Matrix metalloproteinases polymorphisms as baseline risk predictors in malignant pleural mesothelioma

Malignant mesothelioma (MM) is a rare disease, linked to asbestos exposure in more than 80% of the cases. The latency period can last up to thirty years and estimated median survival is 9–12 months. The worldwide incidence of mesothelioma is slowly rising, with approximately 94 000 new cases per year. The most affected areas are parts of Europe, Australia and the USA.1 The rise in the MM incidence has been noticed in the Slovene population as well. The Slovenian national registry follows the data on MM since 1961. The incidence in 2014 was 37 new cases per year in a population of approximately 2 million.2

Several preclinical studies have identified matrix metalloproteinases (MMPs) as modulators of the tumour microenvironment and having an important role in carcinogenesis.3 MMPs are calcium-dependent, zinc-containing endopeptidases, with three common domains containing the propeptide, catalytic and haemopexin-like C-terminal domain.4 They are involved in tissue remodelling by interfering with the cell-cell and cell-extracellular matrix interactions. Studies have shown that MMPs, particularly MMP-2 and MMP-9, play a role in tumour angiogenesis, invasion and metastasis.5 The studies performed thus far show that MMPs and their inhibitory molecules, tissue inhibitors of metalloproteinases (TIMPs), have an important role in proliferation and progression of MM and some other, more frequent malignancies, such as colon and breast cancer. Different MMP genes (MMP2, MMP9, MMP11, MMP14) and their expression were studied in mesothelioma tissue as potential prognostic markers.6 In a previous paper we studied the possible role of single nucleotide polymorphisms (SNPs) as potential markers of treatment response.7 We identified MMP9 rs2250889, MMP9 rs20544, MMP14 rs1042703 as statistically significantly associated with overall survival (OS) in MM. Carriers of the polymorphic MMP9 rs2250889 and MMP14 rs1042703 alleles had shorter OS, compared to non-carriers, while carriers of polymorphic MMP9 rs20544 allele had longer OS.7

Many studies investigated the role of MMP polymorphisms in the baseline genetic risk for common diseases and tumours, however, the role of MMP polymorphisms was found to be conflicting in different diseases. In a large nested case-control study investigating skin cancer risk, MMP9 Arg668Gln polymorphism has been associated with a decreased risk of squamous cell skin cancer (SCC).8

The opposite effect was observed in T-cell acute lymphoblastic leukaemia (T-ALL), where MMP2 rs243865 and MMP9 rs3918242 polymorphisms were associated with an increased risk of T-ALL.9

The data from the literature, linking MMP polymorphisms with tumour risk and the statistically significant associations between the selected MMP2, MMP9 and MMP14 SNPs and time to progression (TTP) and OS in MM, led us to further investigate their potential role in baseline genetic risk of MM development. Our aim was to investigate selected MMP polymorphisms as baseline risk predictors in MM development in combination with other well known risk factors, such as asbestos exposure.

This study investigated the influence of MMP2, MMP9 and MMP14 gene polymorphisms on baseline risk for MM in comparison with healthy control subjects. Carriers of MMP2 rs243865 CT or CT/TT genotypes had significantly decreased risk for developing MM in comparison with CC homozygous genotype, especially in patients with known asbestos exposure.

MMP2 rs243865 (c.-1306C>T) is a promoter polymorphism and our prior in silico analysis has shown that it may influence binding of transcription factors and may alter chromatin states.7 The data on whether the MMP2 rs243865 T allele has a protective function or if it contributes to higher risk for cancer, is somewhat conflicting for different malignancies.

MMP polymorphisms have been extensively studied in many different common and rarer malignancies.12,13 The most attractive and most significant MMPs in risk assessment studies were MMP2, MMP9 and MMP3 polymorphisms. MMP2 rs243865, that was associated with modified cancer risk in our study, had the greatest influence on cancer risk in general. In accordance with our study, two meta-analysis presented the results showing that MMP2 rs243865 polymorphism had a protective role in lung cancer susceptibility in both dominant and recessive models, which is consistent with our results. Seventeen studies were included in the meta-analysis and reported that the MMP2 rs2438651 polymorphism had a protective role only in the Asian population.12,13

Considering that lung cancer is the most common thoracic malignancy, these results can be parallel to a less common thoracic malignancy such as MM. However, MMP polymorphisms in other common malignancies in the Asian population have been frequently studied. A meta-analysis of 12 publications studying urinary (renal and bladder) cancers showed a lower risk for bladder cancer with the T allele of MMP2 rs243865 in Asian patients but not in the Caucasian population.14

All of the above discussed publications present the MMP2 rs243865 T allele as having a somewhat protective role in cancer. There are publications that suggest the opposite effect of the T allele in MMP2 rs243865. A control based study that included a Caucasian population investigated six different polymorphisms in MMPs and TIMPs in bladder cancer patients. They concluded that the combined genotype carrying MMP2 rs243865 allele T with MMP9 rs3918242 allele T was found to increase bladder cancer risk.15 These results are the opposite to the previously mentioned Asian based metaanalysis.14

According to the db SNP and HapMap data on rs243865 frequency in genetically different populations, the C allele is more common in Caucasian populations. That can perhaps contribute to the different results in different studied populations.16

Nevertheless, all of the cited studies find that MMP2 rs243865 could play a role as a risk factor in a variety of different malignancies. With regard to the MMP2 rs243865, T allele containing genotypes seem to have a protective role in predominantly thoracic malignancies, such as lung cancer and MM.

Genome Wide Associated Study (GWAS) of 759 subjects in the Northern Italian population investigated 15 different SNPs in several genes, and one of them was MMP14 rs2236304. Almost all of these SNPs had either a significant positive (higher risk after asbestos exposure) or negative (lower risk after asbestos exposure) interaction with asbestos exposure, even after statistical corrections (Bonferroni) had been applied. But, the study has some limitations, such asthe small sample size, the age unbalanced control group and the possible rare genetics variants that could have been excluded from the GWAS statistical analysis.17

The MMP2 rs243865, T allele genotypes seem to have a protective role in predominantly thoracic malignancies, such as lung cancer and MM. Moreover, thoracic malignancies are also well known to have a strong environmental component (eg. smoking, asbestos exposure).18 The gene-environment interactions have been studied extensively in MM. The study that investigated the role of microsomal epoxide hydrolase (mEH), glutathione S-transferases (GSTM1, GSTT1), N-acetytransferase 2 (NAT2), and cytochrome P1A1 (CYP1A1) genotypes concluded that the presence of synergisms between genotypes, i.e., mEH and NAT2, mEH and GSTM, and NAT2 and GSTM1 combined with the interaction observed with exposure to asbestos, suggests the presence of gene-environment and gene–gene interactions in the development of MM.19

Our results suggest a combined effect of asbestos exposure and MMP2 rs243865. Gene-environment interactions in asbestos related diseases have been previously studied in enzymes such as catalase (CAT), superoxide dismutase (SOD 2, SOD3) and inducible nitric oxide synthase (iNOS), which are part of the enzymatic defence system against reactive oxygen species (ROS). Besides gene-gene interactions between MnSOD Ala -9Val and CAT-262 C>T polymorphisms as well as iNOS and CAT -262 C>T polymorphisms and the risk of asbestosis, gene-environment interactions were also reported. A strong interaction was reported between GSTM1 - null polymorphism and smoking, iNOS (CCTTT)n polymorphism and smoking, and between iNOS (CCTTT)n polymorphism and cumulative asbestos exposure, suggesting that interactions between different genotypes, genotypes and smoking, and between genotypes and asbestos exposure have an important influence on the development of asbestosis.20 These studies on asbestosis suggest, that gene-environment interactions should be investigated also in other asbestos related diseases, including MM, since asbestos exposure is a proven environmental risk factor in MM.

Despite some limitations of our study, such as a small sample size and a control group that was not appropriately age balanced, low rate of patient asbestos exposure and lacking this data of the control group, our results reached statistical significance and showed that there could be a genetic predisposition of certain MMP SNPs for MM and that there is a potential gene-environment interaction between MMP SNPs and asbestos that is a major risk factor for MM.

In conclusion, our data suggests that MMP2 rs243865 polymorphism may have a protective role in malignant pleural mesothelioma. This finding is even more pronounced in patients exposed to asbestos, implying a strong gene-environment interaction.