D. Schwarz et al., Co-expression of human cytochrome P4501A1 (CYP1A1) variants and human NADPH-cytochrome P450 reductase in the baculovirus/insect cell system, XENOBIOTICA, 31(6), 2001, pp. 345-356
1. Three human cytochrome P4501Al (CYP1A1) variants, wild-type (CYP1A1-A),
CYP1A1.2 (I462V) and CYP1A1.4 (T461N), were co-expressed kith human NADPH-P
450 reductase (OR) in Spodoptera frugiperda (SM) insect cells by baculoviru
s coinfection to elaborate a suitable system for studying the role of CYP1A
1 polymorphism in the metabolism of exogenous and endogenous substrates.
2. A wide range of conditions was examined to optimize co-expression with r
egard to Such parameters as relative multiplicity of infection (MOI), time
of harvest, haem precursor supplementation and post-translational stabiliza
tion. Under optimized conditions, almost identical expression levels and mo
lar OR/CYP1A1 ratios (20:1) were attained for all CYP1A1 variants.
3. Microsomes isolated from co-infected cells demonstrated ethoxyresorufin
deethylase activities (nmol/min(-1) nmol(-1) CYP1A1) of 16.0 (CYP1A1.1), 20
.5 (CYP1A1.2) and 22.5 (CYP1A1.4). Pentoxyresorufin was dealkylated similar
to 10-20 times slower with all enzyme variants.
4. All three CYP1A1 variants were active in metabolizing the precarcinogen
benzo[a]pyrene (B[a]P), with wild-type enzyme showing the highest activity,
followed by CYP1A1.4 (60%) and CYP1A1.2 (40%). Each variant produced all m
ajor metabolites including B[a]P-7,8-dihydrodiol, the precursor of the ulti
mate carcinogenic species.
5. These studies demonstrate that the baculovirus-mediated co-expression-by
-coinfection approach all CYP1A1 variants yields functionally active enzyme
systems with similar molar OR/CYP1A1 ratios, thus providing suitable preco
nditions to examine the metabolism of and environmental chemicals by the di
fferent CYP1A1 variants.