Extensive splicing of transcripts encoding the bile acid-conjugating enzyme UGT2B4 modulates glucuronidation.

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• UDP-glucuronosyltransferase (UGT) superfamily is crucial for human detoxification.
• UGT2B4 plays a key role in bile acid metabolism, with significant expression in hepatic and extrahepatic tissues.
• Interindividual variability in UGT2B4 pathway activity necessitates understanding its molecular underpinnings.

Purpose of the Study:

• To identify novel molecular mechanisms contributing to variability in the UGT2B4 pathway.
• To investigate alternative splicing events and their functional consequences in UGT2B4.

Main Methods:

• Comprehensive genomic scan for additional exons within the UGT2B4 locus.
• Analysis of alternative splicing events, including promoter usage, exon skipping, and alternative splice site utilization.
• Assessment of alternatively spliced transcript expression in human tissues and protein activity towards bile acids.

Main Results:

• Discovery of three novel UGT2B4 exons, extending the gene length to 46 kb.
• Identification of at least eight distinct UGT2B4 mRNA variants generated through alternative splicing.
• Predominant expression of these splice variants in liver and gastrointestinal tissues.
• Newly identified UGT2B4 isoforms (i2, i3, i5) exhibit inhibitory effects on glucuronidation when co-expressed with UGT2B4 isoform 1.

Conclusions:

• The newly identified diversity of UGT2B4 mRNAs significantly contributes to variability in the glucuronidation pathway.
• This mRNA diversity, alongside genetic mutations and gene expression control, explains interindividual differences in UGT2B4 function.
• Findings highlight alternative splicing as a critical regulatory mechanism in bile acid metabolism.