Clinical sample collection
BCs tissues and the paired adjacent tissues were obtained from 28 BCs patients (22 males and 6 females) who admitted into the First Affiliated Hospital of Jiamusi University from January 2013 to January 2015 with a mean age of 65 ± 5.67 years. A 4-year follow-up study was performed to record the prognosis of patients at a 3-month interval. The patients were divided into T1 to T4 stages according to the Tumor-Node-Metastasis (TNM) staging, with 7 in T1, 13 in T2, 5 in T3, and 3 in T4. All included patients had neither pre-surgery treatment history nor chemoradiotherapy history, and they were pathologically diagnosed as primary BCs free of other diseases. The tumor tissues and the adjacent tissues (at least 3 cm away from the tumor tissues) were resected during surgery and preserved in liquid nitrogen. The demographic characteristics of the respondents are exhibited in Table 1.
Table 1
Clinical feature of included patients
Item | Group | n |
Gender | Male | 22 |
Female | 6 |
Age | ≤ 60 | 5 |
> 60 | 23 |
TNM stage | T1 | 7 |
T2 | 13 |
T3 | 5 |
T4 | 3 |
History of smoking | yes | 25 |
no | 17 |
Note: TNM, Tumor Node Metastasis. |
miRNA microarray analysis
Four patients in T1, T2, T3 or T4 stage (one in each stage) were enrolled for miRNA microarray analysis. The tumor and the paired adjacent tissues from patients were collected for total RNA extraction using TRIzol Reagent (Invitrogen, Carlsbad, CA, USA). Total RNA was concentrated in isopropanol, and then the RNA purity was detected using NanoDrop 2000C (Thermo Fisher Scientific Inc., Waltham, MA, USA) and the RNA quality was determined by formaldehyde denatured agarose gel electrophoresis. Then, 50 µg total RNA was purified using a Taqman miRNA ABC purification kit (Thermo Fisher) and hybridized with the beads. The beads were then washed with magnet, and the miRNAs were eluted 3 times to collect the miRNAs. Thereafter, the collected miRNAs were labeled using a miRNA Complete Labeling and Hyb Kit (Agilent, USA). In brief, 100 µg total RNA was incubated in 10 µg Labeling Spike-In at 37℃ for 30 minutes, treated with DMSO at 16℃ for 2 hours, dried in a vacuum concentrator at 45℃ for 3 hours, and then treated with Hybridization Mixture and Hyb labeling at 55℃ for 20 hours for hybridization. Then, the miRNAs were further hybridized with Human miRNA Microarray Release 14.0,8 (Agilent, USA) and scanned using a SureScan Dx Microarray Scanner (Agilent, USA). The obtained data were subjected to Quality Center analysis and normalization to produce the heatmap for differentially expressed miRNAs.
Reverse transcription quantitative polymerase chain reaction (RT-qPCR)
Total RNA for cells or tissues was extracted using TRIzol Reagent and reversely transcribed into cDNA using a PromeScriptTMRT Master Mix Kit (Takara Bio, Jan) and amplified. Relative gene expression was quantitated using a SYBR®Premix Ex Taq™II Kit (Takara Bio, Jan). The qPCR was performed on a Mx3005P System (Stratagene, USA). Quantification of each sample was repeated by three times. Relative expression was evaluated using the 2−ΔΔCt method with U6 and GAPDH as internal references. Table 2 exhibits the primer sequences.
Table 2
Primer sequences for RT-qPCR
Gene | Primer sequence (5'-3') |
miR-381 | F: TATACAAGGGCAAGCTCUCTGT |
R: TGCGGGTGCTCGCTTCGGCAGC3 |
BMI1 | F: TGGATCGGAAAGTAAACAAAGAC |
R: TGCATCACAGTCATTGCTGCT |
GAPDH | F: GGGAGCCAAAAGGGTCATCA |
R: TGATGGCATGGACTGTGGTC |
U6 | F: CTCGCTTCGGCAGCACA |
R: AACGCTTCACGAATTTGCGT |
Cell culture and transfection
Human bladder cell lines T24 and RT4, normal bladder epithelial cell line SV-HUC-1, and HEK-293T cells were acquired from ATCC (Manassas, USA). Cells were cultivated in Dulbecco's modified Eagle's medium with 10% fetal bovine serum (FBS, all from Gibco Company, Grand Island, NY, USA) at 37℃ with 5% CO2. The miR-381 mimic and BMI1-overexpressing vectors (BMI1-OE) were synthesized by GenePharma Co., Ltd. (Shanghai, China). To minimize the off-target effects, 3 RNA fragments were loaded into the vectors and transfected into cells. Then cells were plated into 24-well plates once the cell confluence reaching 70%. miR-381 mimic and BMI1-OE vectors were transfected into T24 and RT4 cells in line with the protocols of the Lipofectamine 2000 (Invitrogen). After 6 hours, the fluorescence expression in cells was observed under a fluorescence microscope (Olympus Optical Co., Ltd, Tokyo, Japan)
Cell proliferation by the Cell Counting Kit-8 (CCK-8) method
A total of 100 µL cell suspension was loaded on 96-well plates and pre-incubated for 24 hours. Next, each well was loaded with 10 µL CCK-8 reagent, and then the plates with cells were further incubated for 12, 24, 48 and 72 hours. Then the optical density at 450 nm was evaluated using a microplate reader (SoectraMax iD5, Molecular Devices, USA). The CCK-8 kit was from Dojindo Laboratories (Kumamoto, Japan).
Cell migration by scratch test
Guide lines were produced on the back side of 6-well plates at a 1-cm interval, and 5 × 105 cells were added into the plates. On the second day, a pipette was used to produce a scratch perpendicular to the back side guide lines, and the scratched cells were washed away by phosphate buffer saline (PBS). Then the plates were loaded with serum-free medium and cultured at 37℃ with 5% CO2. Twenty-four hours later, the cells were observed and photographed under a microscope (CX22, Olympus). The scratch area was analyzed using the Image J software (version 1.48, NIH, USA). Relative migration distance (%) = (0 h scratch area − 24 h scratch area)/0 h scratch area [11].
Cell invasion by transwell assay
Matrigel was diluted in serum-free DMEM, and then 100 µL Matrigel was loaded onto each apical chamber at 37℃ for 4 hours. Then, cells were resuspended in 10% FBS to 5 × 105 cells/mL, and each apical chamber was loaded with 200 µL cell suspension, while each basolateral chamber was loaded with 600 µL cell medium (containing 5 µg/mL fibronectin). Then transwells were incubated at 37℃ for 20 hours, and the non-invaded cells in the apical chambers were removed, while the invaded cells in each well were stained with 500 µL 0.1% crystal violet at 37℃ for 30 minutes. Then the number of invaded cells were observed and counted under the microscope with 5 random fields included.
Flow cytometry
In short, 27 mL ddH2O was used to dilute 3 mL Binding Buffer (10 ×), and cells in each group were resuspended in 1 mL 1 × Binding Buffer, centrifuged at 300 g for 10 min to discard the supernatant, and resuspended in 1 mL 1 × Binding Buffer again till a density of 1 × 106 cells/mL. Next, each tube was loaded with 100 µL cells and then 5 µL Annexin V-fluorescein isothiocyanate (FITC) for 10 min of reaction, and then with 5 µL propidium iodide (PI) in the dark for 5 min. The apoptosis was determined using an Annexin V-FITC/PI Apoptosis Kit (Solarbio Science & Technology Co., Ltd., Beijing, China) and run on a flow cytometer (Attune Nxt, Thermo Fisher) within an hour.
Xenograft tumors in nude mice
A total of 48 specific-pathogen-free nude mice (4–6 weeks old, 20 ± 2 g) purchased from Vital River Laboratory Animal Technology Co., Ltd. (Beijing, China) were randomly allocated into 6 groups, 8 in each. Then, each mouse was subcutaneously injected with 4 × 106 T24 or RT4 cells with stable miR-381 mimic or mimic control transfection, or cells with BMI1-OE and vector control transfection. The volume (V) of xenograft tumors was calculated as the following formula every 7 days: V = (L × W2)/2, where ‘L’ indicates the length while ‘W’ indicates the width [12]. On the 28th day after cell implantation, mice were euthanized by overdose of pentobarbital sodium (150 mg/kg), and the tumors were taken out and weighed.
Dual-luciferase reporter gene assay
The binding relationship between miRNA and mRNA was predicted on StarBase (http://starbase.sysu.edu.cn/). The 3’UTR sequence of BMI2 and miR-381 was inserted into pMIR-REPORT™ luciferase reporter vector (Thermo Fisher) using Lipofectamine 3000 (Invitrogen) and then transfected into HEK293T cells. Cells were lysed 24 hours later, and the luciferase activity was determined using a Dual-Luciferase Reporter Assay System (Promega Corporation, WI, USA) [13]. Three independent experiments were performed.
Western blot analysis
Radio-Immunoprecipitation assay cell lysis buffer (Amresco Inc., Texus, USA) was used to collect total protein, which was then and centrifuged at 800 g at 4℃ for 5 min to collect the cells. Then the cells were ice-bated in a 5-fold volume of lysis buffer for 10 min, and then centrifuged at 12,000 g at 4℃ for 10 min to collect the supernatant. The protein was run on SDS-PAGE and transferred to polyvinylidene fluoride membranes (EMD Millipore). Subsequently, the membranes were blocked with 5% skimmed milk and then incubated with the primary antibodies against RhoA (1:5000, ab187027), p-RhoA (1:1000, ab41435), ROCK2 (1:5000, ab71598) and β-actin (1:1000, ab8227) (Abcam Inc., Cambridge, MA, USA) at 4℃ for 16 hours, and then with the secondary antibody (1:3000, ab205718) at room temperature for 2 hours. The immunoblotting image were visualized using the Image J software (Version 1.8.0, National Institute of Health, USA). Three independent experiments were performed.
Statistical analysis
SPSS 22.0 (IBM Corp. Armonk, NY, USA) was used for data analysis. Data were in normal distribution according to Kolmogorov-SmiRnov test and are exhibited as mean ± standard deviation (mean ± SD). Differences in multiple groups were analyzed using one-way or two-way analysis of variance (ANOVA). Tukey’s multiple comparisons test was used for the post-hoc test after ANOVA analysis. Survival curve was drawn using the Kalpan-Meier method and analyzed using the log rank test. p was obtained by two-tailed tests and p < 0.05 was regarded statistically significant.