AIM: To examine the effect of the potential interaction between KIF1B variants (rs17401966 and rs3748578) and environmental factors on the risk of hepatocellular carcinoma (HCC) in a high-risk region in China.

METHODS: Three hundred and six patients with HCC and 306 hospital-based control participants residing in the Shunde region of Guangdong Province, China were enrolled. Clinical characteristics were collected by reviewing the complete medical histories from the patient archives, and epidemiological data were collected using a questionnaire and clinical examination. Two single nucleotide polymorphisms (SNPs) of KIF1B (rs17401966 and rs3748578) were chosen for the current study. All subjects were genotyped using a TaqMan real-time polymerase chain reaction. Multiplicative and additive logistic regression models were used to evaluate various gene-environment interactions.

RESULTS: Smoking, frequent consumption of raw freshwater fish, hepatitis B virus (HBV) infection, and a family history of HCC were important risk factors for HCC in this population. Chronic infection with HBV was the most important environmental risk factor for HCC [odds ratio (OR) = 12.02; 95% confidence interval (95%CI): 6.02-24.00]. No significant association was found between the KIF1B variants alone and the risk of HCC. Nevertheless, a significant additive effect modification was observed between rs17401966 and alcohol consumption (P for additive interaction = 0.0382). Compared with non-drinkers carrying either the AG or GG genotype of rs17401966, individuals classified as alcohol consumers with the AA genotype of rs17401966 had a significantly increased risk of HCC (OR = 2.36; 95%CI: 1.49-3.74).

CONCLUSION: The gene-environment interaction between the KIF1B rs17401966 variant and alcohol consumption may contribute to the development of HCC in Chinese individuals.

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. HCC ranks as the fifth most common cancer in men and seventh most common cancer in women[1]. Eastern Asia experiences a large burden of the geographical distribution of HCC; China alone accounts for approximately 55% of all HCC cases worldwide[2]. Prognosis of HCC patients is poor, with an average 3-year survival rate of 13%-21%[3,4]. Due to the high disease burden worldwide, it is important to identify individuals who are at a higher risk of HCC and to identify risk factors that may be modifiable. Several environmental factors that increase the risk of HCC have been found, including chronic infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), exposure to aflatoxin, and consumption of alcohol[5-7].

However, only a small percentage of individuals who are exposed to these risk factors will eventually develop HCC, highlighting that genetic susceptibility is another factor for the development of HCC. HCC involves a complex interplay of multiple genetic and environmental factors[8]. However, underlying genetic mechanisms of hepatocellular carcinogenesis have not yet been fully elucidated.

Kinesin superfamily proteins (KIFs) make up a large gene family of microtubule motor proteins[9]. KIF1B, a member of the KIF family, maps to a gene locus at 1p36.22 and encodes two alternatively spliced isoforms, KIF1Bα and KIF1Bβ; both isoforms form homodimers and transport mitochondria and synaptic vesicle precursors, respectively. It has been postulated that KIF1B acts as a tumor suppressor. Downregulation of KIFs has been shown to contribute to tumorigenesis of certain cancers, including brain, colon and breast cancers[10]. Recently, Zhang et al[11] performed a genome-wide association study (GWAS) and found that KIF1B is a promising susceptibility gene for HCC in five independent Chinese populations. In this GWAS, the most significant variant of KIF1B (rs17401966), located in the intron of the gene, was associated with a decreased risk of HCC [joint odds ratio (OR) = 0.61, P = 1.7 × 10^-18]. However, more recent studies have not drawn the same conclusion. Al-Qahtani et al[12] reported no significant association between the rs17401966 variant of KIF1B and HBV-related HCC. Sawai et al[13] also showed no association between rs17401966 and HBV-related HCC in a Japanese cohort. These inconsistent results may partly be due to the distinct genetic architecture among the different study populations. Additionally, the significant findings obtained by Zhang et al[11] may have resulted from a phenomenon known as the “winner’s curse,” where the odds ratio of the candidate variant is overestimated in the population, leading to reporting a positive result[14]. Another reason for the discrepancy among studies could be the complex gene-environment interactions involved in the development of HCC that have been neglected. Hence, we conducted a case-control study with HCC patients and hospital-based controls to clarify the effect of rs17401966 in KIF1B on HCC. In addition, one single nucleotide polymorphism (SNP), rs3748578, was in strong linkage disequilibrium (LD) with rs17401966[15], which was also associated with HBV-induced HCC. We also investigated the potential functional role of this variant rs3748578. We applied both additive and multiplicative models using a logistic regression analysis framework to assess the potential interactions between the variants and environmental factors in development of HCC in a Chinese cohort.

A total of 306 patients with HCC (264 males and 42 females) and 306 controls (264 males and 42 females) were enrolled in the study with a mean age (± standard deviation) of 55.84 (± 11.49) and 55.83 (± 11.67) years, respectively. The general characteristics of the subjects are presented in Table 1. No significant differences were found between healthy controls and patients with HCC with regard to age and gender (P = 0.992 and P = 0.998, respectively). Logistic regression analysis suggested that smoking, frequent consumption of raw freshwater fish, HBV infection, and family history of HCC were important risk factors for HCC in the Shunde region of China (Table 1).

The genotypic distributions of rs3748578 and rs17401966 did not differ significantly between the cases and controls (Table 2). Logistic regression analysis failed to show a significant association between HCC with either rs3748578 or rs17401966 for all genetic models (Table 3).

Tables 4 and 5 show the results of additive and multiplicative interaction analysis between the two variants and the main environmental risk factors for HCC. A significant additive interaction was seen between rs17401966 and alcohol consumption (P = 0.0382). Compared with non-drinkers carrying the rs17401966 AG or GG genotype, individuals who consumed alcohol and carried the AA genotype had a significantly increased risk of HCC, with an adjusted OR of 2.36 (95%CI: 1.49-3.74, P = 0.0382). No significant interactions were observed between the rs3748578 variant and environmental factors.

The current study aimed to investigate whether two variants of KIF1B (rs17401966 and rs3748578) interacted with environmental risk factors of HCC to influence the risk of HCC. A significant additive interaction was observed between rs17401966 and alcohol consumption.

HCC is a complex disease associated with many risk factors and cofactors[16]. The major risk factor for HCC in China is clearly chronic HBV infection[17], with an 8%-20% prevalence of HBV[18] and approximately 93 million chronic HBV carriers[19]. The proportion of HBV-positive HCC has significantly increased, with 76% of HCC cases being HBV positive[20], which was consistent with 74.84% in our research. However, compared to China, the proportion of HCV-positive HCC was high in the United States, Italy, Japan, Brazil, Taiwan, Egypt, and other countries[20]. As we know, HCV prevalence in China is low (< 1.5%)[21], which is transmitted primarily through intravenous drug use and invasive medical treatment, particularly hemodialysis[22]. The overall prevalence of anti-HCV antibody (anti-HCV) in Guangdong Province was about 0.50%[23-25], after the implementation of strict blood screening and other procedural measures, and we did not describe the relationship between HCV and HCC in the research.

In this study, we did not find a significant association between rs17401966 and HCC. This result is not consistent with the results reported in the GWAS study by Zhang et al[11]. One possible explanation for this discrepancy is the fact that the study samples were made up of individuals with different genetic architectures, who were from south China and Japan. Additionally, according to evolutionary theory, individual common variants often exert modest effects on common diseases[26]. In other words, sufficient statistical power to detect a disease with low penetrance due to a specific variant would require enrollment of thousands of subjects in the study. A recent meta-analysis of rs17401966 and HCC summarized data from 7596 HCC cases and 9614 controls; this meta-analysis supported Zhang et al’s[15] findings, indicating a significant association between rs17401966 and HCC. Nevertheless, according to the common disease-common variant (CDCV) hypothesis, cumulative effects of multiple common variants or their interactions with environment factors underlie common diseases. The finding in the present study on the interaction between rs17401966 and alcohol consumption fits the CDCV hypothesis. Zhang et al[11] suggested a significant association between rs17401966 genotypes and expression of KIF1B in liver tissues, with carriers of the G allele having a greater KIF1B level than individuals without G allele (AA carriers). However, several studies have found that the G allele of rs17401966 demonstrated a protective effect on the susceptibility to HCC[27-29]. This inconsistency might be attributed to the fact that there were heterogeneous population structures. It is necessary to investigate the exact effect of ethnicity on the association between KIF1B polymorphisms and HCC risk in future. It has been hypothesized that KIF1B can act as a tumor suppressor. The mechanism by which this occurs is still unclear, but KIF1B may induce apoptosis by acting downstream of EglN3 prolyl hydroxylase[30], ultimately leading to inhibition of malignant transformation and progression.

Alcohol consumption is common in Guangdong Province, where the total drinking rate is 33.3%[31], with the region of Shunde having an even higher rate, especially in residents who habitually drink brewed Chinese rice wine[32]. Ethanol, the active compound in alcoholic beverages, is metabolized to acetaldehyde, which has been found to be mutagenic and carcinogenic[33,34], and other studies reported that alcohol was involved in hepatocarcinogenesis[35,36]. Therefore, a significant joint effect and interaction between rs17401966 and alcohol consumption was observed, suggesting that gene-environment interactions may provide further insights for comprehensive understanding of HCC in the Shunde area.

Our study is not without limitations. Hospital-based samples may lead to a selection bias of participants. Secondly, the sample size was limited and statistical power was insufficient for detection of a modest effect size of individual common variants. Thirdly, only two variants in the KIF1B gene were assessed in this study, which may fail to reflect the genetic mechanism of other KIF1B variants in the development of HCC.

In conclusion, we identified a statistically significant interaction between the rs17401966 variant of KIF1B and alcohol consumption that contributes to the development of HCC in the Shunde region of China. This study further supports the hypothesis that KIF1B is an important susceptibility gene for HCC in the Chinese population. Comprehensive studies with larger sample sizes and more diverse independent populations are warranted to better understand the underlying mechanisms of KIF1B genetic variants in the development of HCC.