The Association between Single-Nucleotide Polymorphisms of ORAI1 Gene and Breast Cancer in a Taiwanese Population

1. Background

Breast cancer is the most common female malignancy with an increasing number of new cases around the world [1, 2]. In the United States, the estimated new cases and deaths for female breast cancer patients in 2012 are 226,870 and 39,510, respectively [3]. In recent years, increased incidence rates of breast cancer have been observed in eastern and southeastern Asian women [4]. Epidemiologic studies indicate that patients having a first-degree family history of breast cancer have two-fold increased risk for developing breast cancer compare to the general population [5]. Genetic factor is an important contributor to breast cancer susceptibility. For example, some studies showing genetic variants of BRCA1 (rs799917) or Cyclooxygenase-2 (COX-2) (rs2745559) have been shown to associate with breast cancer susceptibility [6, 7].

A recent combination of family-based and population-based approaches imply that genes involved in DNA repair (CHEK2, ATM, BRIP, and PALB2) are associated with moderate risk in breast cancer subjects [8]. Studies from genomewide association studies (GWASs) in breast cancer reveal SNPs in five genes (TNRC9, FGFR2, MAP3K1, H19, and LSP1) are associated with breast cancer susceptibility in European population [9]. Hunter et al. (2007) [10] and Stacey et al. (2007) [11] independently replicate the FGFR2 and TNRC9 risk alleles in African American population and European descent, respectively. The risk allele locate at the intron 2 of the FGFR2 gene (rs2981582) represents 5–10% of breast cancer patients with estrogen receptor (ER)-positive tumor, whereas the SNP rs3803662 of TNRC9 gene seem to be correlated positively with bone metastases and ER-positive breast cancer patients. Similarly, a GWAS breast cancer predisposition with replication and refinement studies involving more than 10,000 case-control identify two more SNPs (rs4415084 and rs10941679) on 5p12 that confer risk, preferentially for ER-positive tumors [12].

Store-operated Ca²⁺ influx is the predominant mechanism of Ca²⁺ entry in nonexcitable cells, such as mast cells, liver cells, and T lymphocytes [13]. Calcium entry through store-operated Ca²⁺ channel has been shown to be important in the regulation of inflammatory reactions in mast cells [14, 15], B cells [16], and cancer cells [17–20]. The cell- and animal-based studies suggested that inhibition of ORAI1 resulted in stronger focal adhesions and consequently impeded the migration of breast cancer tumor cells [21]. Increasing evidences indicated that about 20% of the cancer candidate genes in breast and colorectal cancers may be adhesion-related genes, suggesting that cell adhesion plays a critical role in cancer progression [22]. Although a recent study has identified the crucial role of ORAI1 in breast cancer cell migration and metastasis [21], the association between genetic variations of ORAI1 and the risk of breast cancer is not known. Thus, the aim of this study is to investigate whether genetic variations of ORAI1 are associated with the histopathological tumor characteristics in Taiwanese breast cancer patients.

2. Material and Methods

3. Results

4. Discussion

Accumulated evidence indicates that Orai1-mediated calcium signaling plays important roles in cancer metastasis. We previously show that calcium influx is critical for cell migration [21, 24]. Abrogation of Orai1-mediated store-operated calcium channel slows down the turnover of focal adhesion and leads to inhibition of metastasis of breast cancer [21]. Orai1 can be activated either by STIM1 in a store-dependent pathway, or by SPCA2 independent of the status of internal calcium store by SPCA2 [25–27]. Interestingly, SPCA2 is overexpressed in the hormone estrogen receptor-positive, luminal subgroup of breast cancer cells [27]. These findings leave open an important issue if the genetic polymorphisms of ORAI1 convey Ca²⁺ signals to cell proliferative, leading to the pathogenesis of breast cancer. In this study, we provide evidence that ORAI1 SNP is associated with breast cancer-related parameters in Taiwanese breast cancer patients.

A GWAS study by Stacey et al. [11] involving 1,600 patients and 11,563 controls identified some common variants on chromosomes 2q35 and 16q12 which confer susceptibility to ER-positive breast cancer. Selected SNPs are subsequently genotyped in five replication of European sample sets. They found that two SNPs, rs13387042 on 2q35; rs3803662 on 16q12 consistently associated with breast cancer. Surprisingly, as many as 25% of European population are homozygous for the risk allele A of rs13387042, which put these individuals having an estimated 1.44 fold greater risk than noncarriers. For allele T of rs3803662, about 7% of the European population are homozygous, having a 1.64 fold greater risk of developing breast cancers. However, risk from both alleles is confined only to ER-positive patients. The following year, two more SNPs (rs4415084 and rs10941679) on 5p12 are identified which confer risk in ER-positive tumors. Interestingly, the closest gene, MRPS30 (also known as PDCD9, programmed cell death protein 9), encodes a component of the small subunit of the mitochondrial ribosome and has previously been implicated playing an important role in apoptosis [12, 28]. Association of breast cancer and these two SNPs has been replicated recently in a 886 cases versus 1089 controls from a African American Women study, in particular the rs4415084 is significantly associated with ER-positive tumors [28]. Most recently, replication of two index SNPs: rs3803662 at 16q12.2/TOX3 and rs10941679 at 5p12 near MRPS30 involving 7,800 African American women (including 316 women with incident invasive breast cancer) have also been established [29].

Breast cancer is a complex disease which is influenced by a variety of genetic factors and environmental factors [1, 30]. Numbers of genes including BRCA1, COX-2, or estrogen receptor [6, 7, 31] have been shown to play critical roles in the development of breast cancer. COX-2, which involves in inflammatory, is positively correlated with larger tumor size and higher histological grades in breast cancer samples [32]. Several lines of evidence have indicated that calcium influx through store-operated calcium channel can trigger inflammatory signaling events. In colon cancer or lung cancer, calcium entry through store-operated calcium channel triggers COX-2 gene activation and expression [18, 20]. Hence, further study is needed to investigate if there is a link between ORAI1 gene expression and inflammation status of breast cancer patients.

We recognize the potential limitations to our study. It is possible that weak association between ORAI1 genetic polymorphisms and the risk or tumor-related parameters of breast cancer may be due to the modest sample size, which lead to a small power in statistical analysis. However, sample size may result from international geographic variation of breast cancer incidence [1] and a limited population in Taiwan. It has been demonstrated that Asia has three-fold lower breast cancer incidence rate as compared to North America or Western Europe [1]. Additionally, there were 192,000 estimated cases of breast cancer alone in the United States during 2001 [1] as compared to a total of 22,758 cases in Taiwan collected from 1998 to 2002 [4]. In this regard, our sample size would be reasonably explained in this context. However, we cannot rule out the possibility that there may be other hidden ORAI1 SNPs which may associate with breast cancer development. Using direct sequence for ORAI1 gene in a subset of Han Taiwanese individuals may be helpful to find novel genetic polymorphisms of ORAI1 that contribute to the development of breast cancer.