JAK1 Gene Polymorphisms Are Associated with the Outcomes of Hepatitis B Virus Infection,but Not with α Interferon Therapy Response in a Han Chinese Population

Introduction

Hepatitis B virus (HBV) infection is a serious public health problem all over the world. HBV infection results in 0.5 to 1.2 million deaths per year, which is mainly caused by chronic hepatitis, cirrhosis, and hepatocellular carcinoma (Rehermann and Nascimbeni, 2005). Generally, clinical consequences of HBV infection vary in different persons. About 90%-95% of infected adults can eliminate the virus spontaneously and only 5%-10% of them become chronic HBV carriers, among whom 20%-30% develop into chronic hepatitis B (CHB) and about 5% go on to liver cirrhosis and hepatocellular carcinoma after a long disease course (Ganem and Prince, 2004). Several factors are known to be involved in the procession of HBV infection, such as age, viral factors, host immunity, and genetic components (Wang, 2003; Schaefer, 2005). Genetic studies provide robust evidence that polymorphisms in the human genome contribute greatly to the susceptibility to HBV infection (Thio et al., 2000).

Janus kinase 1 (JAK1), first identified in 1991, is a member of a new class of protein-tyrosine kinases, and there are four JAKs in mammals, JAK1, JAK2, JAK3, and Tyk2, which are crucial for cytokine receptor signaling and regulate blood formation and the immune response (Wilks et al., 1991; Yamaoka et al., 2004; Vainchenker et al., 2008). The JAK1 gene, with 25 exons and encoding a protein of 1154 amino acids, is located on chromosome 1p31.3. Recent studies have reported that polymorphisms in the JAK1 gene may be functional and contribute to human cancer development and autoimmune diseases (Staerk et al., 2005; Jeong et al., 2008). Also, JAK1 is a key member in both the α/β interferon (IFNα/β) and IFNγ signaling pathways (which included 13 genes) (Kalvakolanu, 2003), so it should be playing an important role in IFN therapy and antivirus mechanism as in HBV infection. However, up to the present, there are no association studies concerning the JAK1 gene and hepatitis B.

Here, we hypothesized that single-nucleotide polymorphisms (SNPs) in JAK1 gene may be associated with outcomes of HBV infection and the efficiency of IFNα therapy. We performed a genetic association study on 12 SNPs (rs310227, rs7531799, rs7546545, rs17127174, rs3790541, rs10493373, rs2780898, rs310247, rs310196, rs2780895, rs4244165, and rs17127024), which showed moderate variations in JAK1 among Han Chinese subjects to elucidate host genetic factors that can affect the outcome of HBV infection and response to IFNα therapy.

Materials and Methods

Results

We first conducted genotyping experiments for the 12 JAK1 polymorphisms. Genotype distributions of rs310247, rs4244165, and rs17127024 were deviated from the HWE in subjects with inactive carrier state. The genotype distributions and allelic frequencies of JAK1 polymorphisms in the CHB patients and subjects with inactive carrier state are presented in Table 2. The SNP rs17127024 was associated with outcomes of HBV infection. The frequency of the G allele was 70.3% in CHB patients vs. 76.5% in subjects with inactive carrier state (p=0.014, odds ratio=0.726, 95% confidence interval=0.561-0.938). The frequencies of the rs17127024 genotypes also differed significantly between the two groups (p=0.031). The SNP rs4244165 had similar allelic frequencies, but different genotype distributions (p=0.008) between CHB patients and subjects with inactive carrier state. The genotype distributions and allelic frequencies of other SNP genotyped did not significantly differ between the CHB patients and subjects with inactive carrier state.

The degree of LD for these 12 SNPs was analyzed, and there was no apparent LD except for that between rs7531799 and rs10493373 (D′=0.99, r²=0.95). We constructed haplotypes using these 12 SNPs and found no apparent associated haplotype.

Out of the 395 CHB patients, 256 patients received IFNα treatment, and the therapy efficacy was evaluated. The total response rate was 69.1% (177/256), with 16.0% of CR (41/256) and 53.1% of PR (136/256), and NR rate was 30.9% (79/256). There was no significant difference in the distribution of age and gender among three groups. Since the CR rate was fairly low, the CR group and the PR group were combined into the response group to be analyzed. There were no significant differences in allele frequencies and genotype distributions of all the studied SNPs between the two groups (Table 3). We also compared allele frequencies and genotype distributions of these SNPs in the CR and NR groups, or in the CR and PR+NR groups, and the results were still negative (data not shown). We then conducted haplotype analyses and found no haplotype that was associated with a response to IFN treatment (data not shown).

Discussion

We carried out an association study and confirmed that the SNPs rs4244165 and rs17127024 in the JAK1 gene are associated with outcomes of HBV infection in Han Chinese subjects. However, the distribution of SNPs may differ greatly with ethnicity and region. Also, the sample size involved in the present study is not large enough, and it is possible that these findings may be incidental. Further studies in other ethnic groups and the confirmation of the present finding in a larger sample set in the Han Chinese population are therefore required to clarify the role of these polymorphisms.

In the present study, the genotype distribution of rs310237, rs4244165, and rs17127024 deviated from HWE in subjects with inactive carrier state. The reason to apply HWE is to eliminate the possibility of genotyping errors in molecular genetics studies. For genotyping quality control, 20% of samples were randomly genotyped again by another person, and we obtained 100% identical results. On the other hand, HWE should be applied in normal control subjects. In the present study, however, we chose subjects with the inactive carrier state as controls, to ensure that both cases and controls were exposed in the same virus background.

JAK1 is a key factor in the IFN signaling pathway (Kalvakolanu, 2003). IFNα has been one of the first line drugs for hepatitis B due to its antiviral and immunomodulatory activities (Saracco and Rizzetto, 1997). Endogenous IFNs (α, β, and γ) should also be important in modulating the antiviral activity of the body. So, we concluded that JAK1 was important in HBV infection. Up to now, however, there are few association studies concerning JAK1 gene polymorphisms and hepatitis B. However, some studies reported that polymorphisms in the IFN signaling pathway genes and IFN genes were associated with outcomes of HBV infection (Liu et al., 2006; Song le et al., 2006; Abbott et al., 2007; Zhou et al., 2007; Wu et al., 2009). Zhou et al. (2007) reported that a T-408C polymorphism in the promoter region of the IFNAR1 gene changed promoter activity and were associated with outcomes of HBV infection in Hong Kong Chinese. Ligand binding (IFNα) to IFNAR1 causes an aggregation of the receptor IFNAR1, leading to a juxtapositioning of JAK. This permits the tyrosine phosphorylation of JAK and the receptor polypeptide (Kalvakolanu, 2003). We reported in the present study that polymorphisms in the JAK1 gene were also associated with outcomes of HBV infection. As these SNPs are intron polymorphisms, it is probable that they are genetic markers in LD with other functional polymorphisms, which should be confirmed in future studies. Our present work indicated that genes in the IFN signaling pathway could be candidates for hepatitis B.

King et al. (2002) studied 22 genetic polymorphisms in the IFN pathway, and identified an intron polymorphism (rs3759756) in the eIF-2α gene that may influence the IFN response in hepatitis B patients. We reasoned that the JAK1 gene polymorphisms may influence the host response to IFN treatment in HBV infection. However, in the present study, we failed to discover any significant association of allele frequency or genotype distribution of the 12 SNPs in the JAK1 gene between response groups and NR groups to IFNα treatment. Nowadays, pegylated interferon (PEG-IFN) therapy has been licensed for hepatitis B and is becoming the standard therapy. However, in the present study, the IFN treatment of patients was all with standard IFNα-1b, which may lead to some limitations. After all, PEG-IFN is essentially similar as standard IFN for they are only different style preparations of IFN, so we speculated that the mechanism of nonresponse to standard IFN might be similar to those with PEG-IFN. Up to now, association studies concerning the IFN response in hepatitis B patients are limited, and the results are in controversy. Further studies choosing more systematized SNPs, together with a larger sample set are required to clarify the association between IFN pathway genes and the IFN response in hepatitis B patients.

In summary, in the present study, we found for the first time that polymorphisms in the JAK1 gene were associated with outcomes of HBV infection, but not with the response to IFNα therapy.