MicroRNA-663 Regulates Melanoma Progression by Inhibiting FHL3.

microRNA-663a (miR-663a) was reported to be highly expressed in cancers. However, its roles in melanoma progression remain unclear. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was conducted to measure miR-663a expression level in melanoma cell lines and normal cells. Cell counting kit-8 assay, wound-healing assay, and transwell invasion assay were conducted to analyze biological roles of miR-663a in melanoma. Luciferase activity reporter assay was conducted to validate the connection of miR-663a and Four and a half LIM domain (FHL) protein 3 (FHL3) in melanoma. Our results showed miR-663a expression level was significantly increased in melanoma cells compared with normal cells. Silencing miR-663a expression suppresses melanoma cell proliferation, migration, and invasion in vitro. Moreover, FHL3 was validated as a functional target of miR-663a. Knockdown of FHL3 partially rescued the inhibitory effects of miR-663a inhibitor on melanoma cell behaviors. Together, our work provided evidence that miR-663a functions as an oncogenic miRNA in melanoma.

Introduction

Diagnosed cases for melanoma each year are continually growing.[1,2] Death cases for melanoma are about 55,500 every year.[2] The main obstacle is we did not fully understand the mechanisms underlying melanoma progression.

microRNAs (miRNAs), 19-24 nucleotides in length, are non-coding RNAs that can regulate target gene expression via a 3’-untranslteed region binding manner.[3] Recent studies suggested miRNAs can play both oncogenic and tumor suppressive roles in cancer progression.[4,5] The abnormal expression of miRNAs in cancers may partially due to epigenetic changes including hypermethylation in CpG island and genetic alterations.[6,7]

miR-663a is reported to have dual roles in carcinogenesis. Xie et al. reported miR-663a expression was found to be increased in ovarian cancer.[8] Forcing the expression of miR-663a promotes ovarian cancer progression in vitro and in vivo by regulating tumor suppressor candidate 2.[8] Moreover, miR-663a expression was also found to be increased in colorectal cancer tissues compared with benign colorectal tissues and health tissues.[9] On the contrary, Li et al. reported miR-663a expression was decreased in glioblastoma.[10] Furthermore, miR-663a overexpression could inhibit glioblastoma proliferation, migration, and invasion via targeting TGF-β1.[11] Considering the distant roles of miR-663a in cancers, hence we are interested to explore its roles in melanoma.

In our study, miR-663a expression was found to be elevated in melanoma cells compared with normal cells. Silencing the expression of miR-663a inhibits melanoma cell proliferation, migration, and invasion in vitro by regulating Four and a half LIM domain (FHL) protein 3 (FHL3).

Materials and Methods

Cell Culture and Transfection

Melanoma cells (A375, SK-MEL-28, and WM451) and normal human epidermal melanocyte HEMa-LP purchased from Cell Bank of Chinese Academy of Science (Shanghai, China) were incubated at DMEM (Invitrogen, Carlsbad, CA, USA) supplemented with 10% FBS in a 37°C moist incubator filled with 95% air and 5% CO2. miR-663a inhibitor and negative control (NC-inhibitor) were transfected into melanoma cells to decrease miR-663a expression levels using Lipofectamine 2000 (Invitrogen). Small interfering RNA targeting FHL3 (si-FHL3) and corresponding negative control (NC-siR) was transfected into melanoma cells using Lipofectamine 2000 to reduce FHL3 expression levels.

Dual-Luciferase Activity Reporter Assay

FHL3 was selected for analyses after TargetScan analysis as it ranks top among all predicted targets for miR-663a and was found to play tumor suppressive role in cancers. Wild-type (wt) or mutant (mt) 3’-untraslated region sequence of FHL3 contains binding region for miR-663a was inserted into pGL (Promega, Madison, WI, USA) to generate FHL3-wt or FHL3-mt luciferase constructs. Cells were co-transfected with luciferase constructs and miRNAs using Lipofectamine 2000. After 48 h, relative luciferase activity was measured using dual-luciferase activity system (Promega) in accordance with the manufacturer’s protocols.

Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR)

RNA samples were isolated by Trizol (Beyotime, Haimen, Jiangsu, China) according to the provided protocols. After concentration quantification using NanoDrop-1000, RNA was reverse transcribed into complementary DNA using PrimerScript kit (Takara, Dalian, Liaoning, China). RT-qPCR was performed at QuanStudio 6 (Invitrogen) using SYBR Green (Takara). Primers were: miR-663a: forward, 5’-GTGCGTGTCGTGGAGTCG-3’ and reverse, 5’-TTTAGGCGGGGCG-3’; U6 snRNA forward, 5’-GCTTCGGCAGCACATATACTAAAAT-3’ and reverse, 5’-CGCTTCACGAATTTGCGTGTCAT-3’; FHL3: forward, 5′-CATGGCATGAGCACTGCTTCCTG-3′ and reverse, 5′-GCTTAGGGCCCTGCCTGGCTACAGC-3′; GAPDH: forward, 5′-GCACCGTCAAGGCTGAGAAC-3′, reverse, 5′-TGGTGAAGACGCCAGTGGA-3′. Comparative Ct method was performed to calculate relative gene expression level.

Cell Proliferation Assay

Cell Counting Kit (CCK)-8 (Beyotime) was used to measure cell proliferation rate. 5,000 cells were seeded into 96-well plates to measure cell proliferation rate at 0, 24, 48 and 72 h after seeding. At these time points, CCK-8 reagent was added to the well and incubated for another 4 h. Absorbance at 450 nm was measured using spectrophotometer.

Cell Migration Assay

Cells in serum-free medium were seeded in 6-well plates and incubated to about 90% confluence. Pipette tip was used to create scratch at cell surface. Then, images of same field were captured using microscope at 0 and 48 h.

Cell Invasion Assay

Cell invasion ability was measured with transwell invasion assay using 24-well transwell chamber. 1 × 10[5] cells in serum-free DMEM were seeded into upper chamber that coated with Matrigel (BD Biosciences, San Jose, CA, USA). DMEM containing 10% FBS was filled into bottom chamber. After 24 h, invading cells were fixed by methanol, stained by 0.1% crystal violet, and counted using Nikon TS100 microscope.

Western Blot

Protein sample was isolated by RIPA lysis buffer and quantified by BCA kit (Beyotime). Same amount of protein sample was separated with 10% SDS-PAGE and transferred to PVDF membrane. After blocked non-specific sites with fat-free milk, membranes were incubated with primary antibodies (anti-FHL3, anti-N-cadherin, anti-Vimentin, anti-E-cadherin, and anti-GAPDH) for overnight at 4°C. Membranes were washed with PBS and incubated with horse radish peroxide conjugated secondary antibody for 1 h at room temperature. Band signals were visualized by BeyoECL kit (Beyotime) and analyzed with Image J software.

Statistical Analysis

Data obtained from at least 3 independent experiments were analyzed at SPSS 19.0 software (IBM Corp., Armonk, NY, USA) and displayed as mean ± standard deviation. Student’s t-test or one-way analysis of variance with Tukey post hoc test were used to analyze differences in groups. P < 0.05 was identified as indicator for statistically significant.

Results

Upregulation of miR-663a in Melanoma Cell Lines

miR-663a expression was significantly upregulated in melanoma cells compared with normal cells HEMa-LP (Figure 1). Melanoma cells A375 (P < 0.001) and WM451 (P < 0.001) have the highest and second highest miR-663a expression level among investigated cells were selected for functional analyses (Figure 1).

Figure 1.

Expression level of miR-663a was increased in melanoma cells (A375, SK-MEL-28, and WM451) compared with normal human epidermal melanocyte (HEMa-LP). *** P < 0.001, ** P < 0.01. miR-663a: microRNA-663.

MiR-663a Knockdown Inhibits Melanoma Cell Proliferation, Migration, and Invasion

We found melanoma cells (A375 and WM451) with miR-663a inhibitor transfection displayed lower miR-663a expression level (P < 0.001), cell proliferation rate (P < 0.001), cell migration ability (P < 0.01), and cell invasion ability (P < 0.01) compared with those with NC-inhibitor transfection (Figure 2A-D). In addition, we showed E-Cadherin expression level was increased, while N-Cadherin and Vimentin expression level was decreased by miR-663a inhibitor in melanoma cells (Figure 2E).

Figure 2.

MiR-663a knockdown inhibits proliferation, migration, and invasion of melanoma cells. (A) miR-663a expression level was decreased by miR-663a inhibitor in melanoma cells. (B) Cell proliferation rate was inhibited by miR-663a inhibitor in melanoma cells. (C) Cell migration ability was suppressed by miR-663a inhibitor in melanoma cells. (D) Cell invasion ability was suppressed by miR-663a inhibitor in melanoma cells. (E) E-Cadherin expression level was increased, while N-Cadherin and Vimentin expression level was decreased by miR-663a inhibitor in melanoma cells. *** P < 0.001, ** P < 0.01. miR-663a: microRNA-663; NC-inhibitor: negative control microRNA.

FHL3 Was a Direct Target of MiR-663a

In order to explore mechanism through which miR-663a promotes melanoma progression, TargetScan algorithm was employed and found FHL3 contains binding site for miR-663a in its 3’-UTR (Figure 3A). Luciferase activity reporter assay showed miR-663a inhibitor transfection increased relative luciferase activity in melanoma cells transfected with FHL3-wt but not FHL3-mt (P < 0.001, Figure 3B). Furthermore, RT-qPCR showed miR-663a inhibitor transfection could increase levels of FHL3 in melanoma cells (P < 0.001, Figure 3C). Importantly, western blot showed FHL3 protein expression level was decreased in melanoma cells compared with normal cells (Figure 3D).

Figure 3.

FHL3 was a target for miR-663a. (A) Predicted miR-663a binding site in the 3’-UTR of FHL3. (B) Luciferase activities of melanoma cells with luciferase activity reporter constructs or synthetic miRNAs transfection. (C) RT-qPCR analysis of FHL3 in melanoma cells with synthetic miRNAs transfection. (D) Expression of FHL3 was decreased in melanoma cells compared with the normal cell line. *** P < 0.001, ** P < 0.01. miR-663a: microRNA-663; NC-inhibitor: negative control microRNA; FHL3: Four and a half LIM domain (FHL) protein 3; RT-qPCR: Reverse transcription quantitative polymerase chain reaction; wt: wild-type; mt: mutant; UTR: untranslated region.

Downregulation of FHL3 Abolished the Inhibitory Effects of MiR-663a Inhibitor on Melanoma Cells

To evaluate whether FHL3 was a functional target of miR-663a, melanoma cells were co-transfected with si-FHL3+miR-663a inhibitor, si-FHL3+NC-inhibitor, or NC-siR+NC-inhibitor. RT-qPCR analysis, CCK-8 assay, wound-healing assay, and transwell invasion assay showed si-FHL3 transfection decreased FHL3 expression level (P < 0.001) but increased cell proliferation rate (P < 0.001), cell migration ability (P < 0.01), and cell invasion ability (P < 0.01) in melanoma cells (Figure 4A-D). Moreover, the inhibitory effects of miR-663a inhibitor on melanoma cell behaviors could be alleviated by si-FHL3 (Figure 4A-D). Interestingly, we showed knockdown of FHL3 increased N-Cadherin and Vimentin expression, and decreased E-Cadherin expression in melanoma cells (Figure 4E).

Figure 4.

Knockdown of FHL3 reversed the effects of miR-663a on melanoma cell behaviors. (A) si-FHL3 transfection decreased FHL3 expression level and partially attenuated the effects of miR-663a inhibitor on FHL3 expression in A375 cells. (B) si-FHL3 transfection increased cell proliferation and partially attenuated the effects of miR-663a inhibitor on cell proliferation in A375 cells. (C) si-FHL3 transfection increased cell migration ability and partially attenuated the effects of miR-663a inhibitor on cell migration ability in A375 cells. (D) si-FHL3 transfection increased cell invasion ability and partially attenuated the effects of miR-663a inhibitor on cell invasion ability in A375 cells. (E) si-FHL3 transfection decreased E-Cadherin and increased N-Cadherin and Vimentin expression level, and partially attenuated the effects of miR-663a inhibitor on the expression of EMT markers in A375 cells. *** P < 0.001, ** P < 0.01, * P < 0.05. miR-663a: microRNA-663; NC-inhibitor: negative control microRNA; FHL3: Four and a half LIM domain (FHL) protein 3; si-FHL3: small interfering RNA targeting FHL3; NC-siR: negative control siRNA.

Discussion

Uncontrolled cell metastasis, resisted to cell death, and evaded from immune surveillance are key cancer hallmarks.[11] miRNAs can regulate almost all cell behaviors, hence they were found have the potential to be used as prognosis prediction or treatment biomarkerss.[12,13] Although the development of first miRNA based therapeutic reagent (MRX34) has been terminated because of adverse events, efforts are continually increasing.[14] miR-138 expression was found to be decreased in melanoma, and correlated with advanced tumor stages.[15] In addition, miR-429 expression was found to be reduced in melanoma, and its overexpression suppresses tumor growth in vitro and in vivo.[16]

miR-663a is characterized as a crucial regulator for cancer progression.[8-10] In our work, we found miR-663a was increased expression in melanoma cells in comparison with normal human epidermal melanocyte HEMa-LP. Notably, silencing of miR-663a could inhibit melanoma cell proliferation, migration, and invasion in vitro. Our results suggested an oncogenic role of miR-663a in melanoma, a finding consistent with previous reports on miR-663a roles.[8,9,17,18] In addition, our results suggested targeting miR-663a may be a potential treatment strategy for melanoma.

Multiple targets including TUSC2 and TGF-β1 for miR-663a have been identified in cancers.[8,9] In our work, we focused on FHL3 among all predicted targets, as it was found to have dual roles in cancer progression.[19,20] FHL3 expression was found to be reduced in breast cancer tissues compared with normal tissues.[19] Gain-of and loss-of experiments showed FHL3 could inhibit breast cancer cell growth via arresting cell cycle.[19] Moreover, a recent work indicated FHL3 expression was increased in pancreatic cancer, and it could stimulate cancer cell growth via regulating EMT process.[20] We also revealed expression levels of EMT markers can be affected by abnormal expression of FHL3 but it is on contrary with findings in pancreatic cancer. These results indicated FHL3 may exert distant biological functions in a cancer type basis manner. Here, we showed silencing of FHL3 could promote melanoma cell behaviors, and reversed the effects of miR-663a on melanoma cell behaviors. Collectively, our study sheds new light on the significance of FHL3 in cancer therapy. Hence, the roles of FHL3 in cancers are worth intensively studying in the future.

In summary, miR-663a expression was found to be upregulated, while FHL3 expression was found to be decreased in melanoma cells compared with normal cells. Silencing the expression of miR-663a inhibits melanoma cell proliferation, migration, and invasion via regulating FHL3. To our knowledge, this is the first evidence that miR-663a/FHL3 axis could contribute to melanoma progression.