Acetyl transferase-mediated metabolic activation of N-hydroxy-4-aminobiphenyl by human uroepithelial cells.
Metabolism and nucleic acid binding of N-hydroxy-4-aminobiphenyl (N-OH-ABP), a proximate carcinogenic metabolite of the human bladder carcinogen 4-aminobiphenyl (ABP), was investigated using cultured normal human uroepithelial cells (HUC). HPLC and TLC of the ethyl acetate extract of the media from cultured HUC after 4 h exposure to N-OH-ABP revealed the formation of two major metabolites, ABP and 4-acetylaminobiphenyl (AABP), suggesting the presence of N-acetyl transferase(s) in HUC. This was further confirmed by the formation of AABP, during the incubation of ABP with acetyl coenzyme A (AcCoA) and HUC cytosol. To test whether these enzymes also catalyze the AcCoA-dependent O-acetylation, we examined the metabolic activation of N-OH-ABP using cytosolic preparations. Cytosol from HUC catalyzed AcCoA-dependent binding of [3H]N-OH-ABP to RNA; the amount of binding was 757 pmol/mg RNA/mg protein. Binding with DNA was quantitatively similar to RNA. HPLC and TLC analyses of the enzymatic hydrolysate of [3H]N-OH-ABP-bound DNA revealed the major adduct to be N-(deoxyguanosine-8-yl)-4-aminobiphenyl, based on mobility of the radioactivity in comparison with the authentic synthetic standard. 32P-Post-labeling analysis of the DNA from the cytosol-mediated binding of N-OH-ABP revealed four radioactive spots. In contrast, post-labeling analysis of the DNA from intact HUC exposed to N-OH-ABP showed five adducts, including two of the adducts observed with HUC cytosols, suggesting the possible involvement of additional activation pathway(s) in intact HUC. These results suggest that bioactivation of N-OH-ABP could occur within the HUC, the target organ for ABP, and that cytosolic acetyl transferase(s) may play a critical role in susceptibility to arylamine-induced bladder carcinogenesis.
Frederickson
S M
SM
Department of Human Oncology, University of Wisconsin Comprehensive Cancer Center, Madison 53792.
Hatcher
J F
JF
Reznikoff
C A
CA
Swaminathan
S
S
D000105:Acetyl Coenzyme A / Q000378:metabolism; D000611:Aminobiphenyl Compounds / Q000378:metabolism* / Q000493:pharmacokinetics*; D001191:Arylamine N-Acetyltransferase / Q000096:biosynthesis*; D001711:Biotransformation; D002273:Carcinogens / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D012343:RNA, Transfer / Q000378:metabolism; D001743:Urinary Bladder / Q000378:metabolism*
D000611:Aminobiphenyl Compounds; D002273:Carcinogens; C006757:4-biphenylamine; C014593:N-hydroxy-4-aminobiphenyl; D000105:Acetyl Coenzyme A; D004247:DNA; D012343:RNA, Transfer; D001191:Arylamine N-Acetyltransferase; C020853:4-acetylaminobiphenyl