CYP1B1 converts procarcinogens into genotoxins in Saccharomyces cerevisiae.

CYP1B1 activates many chemical carcinogens into potent genotoxins, and allelic variants are risk factors in lung, breast, and prostate cancer. However, few eukaryotic genetic instability endpoints have been directly measured for CYP1B1-activated metabolites. In this study, we expressed human CYP1B1 in yeast strains that measure DNA damage-associated toxicity and frequencies of chromosomal translocations. DNA damage-associated toxicity was measured in a rad4 rad51 strain, defective in both DNA excision and recombinational repair. Frequencies of chromosomal translocations were measured in diploid yeast strains containing two his3 fragments. These strains were exposed to benzo[a]pyrene-7,8-dihydrodiol (BaP-DHD), aflatoxin B1 (AFB1), and the heterocyclic aromatic amines, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). We observed that AFB1, BaP-DHD, IQ, and MeIQx conferred toxicity in the DNA repair mutant expressing CYP1B1. Translocation frequencies increased eight-fold and three-fold after exposure to 50 µM AFB1 and 33 µM BaP-DHD respectively. A DNA damage response was observed after AFB1 exposure, as measured by the induction of the small subunit of ribonucleotide reductase, Rnr3. While CYP1B1-mediated activation of BaP-DHD and heterocyclic aromatic amines was expected, activation of AFB1 to become a potent recombinagen was not expected. These studies demonstrate that chromosomal rearrangement is a useful genotoxic endpoint for CYP1B1-mediated carcinogen activation.

Regulation of PTP1B activation through disruption of redox-complex formation.

We have identified a molecular interaction between the reversibly oxidized form of protein tyrosine phosphatase 1B (PTP1B) and 14-3-3ζ that regulates PTP1B activity. Destabilizing the transient interaction between 14-3-3ζ and PTP1B prevented PTP1B inactivation by reactive oxygen species and decreased epidermal growth factor receptor phosphorylation. Our data suggest that destabilizing the interaction between 14-3-3ζ and the reversibly oxidized and inactive form of PTP1B may establish a path to PTP1B activation in cells.