Novel genetic variants in miR-191 gene and familial ovarian cancer

Abstract

Background: Half of the familial aggregation of ovarian cancer can't be explained by any known risk genes, suggesting the existence of other genetic risk factors. Some of these unknown factors may not be traditional protein encoding genes. MicroRNA (miRNA) plays a critical role in tumorigenesis, but it is still unknown if variants in miRNA genes lead to predisposition to cancer. Considering the fact that miRNA regulates a number of tumor suppressor genes (TSGs) and oncogenes, genetic variations in miRNA genes could affect the levels of expression of TSGs or oncogenes and, thereby, cancer risk.

Methods and results: To test this hypothesis in familial ovarian cancer, we screened for genetic variants in thirty selected miRNA genes, which are predicted to regulate key ovarian cancer genes and are reported to be misexpressed in ovarian tumor tissues, in eighty-three patients with familial ovarian cancer. All of the patients are non-carriers of any known BRCA1/2 or mismatch repair (MMR) gene mutations. Seven novel genetic variants were observed in four primary or precursor miRNA genes. Among them, three rare variants were found in the precursor or primary precursor of the miR-191 gene. In functional assays, the one variant located in the precursor of miR-191 resulted in conformational changes in the predicted secondary structures, and consequently altered the expression of mature miR-191. In further analysis, we found that this particular variant exists in five family members who had ovarian cancer.

Conclusions: Our findings suggest that there are novel genetic variants in miRNA genes, and those certain genetic variants in miRNA genes can affect the expression of mature miRNAs and, consequently, might alter the regulation of TSGs or oncogenes. Additionally, the variant might be potentially associated with the development of familial ovarian cancer.

Figure 1

The locations of the genetic variants in the primary precursor of miR-191 in relation to mature miRNA (in red) and precursor miRNA (in blue). The variants are highlighted in yellow.

Figure 2

Sequence variation in the precursor of miR-191 can translate intro structural alterations. The RNA secondary structure was predicted by RNAHYbrid for WT pri-miR-191 and its novel variant. Only the most stable secondary structures with the lowest free energy are depicted.

Figure 3

Real-time quantitative PCR for mature miR-191 expression in the cells transfected with pcDNA3.3 vector containing miR-191 wildtype or one of three variants. Data are means (± SD) from three independent experiments. Data are normalized with reference tRNA, as mentioned in the text. P value was calculated from a two-sided, one-sample t test.

Figure 4

Real time quantitative PCR for MLH1 and FANCD2 gene expression in the cells transfected with pcDNA3.3 vector containing miR-191 or the empty vector. Data are means (± SD) from three independent experiments. Data are normalized with reference β-actin, as mentioned in the text. P value was calculated from a two-sided, one-sample t test.

Figure 5

Family pedigree structure for the proband who carries the novel variant in the precursor of miR-191. To simplify the structure, we only show those relatives for whom we have DNA samples. Circle: women, Square: men, and dark circle: ovarian cancer patients.