Background And Aims: UGT2B4 is a member of the UDP-glucuronosyltransferase (UGT) superfamily, a major detoxifying system in humans. UGT2B4 is involved in bile acids metabolism and highly expressed in liver and extrahepatic tissues. The aim of this study was to uncover new molecular mechanisms underlying interindividual variability in the UGT2B4 pathway.
Methods: We carried out a comprehensive scan for additional exons at this locus and discovered multiple alternative splicing events. We then assessed the expression profile of alternatively spliced transcripts in human tissues and the activity of the corresponding overexpressed proteins toward bile acids.
Results: We discovered three previously unidentified UGT2B4 exons, increasing the total known gene length to 46 kb. Molecular analyses revealed at least eight distinct mRNAs produced by (i) alternative promoter usage, (ii) complete and partial exon skipping, and (iii) use of alternative 3' splice sites. These splice variants were predominantly expressed in liver, gastrointestinal tract, and other extrahepatic tissues. Quantitative analyses of splicing events further sustain their prevalence in the liver. UGT2B4 proteins produced from these mRNA variants had undetectable transferase activity in human cells. However, when stably co-expressed with the active UGT2B4 isoform 1, three newly identified UGT2B4 isoforms (i2, i3, and i5) were found to negatively regulate glucuronidation.
Conclusion: In addition to heritable genetic mutations and control of gene expression, the newly discovered diversity of UGT2B4 mRNAs may introduce variability in this glucuronidation pathway.
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- The study highlights the kidney's significant role in metabolizing drugs and compounds, sometimes exceeding liver activity, and the impact on drug interactions and clearance.
- It evaluated the expression and activity of cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT) enzymes in 3D-cultured human kidney cells, showing they expressed higher enzyme levels than traditional 2D cultures and were comparable to human kidney tissue.
- The findings indicate that 3D-cultured renal cells are a more accurate model for studying renal drug metabolism, enhancing our understanding of kidney function related to drug processing.
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