CYP3A4 intronic SNP rs35599367 (CYP3A4*22) alters RNA splicing.
Cytochrome P450 3A4 (CYP3A4) metabolizes 30 50% of clinically used drugs. Large interperson variability in CYP3A4 activity affects response to CYP3A4 substrate drugs. We had demonstrated that an intronic single nucleotide polymorphism rs35599367 (CYP3A4*22, located in intron 6) reduces mRNA/protein expression; however, the underlying mechanism remained unknown. Here we show that CYP3A4*22 is associated with a two fold or greater increase in formation of a nonfunctional CYP3A4 alternative splice variant with partial intron 6 retention in human liver (P=0.006) but not in small intestines. Consistent with this observation, in vitro transfection experiments with a CYP3A4 minigene (spanning from intron 5 to intron 7) demonstrated that plasmids carrying the rs35599367 minor T allele caused significantly greater intron 6 retention than the C allele in liver derived HepG2 cells, but not in intestine derived LS 174T cells. These results indicate that tissue specific increased formation of nonfunctional alternative splice variant causes reduced CYP3A4 mRNA/protein expression in CYP3A4*22 carriers.
Pharmacogenetics and genomics