A large number of SNPs have been found in many lncRNAs, and increasing research has focused on the association between lncRNA polymorphisms and cancer risk. More and more evidence has showed that SNPs in the promoter of lncRNAs regulated the expression of lncRNAs by affecting the binding of transcription factors [32]. MALAT1 with rs664589 G allele altered the binding affinity to miR-194-5p in the nucleus, resulting in the increased MALAT1 expression and the development of CRC [30]. At the same time, MALAT1 rs664589 polymorphism was associated with a decreased risk of HCC [28]. Hence, the particular mechanism of lncRNA MALAT1 in different cancer types is still unclear. In consideration of the inconsistent results, we performed this meta-analysis to systematically investigate the association of MALAT1 polymorphisms and cancer susceptibility.
In this meta-analysis, no association was found between MALAT1 rs3200401 polymorphism and cancer susceptibility in the all population. However, rs3200401 polymorphism was associated with an increased risk of digestive cancers. Similarly, Qu et al. found that rs3200401 C > T was associated with increased risk of ESCC [19]. Conversely, it had been reported that rs3200401 T allele was associated with a better survival for advanced lung adenocarcinoma patients [33]. The rs3200401 C > T variant was located at the region M of MALAT1 (6008–7011 nts), one of the binding sites to SRSF2 [34]. At the same time, C > T variation of rs3200401 caused 1.62 kcal/mol minimal free energy (MFE, ΔG) change, which may alter structural features of MALAT1, resulting in weaken interaction of MALAT1 and its binding protein SRSF2 [33]. In summary, rs3200401 may affect gene expression levels which are involved in the tumorgenesis and cancer development.
It’s reported that rs664589 was associated with increased colorectal cancer susceptibility [30]. Other studies have mentioned that rs664589 polymorphisms were not associated with ESCC risk and coronary atherosclerotic heart disease [19, 35]. Only a borderline signification was found between rs664589 polymorphism and cancer risk. The secondary structure of lncRNAs was vital due to their function, and SNPs of lncRNAs may affect the folding structure [36, 37]. Besides, SNPfold algorithm had significantly altered the secondary structure along with rs664589 [30].
LncRNAs could accommodate gene expression through isolating miRNAs and preventing them from binding to targets. Rs619586 was a functional SNP which changed the function of MALAT1 on miRNAs, leading to the regulation of mRNA expression [38]. Wen et al. have showed that rs619586 polymorphism induced the epithelial to mesenchymal transition (EMT) cells process, a vital mechanism of tumorgenesis [27, 39]. In addition, MALAT1 induced EMT and suppressed cell apoptosis via Wnt/β-catenin signaling pathway [40]. Consistent with one previous meta-analysis including 2 studies for rs619586 [41], we found it was associated with decreased cancer risk in all populations. Nonetheless, no association was found between rs619586 and melanoma risk [29]. Overall, the results indicate that rs619586 may have different effects on carcinogenesis in different organs.
For rs1194338 polymorphism of cancer susceptibility, significant association was found in four genetic model except for the heterozygote model. Rs1194338 was located in the promoter of MALAT1. It was reported that genetic variation in promoter region will influence transcriptome expression, stability and subcellular localization, leading to functional changes and the occurrence of disease [42]. However, rs1194338 polymorphism did not alter the MALAT1 expression levels in colorectal cancer tissues [26]. In addition, there was no statistically significant difference in MALAT1 expression between CC genotype and AA genotype [43]. It is possible that common variations could change gene expression at the single cell level, rather than affecting the average level of gene expression in the tissues [44]. Through the application of pathophysiologically immune stimulation, it is helpful to analyze functional genetic variation and specific regulatory genes related to cancer [45].
There were several defects should be acknowledged in this meta-analysis. First, some information, such as age, gender, smoking and drinking status and others, was not considered. Second, the results were just based on the individual unadjusted ORs. Third, some studies with small sample size were contained, which may decrease the statistical power of meta-analysis. Finally, there were only 3 studies for rs664589 and rs1194338. The current data were possibly insufficient for reliable evaluation.
In conclusion, this meta-analysis indicated that rs619586 and rs1194338 had decreased association with cancer risk, while rs3200401 and rs664589 had increased association with digestive cancers. For all that, further studies with different ethnic groups and larger sample size were required to verify the associations.