[ARTICLE WITHDRAWN] Dexmedetomidine Inhibits Osteosarcoma Cell Proliferation and Migration, and Promotes Apoptosis by Regulating miR-520a-3p.

THIS ARTICLE WAS WITHDRAWN BY THE PUBLISHERS IN NOVEMBER 2020.

INTRODUCTION

Osteosarcoma (OS) is an aggressive malignant tumor that arises from primitive transformed cells of mesenchymal origin and exhibits osteoblastic differentiation and produces malignant osteoid1. OS is prevalent among teenagers and young adults, occurring less frequently than lymphomas and brain tumors in this age group2,3. This tumor is generally locally aggressive and tends to produce early systemic metastases4. About 10%–20% of OS patients present with metastatic disease at the time of OS diagnosis, most commonly in the lung5. Currently, the management of OS comprises preoperative chemotherapy followed by amputation surgery and postoperative chemotherapy6.

Dexmedetomidine (DEX) is a widely used sedative and analgesic during amputation surgery of OS patients. Its chemical structure is shown in Figure 1A. DEX has specific and selective α2-adrenoceptor agonism and can prolong the duration of sensory block and the postoperative analgesia7–9. However, to our knowledge, the effect of DEX on OS cells in patients who suffer from amputation has not been investigated.

Figure 1

Dexmedetomidine (DEX) and MG63 cell viability. (A) The chemical structure of DEX. (B) Cell viabilities of MG63 cells that were treated with different concentrations of DEX for 1, 12, or 24 h as detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. *p < 0.05, **p < 0.01 compared with control.

Emerging evidence has shown that microRNAs (miRNAs) play an important role in tumorigenesis, acting as oncogenes or tumor suppressors10. An miRNA known as miR-520-3p has been characterized as a tumor suppressor in many human cancers, and its overexpression has been suggested to inhibit tumor cell proliferation and invasion and induce apoptosis11–13. However, few studies have discussed the pivotal roles of miR-520 in OS. Importantly, miR-520 was recently reported to be associated with OS14. Except for this report, no evidence about miR-520 in OS has been found. Therefore, we speculated that there may be a relationship between DEX and miR-520-3p in OS.

In this study, we intended to investigate the effect of DEX on the OS cell line MG63 and to explore the possible relationship between DEX and miR-520-3p in OS. With this purpose, we investigated the effects of DEX on MG63 cell proliferation, migration, and apoptosis, as well as on miR-520-3p expression. Meanwhile, we investigated the effects of miR-520-3p on MG63 cell proliferation, migration, and apoptosis and explored the relationship between DEX and miR-520-3p. These results will help to provide a potential therapeutic strategy and target for OS treatment.

MATERIALS AND METHODS

Cell Culture and Transfection

The human OS cell line MG63, obtained from the China Center for Typical Culture Collection (Wuhan University, Hubei, P.R. China), was cultured in Roswell Park Memorial Institute (RPMI)-1640 medium supplemented with 10% heat-inactivated fetal bovine serum (FBS; HyClone, Logan, UT, USA), 1% penicillin (50 U/ml)/streptomycin (50 μg/ml) (Gibco Life Technologies, Grand Island, NY, USA), and 5 μg/ml prophylactic Plasmocin™ (InvivoGen, San Diego, CA, USA) in a humidified atmosphere with 5% CO2 (37°C). Cells were treated with different concentrations of DEX including 0, 1, 10, and 100 ng/ml for 24 h under controlled conditions.

For cell transfection, miR-520a-3p mimics and inhibitor and the corresponding negative control (GenePharma, Shanghai, P.R. China) were transfected into MG63 cells to manually alter the miR-520a-3p expression in MG63 cells using Lipofectamine 2000 Reagent (Invitrogen, Carlsbad, CA, USA).

MTT Assay

A total of 100 μl of MG63 cell suspension (in mid-log phase) containing 1 × 108 cells/L were added to a 96-well plate. Following 24 h of culture, cells were treated with DEX and incubated at 37°C in 5% CO2 for 1, 12, or 24 h. Then 20 μl of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) stock solution [5 mg/ml in phosphate-buffered saline (PBS); Amresco, Solon, OH, USA] was added to each well, and the cells were incubated at 37°C for 4 h. The cell suspension was then centrifuged at 1,000 × g for 10 min at 37°C, and the supernatant was discarded. Subsequently, 150 μl of dimethyl sulfoxide (Sigma-Aldrich, St. Louis, MO, USA) was added, and the plate was agitated for 10 min in the dark. The optical density (OD) was detected using a microplate reader (Quant™; Bio-Tek Instruments Inc., Winooski, VT, USA) at a wavelength of 490 nm.

Colony Assay

For the cell colony formation assay, transfected cells were incubated in six-well plates at a density of 2 × 103 cells/well at 5% CO2 and 37°C. Following 10 days of incubation, the cells were stained with 0.005% crystal violet for 30 min. The colony numbers were recorded by the ImageJ software (National Institutes of Health, Bethesda, MD, USA).

Transwell Migration Assay

MG63 cell migration was evaluated by the Transwell migration chambers. The cells, at a density of 1 × 105 cells, were seeded in serum-free media on the upper chamber with the noncoated membrane (8-μm pore size; Millipore, Zug, Switzerland). The lower chamber contained RPMI-1640 with 20% FBS, which served as a chemoattractant. After 24 h, cells in the upper chamber were discarded with a cotton wool, and the migrated cells in the lower chamber were counted using a microscope (BX50; Olympus, Tokyo, Japan).

Cell Apoptosis Assay

Apoptosis of MG63 cells was quantified by combined staining with annexin V and propidium iodide (PI) using an Annexin-V-Fluorescein Isothiocyanate (FITC) Apoptosis Detection kit (MBL International Co., Woburn, MA, USA). Briefly, after 24 h of DEX treatment, cells were collected by centrifugation at 1,500 × g for 10 min at 4°C and dissolved in 500 μl of 1× binding buffer, followed by the addition of 10 μl of annexin V-FITC solution and 5 μl of PI solution. After that, cells were incubated at room temperature for 15 min in the dark and then were analyzed using a flow cytometer (FACSort; BD Biosciences, San Diego, CA, USA).

Luciferase Reporter Assay

The possible binding sites of miR-520a-3p in the 3′-untranslated region (3′-UTR) of AKT1 mRNA were predicted by TargetScan (http://www.targetscan.org). The cDNA fragments containing the predicted miR-520a-3p binding sites were amplified and subcloned into pmirGLO Dual-Luciferase miRNA Target Expression Vector, named AKT1-wt (Promega, Madison, WI, USA). The control plasmids were constructed using cDNA fragments containing mutated nucleotides instead of those at the miR-520a-3p binding sites, which were named AKT1-mut. Then 100 ng of AKT1-wt or AKT1-mut vector was cotransfected into MG63 cells in the presence of miR-520a-3p mimics, inhibitor, and control using Lipofectamine 2000 Reagent (Invitrogen). After 48 h of incubation, the cells were harvested, and the luciferase activities were determined using a Dual-Luciferase Reporter Assay Kit (Promega) according to the manufacturer’s instructions.

Western Blot

MG63 cells were trypsinized and resuspended in ice-cold wash buffer and then centrifuged at 700 × g for 5 min at 4°C. After removal of the supernatant, cells were resuspended in 200 μl of ice-cold fractionation buffer mix and placed on ice for 10 min, followed by centrifugation at 10,000 × g for 10 min at 4°C. The supernatants were transferred to a fresh tube. Protein samples (30 mg) were electrophoresed on a 12.5% sodium dodecyl sulfate (SDS) gel (Clontech Laboratories, Inc., Palo Alto, CA, USA) and transferred onto a Hybond enhanced chemiluminescence (ECL) nitrocellulose membrane (Amresco). Next, the membranes were blocked with 4% skim milk in PBS with Tween (PBST; Clontech Laboratories, Inc.) at 4°C overnight and then incubated with the rabbit anti-human polyclonal primary antibodies (1:1,000 dilution). After washing with PBST, membranes were incubated with the horseradish peroxidase-conjugated secondary antibody (Amresco) for 1 h at room temperature. Finally, the membranes were analyzed using an ECL Western Blotting Substrate Kit (Amresco). The Western blotting results were quantified using the Photoshop Image Analysis software CS3 (Adobe Systems, Inc., San Jose, CA, USA).

Quantitative Real-Time Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR) Analysis

Total RNA was collected using the TRIzol® Plus RNA Purification Kit (Ambion, Austin, TX, USA) and quantified using a spectrophotometer at 260 nm. The cDNA was synthesized using a RevertAid First-Strand cDNA Synthesis Kit (Thermo Fisher Scientific, Waltham, MA, USA). Real-time quantitative PCR was performed using SYBR® Premix Ex Taq™ (TaKaRa Biotechnology, Dalian, P.R. China) and the Bio-Rad CFX96 touch q-PCR system (Bio-Rad, Hercules, CA, USA). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) served as an internal reference gene for mRNAs and U6 small nuclear RNA (snRNA) for miR-520a-3p. The specific primers for miR-520-3p were 5′-ACACTCCAGCTGGGAAAGTGCTTCCC-3′ (forward) and 5′-CTCAACTGGTGTCGTGGA-3′ (reverse); for U6 were 5′-CTCGCTTCGGCAGCACATATACT-3′ (forward) and 5′-ACGCTTCACGAATTTGCGTGTC-3′ (reverse); for AKT1 were 5′-ACGGGCACATTAAGATCACA-3′ (forward) and 5′-TGCCGCAAAAGGTCTTCATG-3′ (reverse); and for GAPDH were 5′-TGGGTGTGAACCACGAGAA-3′ (forward) and 5′-GGCATGGACTGTGGTCATGA-3′ (reverse). Fold induction was calculated using the 2−ΔΔCt method.

Statistical Analysis

All experiments in this study were repeated at least three times for each condition. Data were expressed as mean ± standard error. Single-factor analysis of variance was performed for each treatment group. Statistical significant difference was considered at a value of p < 0.05. SPSS 10.0 (SPSS, Inc., Chicago, IL, USA) was utilized for statistical analysis.

RESULTS

DEX Inhibited MG63 Cell Proliferation

The cell viabilities of MG63 cells that were treated with different concentrations of DEX for 1, 12, or 24 h are shown in Figure 1B. As shown in this figure, compared with control (0 ng/ml DEX), no significant difference was found in cell viability after MG63 cells were treated with 1 ng/ml DEX. After 24 h of treatment with 10 ng/ml DEX, the MG63 cell viability was inhibited significantly (p < 0.05). Moreover, 100 ng/ml DEX could significantly inhibit the MG63 cell viability after 12 or 24 h of treatment (p < 0.01). The result indicated that high concentrations of DEX may have an obvious effect on MG63 cell viability; therefore, we used 100 ng/ml and 24 h as the treatment conditions of DEX in further studies.

DEX Inhibited MG63 Cell Migration and Promoted Apoptosis

The colony formation assay showed that DEX treatment significantly decreased the colony number compared to control (p < 0.01) (Fig. 2A). In addition, the Transwell migration assay indicated that DEX treatment also significantly reduced the number of migrated cells (p < 0.01) (Fig. 2B). Flow cytometer analysis showed that DEX significantly promoted apoptosis of MG63 cells in comparison with control (p < 0.01) (Fig. 2C).

Figure 2

Effect of DEX on proliferation, migration, apoptosis, and AKT pathway protein expression of MG63 cells. (A) Colony number of MG63 cells after DEX (100 ng/ml) treatment for 24 h. (B) Number of migrated MG63 cells after 100 ng/ml DEX treatment for 24 h. (C) Percentage of apoptotic MG63 cell after 100 ng/ml DEX treatment for 24 h. (D) Relative expression levels of AKT, phosphorylated (p)-AKT, mechanistic target of rapamycin (mTOR), p-mTOR, extracellular signal-regulated kinase 1/2 (ERK1/2), and p-ERK1/2 in MG63 cells after 100 ng/ml DEX treatment for 24 h. **p < 0.01 compared with control. GAPDH, glyceraldehyde 3-phosphate dehydrogenase.

Furthermore, the pathways of AKT-mechanistic target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK) that are involved in cell proliferation, migration, and apoptosis were detected. As the result presented in the Western blot analysis shows, DEX treatment significantly decreased the expression levels of AKT, phosphorylated (p)-AKT, p-mTOR, and p-ERK1/2, suggesting that DEX may repress the activation of the AKT and ERK pathways (Fig. 2D).

DEX Upregulated miR-520a-3p Expression and AKT1 Was a Target of miR-520a-3p

The miR-520a-3p expression after DEX treatment was detected using qRT-PCR. DEX treatment significantly increased the expression level of miR-520a-3p (p < 0.001) (Fig. 3A).

Figure 3

Contribution of miR-520-3p to the effect of DEX on AKT in MG63 cells. (A) Relative expression levels of miR-520-3p in MG63 cells after DEX (100 ng/ml) treatment for 24 h. (B) The gene sequences of AKT1 regulated by miR-520-3p. (C) The relative luciferase activities in wild-type (wt) 3′-untranslated region (3′-UTR) of AKT1 and mutant-type (mut) 3′-UTR of AKT1 in transfected cells. (D, E) Relative expression level of AKT1 in transfected cells detected by quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) and Western blot, respectively. NS: p > 0.05, **p < 0.01, ***p < 0.001 compared with control.

Various target genes of miR-520 were obtained based on the TargetScan database, and we chose AKT1 as the predicted target gene of miR-520. Consequently, we further analyzed whether the 3′-UTR of AKT1 was bound to the site of miR-520a-3p (Fig. 3B). To verify that AKT1 was a direct target of miR-520a-3p, we carried out a Dual-Luciferase Reporter assay. As shown in Figure 3C, miR-520a-3p could significantly inhibit the luciferase activity of the reporter with AKT1-wt, while the luciferase expression of AKT1-mut was not regulated by miR-520a-3p, suggesting that this site in the AKT1-3′-UTR was the exact regulation site of miR-520a-3p.

Subsequently, the effect of miR-520a-3p mimics or inhibitor on AKT1 was detected. By qRT-PCR (Fig. 3D), miR-520a-3p mimics were shown to significantly decrease the AKT1 expression (p < 0.01), while miR-520a-3p inhibitor significantly increased the AKT1 expression (p < 0.001). Additionally, Western blot analysis showed consistent protein expression of AKT1 (Fig. 3E). These results suggested that miR-520a-3p could directly bind to the 3′-UTR of AKT1 to inhibit the transcription of AKT1 as well as affect AKT1 protein level.

miR-520a-3p Inhibited MG63 Cell Proliferation and Migration, and Promoted Apoptosis

After MG63 cells were transfected or treated with (1) mimic control, (2) miR-520a-3p mimics, (3) inhibitor control, (4) miR-520a-3p inhibitor, (5) DEX + inhibitor control, and (6) DEX + miR-520a-3p inhibitor, cell proliferation, migration, and apoptosis of MG63 cells were respectively detected. As shown in Figure 4A–C, miR-520a-3p mimics significantly inhibited MG63 cell proliferation and migration and promoted apoptosis compared with mimic control, while miR-520a-3p inhibitor promoted MG63 cell proliferation and migration and inhibited apoptosis significantly in comparison with inhibitor control (p < 0.05). However, when miR-520a-3p inhibitor-transfected cells were treated with DEX, cell proliferation and migration of MG63 cells significantly increased and MG63 apoptosis significantly decreased compared with DEX + inhibitor control (p < 0.01). Western blot analysis revealed that miR-520a-3p mimics suppressed protein expressions of AKT, p-AKT, p-mTOR, and p-ERK1/2, whereas miR-520a-3p inhibitor had an opposite effect (Fig. 4D). miR-520a-3p may decrease the AKT and p-AKT expressions by inhibition of AKT1 transcription to inhibit the activation of the AKT/mTOR pathway. Additionally, both DEX and miR-520a-3p could suppress p-ERK1/2, but the underlying mechanism needs to be further explored.

Figure 4

Use of miR-520-3p mimics and inhibitors to explore the contribution of miR-520-3p to the effects of DEX treatment on MG63 cells. (A) Colony number of MG63 cells after cell transfection or treatment with 100 ng/ml DEX for 24 h. (B) Number of migrated MG63 cells after cell transfection or treatment with 100 ng/ml DEX for 24 h. (C) Percentage of apoptotic MG63 cell after cell transfection or treatment with 100 ng/ml DEX for 24 h. (D) Relative protein expression levels of AKT, p-AKT, mTOR, p-mTOR, ERK1/2, and p-ERK1/2 in MG63 cells after cell transfection or treatment with 100 ng/ml DEX for 24 h. *p < 0.05, **p < 0.01, ***p < 0.001 compared with appropriate control.

DISCUSSION

In this study, DEX was found to inhibit MG63 cell proliferation and migration and promote apoptosis, as well as to repress the activation of the AKT and ERK pathways. Interestingly, DEX could upregulate miR-520-3p, while miR-520-3p could directly target AKT1. Further study found that miR-520-3p also inhibited MG63 cell proliferation and migration, promoted apoptosis, and suppressed protein expressions of AKT, p-AKT, p-mTOR, and p-ERK1/2.

A recent study has reported that anesthetics such as propofol and morphine can influence the malignancy of solid tumors15,16. DEX is a new type of receptor agonist highly selective for α2-adrenergic receptor located in the brain and spinal cord. It was recently introduced to anesthesia practice and can produce dose-dependent sedation, anxiolysis, and analgesia without respiratory depression17,18. Recently, DEX was found to significantly increase the proliferation, migration, and invasion of the breast cancer cell line MDA-MB-231 via activation of the α2B-adrenoceptor/ERK signaling pathway in a dose-dependent manner19. In contrast to the finding above, the present study showed that DEX could inhibit MG63 cell proliferation and migration and repress the activation of the AKT and ERK pathways, which may be due to the different types of tumor.

The AKT/mTOR pathway has been documented to play a major role in many cancers20,21. mTOR is activated by AKT and regulates cell survival, migration, and proliferation22. Liu et al.23 suggested that the AKT/mTOR pathway plays an important role in regulating proliferation and apoptosis of human OS cells. In addition, the ERK1/2 pathway is also associated with tumorigenesis, metastasis, and apoptosis in many cancers, including OS24. In this study, the AKT and ERK pathways were inactivated by DEX, suggesting that DEX may regulate OS cell proliferation, migration, and apoptosis by repressing the activation of the AKT and ERK pathways.

The present study found that DEX could upregulate miR-520-3p. miR-520-3p is a potential tumor suppressing noncoding RNA, which is deemed to be associated with a variety of human cancers25. Yu et al.25 have reported that miR-520a-3p is involved in invasion and metastasis in non-small cell lung cancer tissues and cells. Li et al.26 recently revealed that miR-520a-3p suppressed breast cancer cell survival ability and metastasis. The role of miR-520-3p in OS has not been reported to the best of our knowledge. The present study found that miR-520-3p inhibited MG63 cell proliferation and migration and promoted apoptosis, suggesting a tumor-suppressive role for miR-520-3p in OS. On the other hand, previous studies have shown that AKT1, an important regulator in various kinds of diseases, which can be controlled by many factors including phosphatidylinositol 3-kinase (PI3K)27 and miRNAs28,29, played significant roles in the progression or development of diseases. However, few have discussed the expression of AKT1 under the anesthetic DEX, except for Wang et al.’s recent study30. Hence, we chose AKT1 as the predicted target of miR-520 in this study and investigated the possible regulatory correlation between miR-520 and AKT1 in OS under DEX treatment. Moreover, our results suggested that miR-520-3p directly targeted AKT1 and repressed the activation of the AKT and ERK pathways. Therefore, miR-520-3p may inhibit the transcription of AKT1 to affect the AKT1 protein level and then influence the AKT pathway. However, the underlying mechanism of how miR-520-3p affects the ERK pathway needs to be further explored.

In summary, the present study suggests that DEX can inhibit OS cell proliferation and migration and promote apoptosis by upregulating the expression level of miR-520a-3p. DEX may serve as a potential therapeutic agent in OS treatment. Furthermore, miR-520a-3p may be a potential target in the therapy of OS.