Peroxynitrite irreversibly inactivates the human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) in human breast cancer cells: a cellular and mechanistic study.
ABSTRACT Arylamine N-acetyltransferases (NATs) play an important role in the detoxification and metabolic activation of a variety of aromatic xenobiotics, including numerous carcinogens. Both of the human isoforms, NAT1 and NAT2, display interindividual variations, and associations between NAT genotypes and cancer risk have been established. Contrary to NAT2, NAT1 has a ubiquitous tissue distribution and has been shown to be expressed in cancer cells. Given that the activity of NAT1 depends on a reactive cysteine that can be a target for oxidants, we studied whether peroxynitrite, a highly reactive nitrogen species involved in human carcinogenesis, could inhibit the activity of endogenous NAT1 in MCF7 breast cancer cells. We show here that exposure of MCF7 cells to physiological concentrations of peroxynitrite and to a peroxynitrite generator (3-morpholinosydnonimine N-ethylcarbamide, or SIN1) leads to the irreversible inactivation of NAT1 in cells. Further kinetic and mechanistic analyses using recombinant NAT1 showed that the enzyme is rapidly (k(inact) = 5 x 10(4) m(-1).s(-1)) and irreversibly inactivated by peroxynitrite. This inactivation is due to oxidative modification of the catalytic cysteine. We conclude that the reducing cellular environment of MCF7 cells does not sufficiently protect NAT1 from peroxynitrite-dependent inactivation and that only high concentrations of reduced glutathione could significantly protect NAT1. Thus, cellular generation of peroxynitrite may contribute to carcinogenesis and tumor progression by weakening key cellular defense enzymes such as NAT1.
Article: Human arylamine N-acetyltransferase 1 (NAT1) as a target of chemotherapeutic drugs in breast cancer: cisplatin as a model[show abstract] [hide abstract]
ABSTRACT: Human arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic-metabolizing enzyme (XME) involved in the biotransformation of many aromatic amines and heterocyclic amines. This XME is known to play important roles in both the detoxication and/or bioactivation of numerous drugs and carcinogens. NAT1 is a polymorphic enzyme with a large tissue distribution. NAT1 polymorphisms and activity have been extensively studied because of its potential role in the biotransformation of important carcinogens. Several recent studies suggest that NAT1 may have a role in breast cancer progression. Indeed, this XME has been shown to affect the growth and drug resistance of breast cancer cells and appears to be a marker in human estrogen receptor positive breast cancer. Here we provide an overview of our recently published results indicating that NAT1 is a new target of the anticancer drug cisplatin in breast cancer cells. Moreover, these results are discussed in light of the data showing inhibition of human NAT1 and its mouse orthologue by natural and synthetic estrogens.Molecular and Cellular Pharmacology. 01/2009;