RERF Report No. 5-15

Paper published in Human Genome Variation§“CD14 and IL18 gene polymorphisms associated with colorectal cancer subsite risks
among atomic bomb survivors”
Yiqun Hu, Kengo Yoshida, John B. Cologne, Mayumi Maki, Yukari Morishita, Keiko
Sasaki, Ikue Hayashi, Waka Ohishi, Ayumi Hida, Seishi Kyoizumi, Yoichiro Kusunoki,
Katsushi Tokunaga, Kei Nakachi, Tomonori Hayashi
Human Genome Variation 2, Article number: 15035（2015）（doi:10.1038/hgv.2015.35）

Study Findings
Our gene structures contain individual differences (called “gene polymorphisms,”
based upon which are formulated several genotype classifications), with our basic
physical constitutions sometimes being affected by this genetic variation. Dividing
colorectal cancer among atomic bomb (A-bomb) survivors into proximal (i.e., in theupper half of the colon) colon cancer and distal (i.e., in the lower half of the colon)
colorectal cancer, we examined the association between colon cancer risk and radiationdose by CD14 and IL18 genotypes. (CD14 and IL18 are genes related to immune
response and inflammation.) Our findings suggest that CD14 gene polymorphisms*1
may contribute to individual differences in the risk of radiation-related distal colorectal
cancer and that IL18 gene polymorphisms*2 may contribute to individual differences inthe risk of radiation-related proximal colon cancer.
*1CD14 gene polymorphisms are related to innate immunity*2IL18 gene polymorphisms are related to elimination of pathogens from the bodythrough a process of inflammation induction
Explanation
Dr. Tomonori Hayashi, Assistant Department Chief, Department ofRadiobiology/Molecular Epidemiology, Radiation Effects Research Foundation (RERF),and his colleagues examined the association between colon cancer andimmune/inflammatory-related gene polymorphisms using samples collected from
immunological studies conducted since 1981 that followed a subset of participants in
RERF’s Adult Health Study (AHS), which is a long-term follow-up study of the health ofA-bomb survivors in Hiroshima and Nagasaki. The research team published the results in
Human Genome Variation.
1. Study purpose
Colorectal cancer is one of the cancers regarding which risks of mortality and1

RERF Report No. 5-15

incidence are clearly increased for A-bomb survivors. The colorectal cancer incidence in
RERF’s Life Span Study (LSS) population increased with radiation dose and remains
high even today, more than 65 years since exposure. In this study, we specificallyexamined the association between risk of colorectal cancer (proximal colon cancer anddistal colorectal cancer)*3 and radiation exposure by genotype of the CD14 gene, which isinvolved in innate immunity, and the IL18 gene, which is related to elimination ofpathogens from the body by inflammation induction, to investigate individual differencesin colorectal cancer susceptibility to radiation exposure.
*3Since it was recently discovered that major oncogenic pathways differ between
proximal colon cancer and distal colorectal cancer, we investigated in this study
individual differences in proximal and distal colorectal cancer susceptibility toradiation exposure.
2. Study methods
We examined CD14 and IL18 gene polymorphisms in 4,690 subjects of the AHS,
including 222 colorectal cancer cases (81 proximal colon cancer and 131 distal colorectal
cancer cases). CD14 and IL18 genotypes can be divided into the following threecategories: major homozygotes, heterozygotes, and minor homozygotes*4. Using
statistical models, we assessed risks in, and examined the interaction between, different
combinations of radiation doses and the CD14 or IL18 genotypes.
*4When wild-type gene “A” is prevalent in a population and minor type gene “a” islow, the major homozygote is AA, the heterozygote is Aa, and the minor homozygote
is aa.
3. Study results(1) CD14 genotype and distal colorectal cancer:
After adjustment for sex, year of birth, city of exposure, smoking status, andradiation dose, the risks of overall colorectal cancer and distal colorectal cancer with
CD14-911 A/A (major homozygotes of CD14 polymorphisms, localized on 911 basepairs 5’-upstream of CD14 gene) were significantly higher compared with those with
two other genotypes (A/C heterozygotes and C/C minor homozygotes). No
statistically significant interactions were observed between radiation exposure andCD14 genotype*5. The CD14-911 A/A genotype had significantly higher levels of
membrane-bound and soluble CD14 protein than the other two genotypes.
(Membrane-bound CD14 is joined to the cell membrane, and soluble CD14 is protein
originally bound to the membrane that was cleaved by an enzyme and is present inthe blood.)2

RERF Report No. 5-15

*5This study examined whether distal colorectal cancer risk was increased withincreasing radiation dose among populations who have the CD14-911 A/A genotype.
Thus far, no increased risk due to radiation exposure has been observed for rectal
cancer among the larger population in the epidemiological study that is not dividedby genotype. However, it was impossible to evaluate the risk of rectal cancer alone
in association with radiation exposure due to the small number of cases available
for use in this study. Separate analysis by genotype of distal colon cancer and rectal
cancer among all distal colorectal cancer cases remains an important task to be
tackled in the future.
(2) IL18 genotype and proximal colon cancer:
After adjustment for sex, year of birth, city of exposure, smoking status, andradiation dose, the risk of proximal colon cancer with IL18-137 G/G (majorhomozygotes of IL18 polymorphisms localized on 137 base pairs 5’-upstream of IL18gene) was significantly higher compared with the other two genotypes (G/C
heterozygotes and C/C minor homozygotes). No statistically significant interactions
were observed between radiation dose and IL18 genotype. The IL18-137 G/Ggenotype had lower levels of IL18 in the plasma than did the other two genotypes.
Study Significance
These findings suggest the potential involvement of CD14-mediated inflammatory
responses in distal colorectal cancer and IL18-mediated inflammatory responses inproximal colon cancer in atomic bomb survivors.
The Radiation Effects Research Foundation has studied A-bomb survivors and theiroffspring in Hiroshima and Nagasaki for more than 60 years. RERF’s research achievements areconsidered the principal scientific basis for radiation risk assessment by the United Nations
Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and forrecommendations regarding radiation protection standards by the International Commission on
Radiological Protection (ICRP). RERF expresses its profound gratitude to the A-bombsurvivors and survivors’ offspring for their cooperation in our studies.
§Human Genome Variation, an official monthly journal of the Nature PublishingGroup of the UK, features original articles and reviews on the human genome andnewly discovered variability and mutations in human genes. (Impact factor in 2014:2.684)

3