Genetic variations of interleukin-1 and -6 genes and risk of cervical intraepithelial neoplasia

Abstract

Objective

To evaluate the association between five interleukin-1 (IL-1) and -6 gene polymorphisms and risk of high grade cervical intraepithelial neoplasia (CIN 2–3).

Methods

This case-control study investigates five common IL-1 and IL-6 gene polymorphisms in 131 women with CIN 2–3 and 209 controls by pyrosequencing and polymerase chain reaction. Associations between gene polymorphisms and risk of CIN 2–3 are analysed by univariate and multivariable models. Their combined effect on the risk of CIN is evaluated by haplotype analysis.

Results

In a multivariable regression model IL1A −889 (odds ratio 0.3 [95% confidence interval 0.1–0.8], p = 0.01) and smoking (4.0 [1.7–9.1], p = 0.001) are independently associated with the risk of high grade CIN. Haplotype analysis does not reveal any high-risk combinations for the susceptibility of CIN.

Conclusion

The single nucleotide polymorphism IL1A −889 is independently associated with risk of high grade CIN.

Introduction

High grade cervical intraepithelial neoplasia (CIN 2–3) is the precursor of cervical cancer, which is the second most common gynecological cancer among women worldwide [1]. It is well known that a high-risk human papillomavirus (HPV) infection is the necessary cause for CIN [2]. As the majority of these infections are transient and do not lead to CIN, an effective host immune response and genetic factors seem to have a major influence on the risk of CIN [3], [4]. Therefore interleukins (IL) seem crucial for the susceptibility of CIN 2–3 as they play a key role in cellular immunity and carcinogenesis.

Interleukin-1 and IL-6 are prominent members of the interleukin family. IL-1 comprises the cytokines IL-1alpha (IL-1a), IL-1beta (IL-1b) and a specific receptor antagonist (IL-1RA) [5]. IL-1a and IL-1b are proinflammatory cytokines involved in the modulation of host response to microbial invasion, inflammation, and tissue injury [6]. Secretion of IL-1 initiates a proinflammatory cascade with the subsequent production of tumor necrosis factor-α, interferon-γ, IL-2 and IL-12. IL-1RA neutralizes IL-1 action by binding to the IL-1 receptors (IL-1RI and IL-1RII) without exerting any effector function [7]. Several studies suggest that IL-1 production is related to the immune response against HPV-associated cervical cancer [8], [9], [10]. IL-6, a phosphorylated glycoprotein, is involved in various physiological and patho-physiological processes such as hematopoiesis, C-reactive protein synthesis and bone metabolism [11], [12]. Moreover IL-6 seems to be crucially involved in HPV-clearance [13], [14].

The role of IL-1 and IL-6 in carcinogenesis and tumor progression has been extendedly studied [15], [16], [17]. The production and release of IL-1 and IL-6 by tumor cells results in an autocrine and paracrine induction of prometastatic genes and subsequently leads to proliferation and prolonged survival in human squamous cancer cells [18], [19], [20]. Clinical studies in cervical cancer patients report that elevated IL-1 and IL-6 serum levels are associated with poor prognosis [21], [22].

The IL-1 gene cluster on chromosome 2q14.2 comprises 3 related genes within a 430-kb region, IL-1A, IL-1B, and IL-1RN, which encode the pro-inflammatory cytokines IL-1a, IL-1b, and their endogenous receptor antagonist IL-1RA, respectively [23]. In vitro and in vivo studies demonstrate that IL1-A and IL1-B gene polymorphisms [24], [25] correspond with altered IL-1a and IL-1b protein expression, respectively [24], [26]. Regarding the IL1 receptor antagonist, the IL1RN allele 2 has been repeatedly associated with changes of the IL-1RA protein expression [27], [28]. The human IL-6 gene is located within a 303 bp region on chromosome 7p21–24 [29]. The common IL-6 promoter G174C gene polymorphism has been repeatedly reported to be associated with IL-6 protein expression [30], [31], [32].

The IL1RN VNTR intron 2, IL1B −511, and IL1B exon 5 + 3953 gene polymorphisms have been reported to be associated with cervical cancer risk and progression [33], [34], [35]. The IL6 promoter − 174 gene polymorphism is associated with risk of cervical cancer in a Brazilian and an Indian cohort [36], [37].

While IL-1 and -6 gene polymorphisms have been extensively studied in cervical cancer, no studies have evaluated these genetic variations in cervical cancer precursor lesions. Therefore we evaluate the association between five common IL-1 and -6 gene polymorphisms and risk of high grade CIN. As the susceptibility to a disease is usually determined by multiple genetic variations, rather than single-locus polymorphisms, we also perform haplotype analysis to test for high-risk combinations of these five polymorphisms.