Alternative CYP3A4 mRNA Isoforms Are Related to Hepatocyte Differentiation, Liver Development, and Response to Drugs

Abstract

Cytochrome P450 3A4 (CYP3A4) metabolizes over 50% of prescribed drugs. CYP3A4 activity changes during liver development and the administration of drugs. Alternative mRNA isoforms occur in over 90% of human genes and are frequently observed in cells responding to developmental and environmental signals. The purpose of this study was to identify CYP3A4 mRNA isoforms in liver and characterize their differential expression during liver development, hepatocyte differentiation, and in response to drugs. cDNA cloning and RNA sequencing (RNA‐Seq) were used to identify CYP3A4 mRNA isoforms. Three isoforms were found in human HepaRG cells and liver tissues, one represented a canonical full length mRNA, one had a shorter 3′‐UTR, and one contained a partial intron 6 retention. The alternative mRNA isoforms were validated by either rapid amplification of cDNA 3′‐end (3′RACE) PCR or end‐point PCR. Quantification of the isoforms by real‐time PCR revealed that expression levels of the shorter 3′‐UTR isoform increased significantly more than the isoform with the canonical 3′‐UTR during liver development, hepatocyte differentiation, and in response to rifampicin, phenobarbital, and dexamethasone.ConclusionThis study identified two novel CYP3A4 mRNA isoforms. The isoform with the shorter 3′‐UTR might be involved in the regulation of CYP3A4 gene expression during liver development and the administration of some drugs.This study was supported by 1R01GM087376‐01A1, 1R01ES019487‐01A1, and 5P20‐RR021940 (to X.B.Z), 1R01HD058556‐01A1 (J.S.L), and Lila Self Graduate Fellowship from the University of Kansas (to S.N.H.)