In this study, we found significant associations between SNPs in miRNA biogenesis pathway and the risk of RCC. Recent studies have shown that, disrupting miRNA processing through the knockdown of DROSHA, DGCR8, and DICER1, could accelerate cellular transformation and tumorigenesis (17
). Thomson et al. (18
) have shown that the repression of mature miRNAs is not consistent with the reductions in the primary miRNA transcripts, suggesting the existence of altered regulations of miRNA processing in human cancers. These lines of evidence are in concordance with the recent profiling of miRNAs expression, which showed the general repression of miRNAs in a variety of tumors and cancer cell lines (18
). Our results, taken together with these findings, indicate that genetic alterations of the miRNA biogenesis pathway might be associated with cancer development and progression.
In this study, three nonsynonymous SNPs (nsSNPs) of the GEMIN4
(rs7813 and rs2740348) and GEMIN3
gene (rs197412) were found to be associated with altered RCC risk. Both GEMIN3 and GEMIN4 are reported to be core components of the SMN (survival of motor neuron) complex and implicated in the etiology of spinal muscular atrophy (9
). In addition, these GEMIN proteins have been identified in miRNA ribonucleoprotein particle (miRNP) with an Argonauts family protein AGO2 (9
). The additional identification of numerous miRNAs in this complex (8
), concordant with several other independent observations (22
), strongly suggests the involvement of GEMIN proteins in the processing of miRNA precursors through their interaction with key components of the RISC complex. Interestingly, Wan et al found that genetic variants of GEMIN4
(including rs2740348 and rs7813) were significantly associated with cell growth and DNA repair in heptacellular carcinoma cell line (23
), suggesting that the amino acid changes caused by these SNPs might have a physiological significance on cancer development. Moreover, recently our study for bladder cancer has shown the association between an altered risk and GEMIN4
rs7813 polymorphism (24
). However, whether the associations between SNPs of GEMIN4
and altered RCC risks observed in our study are due to a similar mechanism needs to be examined with further functional assays.
In addition to the SNPs on the GEMIN
genes, borderline significant associations with RCC risk were also observed in two genes, XPO5
genes (). In particular, the XPO5
rs11070 exhibited an increased risk of RCC in the recessive model. XPO5 mediate the nuclear transport of pre-miRNAs and its down regulation results in reduced miRNA levels (25
). Down-regulated XPO5 have been observed in low grade lung adenocarcinoma (11
), whereas in high grade prostate cancer XPO5 have been shown to be up-regulated (6
). AGO1 (EIF2C1), a component of RISC with AGO2 and DICER1, are involved in miRNA function leading to target mRNA degradation. This gene is located at chromosome 1p35-p34 frequently lost in human malignancies (26
The SNPs on pre- or pri- miRNA regions were evaluated in our study but none of them had a significant influence on RCC risk. Diederichs and Haber explored the sequence variations in miRNA-containing genomic regions and showed that although sequence variants in miRNA precursor regions may lead to changes of secondary structures, miRNA maturation were not affected in vivo
), suggesting that genetic variants in miRNA precursors are unlikely to have physiologic significances (27
). Saunders et al identified 65 SNPs in 474 pre-miRNAs using public SNP database (13
). However, many of these SNP may not be important to population genetics because of the lack of frequency data. This observation supports predictions that genetic variants in pre-miRNA regions are rare and unlikely to be functionally important, possibly due to the constraint imposed by natural selection on the evolutionarily conserved pre-miRNA sequences (13
). In contrast, several germline and somatic mutations were identified on pre- and pri-miRNA regions in patients with chronic lymphocytic leukemia (CLL) and these mutations might influence the cell transformation and cancer development (28
). Furthermore, it was reported that polymorphisms on miRNA sequences could affect miRNA production through the influence on the function of DROSHA (29
). Therefore, although we could not identify any significant association with RCC risk, we could not exclude the possibility that genetic variations in miRNA genes might have a potential regulatory effect on RCC tumorigenesis because of only a limited number of SNPs examined. Further studies are warranted to assess the effects using a more comprehensive collection of miRNA gene SNPs.
The comprehensive list of potentially functional SNPs in most currently known miRNA biogenesis genes constructed in our study can be readily used by independent researchers for replication studies of different cancer sites. It is possible that some associations we found in this study are chance findings. Nonetheless, we sought to more powerful elucidate the influence of these SNPs on RCC susceptibility using a pathway-based polygenic approach and identified a trend toward an increasing RCC risk with an increasing number of unfavorable genotypes that occurred in a dose-dependent manner. This finding reinforces the notion that RCC is a polygenic process and thus a combined analysis of multiple variants may have a greater ability to characterize high-risk populations. Further epidemiological and functional studies in a larger population are warranted to validate these results.
In conclusion, our study provides the first epidemiological evidence supporting an association between miRNA-related genes and RCC risk. Our results imply that individual as well as combined genotypes of miRNA processing pathway genes might influence RCC tumorigenesis.