Cell lines and culture
American Type Culture Collection (ATCC, Manassas, VA, USA) was the source of glioma cell lines: U87, U251, H4, A172, U118, LN229, SHG-44 and GL261. Cell culture was performed in Dulbecco’s modified Eagle’s medium (DMEM) with 10% fetal bovine serum (FBS), 100 U/mL penicillin and 100 μg/mL streptomycin (HyClone, Thermo, USA) at 37°C and 5% CO2. NHAs (Normal human astrocytes) were procured from Lonza (Switzerland) and cultured as per supplied instructions.
Human glioma samples
Glioma tissues (n = 40) and neighboring healthy tissues (n = 40) were surgically excised at The People’s Hospital of China Medical University and the First Hospital of China Medical University. Table 1displays the clinicopathological features of the patients. Regular follow-up was performed for patients along with informed consent. Other data included relapse-free survival and overall survival (OS). This work received approval from the ethics committee of The People’s Hospital of China Medical University and the First Hospital of China Medical University.
Immunohistochemistry(IHC)
In accordance with previous works[25, 26], staining of tissues was performed with a SETDB1 antibody (Sigma-Aldrich, USA). The scoring of cells was performed in accordance with the following guide: 0 (no positive staining); 1 (1 to 25% positive cells); 2 (26 to 50% positive cells); 3 (51 to 75% positive cells); and 4 (> 75% positive cells). The scoring for staining intensity was performed as follows: 0, negative; 1, weak; 2, moderate; and 3, high. The formula for SETDB1-positive cells was as follows: staining intensity score ×percentage. This score involved both the nucleus and cytoplasm and was analyzed by two pathologists.
Cell migration and invasion assay
The migration assay used Falcon cell culture inserts from BD (Franklin, USA). The invasion assay utilized a BioCoat™ Matrigel™ Invasion Chamber (BD) in accordance with the instructions of the manufacturer. A phase contrast microscope was utilized to count cells; the average of 5 various fields/well was considered.
MTS analysis
A 96-well plate seeded with cells at 5000 cells/well. AMultiskan™ GO Microplate Spectrophotometer (Thermo Fisher Scientific) was employed to measure the absorbance at 570 nm for three independent assays.
RNA extraction and real-time PCR
Real-time PCR was performed as previously described[27, 28]. Briefly, TRIzol (Invitrogen, USA) was utilized for the extraction of total RNA. cDNA was synthesized with thePrimeScript™ RT reagent kit (Takara, Dalian) in accordance with the instructions of the manufacturer. SYBR Premix ExTaq II (Takara, Dalian) was utilized for real-time PCR of this cDNA on an ABI PRISM 7300 (Applied Biosystems, USA) to analyze the chemokines of the immune system. GAPDH was used to normalize mRNA levels. The primers used are listedin Table 2.
Western blotting
Western blotting was performed as previously described[29, 30]. Briefly, cell lysis was performed with the RIPA buffer protein extraction reagent (Pierce, Rockford, IL, USA) containing a protease inhibitor cocktail (Roche, USA). The proteins were resolved by 10% SDS-PAGE followed by transfer to polyvinylidene fluoride (PVDF) membranes (Sigma-Aldrich). Next, the membranes were blocked using 5% bovine serum albumin (BSA) and incubated with primary antibodies at 4°C overnight. Appropriate secondary antibodies were later added and then visualizedby using an ECL chemiluminescence kit. The primary antibodies used are listed as follows: SETDB1 (HPA018142, Sigma-Aldrich), cleaved caspase 3 (9661, Cell signaling technology), cleaved caspase 8 (9748, Cell signaling technology), slug (9585, Cell signaling technology), vimentin (5741, Cell signaling technology), E-cadherin (14472, Cell signaling technology), mTOR (2983, Cell signaling technology), p-mTOR (5536, Cell signaling technology), AKT (4685, Cell signaling technology), p-AKT (4060, Cell signaling technology), CSF-1 (3155, Cell signaling technology), β-actin (3700, Cell signaling technology).
Cell isolation and differentiation
The preparation of human monocytes from buffy coats of healthy volunteers was performed using Ficoll-Hypaque (Pharmacia Corporation) for 50 min at 400 g. Twenty-four-well plates were seeded with 2×106 cells/mL in RPMI 1640 medium containing 10% heat inactivated human AB serum, 50 U of penicillin/mL, 50 U of streptomycin/mL, 2 mM L-glutamine, and 100 ng/mL human M-CSF (which allows differentiation into macrophages). Warm medium was used to gently wash away non-adherent cells 6 days post-culture. CD14+ macrophages were found to account for greater than 95% of the adherent cells. The activation of these monocytes to macrophages in vitro involved the treatment of 2×106 cells/L with 25 μg/mL lipopolysaccharide (LPS, Sigma-Aldrich) to produce M1-polarized macrophages and 45 ng/mL recombinant human interleukin-4 (IL-4; R&D) to produce M2-polarized macrophages. Flow cytometry was employed to detect the formation of macrophages. For the following in vitro assays, cells were cultured for 24 hours with RPMI media minus supplements and meticulously washed with PBS prior to the experiments.
Clone formation assay
Six-well plates were used to plate single-cell suspensions at a density of 1,000 cells per plate. Every 3 days, the culture medium was replaced. After allowing 2 weeks for clone formation, fixation and staining of the clones was performed using 0.1% crystal violet/40% methanol. Microscopy was performed to countcolonies with >50 cells/colony.
Animal experiments
The syngeneic glioma mouse model was generated in accordance with previous reports[31, 32]. Briefly, 2% isoflurane in O2 was used to sedate C57BL/6J mice (4-6weeks old). the addition of 5 × 105 GL261-EV andGL261-SETDB1cells in 100 μL of PBS was performed followed by subcutaneous injection in the flanks of C57BL/6J mice.The mice were sacrificed after 6 weeks and tumor weights were assessed.
For the subcutaneous model, the addition of 5 × 105 U251-EV, U251-SETDB1, U87-shCon or shSETDB1 cells in 100 μL of PBS was performed followed by subcutaneous injection in the flanks of nude mice. The mice were sacrificed 15 days and tumor weights were assessed. The mice were kept at the Mouse Experimentation Core premises of the China Medical University.
Statistical analysis
The mean ± standard deviation (SD) was used to represent the data of triplicate assays. Student’s t-test was applied to assess significant differences between groups. Repeated measures analysis of variance was performed to assess variations between tumor parameters (growth rate and cell growth) of the animals.