Association between XPO5 rs11077 polymorphism and cancer susceptibility: a meta-analysis of 7284 cases and 8511 controls

DOI: 10.32471/exp-oncology.2312-8852.vol-41-no-4.13811

Cancer is a leading cause of mortality worldwide [1, 2]. There were about 4 292 000 newly-diagnosed cancer cases and 2 814 000 cancer-related deaths in United States in 2017. Although the etiology of cancer is still not clearly disclosed, genetic background and environmental factors are believed to be involved in cancer development [3, 4].

MicroRNAs (miRNAs), as regulators of gene expression, are small single-stranded RNA molecules of about 21–23 nucleotides [5, 6]. The biosynthesis of a functional miRNA involves several miRNA bioge­nesis genes and occurs in multiple steps [7]. The process of miRNA synthesis begins within the nucleus where RNA polymerase II produces large primary miRNA transcripts (about 500 to 3000 nucleotides) known as pri-miRNA. The pri-miRNA is then processed by multiprotein complex that includes DROSHA into pre-miRNA (about 60 to 100 nucleotides). Next, RAN GTPase and exportin-5 (XPO5) complex transfers pre-miRNA to the cytoplasm, and pre-miRNA is then cut into miRNA duplexes by DICER [6, 8] finally forming 18–24 nucleotide single-stranded, mature miRNA [8, 9].

In general, polymorphisms in miRNA processing genes as well as miRNA genes (pri-miRNAs, pre-miRNAs and mature miRNAs) could influence cancer risk by affecting miRNA function [10].

Preceding studies examining the relationship between XPO5 rs11077 gene polymorphism and cancer designated inconclusive findings [11–25]. So, this meta-analysis was performed to evaluate the impact of XPO5 rs11077 polymorphism on cancer risk.

MATERIALS AND METHODS

Literature search. A systemic literature searches in the PubMed, Web of Science, Scopus, and Google Scholar databases was done for all articles focused on association between XPO5 polymorphism and cancer risk published up to June 2018. The search term was “cancer or carcinoma or tumor or neoplasm” and “XPO5 or exportin-5 or miRNA biogenesis” and “polymorphism or mutation or variation or rs11077”.

Inclusion and exclusion criteria. Studies were comprised in the meta-analysis by meeting the following criteria: 1) original case-control studies of the association between the XPO5 rs11077 polymorphism and cancer; 2) studies providing sufficient data of the genotype frequencies of XPO5 rs11077 polymorphism in both cases and controls; 3) the studies have not repeated reports in the same population. The following studies were excluded: 1) conference abstracts, letters, case reports, reviews, overlapped data, animal or mechanism studies for XPO5 rs11077 polymorphism and cancer; 2) studies with insufficient information on genotype frequency. Finally, 15 articles were considered for meta-analysis.

Data extraction. The authors independently extracted data that met the inclusion and exclusion criteria. The following information was collected from each study including the name of first author, year of publication, country, ethnicity, number of cases and controls, and the genotype and allele frequencies of cases and controls.

Statistical analysis. Hardy-Weinberg equilibrium (HWE) for the controls of each study was determined by the chi-square test. We used Revman 5.3 software (Version 5.3. Copenhagen: The Nordic Cochrane Centre, the Cochrane Collaboration, 2014) and STATA 14.1 software (Stata Corporation, College Station, TX, USA) for all statistical analyses and to produce the plots. The strength of the association between XPO5 rs11077 polymorphism and cancer risk was evaluated through calculating pooled odds ratios (ORs) with the corresponding 95% confidence intervals (95% CIs) using following genetic models: codominant, dominant, recessive, overdominant and allele model. The significance of the pooled OR was determined with the Z-test, and p-values less than 0.05 were considered statistically significant.

Heterogeneity between selected studies was inspected using the I² statistic and the χ²-based Q test. A p < 0.10 representing the presence of significant hete­rogeneity. When significant heterogeneity values were returned, the random-effects model was used to estimate pooled ORs. Otherwise, the fixed-effects model was employed.

Publication bias across enrolled studies was estimated by Begg’s funnel plot. The degree of asymmetry was assessed using Egger’s linear regression test and p < 0.05 was considered significant publication bias.

Sensitivity analysis was conducted through sequential deleting each of included studies so as to ve­rify the stability of overall estimates.

RESULTS

Fifteen articles [11–25] of 16 studies, with totally 7284 cancer cases and 8511 controls, were eligible for meta-analysis. The main detailed characteristics of the eligible studies are listed in Table 1.

Quantitative synthesis. All eligible studies were pooled into the analysis and the results showed that XPO5 rs11077 polymorphism was not associated with the overall cancer risk in codominant, dominant, recessive, overdominant, and allele genetics models (Fig. 1 and Table 2).

We also performed stratified analysis by cancer type and ethnicity (see Table 2). The findings proposed that XPO5 rs11077 was not associated with gastrointestinal cancer, breast cancer and lung cancer. Besides, the variant was not associated with cancer risk in Asian as well as Caucasian population.

Heterogeneity. Heterogeneity among the studies included in the meta-analysis is shown in Table 2. The results showed that heterogeneity exists between the studies in homozygous codominant, recessive, overdominant and allele genetic models. So, random-effects model was used to determine pooled ORs.

Publication bias. A funnel plot was created as a visual aid to detect risk of publication bias (Fig. 2). Egger’s linear regression test and Begg’s test proposed no publication bias in all genetic model tested (see Table 2).

Sensitivity analysis. Sensitivity analysis was done and the findings revealed that our data are stable and reliable in all inheritance genetic models tested (Fig. 3).

DISCUSSION

The etiology of cancer is multifactorial in which both host genetic factors and environmental factors play a role [26, 27]. Accumulating evidence proposed that genetic variation is associated with cancer susceptibility [4, 28]. In this study, we conducted a meta-analysis to evaluate the association between XPO5 rs11077 gene polymorphism and cancer risk based on 16 eligible case-control studies with a total of 7284 cancer cases and 8511 healthy controls. Overall, pooled risk estimates proposed that this polymorphism is not associated with cancer risk. Stratified analyses by cancer types and ethnicities did not support an association between rs11077 polymorphism and cancer susceptibility.

Preceding studies examining the association between XPO5 rs11077 gene polymorphism and cancer indicated inconclusive results [11–25]. A genome-wide association study conducted by Buas et al. [11] on miRNA biogenesis genes (157 single nucleotide polymorphisms (SNPs), 21 genes); miRNA gene loci (234 SNPs, 210 genes); and miRNA-targeted mRNAs (177 SNPs, 158 genes) showed no significant association between XPO5 rs11077 A>C polymorphism and risk of esophageal adenocarcinoma. Cho et al. [12] revealed no significant association between XPO5 rs11077 and colorectal cancer risk in Korean population. Horikawa et al. [14] have found no significant correlation between rs11077 variant and risk of renal cell carcinoma. No significant association between rs11077 variant and risk of lung cancer, hepatocellular carcinoma, non-small cell lung cancer were found [13–16]. Osuch-Wojcikiewicz et al. [17] have found that rs11077 variant is associated with the risk of laryngeal cancer in Polish population. Sung et al. [18] have found no significant association between rs11077 variant and risk of breast cancer in Korean population. The rs11077 variant was found to be associated with increased risk of thyroid cancer [19]. No significant association between rs11077 variant and risk of gastric cancer was observed in Chinese population [20]. Yang et al. [21] findings revealed no significant association between rs11077 polymorphism and bladder cancer in American population. Ye et al. [22] reported that rs11077 variant significantly increased the risk of esophageal cancer.

XPO5 gene is mapped to a short arm of chromosome 6 (6p21.1) and encodes XPO5 protein which is involved in export of pre-miRNA from nucleus into the cytoplasm. Hoti et al. [29] reported that a XPO5 knockdown resulted in downregulation of 20 mature miRNAs and overexpression of six miRNAs.

Several studies evaluated the expression levels of XPO5 in various cancers and the findings were controversial. The expression levels of XPO5 were found to be higher in several tumors including breast, ovary, prostate, bladder, and melanoma compared to the normal adjacent tissues, while the lower expression level of XPO5 in kidney, adrenal gland, and hepatocellular carcinoma tumors proposing oncogenic or tumor-suppressor features in different cancer types [29–32].

There are some limitations in our meta-analysis needed to be addressed. First, heterogeneity was observed among the studies possibly resulting from the differences of ethnicity, source of control, and cancer type. Second, this study focused on the effect of rs11077 polymorphism and cancer risk. Gene-gene and gene-environment interactions might also impact in cancer risk. Third, the characteristics of included studies such as age and sex which might affect the results of meta-analysis were not evaluated due to the lack of relevant data across the included studies. Fourth, the majority of the individuals studied were Asian, further studies on other ethnicity groups are needed. Finally, the sample size of our meta-analysis is relatively small especially in subgroup analyses by cancer types (5 studies for gastrointestinal cancer, 3 studies for breast cancer, and 2 studies for lung cancer) and ethnicities (9 studies for Asian and 3 studies for Caucasian). Accordingly, the statistical power of the study is limited and the results should be interpreted with caution.

In conclusion, the results of our meta-analysis based on 16 case-control studies suggested that there is no significant association between the XPO5 rs11077 polymorphism and cancer risk. Statistical power can be improved by pooling analysis from more studies. Considering the limitations mentioned above, further well-designed multicenter studies with large sample sizes, more diverse ethnic groups and cancer types are warranted to verify the findings.

CONFLICT OF INTEREST

The authors have declared that no competing interests exist.

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