Downregulation of MicroRNA-147 Inhibits Cell Proliferation and Increases the Chemosensitivity of Gastric Cancer Cells to 5-Fluorouracil by Directly Targeting PTEN.

Gastric cancer is the fourth most common malignancy and the third leading cause of cancer-related deaths worldwide. This study aimed to investigate the expression patterns, biological roles, and underlying mechanisms of microRNA-147 (miR-147) in gastric cancer. The present study demonstrated that miR-147 was significantly upregulated in gastric cancer tissues and cell lines. Downregulation of miR-147 decreased cell proliferation and enhanced the chemosensitivity of gastric cancer cells to 5-fluorouracil (5-FU) through the cell apoptosis pathway. In addition, phosphatase and tensin homolog (PTEN) was mechanically identified as the direct target of miR-147 in gastric cancer. PTEN knockdown reversed the effects of miR-147 downregulation on the proliferation, chemosensitivity, and 5-FU-induced apoptosis of gastric cancer cells. Moreover, miR-147 regulated the PI3K/AKT signaling pathway in gastric cancer by targeting PTEN. In conclusion, miR-147 suppressed the proliferation and enhanced the chemosensitivity of gastric cancer cells to 5-FU by promoting cell apoptosis through directly targeting PTEN and regulating the PI3K/AKT signaling pathway. This study provides important insight into the molecular mechanism that underlies the chemoresistance of gastric cancer cells. The results of this study could aid the development of a novel therapeutic strategy for gastric cancer.

INTRODUCTION

Gastric cancer is the fourth most common malignancy and the third leading cause of cancer-related deaths worldwide1. It accounts for 8% of all newly diagnosed cancer cases and 10% of cancer-related deaths around the world2. Every year, approximately 850,000 newly diagnosed gastric cancer cases and 650,000 deaths are reported worldwide3. Surgical resection is currently the primary and the most effective therapy for patients with early stage gastric cancer4. However, gastric cancer is diagnosed at advanced stages in the majority of patients given the lack of effective techniques for its early diagnosis5. Patients with late stage gastric cancer usually receive chemotherapy as the primary treatment6. However, the effectiveness of chemotherapy is often limited by the development of drug resistance in gastric cancer cells7. Multiple mechanisms, including enhanced DNA repair activity, alterations in cell cycle and proliferation, defective apoptosis, increased rates of drug efflux, alterations in drug metabolism, and the mutation of drug targets, are involved in chemoresistance8,9. Therefore, gaining a better understanding of the mechanisms that underlie the chemoresistance of gastric cancer cells will help improve the curative effect of chemotherapy on patients with gastric cancer.

MicroRNAs (miRNAs) are a large group of noncoding, endogenous, and short RNA molecules that range from 22 to 25 nucleotides in length10. They negatively regulate the expression of their target genes by binding to complementary sequences in the 3′-untranslated regions (3′-UTRs) of their target messenger RNAs (mRNAs), causing subsequent mRNA degradation and/or translational repression11. miRNAs have crucial functions in various biological processes, such as cell proliferation, cycle, development, differentiation, apoptosis, metastasis, and angiogenesis12–14. An increasing number of studies have reported that miRNA expression is dysregulated in various types of human cancers15,16. Whether abnormally expressed miRNAs function as oncogenes or tumor suppressors depends on the nature of their target mRNAs17. Furthermore, miRNAs have important roles in the regulation of the chemoresistance of gastric cancer cells18,19. For example, the upregulation of miR-101 improves the chemosensitivity of gastric cancer cells to cisplatin (DDP) and vincristine (VCR) by directly targeting ANXA220. These findings suggested that miRNAs are potential novel therapeutic targets in the treatment of chemoresistant gastric cancer.

Previous studies have investigated the expression and function of miR-147 in several types of human cancer21–23, but not in gastric cancer. Therefore, this study aimed to investigate the expression patterns, biological roles, and underlying mechanisms of miR-147 in gastric cancer.

MATERIALS AND METHODS

Clinical Sample Collection

A total of 43 paired gastric cancer tissues and matched adjacent normal tissues were collected at the Anhui Provincial Hospital between 2013 and 2016. Patients who underwent radiotherapy or chemotherapy prior to surgery were excluded from this research. All tissues were immediately frozen in liquid nitrogen and then stored at −80°C until further use. This study was approved by the Ethics Committee of Anhui Provincial Hospital. Written informed consent was also obtained from each patient.

Cell Culture and Transfection

Gastric cancer cell lines, including AGS, SGC-7901, MKN-45, BGC-823, and MGC-803, were acquired from the Institute of Biochemistry and Cell Biology at the Chinese Academy of Sciences (Shanghai, P.R. China). Human gastric epithelial cell line GES-1 was purchased from the American Type Culture Collection (ATTC; Manassas, VA, USA). All these cell lines were grown in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 100 U/ml penicillin, and 100 mg/ml streptomycin (all from Gibco; Thermo Fisher Scientific, Inc., Waltham, MA, USA). All cell lines were cultured in a humidified atmosphere containing 5% CO2 at 37°C.

The miR-147 inhibitor and corresponding scramble miRNA inhibitor negative control (NC inhibitor) were obtained from Shanghai GenePharma Co. Ltd (Shanghai, P.R. China).

Phosphatase and tensin homolog (PTEN) small interfering RNA (PTEN siRNA) and negative control small interfering RNA (NC siRNA) were synthesized by Guangzhou RiboBio Co., Ltd. (Guangzhou, P.R. China). Cells were seeded into six-well plates at a density of 60%–70% confluence. After incubation overnight, cell transfection was performed using Lipofectamine™ 2000 (Invitrogen; Thermo Fisher Scientific, Inc.), according to the manufacturer’s protocol.

RNA Extraction and Reverse Transcription-Quantitative Polymerase Chain Reaction (RT-qPCR)

Total RNA was isolated from tissue specimens or cells using a TRIzol® Plus RNA purification kit (Invitrogen, Carlsbad, CA, USA) according to the manufacturer’s instructions. To detect miR-147 expression, reverse transcription was performed to synthesize complementary DNA (cDNA) using a TaqMan MicroRNA Reverse Transcription Kit (Applied Biosystems, Carlsbad, CA, USA), followed by qPCR with TaqMan MicroRNA PCR Kit (Applied Biosystems). For analysis of PTEN mRNA expression, cDNA synthesis and subsequent qPCR were performed using a PrimeScript RT Reagent kit (Takara Bio, Dalian, P.R. China) and an SYBR Premix Ex Taq™ kit (Takara Bio), respectively. U6 snRNA and GAPDH were used as endogenous control for miR-147 and PTEN mRNA, respectively. Data were calculated by the 2−ΔΔCt method24.

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) Assay

Cell proliferation was determined using the MTT assay. Transfected cells were collected at 24 h posttransfection and seeded into 96-well plates at a density of 3 × 103 cells per well. Following incubation of cells for 0, 24, 48, or 72 h, MTT assay was performed according to the manufacturer’s instructions. Briefly, 20 μl of MTT solution (5 mg/ml; Sigma-Aldrich, St. Louis, MO, USA) was added into each well. After 4 h of incubation, the medium was replaced with 150 μl of dimethyl sulfoxide (Sigma-Aldrich) and vortexed for 10 min. Afterward, the absorbance was detected at a wavelength of 490 nm using an automatic multiwell spectrophotometer (Bio-Rad Laboratories, Inc., Hercules, CA, USA). Each experiment was performed in triplicate and repeated three times.

In Vitro Chemosensitivity Assay

Cells were plated into 96-well plates at a density of 3 × 103 cells each well. After incubation overnight, cells were transfected and incubated for 24 h in a humidified atmosphere containing 5% CO2 at 37°C. Subsequently, cells were treated with 5-fluorouracil (5-FU; Sigma-Aldrich) at 0, 2, 4, 8, 16, and 32 μM. At 48 h after 5-FU administration, in vitro chemosensitivity assay was carried out using an MTT assay, as described above. The dose–response curve was charted at various concentrations. Three independent experiments were performed in triplicate.

Flow Cytometry Analysis

Flow cytometry analysis was used to evaluate cell apoptosis. Cells were plated in six-well plates at a density of 8 × 105 cells per well. After transfection for 48 h, cells were treated with 5-FU at a concentration of 8 μM. After incubation at 37°C in a humidified atmosphere containing 5% CO2 for 48 h, cells were collected using trypsinization and washed with PBS. Cell apoptosis was determined with the Annexin-V-FITC apoptosis detection kit (Invitrogen) according to the manufacturer’s instructions. Afterward, the cells were resuspended in 300 μl of 1× binding buffer and then stained with 5 μl of annexin V and 5 μl propidium iodide (PI) for 15 min at room temperature in the dark. Cell apoptosis was quantified using a flow cytometer (Beckman Coulter, Inc., Brea, CA, USA). Each test was performed with at least three repeats.

Bioinformatics Analysis and Luciferase Reporter Assay

To predict the potential targets of miR-147, bioinformatics analysis was performed using two online prediction programs: microRNA.org (http://www.microrna.org/microrna/home.do) and TargetScan (www.targetscan.org). PTEN was predicted as a candidate of miR-147.

Luciferase reporter assay was used to confirm whether PTEN is a direct target of miR-147. Luciferase reporter plasmids, pGL3-PTEN-3′UTR wild type (Wt) and pGL3-PTEN-3′UTR mutant (Mut), were synthesized and confirmed by Shanghai GenePharma Co. Ltd. Cells were seeded into 24-well plates at a density of 60–70% confluence. After incubation overnight, miR-147 inhibitor or NC inhibitor was transfected into the cells, along with pGL3-PTEN-3′UTR Wt or pGL3-PTEN-3′UTR Mut, using Lipofectamine™ 2000, in accordance with the manufacturer’s protocol.

At 48 h posttransfection, firefly and Renilla luciferase activities were measured using a Dual-Luciferase Reporter Assay system (Promega Corporation, Madison, WI, USA) according to the manufacturer’s protocol. Renilla luciferase activity was used as an internal control.

Western Blotting Analysis

Total protein was extracted from tissues or cells using radioimmunoprecipitation assay lysis buffer (Beyotime Institute of Biotechnology, Haimen, P.R. China). The concentration of total protein was measured using the bicinchoninic acid protein assay kit (Beyotime). The same amount of protein was separated by 10% SDS-PAGE and transferred onto polyvinylidene difluoride membranes (EMD Millipore, Billerica, MA, USA). After blocking with 5% skimmed milk in Tris-buffered saline containing Tween 20 (TBST) for 1 h, the membranes were incubated at 4°C overnight with primary antibodies against PTEN (1:1,000 dilution; Cat. No. sc-133197; Santa Cruz Biotechnology, Inc., Dallas, TX, USA), PI3K (1:1,000 dilution; Cat. No. sc-293172; Santa Cruz Biotechnology), AKT (1:1,000 dilution; Cat. No. sc-81434; Santa Cruz Biotechnology), phosphorylated (p)-AKT (1:1,000 dilution; Cat. No. sc-271966; Santa Cruz Biotechnology), and GAPDH (1:1,000 dilution; Cat. No. sc-47724; Santa Cruz Biotechnology). Upon being washed with TBST for three times, the membranes were incubated with goat anti-mouse horseradish peroxidase-conjugated secondary antibodies (1:5,000 dilution; Cat. No. sc-2005; Santa Cruz Biotechnology) at room temperature for 2 h. Protein bands were visualized using the Pierce™ ECL Western Blotting Substrate (Pierce Biotechnology, Inc., Rockford, IL, USA). Quantity One® software 4.62 (Bio-Rad Laboratories) was used to analyze the band intensity. GAPDH was used as a loading control.

Statistical Analysis

Data were expressed as the mean ± standard deviation. All statistical analyses were performed with a two-tailed Student’s t-test or one-way analysis of variance using SPSS version 16.0 software (SPSS, Inc., Chicago, IL, USA). A value of p < 0.05 was considered to indicate a statistically significant difference.

RESULTS

miR-147 Is Upregulated in Gastric Cancer Tissues and Cell Lines

To identify the role of miR-147 in gastric cancer, we first performed RT-qPCR to analyze the expression levels of miR-147 in 43 paired gastric cancer tissues and matched adjacent normal tissues. RT-qPCR results showed that miR-147 expression was significantly upregulated in gastric cancer tissues compared with that in adjacent normal tissues (p < 0.05) (Fig. 1A). We then determined miR-147 expression levels in five gastric cancer cell lines (AGS, SGC-7901, MKN-45, BGC-823, and MGC-803) and the human gastric epithelial cell line GES-1. RT-qPCR analysis revealed that the expression levels of miR-147 were higher in all gastric cancer cell lines than in GES-1 (p < 0.05) (Fig. 1B). Given that AGS and BGC-823 cells expressed the highest levels of miR-147, we selected these two cell lines as models for subsequent experiments. These results implicated miR-147 in the development and progression of gastric cancer.

Figure 1

MicroRNA-147 (miR-147) is upregulated in gastric cancer tissues and cell lines. (A) Relative miR-147 expression was determined in 43 paired gastric cancer tissues and matched adjacent normal tissues. *p < 0.05 compared with normal tissues. (B) Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to detect miR-147 expression in five gastric cancer cell lines (AGS, SGC-7901, MKN-45, BGC-823, and MGC-803) and a human gastric epithelial cell line GES-1. *p < 0.05 compared with GES-1.

Downregulation of miR-147 Suppresses the Proliferation of Gastric Cancer Cells In Vitro

To investigate the potential function of miR-147 in gastric cancer, we transfected AGS and BGC-823 cells with miR-147 inhibitor to decrease miR-147 expression. Following transfection, RT-qPCR was used to evaluate the transfection efficiency. The results showed that the expression of miR-147 was markedly downregulated in miR-147 inhibitor-transfected AGS and BGC-823 cells relative to that in NC inhibitor-transfected cells (p < 0.05) (Fig. 2A). We then conducted the MTT assay to explore the effect of miR-147 underexpression on the proliferation of gastric cancer cells. As shown in Figure 2B, the downregulation of mIR-147 significantly decreased the proliferation of AGS and BGC-823 cells (p < 0.05). These results suggested that miR-147 might suppress tumor development in the growth of gastric cancer.

Figure 2

Downregulation of miR-147 inhibits the proliferation of gastric cancer cells. (A) Relative expression of miR-147 in AGS and BGC-823 cells transfected with miR-147 inhibitor or negative control (NC) inhibitor was determined at 48 h posttransfection. *p < 0.05 compared with NC inhibitor. (B) Results of MTT assay performed to assess the effect of miR-147 underexpression on the proliferation of AGS and BGC-823 cells. *p < 0.05 compared with NC inhibitor.

Downregulation of miR-147 Increases the Chemosensitivity of Gastric Cancer Cells to 5-FU

miR-147 is involved in the development of chemoresistant human cancer cells23. We performed an in vitro chemosensitivity assay to investigate the involvement of miR-147 in the chemosensitivity of gastric cancer cells to 5-FU. The results showed that miR-147-underexpressing AGS and BGC-823 cells exhibited increased sensitivity to 5-FU (p < 0.05) (Fig. 3A). Cell cycle arrest at the G1 phase and/or apoptosis of cancer cells is enhanced by 5-FU; therefore, to explore the mechanism that underlies the effect of miR-147 on the chemosensitivity of gastric cancer cells, we performed flow cytometry analysis to detect the 5-FU-induced apoptosis of gastric cancer cells. As shown in Figure 3B, the downregulation of miR-147 increased the rate of the 5-FU-induced apoptosis of AGS and BGC-823 cells. These results suggested that downregulation of miR-147 increases the chemosensitivity of gastric cancer cells and that miR-147 exerts this effect through the cell apoptosis pathway.

Figure 3

Downregulation of miR-147 enhances the chemosensitivity of gastric cancer cells to 5-fluorouracil (5-FU). (A) In vitro chemosensitivity assays demonstrated that miR-147 underexpression increases the chemosensitivity of AGS and BGC-823 cells to 5-FU relative to that of NC inhibitor-transfected cells. *p < 0.05 compared with NC inhibitor. (B) Downregulation of miR-147 promotes the rate of the 5-FU-induced apoptosis in AGS and BGC-823 cells. *p < 0.05 compared with NC inhibitor.

PTEN Is a Direct Target Gene of miR-147 in Gastric Cancer

Aiming to clarify the molecular mechanisms through which miR-147 inhibits cell proliferation and enhances the chemosensitivity of gastric cancer cells to 5-FU, we performed bioinformatics analysis to predict the potential targets of miR-147. PTEN (Fig. 4A), which is lowly expressed in gastric cancer cells and contributes to the development, progression, and chemoresistance of gastric cancer25–28, was predicted as a candidate of miR-147 and was selected for further confirmatory tests. We conducted luciferase reporter assay to explore whether miR-147 could directly target the 3′-UTR of PTEN. AGS and BGC-823 cells were cotransfected with miR-147 inhibitor or NC inhibitor and pGL3-PTEN-3′UTR Wt or pGL3-PTEN-3′UTR Mut. As shown in Figure 4B and C, the downregulation of miR-147 increased the luciferase activities of pGL3-PTEN-3′UTR Wt (p < 0.05) but not of pGL3-PTEN-3′UTR Mut in AGS and BGC-823 cells.

Figure 4

Phosphatase and tensin homolog (PTEN) is a direct target of miR-147 in gastric cancer. (A) Putative binding sites for miR-147 in the 3′-untranslated region (3′-UTR) of PTEN were identified through bioinformatics analysis. Mutated sites within the binding sites are shown. (B, C) AGS and BGC-823 cells were transfected with miR-147 or NC inhibitor along with pGL3-PTEN-3′UTR wild type (Wt) or pGL3-PTEN-3′UTR mutant (Mut). After 48 h of transfection, luciferase activities were determined using a Dual-Luciferase Reporter Assay system. *p < 0.05 compared with NC inhibitor. PTEN mRNA (D) and protein (E) expression in AGS and BGC-823 cells transfected with miR-147 inhibitor or NC inhibitor was analyzed through RT-qPCR and Western blotting analysis, respectively. *p < 0.05 compared with NC inhibitor.

To confirm that miR-147 regulates the endogenous expression of PTEN in gastric cancer, we performed RT-qPCR and Western blotting analysis to quantify the expression levels of PTEN mRNA or protein in AGS and BGC-823 cells transfected with miR-147 inhibitor or NC inhibitor. As presented in Figure 4D and E, miR-147 underexpression increased PTEN expression in AGS and BGC-823 cells at the mRNA (p < 0.05) and protein (p < 0.05) levels. These results collectively proved that PTEN is a direct target of miR-147 in gastric cancer.

Knockdown of PTEN Reverses the Effects of miR-147 Downregulation on Gastric Cancer Cells

We performed rescue experiments to explore whether PTEN is responsible for the functional roles of miR-147 in gastric cancer. We transfected AGS and BGC-823 cells with miR-147 inhibitor together with NC siRNA or PTEN siRNA. Western blotting analysis revealed that cotransfection with PTEN siRNA recovered the upregulation of PTEN protein caused by the miR-147 inhibitor in AGS and BGC-823 cells (p < 0.05) (Fig. 5A). The results of MTT assay, in vitro chemosensitivity assay, and flow cytometry analysis demonstrated that cotransfection with PTEN siRNA restored the functional effects of miR-147 underexpression on the proliferation (p < 0.05) (Fig. 5B), chemosensitivity to 5-FU (p < 0.05) (Fig. 5C), and 5-FU-induced apoptosis (p < 0.05) (Fig. 5D) of AGS and BGC-823 cells. These results suggested that miR-147 partly targets PTEN to affect the proliferation and chemosensitivity to 5-FU of gastric cancer cells.

Figure 5

PTEN knockdown restores the effects of miR-147 underexpression on gastric cancer cells. AGS and BGC-823 cells were transfected with NC inhibitor, miR-147 inhibitor + NC small interfering RNA (siRNA), or miR-147 inhibitor + PTEN siRNA. (A) Western blotting analysis was performed to quantify PTEN expression at 72 h posttransfection. *p < 0.05 compared with NC inhibitor. #p < 0.05 compared with miR-147 inhibitor + PTEN siRNA. (B) MTT assay was carried out to examine cell proliferation in indicated cells. *p < 0.05 compared with NC inhibitor. #p < 0.05 compared with miR-147 inhibitor + PTEN siRNA. (C) Cell chemosensitivity was assessed in the indicated cells using an in vitro chemosensitivity assay. (D) The rate of 5-FU-induced apoptosis in the indicated cells was evaluated using flow cytometry analysis. *p < 0.05 compared with NC inhibitor. #p < 0.05 compared with miR-147 inhibitor + PTEN siRNA.

miR-147 Targets PTEN to Regulate the PI3K/AKT Signaling Pathway in Gastric Cancer Cells

PTEN is a master negative regulator of the PI3K/AKT signaling pathway in gastric cancer29,30. We performed Western blotting analysis to detect the expression levels of PI3K, AKT, and p-AKT protein in AGS and BGC-823 cells transfected with miR-147 inhibitor along with NC siRNA or PTEN siRNA. The results showed that downregulation of miR-147 decreased PI3K and p-AKT expression and that total AKT expression was unaltered by miR-147 underexpression in AGS and BGC-823 cells (p < 0.05) (Fig. 6A and B). Additionally, cotransfection of PTEN siRNA restored the effects of miR-147 downregulation on PI3K and p-AKT expression in AGS and BGC-823 cells (p < 0.05). These results suggested that miR-147 regulates the PI3K/AKT signaling pathway in gastric cancer by targeting PTEN.

Figure 6

miR-147 regulates the PI3K/AKT signaling pathway in gastric cancer cells. (A, B) Western blotting analysis was performed to detect PI3K, AKT, and phosphorylated (p)-AKT expression in AGS and BGC-823 cells transfected with NC inhibitor, miR-147 inhibitor + NC siRNA, or miR-147 inhibitor + PTEN siRNA. *p < 0.05 compared with NC inhibitor. #p < 0.05 compared with miR-147 inhibitor + PTEN siRNA.

DISCUSSION

Numerous studies have demonstrated that miRNAs are involved in the sensitivity or resistance of multiple types of human cancers to chemotherapy27,31,32. Hence, a comprehensive understanding of the expression pattern and biological roles of chemoresistance-related miRNAs in gastric cancer might facilitate the development of novel therapeutic strategies to improve the efficacy of gastric cancer treatment. The results of this study revealed that miR-147 was significantly upregulated in gastric cancer tissues and cell lines. Downregulation of miR-147 inhibited the proliferation of gastric cancer cells in vitro. In addition, we found that underexpression of miR-147 enhanced the chemosensitivity of gastric cancer cells to 5-FU through promoting 5-FU-induced apoptosis. Furthermore, PTEN was identified as a direct target of miR-147 in gastric cancer. PTEN knockdown rescued the effects of miR-147 downregulation on the proliferation, chemosensitivity to 5-FU, and 5-FU-induced apoptosis of gastric cancer cells. We also found that miR-147 is involved in the regulation the PI3K/AKT signaling pathway in gastric cancer through targeting PTEN. These data provide evidence for the feasibility of combining 5-FU with miR-147 inhibitors in the chemotherapy of patients with gastric cancer.

miR-147 is aberrantly expressed in multiple types of malignant tumors. For example, miR-147 is underexpressed in the cancerous tissues and sera of patients with non-small cell lung cancer21. Low miR-147 expression is associated with tumor grade, lymph node metastasis, and tumor size. The overall survival of patients with non-small cell lung cancer and low miR-147 expression is considerably worse than that of patients with non-small cell lung cancer and high miR-147 expression. In addition, low miR-147 expression level is an independent prognostic factor for the poor prognosis of patients with non-small cell lung cancer21. miR-147 expression is also downregulated in a highly aggressive breast cancer cell line22 and hepatocellular carcinoma23. However, in our current study, we found that miR-147 expression is upregulated in gastric cancer tissues and cell lines. These findings suggested that the expression pattern of miR-147 is tissue specific and may be a promising prognostic biomarker of human cancer.

miR-147 may play tumor-suppressing roles in tumorigenicity and tumor progression. Zhang et al. reported that miR-147 overexpression inhibits cell growth and metastasis in breast cancer by regulating AKT/mTOR signaling22. Sui et al. found that in hepatocellular carcinoma, the upregulation of miR-147 targets HOXC6 to suppress cell proliferation, migration, and chemosensitivity23. Lee et al. showed that restoring miR-147 expression causes mesenchymal-to-epithelial transition (MET), attenuates cancer cell proliferation and invasion, promotes cell cycle arrest at G1, and reverses gefitinib resistance of colon cancer cells33. However, in our present study, we demonstrated that miR-147 plays oncogenic roles in gastric cancer by directly targeting PTEN and indirectly regulating the PI3K/AKT signaling pathway. These contradictory findings suggested that miR-147 acts as a tumor suppressor in certain cancers and as an oncogene in others.

The identification of miR-147 target genes is critical for understanding its biological roles in gastric cancer. In this study, PTEN was identified as a novel target of miR-147 in gastric cancer. PTEN, which is located on human chromosome 10q23, contains nine exons that encode a 403-amino acid protein and is mainly expressed in the cytoplasm34,35. An increasing number of studies reported that PTEN expression is downregulated in various human cancers, such as bladder cancer36, cervical cancer37, colorectal cancer38, ovarian cancer39, glioma40, breast cancer41, and prostate cancer42. PTEN plays essential roles in multiple biological processes, such as cell proliferation, cell cycle, apoptosis, metastasis, metabolism, differentiation, radioresistance, and chemoresistance43–47. The expression of PTEN is also found to be downregulated in gastric cancer and lymph node metastasis, invasion depth, growth pattern, histological classification, and age of gastric cancer patients25,48,49. Functional experiments have demonstrated that PTEN participates in the formation and progression of gastric cancer through the regulation of cell apoptosis, cell cycle arrest, proliferation, metastasis, and chemoresistance49–52. Given these previous findings and our present results, we recommend that further studies should investigate the potential of the miR-147/PTEN pathway, in combination with 5-FU, as a chemotherapeutic target in gastric cancer.

In conclusion, our current study revealed that miR-147 is upregulated in gastric cancer tissues and cell lines. In addition, the downregulation of miR-147 inhibits cell proliferation and enhances the chemosensitivity of gastric cancer cells to 5-FU through the cell apoptosis pathway. Furthermore, we identified PTEN as a direct target gene of miR-147 in gastric cancer. These data might help identify novel therapeutic strategy for the further treatment of patients with gastric cancer.