Allelic expression imbalance of the human CYP3A4 gene and individual phenotypic status.
The human cytochrome P450 3A4 (CYP3A4) plays a dominant role in the metabolism of numerous clinically useful drugs. Alterations in the activity or expression of this enzyme may account for a major part of the variation in drug responsiveness and toxicity. However, it is generally accepted that most of the known single nucleotide polymorphisms in the coding and 5'-flanking regions are not the main determinants for the large inter-individual variability of CYP3A4 expression and activity. We show that the allelic variation is critically involved in determining the individual total hepatic CYP3A4 mRNA level and metabolic capability. There exists a definite correlation between the total CYP3A4 mRNA level and allelic expression ratio, the relative transcript level ratio derived from the two alleles. Individuals with a low expression ratio, exhibiting a large difference of transcript level between the two alleles, revealed extremely low levels of total hepatic CYP3A4 mRNA, and thus low metabolic capability as assessed by testosterone 6beta-hydroxylation. These results present a new insight into the individualized CYP3A4-dependent pharmacotherapy and the importance of expression imbalance to human phenotypic diversity.
Clinical Pharmacokinetics, Division of Clinical Pharmacy, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Takeshi
T
Hirota
Ichiro
I
Ieiri
Hiroshi
H
Takane
Shinji
S
Maegawa
Masakiyo
M
Hosokawa
Kaoru
K
Kobayashi
Kan
K
Chiba
Eiji
E
Nanba
Mitsuo
M
Oshimura
Tetsuo
T
Sato
Shun
S
Higuchi
Kenji
K
Otsubo
D000483:Alleles; D001483:Base Sequence; D018899:CpG Islands; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D017931:DNA Primers; D006801:Humans; D008099:Liver / Q000201:enzymology; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D012333:RNA, Messenger / Q000235:genetics
D017931:DNA Primers; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human