Objective: CYP3A4*1G (G > A) in human CYP3A4 intron 10 is associated with therapeutic effects of CYP3A4-metabolized drugs. The aim of this study was to predict its function in the regulation of CYP3A4 expression.
Methods: Functional analysis of the CYP3A4*1G allele was performed using bioinformatic methods and enhancer or promoter reporter assays in HepG2 cells.
Results: Transcription regulatory elements like CAATboxes, TATA-boxes, Sp1, SMARCA3.01, and Box II-like sequence were present in the intron 10 of CYP3A4. SMARCA3.01 and Box II-like sequence were responsible for differential binding of transcription factors on the CYP3A4*1G allele. In CYP3A4*1G, the G allele enhanced expression of the CYP3A4 promoter in a position-dependent and orientation-dependent manner, however, the A allele enhanced expression of the CYP3A4 promoter in a position-independent and orientation-independent manner. In addition, the G allele and the A allele both displayed strong transcriptional activation, but the latter showed higher promoter activity than the former. Also, the A allele showed greater activity than the CYP3A4 promoter.
Conclusion: These results in vitro suggest that CYP3A4*1G regulates CYP3A4 intron 10 enhancer and promoter activity in an allelic-dependent manner.