Cell culture and human liver sample
Human liver cancer cell line Hep3B was cultured in RPMI 1640 (Sigma, USA) supplemented with 10% fetal bovine serum (FBS, Sigma), 100 U/mL penicillin, and 100 U/mL streptomycin at 37 °C with 5% CO2. Huh-7 cells were cultured in Dulbecco’s modification of Eagle’s medium (Sigma) with 10% FBS. Cells in the exponential growth phase were used in experiments.
All experiments involving human tissues were evaluated by the local ethics committee (Beijing You-an Hospital, Capital Medical University, Beijing, China, EC-B-031-A02-9.0). The sample was collected from a subject who provided informed consent for their tissue to be used for research purposes. For immunochemistry, normal liver tissue (n=13) and liver tumor tissue (n=25) were obtained as paraffin blocks and sectioned at 4 µm thicknesses. Normal and tumor tissues were evaluated by two pathologists. Tissues for Western blotting (n=4) and RT-PCR (n=3), which included liver cancer (C) and paired normal liver tissues (N), were frozen tissue samples. The patient characteristics are listed in Table S1.
Antibodies and reagents
An anti-marvelD3 antibody (ab118916), anti-Claudin 3 antibody (ab15102) and anti-GAPDH (ab6276) were purchased from Abcam (USA). An anti-E-cadherin antibody (#3195) and anti-vimentin antibody (#5741) were purchased from Cell Signaling Technology (MA, USA). An anti-NF-kB antibody kit (#9936) and anti-β-actin (#3700) antibody was purchased from Cell Signaling Technology. Horseradish peroxidase (HRP)-conjugated goat anti-mouse and goat anti-rabbit IgGs were purchased from Zhongshan Jinqiao (Beijing China). TGF-β1 (PeproTech, USA) was dissolved in citric acid (pH 3.0) at a concentration of 10 µg/mL, stored at -20°C, and diluted in culture medium to the required concentration of 10 ng/mL. NF-κB inhibitor BAY 11-7082 (HY-13453; MCE) were added to the culture medium at a final concentration of 20 µM in accordance with the manufacturer’s instructions.
siRNA-mediated knockdown of marvelD3 expression
siRNA knockdown was performed using siRNA ID stB0014718A (RiboBio, Guangzhou, China) to target the marvelD3-coding region and negative control siRNA (ID siN0000001-1-5). Cancer cells were transfected with 20 nM siRNA using LTX reagent (Invitrogen, USA) in accordance with the manufacturer’s instructions. The culture medium was replaced after 12 hours and subsequent assays were performed after 24 or 48 hours.
Plasmid transfection
The entire coding sequences of human snail and slug were inserted into the mammalian expression plasmid pcDNA3.1. Cells were transfected with the constructed plasmid using transfection reagent LTX (Invitrogen, USA) in accordance with the manufacturer’s instructions. The culture medium was changed at 6 hours after transfection and the cells were harvested at 24 or 48 hours after transfection for subsequent assays.
Cell survival assay and Transwell migration assay
The effect of marvelD3 on HCC cells viability was determined by MTS cell proliferation assay kit (Promega, Madison, WI, USA) in accordance with the manufacturer’s instructions. SiRNA-marvelD3 and siRNA-NC HCC cells (5 × 103 cells/well) were seeded into a 96‐well plate. The OD value was read after 24 and 48 h. For the migration assay, we used modified Boyden chambers with filter inserts (8 μm pore size). Approximately 1×105 cells in 200 μL of medium were placed in the upper chamber, and 1 ml of complete medium was placed in the lower chamber. After 12–36 h in culture, cells were fixed in 4% paraformaldehyde for 30 min and then stained with 0.05% crystal violet in deionized water for 2 h. Cells on the upper side of the filters were removed with cotton-tipped swabs and the filters were washed with PBS. Cells on the underside of the filters were viewed and counted under a microscope.
Wound healing assay
HCC cells were seeded into a six-well plate and cultured overnight. The next day, after reaching approximately ≥ 90% confluence, three linear wounds were created using a 200 µl pipette tip. Cells were washed with PBS and cultured for 24 h. Photographs of the wounded area were obtained immediately after making the scratch (0 h time point) and at 24 h to monitor the wounding healing capacity of the cells. The experiment was repeated at least once.
Real-time PCR (RT-PCR)
Total RNA was extracted from HCC cells and liver tissues using TRI Reagent (Sigma) in accordance with the manufacturer’s instructions. A total of 2 μg RNA was used for cDNA synthesis with a Reverse Transcription Kit (Roche, Germany) in a 20 μl reaction. Equal amounts of cDNA were subjected to PCR using the following conditions: initial denaturation at 95 °C for 10 min, followed by 40 cycles of 95 °C for 15 s and 60 °C for 1 min, and terminal extension at 72 °C for 5 min. Each sample was examined in triplicate. GAPDH was used as the internal control. Real-time PCR primers are listed in supporting Table S2. GraphPad Prism v7 (GraphPad Software, San Diego, CA, USA) was used to create histograms.
Western blotting
Proteins were extracted from HCC cells and fresh liver tissue by lysis in RIPA buffer with protease and phosphatase inhibitors (Roche, USA). Equal quantities of proteins were separated by 12 % SDS-PAGE and transferred onto a PVDF membrane (GE, USA) using a Bio-Rad wet transfer unit. After blocking with 5% (w/v) non-fat dried milk in TBST [25 mM Tris, pH 7.5, 150 mM NaCl, and 0.1% (v/v) Tween-20] for 1 h at room temperature, the membrane was incubated with a primary antibody overnight at 4 °C, followed by HRP-conjugated goat anti-mouse or goat anti-rabbit IgGs (1:5000) for 1 h at room temperature. Immunocomplexes on the membrane were visualized with Immobilon Western Chemiluminescent HRP Substrate (Millipore USA) using Image Lab Software (BIO-RAD).
Immunofluorescence (IF)
Treated HCC cells were washed three times in PBS, fixed for 30 min in 4% paraformaldehyde in PBS, and permeabilized for 10 min with 0.3% Triton X-100 in PBS. Non-specific binding sites were blocked by 60 min of incubation in 5% bovine serum albumin in PBS. Then, the cells were incubated with primary antibody against anti-E-cadherin or anti-vimentin (1:200) at 4 °C overnight. After three 5-min washes with PBS, the cells were incubated with a mixture of anti-rabbit Alexa fluor 488-conjugated secondary antibodies (1:200) for 2 h at room temperature. Following three 5-min wash with PBS, the cells were mounted on a slide in mounting medium with DAPI (Molecular Probe, USA). Cells were examined and photographed under a confocal microscope (FV 300, Olympus).
Immunohistochemistry (IHC)
Liver tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, and stained for routine histology. Sections were dewaxed in xylene and dehydrated in alcohol. Antigen retrieval was performed by microwaving in citric saline for 15 min. Thin sections were deparaffinized and treated with 0.3% hydrogen peroxide for 15 min to block endogenous peroxidase activity. The sections were blocked further in 3% bovine serum albumin, followed by incubation with a primary antibody against E-cadherin (1:400) or marvelD3 (1:500) for 20 h at 4 °C. After rinsing, the sections were incubated with a biotinylated secondary antibody for 60 min at room temperature. Protein expression was visualized by 3,3ʹ-diaminobenzidine tetrahydrochloride staining. The sections were counterstained with hematoxylin before dehydration for 30 s. Staining intensities were determined by measuring the integrated optical density (IOD) by light microscopy using Image-Pro v6.0.
Statistical analysis
All experiments were carried out at least three times. Data are represented as means ± SEM. Differences between groups were calculated using the Student’s t-test. Statistical significance was defined as P<0.05 for a two-tailed test. All statistical analyses were carried out with Graphpad Prism 7.0 software.