Cell lines and reagents
Huh7, HepG2 and QJY‐7703 cells cells were purchased from TongPai Biotechnology (Shanghai, China) and were maintained in Dulbecco’s Modified Eagle Medium (DMEM, WISENT, CA, USA) containing 10% fetal bovine serum (FBS) (ExCell Bio, China). Recombinant human IL-2 was purchased fromSigma-Aldrich LLC.
Patients and Primary human TAMs isolation and culture from tissue specimens
Primary human HCC specimens were collected from the patients who suffered from hepatectomy at Yijishan Hospital of Wannan Medical College. Patient’s consent was obtained and the procedures were approved by the Ethics Committee of Yijishan Hospital. Human fresh tumor samples were minced with scissors. The macrophages were isolated and cultured as previously described (refer to Tumor Microenvironment Study Protocols by Springer). TAMs were treated with (20ng/ml) for 24 hours before the supernatants were collected.
Isolation and labelling of exosomes
Exosomes were isolated from the cell culture media with Total Exosome Isolation Reagent (Thermo Scientific) according to the manufacturer's instructions. The purified exosomes were then labelled with the red fluorescent linker PKH26 (Umibio) according to the manufacturer's directions.
Exosomes and TAMs cells observed by transmission electron microscopy
The samples were fixed with 2% glutaraldehyde and 2% paraformaldehyde in 0.1 mol/L sodium cacodylate buffer at pH 7.3 for 3 hours at room temperature. After air drying, samples were mounted on specimen stubs and visualized using transmission electron microscope.
RNA isolation and qPCR
Total RNA was isolated from cells or mouse tissues using Trizol reagent (Invitrogen), following the manufacturer's instructions. The RNA was then analysed using real‐time qPCR with SYBR Green PCR Master mix (Roche Applied Science, Mannheim, Germany). The relative gene expression was normalized to U6.
agomiR and antagomiR transfection
The constructs of miR-375 from GenePharma (Shanghai) were utilized, and transfection was performed at a concentration of 200 × 10-3 M concentration using Lipofectamine 3000.
Western blot analysis
Exosomes or cells were lysed in RIPA containing protease inhibitors. A total of 20 μg of exosomes were separated by SDS‐PAGE and transferred to PVDF membranes (Millipore, Bedford, MA, USA). The membranes were then incubated with antibodies CD63 (1:1000; Abcam, Cambridge, MA, USA), Calnexin (1:1000; CST,USA), PCNA (1:1000; CST, USA), cyclin D1 (1:1000; CST, USA) E‐cadherin (1:1000; CST, USA), N‐cadherin (1:1000; CST, USA), tubulin (1: 5000, Abcam, Cambridge, UK ),Bax (1:1000; CST,USA), Bcl-2 (1:1000; CST,USA), MMP-2 (1: 1000, Proteintech, Chicago, Illinois, USA), and MMP-9 (1: 1000, Proteintech, Chicago, Illinois, USA).
Quantification of apoptosis by flow cytometry
Apoptosis was determined using an Annexin V-FITC/PI apoptosis detection kit (eBioscience, USA). For both approaches cells were assessed via flow cytometry.
CCK8 assay
HepG2 cells were added to 96-well plates and cultured for 24, 48, 72, 96, 120 or 144 hours. Then, CCK-8 reagent was added to cells in serum-free medium for 2 hours, followed by measurements of absorbance at 450 nm.
EDU Assays
For EDU assays, HepG2 Cells were added to 24-well plates, and after incubation after 24 h with exosomes , EDU (Sigma-Aldrich) staining was conducted based on the protocols.
Migration assay
Cell invasion assays were conducted on 24-well Transwell cell culture chambers with 8-μm sized pores without precoated Matrigel (Corning, USA). HepG2 cells were suspended in 500 μl of medium and added to the upper inserts. After 24 hour of incubation, the cells remaining in the upper chamber were removed, and the cells on the lower surface of the chamber were fixed with 4% paraformaldehyde and stained with 0.5% crystal violet.
Scratch test
A scratch assay was performed to assess cell migration in vitro. First, HepG2 cells were seeded in 6‐well plates until a confluent monolayer was formed. Then, upon confluence, cells were scratched with a 10 μL sterile pipette tip. Pictures were then taken of the scratch at different time‐points under the microscope. The cell migration rate was calculated as (width at 0 hours–width at 24 hours)/width at 0 hours.
Experimental animals
Xenograft mouse models
All animal experiments were performed in accordance with the approval of the Animal Ethics Committee of Youjiang Medical University for Nationalities. QJY‐7703 cells in logarithmic growth phase were prepared into cell suspension. Axillary subcutaneous injection of cells (5 × 105) was performed BALB/c nude mice (4-6 weeks-old, n = 6 per group) accompanied with exosomes (40 ug/mL) injection via the tail vein every 2 days for 7 times. Tumor volumes were measured after 5 days every 10 days until mice were sacrificed 30 days later.
The liver and lung metastasis experiment
The 6–8 weeks old nude mice were divided into three randomized groups (n = 12 per group), and QJY‐7703 (5 × 105) alone or with ExoTAM (40 ug/mL) or with ExoTAM-IL2 (40 ug/mL) in 100 ul were injected into the mice via tail vein every 2 days for 7 times. 30 days after cell injection, the mice were euthanized and were necropsied to assess metastatic burden. The tumor tissues, liver and lung tissues of mice were further examined by H&E and IHC staining.
TUNEL staining
Apoptotic cells in tumor tissues were detected by TUNEL assay according to the standard procedure. After fixed in 4% paraformaldehyde, the tissues were stained by 50 μL TUNEL reaction mixture (Roche) for 60 min at 37°C. The cell nucleus was stained with DAPI and observed through the Olympus microscope.
Bioinformatics analysis
The Cancer Genome Atlas (TCGA) databse and UALCAN database which is built on PERL-CGI with high quality graphics using javascript and CSS were used to explore the expression of miR-375 in HCC patients.
Statistical Analysis
Data are presented as mean ± SD. Comparisons between groups were performed using one-way ANOVA, and Tukey’s procedure for multiple range tests was performed. All experiments for cell cultures were performed independently at least three times and in triplicate each time. Value of P<0.05 was considered to be significant.