N-acetyl transferase 1: two polymorphisms in coding sequence identified in colorectal cancer patients

Abstract

Summary Increased cancer risk has been associated with functional polymorphisms that occur within the genes coding for the Nacetyltransferase enzymes NAT1 and NAT2. We detected two NAT1 polymorphisms in colorectal cancer patients by heteroduplex analysis. DNA sequencing revealed the wild-type sequence (NAT1*4) and two single base substitutions at adjacent positions 999 bp (C to T, NAT1*14) and 1000 bp (G to A, NAT1*15) of the gene, changing Arg187 to a stop codon and Arg187 to Gin respectively. NAT1 alleles NAT1*4 (0.98) and NAT1*15 (0.02) were present at a similar frequency in patients with colorectal cancer (n = 260) and in a Scottish control group (n = 323). The third allele, NAT1*14, was present only in the colorectal cancer group at a frequency of 0.006. NAT1 genotype NAT1*4/ NAT1*15 was significantly less frequent in individuals that had a slow NAT2 genotype. This was observed in both cancer and control groups and suggests that this association was unrelated to cancer risk. We conclude that polymorphisms within the coding region of the NAT1 gene are infrequent and do not appear to have an independent association with colorectal cancer risk. However, the relationship between NAT1 and NAT2 polymorphisms appears non-random, suggesting a linkage between these enzymes.Keywords: colorectal cancer, N-acetyltransferase 1, polymorphism, cancer riskThe N-acetyl transferases (NAT1 and NAT2, also known as AACl and AAC2) are xenobiotic enzymes that metabolize inhaled or ingested carcinogenic compounds, including arylamine and heterocyclic amine compounds present in cigarette smoke (Vineis, 1994) and in cooked food (Sugimura et al, 1994). Both NATI and NAT2 genes are known to reside on chromosome 8p (Blum et al, 1990;Franke et al, 1994). Polymorphic forms of NAT genes have the potential to affect an individual's response to carcinogens thereby influencing cancer risk. Polymorphisms of NAT2 that result in slow acetylation of metabolites have been associated with bladder cancer (Risch et al, 1995) and, conversely, fast acetylators may be more common in colorectal cancer and some types of breast cancer (Lang et al, 1986;Agundez et al, 1995). However these associations are weak and are not supported by all studies (Bell et al, 1995a;Hubbard et al, 1997).A potentially confounding factor in these assessments is the contribution of NATI, a closely related enzyme that shares some substrate specificity with NAT2 (Hein et al, 1992), which is expressed at higher levels than NAT2 in colonic epithelial cells (Turesky et al, 1991). Recent studies have shown that NATI is also polymorphic and 15 variants have been detected in animal and human gene sequences Weber and Vatsis, 1993;Grant et al, 1997). One variant, the NAT1*10 allele, is more frequent in patients with bladder and colon cancer (Bell et al, 1995a). The NAT1 * 10 allele contains a single base substitution in the polyadenylation signal in the 3' untranslated region of the gene which results in increased NATI enzyme activity (Bell et al, 1995b) Correspondence to: AL Hubbard a...

Genetic polymorphisms and modulation of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP)‐DNA adducts in human lymphocytes

“…Inability to discriminate NAT1*10 from NAT1*14 is hardly likely to have a major effect on the outcome of the NAT1 analyses. 50,53 Contrary to our results, earlier studies showed that the NAT1*10 allele was associated with higher aromatic adducts in the urinary bladder DNA. 54 In this study, the lack of association between NAT1 polymorphism and PhIP-DNA adducts in human lymphocytes suggests the enzyme has less effect in activating PhIP in these blood cells and does not rule out that the effect of NAT1*10 may be different in target tissues, such as colon, because of the presence of different factors.…”

Structure and Mechanism of Arylamine N-Acetyltransferases

“…Sinclair and co-workers demonstrated that a third-domain truncation mutant of human NAT1 (1-204) can bind to AcCoA, but does not have any catalytic activity in acetylating arylamines [55]. This provides the basis for the NAT1*15 allele, in which a stop codon (Arg 187 Stop) results in a truncated and catalytically inactive protein [56,57].…”

Arylamine N‐acetyltransferases: from drug metabolism and pharmacogenetics to drug discovery

“…A list of the main mutations that affect amino acids in human NAT1 and NAT2 are shown in Table 1 . The premature stop codons in human NAT1 are readily understood (Hubbard et al ., 1998 ; Hughes et al ., 1998 ; Payton and Sim, 1998 ).…”