Substrate-Dependent Regulation of Human ArylamineN-Acetyltransferase-1 in Cultured Cells
- 1Department of Pharmacology, University of Western Australia, Nedlands, Western Australia, 6907, Australia (N.J.B., K.F.I., R.F.M.);2Laboratory for Cancer Medicine, Royal Perth Hospital, Perth, Western Australia, 6000, Australia (N.J.B., R.F.M.); and 3Clinical Pharmacology and Toxicology Laboratory, The Western Australian Centre for Pathology and Medical Research, Nedlands, Western Australia, 6009, Australia (K.F.I.)
Abstract
Arylamine N-acetyltransferase-1 (NAT1) is a polymorphically expressed enzyme that is widely distributed throughout the body. In the present study, we provide evidence for substrate-dependent regulation of this enzyme. Human peripheral blood mononuclear cells cultured in medium supplemented withp-aminobenzoic acid (PABA; 6 μM) for 24 h showed a significant decrease (50–80%) in NAT1 activity. The loss of activity was concentration-dependent (EC50 ∼ 2 μM) and selective because PABA had no effect on the activity of constitutively expressed lactate dehydrogenase or aspartate aminotransferase. PABA also induced down-regulation of NAT1 activity in several human cell lines grown at confluence. Substrate-dependent down-regulation was not restricted to PABA. Addition of other NAT1 substrates, such as p-aminosalicylic acid, ethyl-p-aminobenzoate, or p-aminophenol to peripheral blood mononuclear cells in culture also resulted in significant (P < .05) decreases in NAT1 activity. However, addition of the NAT2-selective substrates sulfamethazine, dapsone, or procainamide did not alter NAT1 activity. Western blot analysis using a NAT1-specific antibody showed that the loss of NAT1 activity was associated with a parallel reduction in the amount of NAT1 protein (r 2 = 0.95). Arylamines that did not decrease NAT1 activity did not alter NAT1 protein levels. Semiquantitative reverse transcriptase polymerase chain reaction of mRNA isolated from treated and untreated cells revealed no effect of PABA on NAT1 mRNA levels. We conclude that NAT1 can be down-regulated by arylamines that are themselves NAT1 substrates. Because NAT1 is involved in the detoxification/activation of various drugs and carcinogens, substrate-dependent regulation may have important consequences with regard to drug toxicity and cancer risk.
Footnotes
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Send reprint requests to: Dr. R. F. Minchin, Department of Pharmacology, University of Western Australia, Nedlands, Western Australia, 6907, Australia. E-mail:rminchin{at}receptor.pharm.uwa.edu.au
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This work was supported by a grant from the Medical Research Foundation, Royal Perth Hospital. N.J.B. is supported by the Elizabeth Stalker McEwan Trust.
- Abbreviations:
- NAT1
- N-acetyltransferase-1
- AcCoA
- acetyl-coenzyme A
- AST
- aspartate aminotransferase
- BME
- Basal Medium Eagle
- CHX
- cycloheximide
- DAPS
- dapsone
- DMEM
- Dulbecco's modified Eagle's medium
- DTT
- dithiothreitol
- EPAB
- ethyl-p-aminobenzoate
- LDH
- lactate dehydrogenase
- NAPABA
- N-acetyl-p-aminobenzoic acid
- NAPAP
- N-acetyl-p-aminophenol
- NAT2
- N-acetyltransferase-2
- PA
- procainamide
- PABA
- p-aminobenzoic acid
- PAP
- p-aminophenol
- PAS
- p-aminosalicylic acid
- PBMC
- peripheral blood mononuclear cells
- PMA
- phorbol 12-myristate 13-acetate
- SMX
- sulfamethoxazole
- SMZ
- sulfamethazine
- PCR
- polymerase chain reaction
- RT
- reverse transcription
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- Received July 26, 1999.
- Accepted November 17, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
