Variant In Alternative Splicing Of PXR Cause Loss Of PXR And MDR1 MRNA Expression

BACKGROUND: Pregnane X receptor (PXR) is a master transcriptional regulator ofmany drug/xenobiotic-metabolizing enzymes, including P450s and drug transporters.Thus, genetic variability in PXR will contribute to human variation, such as drugclearance variation and drug-drug interactions in combination therapies. Researchesabout variants of PXR are the main direction of explaining remarkable interindividualdifference of CYP3A4 and MDR1. But the SNP which have been found in PXR can notexplain target gene huge variation, such as the MDR1 and CYP3A4. With thedevelopment in transcriptome, alternative splicing is considered as the most importantfactor resulting in the 3000-5000 genes producing millions of proteins, and itsabnormity will change the quantity and quality of protein, causing alteration ofpharmacokinetics, pharmacodynamics, even diseases and so on. Recently, many humanPXR splicing variants have been found, and the PAR-2(SV1) has similar expressionprofile and activity as PXR WT, which indicated that decrease of PAR-2(SV1)expression might affect the total PXR expression. Currently, a 6bp-deletion variant(^-133GAGAAG^-128) in promoter region of PAR-2(SV1) was reported by Japanese, and thedeletion is at a putative HNF1 binding site in the promoter region.AIM: In present study, we delineated the characterization of a 6bp-deletion inalternative splicing of PAR-2(SV1), to learn about the distribution of 6bp-deletion inChinese population and any difference compared with other population, and wether thismutation cause reduce of PXR expression and concomitantly loss of its target geneMDR1 expression in vivo, hence to reveal the reason of MDR1 individual variety andprovide direction in clinic for a series of abnormal pharmacokinetic drug interactionMETHODS: In this study, we described 6bp-deletion of PXR in 177 Chinese healthyvolunteers and 56 liver samples by allelic special-touchdown PCR, And thenquantitated the PAR-2(SV1), total PXR and MDR1 mRNA expression by real-time PCRin 56 liver samples.RESULT: The results showed that the allelic frequency was 22.4% in Chinesehealthy, which was significant different with Japanese healthy(27.4%). The allelicfrequency was 38.4% in hepatic donate patients, that was significant higher than healthy.As there were two main diseases in the donation, carcinoma and calculus of bile ductwhich frequency was 38.4% and 23.7% respectively. Moreover, the deletion cutted down the transcription expression of PAR-2(SV1)mRNA(WW vs WM P＜0.001, WW vs MM P=0.003, WM vs MM P=0.619). Total PXRmRNA expression was also decreased (WW vs WM P=0.042, WW vs MM P=0.298,WM vs MM P=0.596), and leading to the decrease of MDR1 mRNA (WW vs WMP=0.001, WW vs MM P=0.058, WM vs MM P-0.463.We quantitated the amount of individual PAR-2(SV1) mRNAs by real-time PCR, andPAR-2(SV1) transcripts represented approximately 15.3% of the total PXR transcripts in56 human livers.CONCLUSION: Our results showed PAR-2 (SV1) played an important role in totalPXR mRNA expression. If 6-deletion happened, it will significant affect the PAR-2(SV1) expression and then influence total PXR expression and function, therebycontribute to reduce of MDR1 mRNA level that may explain partly MDR1interindividual difference, which may be more susceptitive to impair of xenobiotics.