Comprehensive analysis of the genetic factors determining expression and function of hepatic CYP2D6

Variable expression and function of the cytochrome P4502D6 (CYP2D6) leads t o distinct phenotypes termed ultrarapid (UM), extensive (EM), intermediate (IM) and poor metabolizer (PM). Whereas the PM phenotype is known to be cau sed by two null-alleles leading to absence of functional CYP2D6 protein, th e large variability among individuals with functional alleles remained larg ely unexplained. In this study, we systematically investigated 76 liver bio psies from individuals with known sparteine metabolic ratios (MRS) for the relationships between CYP2D6 genotype, microsomal protein expression, bufur alol 1'-hydroxylase activity and in-vivo phenotype. Average CYP2D6 protein levels ranged from undetectable in PMs (MRS > 20) to 2.6 +/- 2.7 pmol/mg mi crosomal protein in IMs (1.2 < MRS< 20), 7.6 +/- 4.7 in EMs (0.2 < MRS < 1. 2) and 23.8 +/- 7.7 in UMs (MRS < 0.2), respectively. Analysis with respect to genotype demonstrated gradually increased expression and function for i ndividuals with no, one, two or three functional gene copies per genome. Th e recently discovered -1584 C/G promoter polymorphism was identified as ano ther major factor for expression and function with the mutant [-1584G] prom oter type being consistently associated with significantly higher expressio n than [-1584C]. To investigate functional differences between the detected variant protein forms CYP2D6.1, 2D6.2, 2D6.9 and 2D6.10, we expressed them recombinantly in insect cells. The most significant difference was a decre ase in the relative P450 holoprotein content of all allelic forms, includin g the common functional variant 2D6.2, in comparison to 2D6.1, whereas only modest K-m changes were observed. Taken together, these data provide furth er insight into the complex mechanisms that govern the highly variable expr ession and function of CYP2D6. Pharmacogenetics 11:573-595 (C) 2001 Lippinc ott Williams & Wilkins.