Expression of human cytochrome P4501A1 (CYP1A1) in Saccharomyces cerevisiae inhibits cell division.

Abstract

1. Saccharomyces cerevisiae cells, genetically engineered to express human cytochrome P4501A1 (CYP1A1), have a mean doubling time of 5.8 h, which is considerably slower than that of control yeast cells that have undergone the same transformation process but with a plasmid lacking CYP1A1 cDNA (3.3 h). 2. A smaller reduction in the rate of cell division is observed in yeast cells expressing the closely related human P450, CYP1A2. No reduction is seen with plaice CYP1A, despite similar levels of P450 expression and enzyme activity (ethoxyresorufin O-deethylation) and no inhibition of growth is observed with yeast cells expressing higher levels of human CYP2D6. 3. Repeated culture of cells from a single CYP1A1 transformant colony results in a gradual loss of P450 expression and of CYP1A1-associated enzymatic activity over a 5-6 week period. In contrast, expression of human CYP2D6 by a single transformant colony is stable for at least 6 months. 4. The loss of CYP1A1 activity from transformed cells is accompanied by a return to normal growth rate, similar to that of control cells. 5. Inhibition of CYP1A1 enzyme activity during culture, by either type I (alpha-naphthoflavone), type II (ellipticine) or mechanism-based (1-(1'propynyl)pyrene) CYP1A inhibitors, does not affect growth rate, suggesting that some other property of human CYP1A1 protein is responsible for the growth inhibition observed.