There are 24 RCC specimens and paired adjacent normal tissue samples (5 cm far away from the RCC tissue) from the Department of Urology, Peking University Shenzhen Hospital (Shenzhen, China). All patients have signed the informed consents. And the research was approved by the ethics committee of the Peking University Shenzhen Hospital. The clinical feature of 24 patients are listed in Table I. Once the specimens were resected from the patients, they were immersed in RNAlater® RNA Stabilization Agent (Qiagen, Hilden, Germany). And then frizzed in liquid nitrogen and kept in reserve at −80°C.

The human embryo kidney cells (293-T) and RCC cell lines (786O, ACHN and Caki-1) are used in this research from the Guangdong and Shenzhen Key Laboratory of Male Reproductive Medicine and Genetics (Shenzhen, China). The cells were seeded and grown in the 10cm-petri dish, including 90% Dulbecco's modified Eagle's medium (DMEM; Invitrogen Life Technologies, Carlsbad, CA, USA), 10% fetal bovine serum (FBS; Invitrogen Life Technologies), 1% antibiotics (100 U/ml penicillin and 100 mg/ml streptomycin; Gibco, Thermo Fisher Scientific, Inc., Waltham, MA, USA) and 1% glutamine. And they were placed in 5% CO₂ incubator at 37°C. For the upregulation and downregulation of miR-23a-5p, the synthesized miR-23a-5p mimic, inhibitor, negative control (NC), inhibitor negative control (Shanghai GenePharma, Co., Ltd., Shanghai, China) were respectively transfected into cells using Lipofectamine® 2000 (Invitrogen Life Technologies) and Opti-MEM® I Reduced Serum Medium (Gibco) according to the manufacturer's instructions. The efficiency of transfection was measured by quantitative polymerase chain reaction (qPCR). The sequences were present in Table II.

TRIzol reagent (Invitrogen Life Technologies) was used to extract RNA from the specimens and the RNeasy Maxi kit (Qiagen) was used to purify the RNA according to the protocol. Then the concentration of RNA was measured by NanoDrop 2000c (Thermo Fisher Scientific, Inc.). Synthesis of cDNA with reverse transcriptase was performed with the miScript II RT kit (Qiagen). qPCR was performed to detect the expression level of miR-23a-5p with miScript SYBR®-green PCR Kit (Qiagen) on the Roche lightcycler 480 Real-Time PCR System following the protocol. The 10-µl reaction mixture contained 5 µl 2X QuantiTect SYBR-Green PCR Master mix, 3.7 µl RNase-free water, 1 µl cDNA template, 0.4 µl specific miRNA primer and 10X miScript Universal Primer. U6 was used as the internal control. The forward primer of miR-23a-5p was: 5′-GGGGUUCCUGGGGAUGGGAUUU-3′ and the reverse primer was universal primer which was provided by the miScript SYBR®-green PCR kit. The forward primer of U6 was 5′-CTCGCTTCGGCAGCACA-3′ and reverse primer was 5′-ACGCTTCACGAATTTGCGT-3′. The ΔΔCq method was used to analyze the expression levels of miR-23a-5p in specimens and cell lines.

The transwell assay was used to prove the migration and invasion of the 786O and ACHN cells. According to the requirements of the specification, the transwell chamber inserts (BD Biosciences, Franklin Lakes, NJ, USA) with Matrigel were used to assess invasion ability. The cells were transfected with miR-23a-5p mimic, inhibitor, NC or inhibitor NC with Lipofectamine® 2000. After transfected by 24 h, approximately 1×104 cells were seeded in the each upper chamber and the bottom of the inserts was incubated in the medium containing 10% FBS. The cells were stained with crystal violet in the bottom of chamber and observed by a microscope after 48 h incubation.

The wound scratch assay was also used to prove the migration of the 786O and ACHN cells in vitro. Approximately 3×105 cells were inoculated in each well of the 6-well plate. 24 h later, they were transfected with miR-23a-5p mimic, inhibitor, NC or inhibitor NC with Lipofectamine® 2000. The sterile 1 ml pipette tip was used to scratch a vertical horizontal line. The images of the scratches were captured by a digital camera system at 0, 12 and 24 h. The assay was done in triplicate and repeated at least three times.

Cell Counting Kit-8 (CCK-8) assay. The proliferation ability of the ACHN and 786O cells was depend on the resule of the CCK-8 (Beyotime Institute of Biotechnology, shanghai, China). After plated in 96-well plate by 24 h, the cells were transfected following the manufacturer's instructions. It's necessary to culture for 30 min in the dark place at room temperature after added CCK-8 to each well. The optical density (OD) of each well was measured by the ELISA microplate reader (Bio-Rad Laboratories, Inc., Hercules, CA, USA) at a wave length of 450 nm (with 620 nm as the reference wave length) at 0, 24, 48 and 72 h with the CCK-8 according to the protocol.

The viability of the ACHN and 786O cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide [Methylthiazolyldiphenyl-tetrazolium bromide (MTT); Sigma-Aldrich, St Louis, MO, USA] assay. The cells were transfected with miR-23a-5p mimic, inhibitor, NC or inhibitor NC after appropriate cell seeded in the 96-well plate for 24 h. 4 days later, 20 µl MTT (5 mg/ml) was added into the each well. Then continued to incubate for 4 h, discard supernatant, and added 100 µl dimethylsulfoxide (DMSO; Sigma, Shanghai, China). Next, the 96-well plate was shock in a reciprocating decolorization shaking table (TSB-108; Qilinbeier, Jiangsu, China) for 10 min in a dark condition. Finally, the OD value of each well was measured by the ELISA microplate reader (Bio-Rad Laboratories, Inc.) at a wave length of 595 nm (with 620 nm as the reference wave length).

The flow cytometry assay was used to analyze the apoptotic rates of 786O and ACHN cells in vitro. Appropriate cells were plated in 6-well plate and then transfected following the manufacturer's instructions. 48 h later, all cells were harvested and washed twice with 4°C. After that, the cells were resuspended in 100 µl 1*binding buffer. And then 5 µl Annexin V-FITC (Invitrogen Life Technologies) and 5 µl propidium iodide (PI; Invitrogen Life Technologies) were added into the experimental group. Stained for 15 min in the dark place at room temperature, and then added 400 µl binding buffer to each tube. Finally flow cytometry (EPICS, Xl-4; Beckman Coulter, Inc., Brea, CA, USA) was used to analyze the apoptotic rate.

All data are presented as the mean ± standard deviation from above independent experiments. The statistical significance was determined with Student's t-test. Paired t-test was used to compare the expression levels of miR-23a-5p in matched tumor/normal tissues. And the SPSS 23.0 statistical software package (IBM SPSS, Armonk, NY, USA) was use to statistical analysis. P<0.05 was considered to indicate a statistically significant difference. (*P<0.05, **P<0.01, ***P<0.001).

The Fig. 1A shows the relative expression level of miR-23a-5p (Log2 (T/N)). And the expression level of miR-23a-5p in RCC tissues (7.574±0.609) was obviously higher than adjacent normal tissues (1.000±0.317) in the Fig. 1B (P=0.004). The above result also appeared in cell line. The result in cell line demonstrated that relative expression of miR-23a-5p was higher in 786O (1.506±0.101, P=0.000), ACHN (1.426±0.081, P=0.000) and Caki-1 (1.254±0.030, P=0.000) than 293T (1.000±0.048), which showed in Fig. 1C.

RT-qPCR was performed to detect whether the relative expression level of miR-23a-5p was changed by transfecting miR-23a-5p mimic or inhibitor. The results showed that the expression levels of miR-23a-5p were 111.843 times higher (786O cell, P=0.000) and 98.082 times higher (ACHN cell, P=0.000) in cells transfected with miR-23a-5p mimic vs negative control (NC) after 24 h while the expression levels of miR-23a-5p were 0.243 times higher (786O cell, P=0.000) and 0.233 times higher (ACHN cell, P=0.000) in cells transfected with miR-23a-5p mimic vs negative control (NC) after 24 h. The results are shown in Fig. 1D (786O) and Fig. 1E (ACHN).

CCK-8 assay was designed to assess the proliferation ability of the ACHN and 786O cells. The result demonstrated that the upregulation/downregulation of miR-23a-5p could promote/inhibit proliferation of the ACHN and 786O cells. The proliferation of the 786O and ACHN cells was upregulated by 9.311% (P=0.027), 20.333% (P=0.014), 30.333% (P=0.000) (Fig. 2A) and 13.271% (P=0.016), 19.311% (P=0.006), 21.055% (P=0.001) (Fig. 2C) in CCK-8 after transfected with miR-23a-5p mimic at 24, 48, 72 h, while the proliferation of the 786O and ACHN cells was downregulated by 9.176% (P=0.022), 8.051% (P=0.019), 15.023% (P=0.007) (Fig. 2B) and 15.001% (P=0.040), 14.811% (P=0.008), 26.267% (P=0.001) (Fig. 2D) in CCK-8 after transfected with miR-23a-5p inhibitor at 24, 48, 72 h.

To detect the mobility of the ACHN and 786O cells, wound scratch assay and transwell assay were performed. The result of scratch assay was showed that the migratory ability of ACHN cells was upregulated by 64.018% (P=0.008) in miR-23a-5p mimic group while the migratory ability was downregulated by 47.801% (P=0.001) in miR-23a-5p inhibitor group. And the result in 786O cells was similar to result in ACHN cell, showed that the migratory ability was upregulated by 20.793% (P=0.041) in miR-23a-5p mimic group while the migratory ability was downregulated by 26.608% (P=0.005) in miR-23a-5p inhibitor group. The above results showed in Fig. 3.

The results of transwell assay were performed in Fig. 4. As shown in Fig. 4A, the invasive ability of ACHN cells was upregulated by 28.631% (P=0.028) in miR-23a-5p mimic group while the invasive ability of ACHN cells was downregulated by 61.812% (P=0.012) in miR-23a-5p inhibitor group. In addition, the invasive ability of 786O cells was upregulated by 12.433% (P=0.027) in miR-23a-5p mimic group while the invasive ability of 786O cells was downregulated by 13.070% (P=0.015) in miR-23a-5p inhibitor group (Fig. 4C). And the result of transwell migration assay displayed that the migratory ability of ACHN cells was upregulated by 40.149% (P=0.025) in miR-23a-5p mimic group, and the migratory ability of ACHN cells was downregulated by 49.896% (P=0.006) in miR-23a-5p inhibitor group (Fig. 4B). And in 786O cells, the result showed that the migratory ability was upregulated by 49.878% (P=0.010) in miR-23a-5p mimic group while the migratory ability was downregulated by 68.778% (P=0.002) in miR-23a-5p inhibitor group (Fig. 4D).

The cell viability was performed by MTT assay. The result revealed that the relative viability of 786O cells transfected with miR-23a-5p inhibitor or inhibitor NC was 0.835±0.056 vs. 1.000±0.085 (P=0.000) (Fig. 5A) while the relative viability of ACHN cells was 0.814±0.094 vs. 1.000±0.103 (P=0.000) (Fig. 5B). However, there is no difference between the mimic group and NC group for both viability of 786O and ACHN cells (P>0.05).

The apoptotic rate was performed by flow cytometry assay. The results demonstrated that the apoptotic rate of ACHN cells transfected with miR-23a-5p mimic or NC was 23.733±3.011% vs. 35.467±4.636% (P=0.007) (Fig. 6A) while the apoptotic rate of 786O cells was 7.123±2.816 vs. 19.623±6.767% (P=0.037) (Fig. 7A). Besides, the apoptotic rate of ACHN cells transfected with miR-23a-5p inhibitor or inhibitor NC was 40.000±20.548 vs. 21.533±14.476% (P=0.036) (Fig. 6B) while the apoptotic rate of 786O cells was 26.967±9.351 vs. 18.070±7.122% (P=0.031) (Fig. 7B). The results revealed that upregulation of miR-23a-5p inhibited ACHN and 786O cell apoptosis while downregulation of miR-23a-5p could induce cell apoptosis in RCC.