EXPRESSION OF HUMAN CYTOCHROME-P450 1A1 IN DNA-REPAIR DEFICIENT AND PROFICIENT HUMAN FIBROBLASTS STABLY TRANSFORMED WITH AN INDUCIBLE EXPRESSION VECTOR

Cytochromes P450 catalyze the bioactivation of many carcinogens. In pa rticular, cytochrome P450 1A1 (CYP1A1) catalyzes the conversion of pol ycyclic aromatic hydrocarbons, such as benzo[a]pyrene, into potent mut agenic agents. Human skin fibroblasts, both DNA repair deficient (xero derma pigmentosum group A: XPA) and DNA repair normal have been co-tra nsformed with a chimeric gene construct containing human CYP1A1 coding sequences controlled by the cadmium (Cd) ion inducible mouse metallot hionein-I promoter and pRSV-NEO, a dominant selectable marker for G418 resistance. Individual G418 resistant colonies were cloned and analyz ed for Cd inducible CYP1A1 activity. Six clones of DNA repair deficien t cells and rive clones of DNA repair proficient cells have been isola ted which express Cd inducible CYP1A1. Benzo[a]pyrene-trans-7,8-diol ( BPD) is cytotoxic in Cd induced CYP1A1 expressing cells. The cytotoxic ity can be inhibited by 10 muM alpha-napthoflavone. Differential cytot oxicity between the DNA repair deficient and proficient CYP1A1 express ing transformants is observed. BPD is cytotoxic to Cd induced CYP1A1 e xpressing XPA cells at > 10-fold lower doses than it is to Cd induced CYP1A1 expressing DNA repair normal cells. These data indicate that BP D is metabolized to a DNA damaging agent by induced CYP1A1. In contras t, benzo[a]pyrene-trans-7,8-diol-9,10-epoxide added to the media is on ly slightly more cytotoxic to DNA repair deficient than to proficient cells regardless of CYP1A1 expression. These studies demonstrate the u sefulness of the CYP1A1 transformed fibroblasts in examining the cytot oxic effects of benzo[a]pyrene metabolites and suggest the future usef ulness in examining the toxic effects of polycyclic aromatic hydrocarb ons and other xenobiotics bioactivated by CYP1A1.