Plasminogen activator inhibitor-1 4G/5G polymorphism in breast cancer patients and its association with tissue PAI-1 levels and tumor severity

Abstract

Background

The plasminogen activator inhibitor type 1 (PAI-1) 4G/5G polymorphism may have significance for PAI-1 expression. High levels of PAI-1 in breast cancer patients are associated with a poor prognosis. In this study, we analyzed the influence of the PAI-1 4G/5G polymorphism on tissue PAI-1 levels and its association with tumor severity in women with breast cancer.

Material and methods

We studied 104 women with breast carcinoma (patient group) and 104 healthy age-matched women (control group). In patients and controls, the PAI-1 4G/5G polymorphism was determined by PCR amplification using allele-specific primers. In patients, PAI-1 levels were quantified in breast cancer tissue by using an ELISA.

Results

The frequency of the PAI-1 4G allele tended to be higher in patients than in controls (p = 0.062). The presence of the 4G allele (4G/5G plus 4G/4G genotypes) was significantly higher among patients with histological grade 3 tumors than among those with grade 1 tumors (p = 0.026). Furthermore, patients with the 4G/4G genotype had significantly higher tissue PAI-1 levels than those with the 5G/5G genotype. Moreover, tissue PAI-1 antigen levels were significantly and positively correlated with tumor severity (p = 0.003) and tumor size (p = 0.009). However, no significant differences in PAI-1 level were observed in relation to menopause, hormone receptor or nodal status.

Conclusion

Tissue PAI-1 antigen levels and tumor severity seem to be associated with the PAI-1 4G/5G polymorphism. Further studies with a larger number of patients are needed to clarify the influence of this polymorphism in breast cancer.

Introduction

Tumor cell invasion and metastasis result from interactions between cell migration potential, cell adhesion properties, and extracellular matrix proteolysis [1]. Urokinase type plasminogen activator (uPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin, an active enzyme that can degrade a variety of extracellular matrix proteins [1]. It is generally believed that uPA initiates a proteolytic cascade on the cell surface, which promotes tumor invasion and angiogenesis [2]. uPA is inhibited mainly by plasminogen activator inhibitor type 1 (PAI-1), but can also be inhibited by PAI-2 and PAI-3. All PAIs are members of the superfamily of serine protease inhibitors [3], [4], [5], [6], [7].

PAI-1, the primary inhibitor of the plasminogen activation system, inactivates tissue type plasminogen activator (tPA) and uPA [3] but also plays an important role in signal transduction, cell adherence, and migration. Indeed, studies of several types of cancers, including breast cancer, have paradoxically shown that increased uPA and PAI-1 levels are associated with aggressive tumor behavior and poor prognosis [8], [9], [10]. One might speculate that, since uPA promotes invasion and metastasis, increase in tumor tissue PAI-1 levels should produce a reduction in the local invasion and development of metastasis. However, several studies have shown, on the contrary, that PAI-1 actually promotes those aggressive behaviors [11], [12], [13], [14]. Possible mechanisms by which PAI-1 contributes to cancer dissemination include prevention of excessive degradation of the extracellular matrix, modulation of cell adhesion [15], [16], and stimulation of angiogenesis [17], [18], [19] and cell proliferation [20].

In vitro studies have shown that PAI-1 levels can be altered by cytokines, growth factors, and hormones [21], [22], but the genetic and environmental determinants of PAI-1 expression are not fully understood. Changes in PAI-1 biosynthesis are usually preceded by changes in its gene transcription [23], [24], [25]. A guanosine insertion/deletion polymorphism in the promoter region of the PAI-1 gene at the − 675 bp position, named 4G/5G, has been described [26]. In vitro studies suggest that the 4G allele has higher activity than the 5G allele because the 5G allele contains an additional binding site for a DNA-binding protein that acts as a transcriptional repressor [27], [28]. Studies involving healthy subjects or patients with coronary artery disease or metabolic syndrome have reported that high plasma levels of PAI-1 are associated with a high prevalence of the 4G allele [27], [28], [29], [30].

Results of studies on the association between the PAI-1 4G/5G polymorphism and the invasive behavior of cancer are contradictory. Although one study reported that there was no association between the polymorphism and cancer progression [25], another suggested that the 5G/5G genotype is associated with less aggressive cancer phenotypes [32].

In this study, we examined the influence of the PAI-1 4G/5G polymorphism on tissue PAI-1 levels and its association with tumor severity in women with breast cancer.