Comparative analysis of CYP3A expression in human liver suggests only a minor role for CYP3A5 in drug metabolism.
To study mechanisms behind the interindividual variability in CYP3A expression and the relative contribution of the different CYP3A enzymes to the overall CYP3A activity, we have analyzed CYP3A4, CYP3A5, CYP3A43, and PXR mRNA and CYP3A4 and CYP3A5 protein expression, catalytic activity, and polymorphism in the CYP3A5 gene in a panel of 46 Caucasian human livers. Protein quantification was performed by Western blotting using enzyme-specific antibodies directed to the C termini of CYP3A4 or CYP3A5, and carrier protein-coupled peptides as standards. The mRNA levels were determined by quantitative real-time PCR. CYP3A activity was measured by analysis of the rate of testosterone 6beta-hydroxylation. A correlation existed between all CYP3A and PXR mRNA transcripts measured. The interindividual variability in CYP3A4 and CYP3A5 mRNA expression was higher than that of CYP3A protein and activity. The CYP3A5 protein was expressed at quantifiable levels in 5 (10.9%) of the livers. Four of those were heterozygous for the CYP3A5*1 allele and had CYP3A5 protein at a mean level of 17% of that of total CYP3A, whereas one liver sample was from a CYP3A5*3 homozygote individual having lower amounts of CYP3A5. In total, CYP3A5 only contributed 2% of the overall CYP3A protein among all samples. In conclusion, our data indicate that CYP3A4, CYP3A5, CYP3A43, and PXR hepatic mRNA expression correlate, indicating common regulatory features, and that the contribution of CYP3A5 to hepatic drug metabolism in Caucasians is insignificant.
Westlind-Johnsson
Anna
A
Division of Molecular Toxicology, IMM, Karolinska Institutet, Box 210, SE-171 77 Stockholm, Sweden.
Malmebo
Sarah
S
Johansson
Anna
A
Otter
Charlotta
C
Andersson
Tommy B
TB
Johansson
Inger
I
Edwards
Robert J
RJ
Boobis
Alan R
AR
Ingelman-Sundberg
Magnus
M
D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis*; D015153:Blotting, Western; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D015870:Gene Expression; D005838:Genotype; D006801:Humans; D006900:Hydroxylation; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000096:biosynthesis*; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis; D011987:Receptors, Steroid / Q000096:biosynthesis; D013739:Testosterone / Q000378:metabolism; D044465:White People
D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D013739:Testosterone; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C104464:CYP3A protein, human; C422408:CYP3A43 protein, human; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human