MiR-219-5p Inhibits the Growth and Metastasis of Malignant Melanoma by Targeting BCL-2

Malignant melanoma is a very dangerous tumor which is resistant to conventional therapy. MicroRNA exerts a vital function in promoting or inhibiting tumor development. The research has investigated the expression and function of miR-219-5p in melanoma. As a result, miR-219-5p expression was distinctly reduced in melanoma tissues and cell lines and was negatively correlated with Bcl-2 protein level in melanoma. Patients with low miR-219-5p level represented obviously a low overall survival in comparison with patients with high miR-219-5p level. The upregulation of miR-219-5p inhibited melanoma growth and metastasis and strengthened melanoma cells chemosensitivity by targeting Bcl-2. Therefore, the modulation of miR-219-5p expression may be a novel treatment strategy in melanoma.


Introduction
Malignant melanoma developing from melanocytes has shown significantly clinicopathological characteristics of high invasion, high metastasis, and high mortality [1,2]. Although remarkable advances have been achieved in the treatment of tumors recently [3], the prognosis of metastatic melanoma remains still unsatisfied [4]. The etiology of melanoma is very complicated, involving cell differentiation, cell proliferation, cell apoptosis, and so on [5]. With the development of bioinformatics, new molecular targets have been discovered and implemented at the diagnosis and treatment of tumors [6].
MicroRNAs (miRNAs) are a kind of small 15-22-nucleotide noncoding RNA [7]. Many researches point out that miRNA is correlated with tumor growth and metastasis via acting as protumor or antitumor factors in a few neoplasms [8]. Meanwhile, some miRNAs are helpful to the occurrence, development, growth, metastasis, and chemotherapy resistance of melanoma through binding to the targeting mRNA [9][10][11]. Abnormal expression of miR-219-5p has been ascertained in some malignant tumors, and miR-219-5p has been identified to exert tumor suppressor function in a procession of different tumors [12,13]. The expression and function of miR-219-5p have not been elucidated in melanoma up to date. The research aims to determine miR 219-5p level and investigate the specific effect of miR-219-5p on the development of melanoma.

Patients and Melanoma
Samples. 42 of melanoma tissues and 20 nevi tissues were acquired from the Hubei provincial hospital of Traditional Chinese Medicine by resection and were stored in liquid nitrogen. Patients did not receive chemotherapy or radiation therapy before resection. This research was approved by the ethical committee of the Hubei Provincial Hospital of Traditional Chinese Medicine, and written informed consent was obtained from individuals with melanoma. These clinical features of the individuals with melanoma are represented in Table 1.

Cell
Line and Reagents. A375, WM35, SK-MEL-5, and SK-MEL-2 cell lines were obtained from cell bank of Wuhan university and incubated in DMEM added with 10% fetal bovine serum, 100 U/mL penicillin, and 100 g/mL streptomycin (Gibco, USA) in an atmosphere of 5% CO2 at 37 ∘ C. Human epidermal melanocytes (HEMa-LP) were gained from Cascade biologists, UK, and were incubated in HMGS-2 medium in the same condition as described in melanoma cell lines.

Qualitative RT-PCR.
Total RNA was extracted from tissues and cells through the TRIzol reagent (Invitrogen) on the basis of the reagent kit protocol. The cDNA was synthesized and amplified using the TaqMan miRNA reverse transcription kit. The mRNA levels of miR-219-5p and U6 were determined by qRT-PCR using TaqMan human MiRNA assay kit. The 2 −ΔΔCT method was utilized to measure the relative fold difference, MiR-219-5p: (F) 5 -ACACTCCAG-CTGGGTGATTGTCCAAACGCAAT-3 and (R) 5 -CTC-AACTGGTGTCGTGGA-3 , U6: (F) 5 -CTCGCTTCGGCA-GCACA-3 and (R) 5 -AACGCTTCACGAATTTGCGT-3 .  2.11. Chemosensitivity Assay. 48 h after transfection, A375 cells were incubated in fresh medium and then added to 96well plates. Various doses of cisplatin or 5-FU were added to the cell culture for 72 h. Next, CCK-8 assay was applied to detect the cell survival. 2.13. Statistical Analysis. The SPSS 15.0 was applied for statistical analyses, including -test, one-way analysis of variance, Fisher exact probability test, the Kaplan-Meier plot, and Pearson correlation analyses. All of the results were recorded as mean ± standard deviation.

CCK
< 0.05 was believed as statistically significant.

MiR-219-5p Is Downregulated in Melanoma and Correlated with Unfavorable Prognosis in Individuals with
Malignant Melanoma. The miR-219-5p levels in 42 of melanoma tissues and 20 of benign nevi tissues were investigated using qRT-PCR. Our results manifested that the miR-219-5p levels were obviously decreased in melanoma samples in comparison with benign nevi tissues (Figure 1(a)). The miR-219-5p levels in A375 cells, WM35 cells, SK-MEL-2 cells, and SK-MEL-5 cells were distinctly downregulated compared with HEMa-LP cells (Figure 1(b)). Patients with melanoma were divided into high miR-219-5p expression group ( = 21) and low miR-219-5p expression group ( = 21) according to the miR-219-5p average level. The correlation between the miR-219-5p expression and the clinical features of individuals with melanoma was investigated. There was no obvious correlation between the age and sex of patients and miR-219-5p expression, but the low expression of miR-219-5p was distinctly related to the TNM stage and distant migration of malignant melanoma as described as Table 1. Besides, low miR-219-5p level was correlated with decreased overall survival (Figure 1(c)). The results manifested that downregulation of miR-219-5p was closely correlated with the progression of melanoma. The transfection of miR-219-5p elevated the level of miR-219-5p in A375 cells and inhibited the proliferation of A375 cells, but the cotransfection of Bcl-2 weakened the inhibition function induced by miR-219-5p in A375 cells (Figures 1(d) and 1(e)). Pearson's correlation test was applied to detect the relationship between miR-219-5p level and Bcl-2 level in melanoma samples. An obviously inverse association was confirmed between miR-219-5p level and Bcl-2 protein level in melanoma tissues (Figure 1(f)).

Upregulation of miR-219-5p Inhibited A375 Cells Proliferation and Enhanced
Apoptosis of A375 Cells. A375 cells transfected with miR-219-5p were subjected to proliferation assay and flow cytometric analysis. The results as illustrated in Figure 2 confirmed that high expression of miR-219-5p suppressed the A375 cells growth and promoted cell apoptosis; however, the cotransfection of Bcl-2 inversed partially the proliferation and apoptosis of A375 cells induced by miR-219-5p. Subsequently, we detected the protein expression related to apoptosis; indeed, the decreased level of Bcl-2 and the increased level of cleaved caspase 3 and cleaved caspase 9 were identified in miR-219-5p group compared with miR-control group. However, the effect of miR-219-5p on A375 cells was inhibited by the cotransfection of Bcl-2.

Upregulation of miR-219-5p Inhibited the Invasion and
Migration of A375 Cells. Metastasis is the important causation of death associated with malignant melanoma; transwell assay and wound healing assay were performed to determine the influence of miR-219-5p on A375 cells metastasis (Figure 3). Ectopic expression of miR-219-5p obviously inhibited the metastasis of A375 cells. But the cotransfection of Bcl-2 weakened the function of miR-219-5p on A375 cells.

BCL-2 mRNA Was Confirmed as a Binding
Target of miR-219-5p. Two important databases TargetScan 7.0 and miRanda were used for searching for the underlying downstream targets of miR-219-5p in melanoma cells. Bcl-2 was considered as a possible target for further study. The Luciferase Reporter analysis identified that 3-UTR of Bcl-2 was a downstream binding target of miR-219-5p as illustrated as Figure 4(a). The results manifested miR-219-5p obviously inhibited Luciferase activity in wild type but did not affect that in mutated type (Figure 4(b)).

miR-219-5p Inhibited Melanoma Growth in an Animal Experiment and Enhanced Chemosensitivity in A375 Cells.
The role of miR-219-5p in melanoma was identified in nude mice models. The volume of tumors was obviously reduced in the miR-219-5p mimics group in comparison with those in the miR-control group (Figure 4(d)). The final weight of tumors was distinctly decreased in miR-219-5p mimics group compared with miR-control group (Figure 4(c)). Accordingly, the inhibition function of miR-219-5p on the melanoma growth was identified in vivo. Meanwhile, the transfection of miR-219-5p reinforced chemosensitivity to cisplatin or 5-FU treatment of A375 cells, but cotransfection of BCL-2 weakened this function of miR-219-5p on A375 cells.

Discussion
Tumor development is a complicated evolution and regulated by protumor and antitumor elements [14]. More and more researches have identified that microRNAs exert important function in tumorigenesis via modulating the targeting gene expression, including cell proliferation, differentiation, apoptosis, and metastasis [15,16], MiR-219-5p has been confirmed to be expressed abnormally and play antitumor roles in a few tumors. For example, miR-219-5p inhibited the growth and metastasis of gastric cancer cells via targeting LRH-1 [17], and miR-219-5p exerted a antitumor function in colon cancer via binding to Sall4 [12]; however, the expression and effect of miR-219-5p in melanoma still remained unclear. In this article, the miR-219-5p level in melanoma tissues and cell lines was found to be downregulated. The low miR-219-5p level was obviously related to the malignant clinical features of patients with melanoma. Furtherly, it was identified that miR-219-5p suppressed the A375 cells proliferation and metastasis and promoted A375 cells apoptosis. Ectopic expression of miR-219-5p inhibited melanoma growth in vivo. These data demonstrated that miR-219-5p exerted a tumor suppressor function in melanoma. To investigate the peculiar regulatory mechanism of miR-219-5p on the development of melanoma, we retrieved two important databases, TargetScan 7.0 and miRanda, and found Bcl-2 may be an important downstream targeting gene, and we confirmed that the Bcl-2 protein level was significantly inversely correlated with the miR-219-5p level in tumor tissues. Furthermore, the Luciferase Reporter analysis revealed BCL-2 mRNA was exactly a binding target of miR-219-5p. Bcl-2 gene, an important antiapoptotic gene, influences the intrinsic apoptosis pathway [18,19]. Meanwhile, Bcl-2 can promote tumor invasion and metastasis [20]. Inhibition of BCL-2(wt) BCL-2(mut) Bcl-2 expression has been believed as an important treatment strategy for various cancers [21]. The following assays identified that the Bcl-2 level was significantly reduced, and the cleaved caspase 3 and 9 level were elevated in miR-219-5p group compared with the control group. Cotransfection of Bcl-2 recovered partially the proliferation and metastasis function of A375 cells inhibited by miR-219-5p and suppressed the apoptosis of A375 cells. These results showed that the impact of miR-219-5p on melanoma development was made by in part targeting the Bcl-2 mRNA. In briefly, the research confirms that miR-219-5p exerts an antitumor function via partially regulating the Bcl-2 protein expression. The mediation of miR-219-5p may be a new and crucial scheme for molecular treatment of melanoma.

Conflicts of Interest
The authors declare that they have no conflicts of interest.