Introduction
Colorectal cancer is a major cause of death and is influenced by genetic characteristics and environmental factors. Humans are exposed daily to a large variety of toxic and carcinogenic compounds due to habits such as tobacco smoking. Tobacco smoking produces major classes of carcinogenic compounds: polycyclic aromatic hydrocarbons (PAHs), aromatic amines, and heterocyclic amines (HCA). Several of these compounds can produce bulky DNA adducts [
1]. The colorectal mucosa is exposed to these compounds through either the alimentary tract or the circulatory system. DNA adducts were detected in the colonic mucosa of smokers than in nonsmokers [
2]. A previous study found that heavy smokers have a 2–3-fold elevated risk of colorectal adenoma [
3]. Our previous data showed that genetic polymorphisms of
NAT2 and
CYP1A2 in metabolic processes contributed to colorectal cancer risk depending on smoking status in Japanese population [
4]. Therefore, tobacco smoking might be a potential risk factor for colorectal cancer.
DNA repair genes are increasingly being studied for cancer risk because of their critical role in maintaining genome integrity. The base excision repair (BER) pathway, one of four major DNA repair pathways, has a principal role in the repair of mutations caused by oxidized or reduced bases [
5]. Therefore, polymorphisms of DNA repair genes may increase the risk of colorectal cancer. In addition, smoking-induced oxidative DNA base modifications and single-strand breaks are repaired by the BER pathway. In the current study, we focused on genes encoding four key proteins in the BER pathway: OGG1 (8-oxoguanine DNA glycosylase), MUTYH/MYH (Mut Y homolog), APEX1/APE1 (Apurinic/apyrimidinic endonuclease-1), and XRCC1 (X-ray cross-complementing group 1).OGG1 is a DNA glycosylase that removes 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxo-G), which is the most stable form of a highly mutagenic oxidative DNA adduct that pairs with cytosine [
6]. MUTYH is another DNA glycosylase that removes adenine paired with 8-oxo-G or 1, 2-dihydro-2-oxoadenine (2-OH-A) paired with guanine [
7]. The 2-OH-A level is increased by exposure to reactive oxygen species [
8]. APEX1 removes abasic sites formed in DNA cleavage by OGG1 and MUTYH and recruits DNA polymerase β and DNA ligase III [
9]. X-ray cross-complementing group 1 (XRCC1) is a multidomain protein that interacts with poly-ADP-ribose polymerase, DNA ligase III and DNA polymerase β, and repairs DNA single-strand breaks by generating a single nucleotide repair patch (short-patch BER)[
10].
We conducted a hospital-based case-control study to elucidate the DNA repair gene polymorphisms,
OGG1 Ser326Cys (rs1052133),
MUTYH Gln324His (rs3219489),
APEX1 Asp148Glu (rs1130409) and
XRCC1 Arg399Gln (rs25487).
OGG1 Ser326Cys,
APEX1 Asp148Glu and
XRCC1 Arg399Gln have also been linked to a risk of colorectal cancer [
11‐
13]. Germ-line variants,
Tyr165Cys and
Gly382Asp, of the
MUTYH gene have been associated with colorectal adenomas in Caucasians, not in Asians [
14‐
16]. Recent studies reported that
MUTYH Gln324His mutation was the most frequent mutation in Japanese patients with adenomatous popyposis, and the gene polymorphisms was associated with the risk of proximal colon cancer in the Japanese population [
17,
18]. To our knowledge, few previous studies have examined the effect of these polymorphisms on the association between smoking and colorectal cancer [
19,
20]. These polymorphisms were analyzed to evaluate genetic susceptibility to colorectal cancer and the possible modification effect on the relationship between smoking and colorectal cancer risk.
Results
The study included 68 patients and 121 controls (Table
1). The distribution of males (patients, 54.4%; controls, 61.2%) and females (patients, 38.2%; controls, 38.8%) did not differ significantly between the two groups (p = 0.872), and there was also no difference in the average age (± SD) of the patients (67.3 ± 10.9 years old) and controls (67.4 ± 6.7 years old) (p = 0.923). Non-smokers comprised 52.9% of patients and 45.5% of controls and smokers comprised 38.2% of patients and 49.6% of controls. There was no difference in smoking status between patients and controls (p = 0.253). Subsites were divided into 40 colon (58.8%) and 23 rectum (33.8%), and 5 unknown (7.4%).
Table 1
Characteristics of colorectal cancer case and control subjects
Number | 68 | | 121 | | |
Gender | | | | | |
males | 37 | 54.4 | 74 | 61.2 | 0.872a |
females | 26 | 38.2 | 47 | 38.8 | |
unknown | 5 | 7.4 | 0 | 0.0 | |
Age | | | | | |
~64 | 21 | 30.9 | 50 | 41.3 | |
65~69 | 13 | 19.1 | 29 | 24.0 | |
70~74 | 13 | 19.1 | 20 | 16.5 | |
75~ | 16 | 23.5 | 22 | 18.2 | |
unknown | 5 | 7.4 | 0 | 0.0 | |
Mean ± S.D. | 67.3 ± 10.9 | | 67.4 ± 6.7 | | 0.923b |
Smoking status (Pack-years) | | | | | |
non-smokers (Pack-years = 0) | 36 | 52.9 | 55 | 45.5 | 0.253a |
smokers (Pack-years > 0) | 26 | 38.2 | 60 | 49.6 | |
unknown | 6 | 8.8 | 6 | 5.0 | |
Subsites | | | | | |
colon | 40 | 58.8 | | | |
rectum | 23 | 33.8 | | | |
unknown | 5 | 7.4 | | | |
Genotyping and allele frequencies of
OGG1 Ser326Cys,
MUTYH Gln324His,
APEX1 Asp148Glu, and
XRCC1 Arg399Gln adjusted for gender, age and smoking habit are shown in Table
2. The allele frequencies of the four gene polymorphisms in controls were consistent with the Hardy-Weinberg equilibrium. The ORs for the
OGG1 Ser/Cys and
Cys/Cys genotypes compared with the
Ser/Ser genotype were not statistically significant (crude odds ratio [OR] 1.43, 95% confidence interval [95%CI] 0.73–2.78, p = 0.297; adjusted OR 1.43, 95%CI 0.69–2.95, p = 0.332). The ORs for the
MUTYH Gln/His and
His/His genotypes were shown to be statistically associated with the
Gln/Gln genotype (crude OR 3.30, 95%CI 1.44–7.60, p = 0.005; adjusted OR3.53, 95%CI 1.44–8.70, p = 0.006). The ORs for the
APEX1 Asp/Glu and
Glu/Glu genotypes compared with
Asp/Asp genotype were significantly increased (crude OR 2.69, 95%CI 1.45–4.99, p = 0.002; adjusted OR 2.33, 95%CI 1.21–4.48, p = 0.011). The ORs for the
XRCC1 Arg/Gln and
Gln/Gln genotypes compared with the
Arg/Arg genotype were not statistically significant (crude OR 0.65, 95%CI 0.36–1.19, p = 0.164; adjusted OR 0.60, 95%CI 0.31–1.15, p = 0.125). These results indicate that the
MUTYH Gln324His and the
APEX1 Asp148Glu carry a significant risk for carcinogenesis of colorectal cancer.
Table 2
Genotype distribution in colorectal cancer and Allele frequency
OGG1
| | | | | | | | | | | |
Ser/Ser | 17 | 25.0 | 39 | 32.2 | 1.00 | | 1.00 | | Ser | 52.9 | 54.6 |
Ser/Cys,Cys/Cys | 51 | 75.0 | 82 | 67.8 | 1.43 (0.73–2.78) | 0.297 | 1.43 (0.69–2.95) | 0.332 | Cys | 47.1 | 45.5 |
MUTYH
| | | | | | | | | | | |
Gln/Gln | 8 | 11.8 | 37 | 30.6 | 1.00 | | 1.00 | | Gln | 39.0 | 59.1 |
Gln/His,His/His | 60 | 88.2 | 84 | 69.4 | 3.30 (1.44–7.60) | 0.005 | 3.53 (1.44–8.70) | 0.006 | His | 61.0 | 40.9 |
APEX1
| | | | | | | | | | | |
Asp/Asp | 23 | 33.8 | 70 | 57.9 | 1.00 | | 1.00 | | Asp | 64.0 | 74.8 |
Asp/Glu,Glu/Glu | 45 | 66.2 | 51 | 42.1 | 2.69 (1.45–4.99) | 0.002 | 2.33 (1.21–4.48) | 0.011 | Glu | 36.0 | 25.2 |
XRCC1
| | | | | | | | | | | |
Arg/Arg | 42 | 61.8 | 62 | 51.2 | 1.00 | | 1.00 | | Arg | 78.7 | 71.1 |
Arg/Gln,Gln/Gln | 26 | 38.2 | 59 | 48.8 | 0.65 (0.36–1.19) | 0.164 | 0.60 (0.31–1.15) | 0.125 | Gln | 21.3 | 28.9 |
The distributions of the four polymorphisms were compared among cases of colon and rectal cancer, and the OR adjusted for gender, age and smoking habit is shown in Table
3. The adjusted ORs for the
OGG1 Ser/Cys and
Cys/Cys genotypes compared with the
Ser/Ser genotype were not statistically significant (OR 1.28, 95%CI 0.55–2.99, p = 0.567 for colon cancer; OR 1.66, 95%CI 0.56–4.87, p = 0.359 for rectal cancer). The adjusted ORs for the
MUTYH Gln/His and
His/His genotypes were significant compared with the
Gln/Gln genotype for colon cancer, but not for rectal cancer (OR 3.95, 95%CI 1.28–12.20, p = 0.017 for colon cancer; OR 3.06, 95%CI 0.84–11.11, p = 0.089 for rectal cancer). The adjusted ORs for the
APEX1 Asp/Glu and
Glu/Glu genotypes compared with
Asp/Asp genotype were statistically significant for colon cancer, but not for rectal cancer (OR 3.04, 95%CI 1.38–6.71, p = 0.006 for colon cancer; OR 1.61, 95%CI 0.64–4.09, p = 0.315 for rectal cancer). The adjusted ORs for the
XRCC1 Arg/Gln and
Gln/Gln genotypes compared with the
Arg/Arg genotype were not statistically significant (OR 0.60, 95%CI 0.28–1.30, p = 0.194 for colon cancer; OR 0.62, 95%CI 0.24–1.58, p = 0.315 for rectal cancer).Therefore, the cancer subsite-specific study indicated that the
MUTYH Gln324His and the
APEX1 Asp148Glu have a colon cancer-specific risk.
Table 3
Genotype distribution in relation to subsites in colorectal cancer
OGG1
| | | | | | | | | | | | | | | | |
Ser/Ser | 10 | 25.0 | 39 | 32.2 | 1.00 | | 1.00 | | 5 | 21.7 | 39 | 32.2 | 1.00 | | 1.00 | |
Ser/Cys,Cys/Cys | 30 | 75.0 | 82 | 67.8 | 1.43 (0.63–3.21) | 0.390 | 1.28 (0.55–2.99) | 0.567 | 18 | 78.3 | 82 | 67.8 | 1.71 (0.59–4.95) | 0.321 | 1.66 (0.56–4.87) | 0.359 |
MUTYH
| | | | | | | | | | | | | | | | |
Gln/Gln | 4 | 10.0 | 37 | 30.6 | 1.00 | | 1.00 | | 3 | 13.0 | 37 | 30.6 | 1.00 | | 1.00 | |
Gln/His,His/His | 36 | 90.0 | 84 | 69.4 | 3.96 (1.32–11.95) | 0.014 | 3.95 (1.28–12.20) | 0.017 | 20 | 87.0 | 84 | 69.4 | 2.94 (0.82–10.49) | 0.097 | 3.06 (0.84–11.11) | 0.089 |
APEX1
| | | | | | | | | | | | | | | | |
Asp/Asp | 12 | 30.0 | 70 | 57.9 | 1.00 | | 1.00 | | 11 | 47.8 | 70 | 579 | 1.00 | | 1.00 | |
Asp/Glu,Glu/Glu | 28 | 70.0 | 51 | 42.1 | 3.20 (1.49–6.89) | 0.003 | 3.04 (1.38–6.71) | 0.006 | 12 | 52.2 | 51 | 42.1 | 1.50 (0.61–3.66) | 0.376 | 1.61 (0.64–4.09) | 0.315 |
XRCC1
| | | | | | | | | | | | | | | | |
Arg/Arg | 25 | 62.5 | 62 | 51.2 | 1.00 | | 1.00 | | 14 | 60.9 | 62 | 51.2 | 1.00 | | 1.00 | |
Arg/Gln,Gln/Gln | 15 | 37.5 | 59 | 48.8 | 0.63 (0.30–1.31) | 0.217 | 0.60 (0.28–1.30) | 0194 | 9 | 39.1 | 59 | 48.8 | 0.68 (0.27–1.68) | 0.398 | 0.62 (0.24–1.58) | 0.315 |
The ORs for the combined effect of tobacco exposure (pack-years) and the four polymorphisms, adjusted for gender and age, are shown in Table
4. The adjusted ORs for the
OGG1 Ser/Cys and
Cys/Cys genotypes compared with the
Ser/Ser genotype showed no statistically significant risk in non-smokers and smokers (OR 1.14, 95%CI 0.41–3.13, p = 0.807 in non-smokers; OR 1.68, 95%CI 0.60–4.67, p = 0.321 in smokers). The adjusted ORs for the
MUTYH Gln/His and
His/His genotypes compared with the
Gln/Gln genotype showed a significant association with colorectal cancer risk in non-smokers, but not in smokers (OR 4.08, 95%CI 1.22–13.58, p = 0.022 in non-smokers; OR 2.95, 95%CI 0.77–11.25, p = 0.113 for smokers). These results show that the
MUTYH Gln/His and
His/His genotypes are associated with colorectal cancer susceptibility with never smoking history. The adjusted ORs for the
APEX1 Asp/Glu and
Glu/Glu genotypes compared with the
Asp/Asp genotype in smokers was significantly increased (OR 5.02, 95%CI 1.80–13.99, p = 0.002), whereas that in non-smokers did not show a significant (OR 1.56, 95%CI 0.66–3.68, p = 0.311). Smokers with the
APEX1 Asp/Glu and
Glu/Glu genotypes showed an increased risk of colorectal cancer. The adjusted ORs for the
XRCC1 Arg/Gln and
Gln/Gln genotypes compared with the
Arg/Arg genotype were not statistically significant (OR 0.86, 95%CI 0.37–2.03, p = 0.732 in non-smokers; OR 0.43, 95%CI 0.16–1.16, p = 0.097 in smokers). These results indicate that the
MUTYH Gln324His and the
APEX Asp148Glu have statistically a significant risk of colorectal cancer according to smoking status.
Table 4
Genotype distribution in relation to smoking status in colorectal cancer
OGG1
| | | | | | | | | | | | | | | | |
Ser/Ser | 8 | 22.2 | 14 | 25.5 | 1.00 | | 1.00 | | 7 | 26.9 | 23 | 38.3 | 1.00 | | 1.00 | |
Ser/Cys,Cys/Cys | 28 | 77.8 | 41 | 74.5 | 1.20 (0.44–3.23) | 0.725 | 1.14 (0.41–3.13) | 0.807 | 19 | 73.1 | 37 | 61.7 | 1.69 (0.61–4.64) | 0.310 | 1.68 (0.60–4.67) | 0.321 |
MUTYH
| | | | | | | | | | | | | | | | |
Gln/Gln | 4 | 11.1 | 18 | 32.7 | 1.00 | | 1.00 | | 3 | 11.5 | 17 | 28.3 | 1.00 | | 1.00 | |
Gln/His,His/His | 32 | 88.9 | 37 | 67.3 | 3.89 (1.19–12.69) | 0.024 | 4.08 (1.22–13.58) | 0.022 | 23 | 88.5 | 43 | 71.7 | 3.03 (0.80–11.43) | 0.102 | 2.95 (0.77–11.25) | 0.113 |
APEX1
| | | | | | | | | | | | | | | | |
Asp/Asp | 15 | 41.7 | 29 | 52.7 | 1.00 | | 1.00 | | 8 | 30.8 | 41 | 68.3 | 1.00 | | 1.00 | |
Asp/Glu,Glu/Glu | 21 | 58.3 | 26 | 47.3 | 1.56 (0.67–3.65) | 0.303 | 1.56 (0.66–3.68) | 0.311 | 18 | 69.2 | 19 | 31.7 | 4.86 (1.80–13.13) | 0.002 | 5.02 (1.80–13.99) | 0.002 |
XRCC1
| | | | | | | | | | | | | | | | |
Arg/Arg | 20 | 55.6 | 29 | 52.7 | 1.00 | | 1.00 | | 18 | 69.2 | 30 | 50.0 | 1.00 | | 1.00 | |
Arg/Gln,Gln/Gln | 16 | 44.4 | 26 | 47.3 | 0.89 (0.38–2.08) | 0.791 | 0.86 (0.37–2.03) | 0.732 | 8 | 30.8 | 30 | 50.0 | 0.44 (0.17–1.18) | 0.103 | 0.43 (0.16–1.16) | 0.097 |
Discussion
The association between the risk of colorectal cancer and polymorphisms of four DNA repair genes in the BER pathway was investigated in a small case-control study. No significant relationship was apparent between
OGG1 Ser326Cys and colorectal cancer risk. Previous reports have suggested that
OGG1 Ser326Cys is associated with colorectal cancer in Caucasians [
11,
24], but not among Koreans [
25]. Our findings in a Japanese population are consistent with the results from the Korean population study.
Interestingly, we found that the
MUTYH Gln324His genotype has a strong significant association with colorectal cancer risk, especially colon cancer. Tao
et al. [
18] reported
MUTYH Gln324His in Japanese was statistically significantly associated with increased risk of proximal colon, but not distal colon or rectal cancer. Therefore, their results are consistent with our study. Moreover, a recent study found that the activity of
MUTYH Gln324His is 34% less active than that of wild type [
26]. 8-oxo-G is generated by direct oxidation of DNA by a hydroxyl radical, whereas 2-OH-A is exclusively generated by oxidation of dATP in the nucleotide pool [
6,
7]. The 2-OH-A level is increased in human cancerous tissues compared to normal tissues [
27]. Thus, for colorectal cancer, it is also possible that the enzyme of
MUTYH Gln324His may have partially impaired in repair of 2-OH-A opposite guanine, compared to repair of adenine opposite 8-oxo-G, because of the difference in the origin of each oxidized base. We also found that
MUTYH Gln324His was statistically associated with increased risk in never smokers. These results suggest that the
MUTYH 324His variation may be associated with a risk of colorectal cancer due to an increased mutation frequency, containing environmental factors except smoking.
We indicated that the
APEX1 Asp148Glu genotype has a specifically association with colon cancer risk. A previous study reported that this genotype was especially an increased risk of colon cancer risk [
28]. We also found a statistically significant association between the
APEX1 Asp148Glu genotype and colorectal cancer risk in combination with smoking exposure. Ito et al. [
29] reported that the gene-environment interaction between current smoking and
APEX1 148 Glu/Glu genotype was statistically significant for lung cancer risk. However, a previous study didn't found about the effect of smoking habit on association between the
APEX1 Asp148Glu genotype and colorectal cancer risk [
28]. This polymorphism is located within the endonuclease domain of the protein [
30], but it does not reduce endonuclease activity [
31]. The 148
Glu allele has also been associated with increased mitotic delay after exposure to ionizing radiation [
22]. Our results indicate that the
APEX1 variation may play an important role in colorectal cancer risk, containing a reduced ability to communicate with the other BER proteins. In contrast, for
XRCC1 Arg399Gln variants, we found no relationship with colorectal cancer. The
XRCC1 399Gln allele has been linked with a reduced risk of colorectal adenomas [
12,
13], and XRCC1 has also been associated with improved progress in patients who underwent chemotherapy, but not in those who received surgery alone [
11]. The smoking has an effect on colon adenoma risks among carriers of
XRCC1 codon 399
Arg alleles [
19,
20]. However, we were unable to detect these relationships in our cases.
Our data may be biased by the relatively small number as a hospital-based case-control study, because we have several limitations. Therefore, we would require further verification as predictive biomarkers in a larger study population and need to clarify the gene-environment interaction between smoking and these genotypes.
In conclusion, MUTYH Gln324His and APEX1 Asp148Glu polymorphisms are important risk factors for colorectal cancer, especially colon cancer, in the Japanese population. In particular, the MUTYH Gln324His genotype is associated with colorectal cancer susceptibility in never smoking history, whereas the APEX1 Asp148Glu genotype constitutes an increased risk of colorectal cancer in combination with smoking exposure. MUTYH Gln324His and APEX1 Asp148Glu polymorphisms may be useful markers of genetic susceptibility to colorectal cancer.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
MK, KO and JT plan the study made all coordination and was involved in the laboratory processing. KY, AM, YO and NI participated in the study and performed the statistical analysis. AT, YT, KT, MY and ES carried out handling the samples. All authors read and approved the final version of manuscript.