miR-10b Promotes Migration and Invasion in Nasopharyngeal Carcinoma Cells

Nasopharyngeal carcinoma is a prevalent head and neck cancer which is very common in southern China and southeastern Asia. High transfer of nasopharyngeal carcinoma is the main cause of treatment failure (McDermott et al., 2001; Li et al., 2004; Yu et al., 2009). As diagnostic and treatment technology have improved, certain early-stage patients have come to be cured. However, the 5-year survival rate of most middle-lateand late-stage nasopharyngeal carcinoma patients is only about 50%. For this reason, exploring the molecular mechanisms underlying the metastasis of nasopharyngeal carcinoma, searching for the new therapeutic targets, and reducing the transfer rate are all of considerable significance. MicroRNAs (miRNAs) are an abundant class of endogenous, highly conserved, non-coding RNAs. They are about 18–25 nucleotides in length and are expressed in a wide range of organisms (Griffiths-Jones 2004; Davis-Dusenbery et al., 2010; Dawood 2010). This is primarily accomplished by binding to the 3’ UTRs of the mRNAs that target the transcripts for degradation or by blocking translation. miRNAs are estimated to regulate


Introduction
Nasopharyngeal carcinoma is a prevalent head and neck cancer which is very common in southern China and southeastern Asia.High transfer of nasopharyngeal carcinoma is the main cause of treatment failure (McDermott et al., 2001;Li et al., 2004;Yu et al., 2009).As diagnostic and treatment technology have improved, certain early-stage patients have come to be cured.However, the 5-year survival rate of most middle-late-and late-stage nasopharyngeal carcinoma patients is only about 50%.For this reason, exploring the molecular mechanisms underlying the metastasis of nasopharyngeal carcinoma, searching for the new therapeutic targets, and reducing the transfer rate are all of considerable significance.
MicroRNAs (miRNAs) are an abundant class of endogenous, highly conserved, non-coding RNAs.They are about 18-25 nucleotides in length and are expressed in a wide range of organisms (Griffiths-Jones 2004;Davis-Dusenbery et al., 2010;Dawood 2010).This is primarily accomplished by binding to the 3' UTRs of the mRNAs that target the transcripts for degradation or by blocking translation.miRNAs are estimated to regulate RESEARCH ARTICLE

miR-10b Promotes Migration and Invasion in Nasopharyngeal Carcinoma Cells
Xiao-Jin Sun 1 , Hao Liu 1 *, Pei Zhang 1 , Xu-Dong Zhang 1,2 , Zhi-Wen Jiang 1 , Chen-Chen Jiang 1,2 * the translation of more than 60% of protein-coding genes (Baffa et al., 2009;Edmonds et al., 2009;Tie et al., 2011).miRNAs are involved in a series of normal biological mechanisms, such as embryonic development, cell growth, proliferation, apoptosis, and differentiation, where it acts by preventing the expression of target genes (Bartel 2004;Baffa et al., 2009;Iorio et al., 2009).Abnormal expression of miRNAs figures in many diseases, including cancer (Lu et al., 2005).miR-10b has been reported to be dysregulated in some types of cancer and to play an important role in invasion and metastasis.miR-10b has been shown to be highly expressed in metastatic breast cancer cell lines and in metastatic breast tumors from patients.The present study focuses on the expression and roles of miR-10b in NPC.It has been found that miR-10b is up-regulated in metastatic NPC cell lines.This study may provide new ideas and methods suitable for the treatment of nasopharyngeal carcinoma.

Cell lines
CNE-2Z is one of nasopharyngeal carcinoma cell lines with low differentiation and high transfer which could be conductive to the study in migration and invasion in nasopharyngeal carcinomca cells.Poorly differentiated human CNE-2Z cell lines were obtained from Zhongshan University and cultured in the current laboratory.Cells were cultured in RPMI-1640 supplemented with 5% FBS and 100 U of penicillin-streptomycin with 5% CO2 in a humidified incubator at 37°C.

Quantitative reverse transcription and real-time PCR analysis of miRNA
Total RNA was extracted using TRIzol (Invitrogen, USA ) from CNE-2Z transfected with miR-10b inhibitors or miR-10b mimics.The primers for RT-PCR to detect miRNA were designed based on the miRNA sequences provided and synthesized by the Takara (Kyoto, Japan.).The quantitative PCR was performed according to the indications of miR-10 qPCR Quantitation Kit (Takara, Kyoto, Japan).RT reactions were performed by means of the iScript cDNA synthesis kit (Takara, Kyoto, Japan) in an ABI StepOne™ Real-Time PCR System (Applied Biosystems, Foster City, CA, U.S.).U6 RNA was used as an endogenous control for miRNA detection.

Cell proliferation assay
Cell viability was detected by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium (MTT) assay.Cells were seeded at a density of 5×10 3 cells/well in 96 well plates 24h with growth medium after 48h transfection.Then, MTT solution (5 mg/mL, 20 μL) was added to each well.After incubation at 37°C for additional 4 h, 150 ml DMSO (Sigma, U.S.) was added to each well to dissolve the crystals.The plates were shaken for 10 min to dissolve the MTT formazan crystals.The optical density (OD) of the wells were determined using a scanning multi-well spectrophotometer at 490 nm wavelength.Experiments were repeated in triplicate and 4 parallel samples were measured each time.

Cell invasion assay
Before cell seeding, a 24-well cell culture plate was coated with 8.0 µm Matrigel (Bedford, MA, U.S.).Cells were seeded in the inserts after transfections which were resuspended in 200 µl serum-free medium and placed in the upper chambers at 5×10 4 cells and normal growth medium were placed in underneath chambers.Then, 24 h after treatment, the cells on the upper surface of the membrane were removed with cotton swabs, and the cells on the lower chamber were incubated with 4% paraformaldehyde in PBS buffer and stained with 0.1% crystal violet.Finally, migratory and invasive cells were counted at 200× magnification in 5 different fields per filter.The experiments were performed in triplicate.

Cell migration assay
A cell migration assay was performed with uncoated transwell cell culture chambers.Cells were seeded in the inserts after transfections, which were resuspended in 200 µl serum-free medium and placed in the upper chambers at 5×10 4 cells and 600 µl RPMI-1640 medium containing 5% FBS were placed in underneath chambers.Then, 24 h after treatment, the cells on the upper surface of the membrane were removed with cotton swabs, and the cells on the lower chamber were incubated with 4% paraformaldehyde in PBS buffer and stained with 0.1% crystal violet.Five visual fields were randomly selected for each membrane and photographed under a light microscope at 200× magnification.Experiments were performed in triplicate.

Wound healing assay
After transfection, cells were seeded on six-well plates at 5×10 5 cells/well.After 24 h, the cells were washed with PBS and wounds were created using a sterile 200 μL pipette tip.The cells were then washed 3 times with PBS and incubated in RPMI-1640 medium containing 5% FBS.Migration at the wound site was observed under an inverted microscope and imaged at the appropriate

Western blot analysis
After transfection, the cells were plated in 6-well culture dishes at a density of 5×10 5 cells/well.Cells were washed 3 times with cold PBS 1 ml/well and digested using trypsin.The protein concentrations were detected using a bicinchoninic acid (BCA) assay.A total of 50 µg of protein was separated using 10% SDS-PAGE and electro-blotted onto PVDF membranes using a semi-dry blotting apparatus.After blocking in 5% non-fat milk, the membranes were incubated overnight at 4°C with primary antibodies.The membranes were then incubated in the secondary anti-bodies for 2 h at room temperature on a shaker.The bands were visualized using Western Lightning ECL Pro with horseradish peroxidase (HRP).β-actin was used as a loading control.

Statistical analysis
All experiments were repeated at least three times.Data are presented as the mean ± SEM.The differences between means were analyzed using the two-tailed Student's t-test.All statistical analyses were performed using SPSS 13.0 software (Chicago, IL, U.S.).Differences with P<0.05 were considered statistically significant.

Overexpression vs. silencing of miR-10b and cell proliferation
The real-time RT-PCR assay showed that the miR-10b inhibitors and miR-10b mimics have been successfully transfected (Figure 1A, P<0.05).An MTT assay was used to observe the effects of miR-10b on the growth of NPC cell lines.Neither silencing nor overexpression of miR-10b had any effect on cell proliferation (Figure 1B, P<0.05).

Overexpression vs. silencing of miR-10b and human NPC cell migration and invasion
The transwell migration and invasion assay revealed that cells transfected with miR-10b mimics led migrated more than 50% further and the cells transfected with (A, B) Overexpression of miR-10b using mimics markedly promoted the wound gap closure and did so in a time-dependent manner.Knocking down miR-10b using chemically synthesized miR-10b inhibitors delayed the closure of the wound gap A B miR-10b inhibitors showed a 20% reduction in distance migrated (Figure 2; P<0.05).These results indicate that miR-10b plays a positive role in migration and invasion of human NPC cell lines and that this effect had nothing to do with any changes in cell viability.A wound healing assay was used to detect the mobility of NPC cell lines.Results showed that overexpression of miR-10b using mimics promoted closure of the wound gap in a timedependent manner (Figure 3B, P<0.05).Silencing miR-10b using chemically synthesized miR-10b inhibitors delayed closure of the wound gap (Figure 3A, P<0.05).

Relative expression of migration and invasion genes in human NPC cells
Quantitative real-time RT-PCR was used to detect the levels of mRNA expression of genes related to migration and invasion.The level of expression E-cadherin was lower in cells transfected with miR-10b mimics than in cells transfected with miR-10b inhibitors (Figure 4A, B, C; P<0.05).However, the levels of expression of vimentin and MMP-9 were up-regulated in cells transfected with miR-10b mimics while the expression levels of vimentin and MMP-9 were lower in cells transfected with miR-10b inhibitors than in other cells (Figure 4 D, E, F; P<0.05).

miR-10b and expression of E-cadherin and MMP-9
Although the precise mechanisms underlying NPC metastasis are not well understood, the expression of genes related to migration and invasion may contribute to specific stages of the metastatic cascade.In order to elucidate the molecular mechanisms of the effect of miR-10b on the metastasis of NPC, E-cadherin and MMP-9 expression levels were assessed using Western blot analysis.Transfection with miR-10b mimics reduced the rate of E-cadherin expression and increased the rate of MMP-9 expression, but transfection with miR-10b inhibitor increased the rate of E-cadherin expression and reduced the rate of MMP-9 expression (Figure 5, P<0.05).

Discussion
Since miRNA was first discovered in 1993 (Iorio et al., 2009), over 700 miRNAs have been identified in humans, and many of them are involved in tumor generation and development (Sossey-Alaoui et al., 2009).Recently, miRNAs have received a great deal of attention because they have been reported to inhibit the epithelialmesenchymal transition (Luo et al., 2011).The roles of miRs in tumorigenesis have been thoroughly studied.In human cancer, miRNA expression profiles differ between normal tissues and the tumors that are derived from them.They also and between different types of tumors.miRNAs can act as oncogenes or as tumor suppressors and they have key functions in tumorigenesis (Wang et al., 2012;Wei et al., 2013;Wu et al., 2013).
Although previous studies have shown that treatment with anti-miR-10b effectively inhibits the invasiveness of breast cancer cells (Ma et al., 2007) and that inhibition of miR-10b expression may be a new preventative measure against the spread of deadly tumors (Schuldt 2007; Steeg  DOI:http://dx.doi.org/10.7314/APJCP.2013.14.9.5533 miR-10b Promotes Migration andInvasion in Nasopharyngeal Carcinoma Cells 2007), targeting miR-10b for the disruption of cancer metastasis remains a matter of debate (Gee et al., 2008).At the same time, our data indicated that high levels of miR-10b expression promoted the metastasis of NPC cells.
The MTT and wound healing assays demonstrated that miR-10b mimics had no effect on growth but did increase the movability of NPC cells.However, miR-10b inhibitors obviously restricted the mobility of NPC cells.In the present study, overexpression of miR-10b downregulated the expression of E-cadherin and upregulated that of MMP-9, but miR-10b inhibitor markedly upregulated the expression of E-cadherin and reduced the expression of MMP-9.This suggested that miR-10b may be involved in NPC metastasis.
In summary, the data collected here indicated high levels of miR-10b expression increased the mobility of NPC cells and promoted invasion of NPC cells in vitro.In conclusion, these results support the possibility that miR-10b may be involved in the NPC progression, especially in the metastasis of NPC.Further studies are needed to evaluate the function of miR-10b and its target genes.It has been suggested that miR-10b expression may be a prognostic factor for NPC patients.

Figure 1 .
Figure 2. miR-10b and human NPC cell migration and invasion.(A, B) Transwell migration assay of CNE-2Z cells transfected with miR-10b inhibitors and miR-10b mimics or NC.(C, D) Transwell Matrigel invasion assay of CNE-2Z cells transfected with miR-10b inhibitors and miR-10b mimics or NC.The cells passing through the 8 μm pore insert to the underneath well were stained.The number of cells transfected with miR-10b mimics passing through to the underneath well was significantly greater than the number of cells transfected with control factors

Figure 4
Figure 4. miR-10b and Levels of Endogenous Proteins Related to Migration and Invasion.(A, B, C) CNE-2Z cells were transfected with miR-10b inhibitors or Inhibitors-NC.D, E, F) CNE-2Z cells were transfected with miR-10b mimics or Mimics-NC.The levels of E-cadherin, Vim, MMP-9 treated as described above were measured using qRT-PCR