No association between the C-1562T polymorphism in the promoter of matrix metalloproteinase-9 gene and non-small cell lung carcinoma

Summary

The matrix metalloproteinases (MMPs) are a family of highly conserved metal-dependent proteolytic enzymes, their main function is to degrade different components of extracellular matrix (ECM). Moreover, they play roles in regulation of cell growth, apoptosis, angiogenesis and immune surveillance. Natural sequence variations in the MMP genes may result in differential expression of MMPs in different individuals and therefore may be associated with the development and progression of diseases. The aim of this study is to assess the effects of the C-1562T polymorphism in the MMP-9 promoter on the risk of occurrence and lymphatic metastasis of non-small cell lung carcinoma (NSCLC). The MMP-9 genotyping was performed in 243 pathologically diagnosed NSCLC patients and 350 healthy controls without overt cancer by using polymerase chain reaction—restriction fragment length polymorphism analysis. The distribution of the MMP-9 genotypes in NSCLC patients and healthy controls was in consistent with Hardy–Weinberg equilibrium. The frequency of the C/C, C/T and T/T genotypes in healthy controls was 79.4, 20.6 and 0%, respectively. Neither the overall genotype nor allelotype distribution in NSCLC patients showed significant difference from that in healthy controls (P = 0.21 and 0.43, respectively). Compared with the C/C genotype, genotypes with the T allele did not show significant influence on the risk of NSCLC development (age and gender adjusted OR = 1.13, 95% CI = 0.76–1.68). Stratification by onset age, smoking status and tumor histological type also showed no association between the MMP-9 polymorphism and the risk of NSCLC. Furthermore, the genotype distribution between NSCLC patients with and without lymphatic metastasis was not significantly different. Therefore, the present study suggests that the MMP-9 C-1562T polymorphism may not be used as a useful marker to predicate susceptibility and lymphatic metastasis in NSCLC.

Introduction

The matrix metalloproteinases (MMPs) are a family of highly conserved metal-dependent proteolytic enzymes, which are involved in the degradation of many different components of extracellular matrix (ECM). MMPs play important roles in tumor invasion and metastases [1], [2], [3], and are also involved in the initial stages of tumor development by regulating cell proliferation, apoptosis, angiogenesis and immune surveillance [4]. At present, at least 26 MMPs have been discovered and they are classified into five main classes (collagenases, gelatinases, stromelysins, membrane-type and others, including the matrilysin) on the basis of their putative substrate specificity and internal homologies [5]. Although MMPs can be activated by activation of latent MMPs and inhibited by tissue inhibitors of metalloproteinases (TIMPs), the most important step of MMP expression regulation may be at the transcription level, since most MMP genes are expressed only when active physiological or pathological tissue remodeling takes place [5]. Growing evidences indicate that naturally occurring sequence variations in the promoters of MMP genes may result in differential expression of MMPs in different individuals [6]. These promoter polymorphisms have been associated with susceptibility to diseases such as acute myocardial infarction, rheumatoid arthritis, multiple sclerosis, and cancers [7], [8], [9], [10], [11], [12], [13].

MMP-9 (gelatinase B, HNG) is the most complex family member of MMPs in terms of domain structure and regulation, possessing proteolytic activity mainly against type IV collagen, which is a major component of basement membranes [14]. MMP-9 has also been shown to be important for angiogenesis and play a key role in preparing premetastatic sites for eventual malignant cell growth in a manner of dependent upon vascular endothelial growth factor receptor-1 [15], [16]. In transgenic mice, the lack of MMP-9 has been shown to reduce keratinocyte hyperproliferation at all neoplastic stages and decrease incidence of invasive tumors, while reduced carcinogenesis in MMP-9 deficient mice can be completely restored by bone marrow transplantation of MMP-9 expressing cells [17], suggesting that MMP-9 may play important roles in both of the genesis and invasiveness of tumor. The MMP-9 gene is located on chromosome 20q12.2–13.1. A total of 10 natural sequence variants have been identified in the MMP-9 gene, four of which are in the promoter region [18]. Among them, a C–T transition at the 1562 base pair position upstream of the transcription initiation site (C-1562T) has been proved to have a functional effect on transcription by loss of binding of a transcription repressor protein to this promoter region [19]. An association of this single nucleotide polymorphism (SNP) has been associated with severity of coronary atherosclerosis [19], [20] and also correlated with the risk of smoking-induced pulmonary emphysema [21]. Recently, the T allele of the MMP-9 polymorphism has been linked with the invasive phenotype of gastric cancer [22]. However the influence of the MMP-9 C-1562T polymorphism on risk of developing other cancer types has not been demonstrated so far.

Lung cancer, the leading cancer type in the developed countries, has been widely investigated for its etiological factors. Some natural genetic variations have been associated with individual susceptibility to this tumor [23], [24], [25], [26]. Since the elevation of MMP-9 protein has been strongly associated with metastasis [27], [28] and shorter survival time [29], [30], we hypothesized that allele inducing higher level of MMP-9 expression may facilitate metastasis via degradation of ECM surrounding the tumor cells and may increase susceptibility to lung cancer through modification of the microenvironment or regulation of cell proliferation and apoptosis. Therefore, we conducted the present hospital-based case-control study to test the above hypothesis.