Patients
Patients diagnosed with prostate cancer were enrolled at the University of Hong Kong-Shenzhen Hospital. These patients (mean age of 65.3 years, age range of 59–70 years) underwent pelvic magnetic resonance imaging (MRI) and bone scan before prostate tumor biopsy. Immunohistochemical staining confirmed the diagnosis of prostate cancer. These patients were divided into two groups, namely, prostate cancer with bone metastases and prostate cancer without bone metastases, according to bone scan diagnosis. Informed consents were obtained from patients regarding the use of the prostate cancer tissue samples for this study. The project was approved by the University of Hong Kong-Shenzhen Hospital Research Ethics Committee (No. [2019]260). All the work was conducted in accordance with the Declaration of Helsinki (1964).
Total Rna Extraction And Sequencing
Total RNA extraction and sequencing
Total RNA was isolated from prostate cancer tissues using TRIpure Total RNA Extraction Reagent (ELK Biotechnology, Wuhan, China) according to the manufacturer’s protocol. RNA pellets were washed in 75% ethanol, air dried, resuspended in RNase-free water supplemented with RNase inhibitor (Thermo Fisher Scientific, Vienna, Austria) and stored at − 80°C. The RNA yield and purity were measured using an Agilent 2100 Bioanalyzer (Agilent Technologies Inc., California, America). Sequencing libraries were prepared at the Chi-biotech Corporation (Shenzhen, China) followed by sequencing with Illumina HiSeq2500. The quality of the microRNA sequencing reads was assessed with FastQC, and the reads were aligned with the human genome reference (GRCh38, Ensembl release 76) with bowtie. The expression of miRNAs was quantified using HTSeq version 0.6.1p1 according to miRbase (http://www.mirbase.org/) for human miRNAs.
Differential Expression Analyses Of Mirnas
DESeq2 (version 1.20.0) was used to analyze the differential expression of miRNAs. The Benjamini-Hochberg method was used to calculate false discovery rate (FDR)-adjusted p-values, accounting for multiple testing correction. miRNAs were considered differentially expressed when the FDR adjusted p-values were less than 0.01 and the fold-change was more than the threshold of 2. The miRTarBase database was used to predict miRNA target genes. The enrichment analysis used KOBAS annotation, which includes Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses and Gene Ontology (GO). Cytoscape software V3.2.1 was used to generate the miRNA-mRNA interaction network, and the data output was received in Excel spreadsheets.
Quantitative Reverse Transcription Pcr Validation Of Mirna
To validate the sequencing results, we assessed the miRNAs with differential expression levels in 20 prostate cancer samples (patients with bone metastases, n = 10, and patients without bone metastases, n = 10) using quantitative reverse transcription PCR (RT-qPCR). cDNA was synthesized from total RNA using the EntiLink™ 1st Strand cDNA Synthesis Kit (ELK Biotechnology, Wuhan, China). PCR was performed using EnTurbo™ SYBR Green PCR SuperMix (ELK Biotechnology). All reactions were incubated in a 96-well plate at 95°C for 3 min, followed by 40 cycles of 95°C for 10 s, 58°C for 30 s, and 72°C for 30 s. U6 was used as the internal control. The stem-loop primers were as follows: U6 (NR_004394.1), forward primer, CTCGCTTCGGCAGCACAT, and reverse primer, AACGCTTCACGAATTTGCGT; hsa-miR-145-5p (MIMAT0000437), forward primer, CAGTTTTCCCAGGAATCCCT, and reverse primer, CTCAACTGGTGTCGTGGAGTC. The quantification of miRNA expression was performed by the double delta Ct method.
Cell Culture And Mirna Mimic Transfection
The prostate cancer bone metastatic cell line PC-3 was maintained in Dulbecco’s modified Eagle’s medium (Gibco, California, America), including 10% FBS (Gibco), 100 U/mL penicillin, and 100 µg/mL streptomycin in a humidified CO2 incubator. Cells (3×105) were plated in 6-well plates and transfected with a hsa-miR-145-5p mimic (forward: GUCCAGUUUUCCCAGGAAUCCCU, and reverse: CUGGUCUUUUGGGUCCUUUGGGU) and control mimic (forward: UUUGUACUACACAAAAGUACUG and reverse: AAACAUGAUGUGUUUUCAUGAC) using Lipofectamine 2000 (Invitrogen, California, America) according to the manufacturer’s protocol.
Proliferation, Migration And Invasion Assay
The cell migration activity after miRNA mimic treatment was investigated using an in vitro proliferation, migration and invasion assay. Cells were seeded in a 96-well plate for proliferation assay. CCK8 (Cell Counting Kit-8, Biosharp) reagent was added to cell culture and absorbance was measured at 450 nm after 1 h of incubation. For wound healing migration assay, 3× 105 cells/well were grown in a 24-well microplate for 16–18 h. The cells were then serum-starved overnight. The centers of the cell monolayers were then scraped in a straight line by pipette tip to create a wound, and then, the cells were washed with PBS. Medium was added, and the cells were incubated for 24 h. The wound closure was photographed by an inverted microscope with a digital microscope camera. The symmetry of the median distance between both borderlines was used to calculate the migration index. Invasion assays were carried out in transwell chambers separated by a semipermeable membrane with an 8-µm pore size (Corning). After transfection as described above, the cells were detached from the culture plates and resuspended in serum-free medium containing 0.1% BSA. The cells were allowed to migrate to the lower chamber for 24 h at 37°C in 5% CO2. The cells were removed from the chamber, the medium was removed by washing with PBS, and the cells were fixed with paraformaldehyde for 20 min, washed with PBS again, and stained with 0.1% crystal violet for 10 min; PBS was used to wash the extra crystal violet from the cells, and the side on which the cells were not seeded was photographed under the inverted microscope.
Western Blotting Analysis
Protein was extracted from cells with radioimmunoprecipitation assay (RIPA) buffer and analyzed by western blotting analysis. The proteins were resolved by SDS/PAGE with 10% Bis-Tris (Invitrogen, America) and transferred to nitrocellulose membranes. The membrane was incubated in a 5% solution of nonfat milk for 1 h at 4°C. After overnight incubation with the primary antibody (Abcam, America) at 4°C (Table 1), the blots were washed in Tween-TBS for 20 min and incubated with the secondary antibody. The blots were washed in T-TBS for 20 min and detected with an electroluminescence kit (ASPEN, Wuhan, China). GAPDH staining was used as the loading control.
Table 1
The information of the primary antibodies
Name | Information | ID |
MMP9 | Abcam | ab137867 |
MMP2 | Abcam | ab97779 |
E-cadherin | Abcam | ab1416 |
caspase 9 | Abcam | ab115792 |
GAPDH | Abcam | ab8245 |
Statistical analysis
All experiments were performed in triplicate incubations. Data were analyzed as mean ± SD of three independent experiments. Data were analyzed by two-tailed unpaired Student's t-test between any two groups. A value of P < 0.05 was considered statistically significant. Statistical tests were performed using GraphPad software v. 4.1 (CA, USA).