol, bilirubin, imipramine, trifluoperazine, serotonin, diclofenac).
- Employed native polyacrylamide gel electrophoresis to detect protein complexes, indicating dimer formation.
Main Results:
- Coexpression of UGT1A4 and UGT1A6 altered UGT1A1 activity towards estradiol and bilirubin.
- Coexpression of UGT1A1 impacted UGT1A4 activity towards imipramine but not trifluoperazine.
- Coexpression of UGT1A6 affected UGT1A4 activity towards trifluoperazine, and coexpression of UGT1A1 and UGT1A4 influenced UGT1A6 activity.
- Native PAGE revealed multiple bands at ~110 kDa, suggesting the formation of both homodimers and heterodimers.
Conclusions:
- Human UGT1A1, UGT1A4, and UGT1A6 isoforms interact with each other, likely via heterodimerization.
- These interactions lead to complex and varied modulations of their enzymatic activities, which are dependent on the specific UGT isoforms and substrates involved.
- The findings highlight the importance of considering UGT isoform interactions in pharmacokinetic and pharmacodynamic studies.
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