Proteasomal degradation of N-acetyltransferase 1 is prevented by acetylation of the active site cysteine: a mechanism for the slow acetylator phenotype and substrate-dependent down-regulation

• Published in: The Journal of biological chemistry 2004-05, Vol.279 (21), p.22131-22137
• Main Authors: Butcher, Neville J, Arulpragasam, Ajanthy, Minchin, Rodney F
• Format: Article
• Language: English
• Subjects: 4-Aminobenzoic Acid - pharmacology; Alleles; Arylamine N-Acetyltransferase - metabolism; Binding Sites; Blotting, Western; Cell Line, Tumor; Cloning, Molecular; Cycloheximide - pharmacology; Cysteine - chemistry; Cysteine Endopeptidases - metabolism; Cysteine Proteinase Inhibitors - pharmacology; DNA, Complementary - metabolism; Down-Regulation; Escherichia coli - metabolism; Genotype; Glutathione Transferase - metabolism; Humans; Isoenzymes - metabolism; Leukocytes, Mononuclear - metabolism; Leupeptins - pharmacology; Models, Biological; Multienzyme Complexes - metabolism; Mutagenesis, Site-Directed; Mutation; Oxidative Stress; Peptide Hydrolases - chemistry; Phenotype; Precipitin Tests; Proteasome Endopeptidase Complex; Protein Binding; Protein Synthesis Inhibitors - pharmacology; Recombinant Proteins - metabolism; Time Factors; Ubiquitin - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M312858200

Many drugs and chemicals found in the environment are either detoxified by N-acetyltransferase 1 (NAT1, EC 2.3.1.5) and eliminated from the body or bioactivated to metabolites that have the potential to cause toxicity and/or cancer. NAT1 activity in the body is regulated by genetic polymorphisms as well as environmental factors such as substrate-dependent down-regulation and oxidative stress. Here we report the molecular mechanism for the low protein expression from mutant NAT1 alleles that gives rise to the slow acetylator phenotype and show that a similar process accounts for enzyme down-regulation by NAT1 substrates. NAT1 allozymes NAT1 14, NAT1 15, NAT1 17, and NAT1 22 are devoid of enzyme activity and have short intracellular half-lives ( approximately 4 h) compared with wild-type NAT1 4 and the active allozyme NAT1 24. The inactive allozymes are unable to be acetylated by cofactor, resulting in ubiquitination and rapid degradation by the 26 S proteasome. This was confirmed by site-directed mutagenesis of the active site cysteine 68. The NAT1 substrate p-aminobenzoic acid induced ubiquitination of the usually stable NAT1 4, leading to its rapid degradation. From this study, we conclude that NAT1 exists in the cell in either a stable acetylated state or an unstable non-acetylated state and that mutations in the NAT1 gene that prevent protein acetylation produce a slow acetylator phenotype.