Upregulation of microRNA-23b-3p induced by farnesoid X receptor regulates the proliferation and apoptosis of osteosarcoma cells
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The downstream targets of farnesoid X receptor (FXR) such as miRNAs have a potent effect on the progression of many types of cancer. We aim to study the effects of FXR on osteosarcoma (OS) development and the potential role of microRNA-23b-3p.
The expressions of FXR and miR-23b-3p in normal osteoblasts and five osteosarcoma cell lines were measured. Their correlations were analyzed by Pearson’s test and verified by the introduction of FXR agonist, GW4064. TargetScan predicted that cyclin G1 (CCNG1) was a target for miR-23b-3p. The transfection of FXR siRNA was performed to confirm the correlation between FXR and miR-23b-3p. We further transfected miR-23b-3p inhibitor into MG-63 cells, and the transfected cells were treated with 5 μM GW4064 for 48 h. Quantitative PCR (qPCR) and Western blot were performed for expression analysis. Cell proliferation, cell apoptosis rate, and cell cycle distribution were assessed by clone formation assay and flow cytometry.
Scatter plot showed a positive correlation between FXR and miR-23b-3p (Pearson’s coefficient test R2 = 1.00, P = 0.0028). As CCNG1 is a target for miR-23b-3p, the treatment of GW4064 induced the downregulation of CCNG1 through upregulating miR-23b-3p. The inhibition of miR-23b-3p obviously promoted cell viability, proliferation, and cell cycle progression but reduced apoptosis rate of MG-63 cells; however, the treatment of GW4064 could partially reverse the effects of the inhibition of miR-23b-3p on OS cells.
Upregulated FXR by GW4064 can obviously suppress OS cell development, and the suppressive effects may rely on miR-23b-3p/CCNG1 pathway.
KeywordsFarnesoid X receptor Osteosarcoma Cyclin G1 Clone formation assay
FITC-labeled annexin V
American Type Culture Collection
- C caspase-3
Cannabinoid receptor 1
Cell Counting Kit-8
Cyclin G1/murine double minute gene 2/tumor protein p53
Dulbecco’s modified Eagle’s medium
Fetal bovine serum
Farnesoid X Receptor
E3 ubiquitin-protein ligase
OS stem cells
Pearson’s correlation coefficient
Peroxisome proliferator-activated receptor gamma
Polyvinylidene difluoride membranes
Retinoid X receptor α
Sodium lauryl sulfate-polyacrylamide gels
Osteosarcoma (OS) is a frequent aggressive malignant bone tumor , and it is the second leading cause of cancer-related death among children and young adolescents . The standard treatment for OS is surgery in combination with chemotherapy; however, OS has high recurrence and drug resistance and the 5-year survival rate is still less than 70% [3, 4]. Some recent studies revealed that the molecular pathogenesis of OS was highly associated with OS stem cells (OSCs) [5, 6]; however, the effective therapeutic targets and diagnostic markers for OS have not been identified yet . Therefore, it is highly critical to better understand the OS pathology and the mechanism underlying the initiation and recurrence of the disease in order to develop strategies and new therapeutic methods in improving the prognosis of patients with osteosarcoma.
MicroRNAs (miRNAs) are a species of the non-protein coding RNA family, represented by short, single-stranded RNA approximately 18–22 nucleotides in length, and are the key regulators of post-transcriptional gene expression [8, 9]. Importantly, studies suggested a high association between abnormal miRNA expressions and the development and progression of numerous cancer types [9, 10, 11, 12]. MiR-23b-3p, one of the many in miRNA family, has been considered as a biomarker for assisting the diagnosis and prognosis of different types of cancers such as ovarian cancer , prostate cancer , and hepatocellular carcinoma (HCC) . In 2018, Xian et al. found that upregulating miR-23b-3p level could effectively inhibit gastric carcinoma cell proliferation, migration, and invasion through targeting cannabinoid receptor 1 (CB1R) . Furthermore, miR-23b-3p could also inhibit cell proliferation in lung carcinoma by regulating the expression of cyclin G1 (CCNG1), which has been reported as an oncogene in OS development [17, 18]. These studies suggest that miR-23b-3p may also have a suppressive effect on OS cell proliferation by regulating CCNG1 expression.
Farnesoid X receptor (FXR, NR1H4), which serves as a ligand-activated transcription factor with multiple functions, is mainly expressed in the liver, intestine, kidneys, and adrenal glands [19, 20]. In the recent years, growing studies showed that the downstream targets of FXR such as miRNAs have a potent effect on multiple cancer progression, for example, Qiao et al. demonstrated that the upregulation of FXR by GW4064, an agonist of FXR, could significantly inhibit human colorectal cancer cell proliferation via miR-135A1/CCNG2 pathway . In this study, we found a positive correlation between FXR expression and miR-23b-3p level. We also investigated whether FXR expression participated in OS development via miR-23b-3p/CCNG1 pathway.
Normal human osteoblasts (hFOB1.19) and osteosarcoma cell lines (MG-63, HOS, U2OS, SAOS2, and SJSA1) were obtained from American Type Culture Collection (ATCC, Manassas, VA, USA). All cell lines were cultured in Dulbecco’s modified Eagle’s medium (DMEM, Gibco, Thermo Fisher Scientific, Inc., Waltham, MA, USA) containing 10% fetal bovine serum (FBS; Gibco) and maintained in a 5% CO2 humidified incubator. The culture environment of normal osteoblasts was set at 34 °C, whereas osteosarcoma cells were cultured at 37 °C.
Quantification of RNA
Primers for RT-qPCR
Reverse: 5′- CAGAATGCCCAGACGGAAG-3′
Forward: 5′- TTACCGCTGAGGAGCTGCAGTC-3′
Reverse: 5′- CAGCCATCCTGGATGGATTCAG-3′
Forward: 5′- CACCGTCAAGGCTGAGAAC-3′
Reverse: 5′- GGTGAAGACGCCAGTGGA-3′
Reverse: 5′- CGCTTCACGAATTTGCGTGTCAT-3′
GW4064, a FXR agonist, was purchased from Sigma-Aldrich (#5172, Merck KGaA, Darmstadt, Germany). In order to study the correlation between FXR and miR-23b-3p, MG-63 cells were incubated with GW4064 at different concentrations. In the blank group, MG-63 cells were cultured in dimethyl sulfoxide vehicle, while in the GW4064 group, MG-63 cells were respectively treated by 0.5 and 5 μM GW4064. After 48 h of incubation, the cells were harvested for expression analysis.
Luciferase reporter assay
TargetScan predicted that the sequence of CCNG1-3′-untranslated regions (UTR) contains a binding site of miR-23b-3p. PGL3-CCNG1 luciferase vector was constructed by cloning the fragment of CCNG1-3′-UTR, which contained putative binding sites for miR-23b-3p in the pGL3-Basic (Promega, Madison, WI, USA). HEK293T cells (ATCC) were plated onto 12-well plates (5 × 105 cells/well) before the cell transfection. Subsequently, pGL-3 firefly luciferase reporters (1 μg per well) were respectively co-transfected with mimics control, miR-23b-3p mimics, and mutant (50 nM) using Lipofectamine 2000 reagent (Invitrogen). After 48 h of transfection, the luciferase activities were determined by dual-luciferase reporter assay system (Promega).
SiRNA for FXR (siFXR: 5′-CCUCAGGAAAUAACAAAUATT-3′), and non-specific scrambled siRNA (siNC: 5′-UUCUCCGAACGUGUCACGUTT-3′) were obtained from GenePharma (Shanghai GenePharma Co., Ltd., Shanghai, China). MG-63 cells at logarithmic phase were divided into four groups, and the cells were transfected by Lipofectamine 2000 (Invitrogen, Carlsbad, USA). In the siNC group, cells were transfected with siNC (50 nM). In siNC + GW4064 group, after transfection for 24 h, the cells were treated with GW4064 (5 μM) for 48 h. In the siFXR + GW4064 group, the cells with FXR knockdown were treated with GW4064 (5 μM) and incubated for 48 h. After the treatment, the cells were harvested for detecting transfection efficiencies by quantitative PCR (qPCR) and Western blot.
MiR-23b-3p inhibitor (anti-miR-23b-3p, 5′-UCUCAGUGCUUCUGGCUGC-3′) and inhibitor NC (anti-miR-NC, 5′-UCUACUCUUUCUAGGAGGUUGUGA-3′) were synthesized by GenePharma. The miR-23b-3p inhibitor and inhibitor control were transfected into MG-63 cells following the protocols of Lipofectamine 2000 (Invitrogen). The cells were assigned to four groups, namely, (A) IC group, in which MG-63 cells were transfected with inhibitor control; (B) IC + GW4064 group, in which cells were cultured with GW4064 (5 μM) for 48 h based on the IC group; (C) I group, in which MG-63 cells were transfected with miR-23b-3p inhibitor; and (D) I + GW4064 group, in which the transfected cells were treated with GW4064 (5 μM) for 48 h based on the I group. We further determine the levels of CCNG1 mRNA and protein to determine the transfection efficiencies of inhibitor control and miR-23b-3p inhibitor.
Cell viability assay
Cell Counting Kit-8 (CCK-8, Dojindo, Kumamoto, Japan) was used for cell viability detection according to the manufacturer’s protocol. Cells from different treatment groups were seeded in a 96-well plate (5 × 103 cells/well). CCK-8 reagent was added to each well to react and then incubated for 2 h. Absorbance value was determined using an enzyme microplate reader at 450 nm (Bio-Tek, Winooski, VT, USA).
Clone formation assay
The ability of cell proliferation was assessed by soft agar clone formation assay as described previously . Briefly, the cells (1 × 103) were suspended in 1 ml DMEM containing 10% FBS and 0.3% low-melting agar (GE Healthcare, USA) on 6-well plates, which had been pre-coated by a solidified bottom layer made of 0.6% agarose in DMEM medium. After incubation for 2 weeks, cell culture was terminated when macroscopic apophyses were observed. The cells were fixed with 20% methanol for 15 min. Then, Giemsa solution was added to stain the cells for 40 min. After washing and air-drying, the clones were counted using a cloning counter.
Annexin V/PI staining assay for apoptosis
Fluorescein isothiocyanate (FITC)-labeled annexin V (Annexin-V-FITC) apoptosis detection kit (Sigma-Aldrich) was performed to determine cell apoptosis on a flow cytometry (Gallios, Beckman Coulter, Inc., Brea, CA, USA). In brief, the transfected cells from each group were trypsinized and centrifuged at 1000×g for 5 min. Cells were washed twice by phosphate-buffered saline (PBS) and then incubated with 100 μL Annexin V-FITC and 5 μL propidium iodide (PI) in the dark for 15 min. The apoptosis rates were determined by flow cytometry.
Cell cycle analysis
After 24 h of transfection, the transfected cells were cultured in 5 μM GW4064 and incubated for 48 h. Then, the cells were trypsinized and collected by centrifuging at 1000×g for 5 min. The cells were washed by PBS and fixed in 70% ethanol at 4 °C overnight and subsequently suspended in 400 μL buffer containing PI and RNase (BD Pharmingen, San Diego, CA, USA) for 30 min. The rates of cell cycle distribution were determined by flow cytometry (Gallios).
Western blot analysis
Total proteins were extracted from the cells by RIPA protein extraction reagent (Thermo Fisher Scientific, Inc.). Then, cell lysate was subjected to 10% sodium lauryl sulfate-polyacrylamide gels (SDS-PAGE) and transferred onto polyvinylidene difluoride membranes (PVDF, Bio-Rad, Hercules, CA). After blocking the membranes by 5% non-fat milk for 1 h at room temperature, the membranes were cultured with primary antibodies. GAPDH (Mouse, #ab8245, 1:20000, 36 KD, Abcam, Cambridge, MA) served as an internal control. After incubation with secondary antibodies (goat anti-rabbit (1:20,000, 42 KD, #ab205718, Abcam), goat anti-mouse IgG (1:20,000, 52 KD, #ab205719, Abcam)) for 1 h at 4 °C, the specific signals were visualized by a LI-COR Odyssey Infrared Imaging System. Primary antibodies against CCNG1 (Mouse, 1:1000, #8016, 34 KD, Santa Cruz Biotechnology, Inc., Dallas, USA), FXR (Mouse, 1:1000, #25309, 70 KD, Santa Cruz Biotechnology, Inc.), B-cell lymphoma-2 (Bcl-2, Rabbit, #ab59348, 1:1000, 26 KD Abcam), Bax (Rabbit, #ab32503, 1:2000, 21 KD, Abcam), and Cleaved Caspase-3 (Rabbit, #ab2302, 1:1000, 17 KD, Abcam) were used.
All data were expressed as the mean ± SEM. Pearson’s correlation coefficient (PCC) was determined in Microsoft Excel according to the expressions of FXR and miR-23b-3p. Student’s t test was used for evaluating the difference between two group values, and ANOVA analysis followed by Dunnett’s t test was used for determining statistical significance of multiple groups. P < 0.05 was considered as statistically significant.
Correlation of FXR and miR-23b-3p expression in OS cells
MiR-23b-3p specifically targets CCNG1
TargetScan predicted that the position of 225–232 of CCNG1-3′-UTR contained a binding site of miR-23b-3p (Fig. 1e, f). After the verification of luciferase reporter assay, the luciferase activity of cells co-transfected with PGL3-CCNG1 luciferase and miR-23b-3p WT vectors was found much lower than the blank group (p < 0.01), indicating that miR-23b-3p could effectively bind to CCNG1-3′-UTR. Meanwhile, no difference was observed between the luciferase activity of cells co-transfected with PGL3-CCNG1 luciferase and miR-23b-3p MUT vectors and that of the blank group. Thus, CCNG1 could be seen as a promising target for miR-23b-3p.
GW4064 treatment indirectly regulates CCNG1 expression via miR-23b-3p
In order to confirm whether the negative regulatory effects of FXR on CCNG1 expression were mediated through the regulation of miR-23b-3p, miR-23b-3p inhibitor and inhibitor control were transfected into MG-63 cells. As shown in Fig. 2e, both the levels of CCNG1 mRNA and protein were obviously downregulated under the treatment of GW4064 and peaked in the cells transfected miR-23b-3p inhibitor without GW4064 treatment (p < 0.01). When the blockage of miR-23b-3p of cells was treated with GW4064, the CCNG1 expressions were greatly downregulated (p < 0.01). We additionally measured the changes in the cell viability and observed that MG-63 cell viability was obviously decreased in the IC + GW4064 group (p < 0.01) but reached a peak in the I group. After the treatment of GW4064, the enhanced cell viability by miR-23b-3p inhibitor was decreased significantly again (p < 0.05, Fig. 2f). Together, the upregulated FXR expression by GW4064 could promote miR-23b-3p expression, which could subsequently inhibit CCNG1 expression.
GW4064 treatment suppresses cell proliferation and promoted apoptosis and cell cycle arrest in MG-63 cells
The protein levels of Bcl-2, Bax, and C caspase-3 were key indicators of cell apoptosis (Fig. 3g, h). In the study, GW4064 treatment obviously inhibited Bcl-2 protein level but increased Bax and C caspase-3 levels (p < 0.01), while the mir-23b-3p inhibitor significantly promoted Bcl-2 expression and inhibit Bax and C caspase-3 levels (p < 0.01). Importantly, the treatment of GW4064 could partially reverse the effects of mir-23b-3p inhibitor on Bcl-2, Bax, and C caspase-3 protein levels. Taken together, our data indicated that the upregulation of FXR could induce cell cycle arrest and promote apoptosis in OS.
We observed that both FXR and miR-23b-3p expressions decreased observably in OS cell lines, compared with normal osteoblasts (hFOB1.19) cells. Then, by treating the cells with FXR agonist GW4064, we confirmed a positive correlation between the expressions of FXR and miR-23b-3p in human OS cells. CCNG1 was confirmed as a target for miR-23b-3p, and FXR participated in the regulation of CCNG1 via miR-23b-3p. In addition, we also observed that the upregulated FXR by GW4064 could reduce cell proliferation, enhance apoptosis, and induce cell cycle arrest in OS cells. Therefore, based on the positive correlation between FXR and miR-23b-3p, the anti-cancer effects of FXR on OS cell development were associated with the regulation of miR-23b-3p/CCNG1 pathway.
Growing studies have reported that miR-23b-3p functions as a predictor and prognostic molecular marker for different cancer types such as esophageal squamous cell carcinomas , pancreatic ductal adenocarcinoma , and HCC . In our study, we found a positive correlation between miR-23b-3p and FXR and that GW4064 treatment could induce the upregulation of FXR and miR-23b-3p. Therefore, we reasonably speculated that miR-23b-3p was involved in the upregulation of FXR by GW4064 in suppressing cell proliferation and promoting apoptosis and cell cycle arrest in OS. These data are consistent with previous researches, in which enhancing miR-23b-3p expression mediated several targets to effectively affect tumor cell development, proliferation, and metastasis, and ultimately inhibited cancer development and progression [13, 25, 26].
The regulatory effects of miRNAs on the progression of cancer largely rely on directly regulating the expressions of their target genes. Previous study has revealed that miR-23b-3p specifically targets CCNG1 to regulate HCC cell proliferation and invasion . We also confirmed the close relationship between CCNG1 and miR-23b-3p. CCNG1 is a pivotal component of commanding cyclin G1/murine double minute gene 2/tumor protein p53 (CCNG1/Mdm2/p53) axis . P53 functions as a key regulator of cell cycle progression . CCNG1 could stimulate and propel PP2A catalytic activity toward E3 ubiquitin-protein ligase (Mdm2), which has increased or abnormal expression in numerous cancer types including OS [29, 30]. Then, activation of Mdm2 antagonizes the p53 tumor suppressor function by forming a physical complex with p53 . Previous studies have demonstrated the promoting effects of CCNG1 on cell growth and that the inhibition of CCNG1 could effectively suppress the growth of human tumor xenografts in a nude mouse model [18, 31]. Currently, the potential of companion diagnostics of CCNG1 pathway in the staging, prognosis, and treatment of cancers is widely recognized. In the current study, our data showed that FXR could negatively regulate the expression of CCNG through miR-23b-3p, indicating that the inhibitory effects of FXR on OS cell proliferation and growth were highly associated with the downregulated CCNG1 level.
In recent years, FXR has attracted increasing attention as a therapeutic target in the treatment of cancers . Data from previous reports indicated that FXR deficiency could induce the formation of spontaneous liver tumors and small intestine adenocarcinoma in APCmin mice and promote colon cell proliferation [33, 34]. These studies showed that FXR plays a tumor-suppressive role in certain cancers [35, 36]. In our study, the expressions of FXR in the OS cell lines were also generally lower than that of normal osteoblasts, while the upregulation of FXR by GW4064 showed a potent effect on OS cell proliferation, apoptosis, and cell cycle distribution. The downstream factors of FXR, including miRNAs, have been proved to participate in multiple carcinogenesis . In 2013, Song et al. demonstrated a novel role of peroxisome proliferator-activated receptor gamma (PPARγ), that is, it could epigenetically induce the upregulation of miRNA transcription . FXR shares a number of characteristics with PPARγ and it could bind to retinoid X receptor α (RXRα) as a monomer, and subsequently recruits different cofactors to induce the expressions of target genes in HCC cells [32, 39]. However, whether FXR can epigenetically induce miR-23b-3p expression as PPARγ is still unclear; however, this may be partially explained by the positive correlation between miR-23b-3p and FXR; however, the molecular mechanism requires further study. It should be noted that in vivo model was not constructed in this study, which was a limitation in this study.
In conclusion, our data observed that both FXR and miR-23b-3p were downregulated in OS cells. Pearson’s test demonstrated a positive correlation between miR-23b-3p and FXR, and the positive correlation was further verified by the introduction of GW4064. Furthermore, the upregulation of FXR by GW4064 can suppress OS cell proliferation and promote apoptosis and cell cycle arrest, while inhibiting miR-23b-3p has a promoting effect on OS cell development. CCNG1 is a target for miR-23b-3p, indicating that the tumor-suppressive effects of FXR may be highly associated with miR-23b-3p/CCNG1 pathway. These results showed that FXR/miR-135A1/CCNG2 axis is possibly a potential therapeutic target for OS.
BW contributed substantial contributions to conception and design. CX and JT contributed to the data acquisition and data analysis and interpretation. BW and JT drafted the article or critically revised it for important intellectual content. All authors approved the final version to be published. CX agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of the work are appropriately investigated and resolved.
Ethics approval and consent to participate
This article does not contain any studies with human participants performed by any of the authors.
Consent for publication
The authors declare that they have no competing interests.
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