Cells culture
Two NSCLC cell lines (A549, H1299) was purchased from the Cell Bank of the Chinese Academy of Sciences (Shanghai, China). NSCLC cells were maintained in DMEM (Gibco, Grand Island, NY, USA) supplemented with 10% fetal bovine serum (FBS; Gibco), penicillin (100 U/ml) and streptomycin (100 µg/ml) (Beyotime Biotech, Haimen, China) in humidified air at 37 °C with 5% CO2.
Knockdown/ overexpression of ANGPTL4 in NSCLC
To knock down ANGPTL4 expression, siRNA (Thermo Fisher Scientific) was transfected using RNAiMax (Invitrogen, Carlsbad, CA) according to the manufacturer’s recommendations. The sequence of the siRNAs was referred to existing reports. 13 Control cells were transfected with scrambled siRNA (Thermo Fisher Scientific). Overexpression of ANGPTL4 Cells were transfected in A549 cells (Santa Cruz, USA) to increased the level of ANGPTL4(S-5’-TCTCTCACCGGGTATGAGCGGTGCTCCGACGGCC-3’, AS-5’-GTGTCTTAATTAACTAGGAGGCTGCCTCTGCTGC-3’). Full-length cDNA encoding human ANGPTL4 were cloned into the vector plasmid (Shanghai Genechem Co., Ltd).
Glutamine-deprivation cell model
Glutamine deprivation cell model was established, remove normal DMEM, and wash normal cells or transfect cells with PBS. Adding DMEM (ThermoFisher Science, A14431) which without glutamine. In addition, 10% DFBS (Gemini Bio Products, Sacramento, California, USA) was added to the medium. The cells were cultured in this medium for 24 hours. After the cells adapted to the medium, they were passaged normally and continued to be used.
Cell proliferation assay with cell counting Kit-8 (CCK-8)
96-well plate was used to implant cells. The initial cell concentration was 5000 cells/pore, and the cell proliferation activity was measured by CCK-8 (Beyotime Biotech, Haimen, China). CCK-8 reagent was added to the pore after 24, 48, 72 and 96 hours of cell growth. The cells were cultured in cell culture box for 1.5 hours. Absorption was measured at 450 nm to investigate the cell proliferation activity.
Animal and tumor model
Six- to eight-week male nude mice were obtained from the Hebei Medical University experimental animal center. The mice were housed in a specific pathogen-free facility with free access to normal chow and water. Individual nude mice were inoculated subcutaneously with A549 cells (1 × 106 cells in 0.1 ml of PBS) on the right leg. When a tumor volume reached ~ 50 mm3, individual mice were randomized and treated intravenously with 0.1 ml of 5% glucose solution through the caudal vein as a vehicle, 10 µg liposomeencapsulated pshRNA-Con or pshRNA- ANGPTL4. Their body weights and tumor growth were measured every day, and the tumor volumes (V) were calculated using the formula: V = a × b2/2, where a and b are the largest and smallest tumor diameter, respectively. The mice were sacrificed 24 hours after the final treatment. Each experiment was performed twice.
ATP and lactate production
Normal or transfected cells were inoculated into 6-well plates. After washing with PBS, the cells were digested with 0.25% trypsin and the protein content was quantified by BCA kit. The ATP (Biovision, K354-100) and lactic acid (Biovision, K462) content in cells and tumor model in mice were measured by spectrophotometer and commercial kit.
Isotope tracing metabolomics of glutamine and FAO
The isotope tracing metabolomics was used. We used DMEM medium that was glucose- and glutamine-free (Gibco, Thermo Fisher Scientific, USA) which supplemented with 5 mM 13C5-glutamine (Sigma) and 13C16-palmitate. Following 16 hours of incubation, cells were harvested and the metabolites extracted with ice cold methanol and measured by LC/MS as described
Gene detection and western blotting
Total RNA was extracted from cells using TRIzol reagent (Thermo Fisher Scientific). The purity of RNA was determined by NanoDrop ND-1000 spectrophotometer (Thermo Scientific) qPCR was conducted using the appropriate primers and a Bio-Rad CFX96 system with SYBR green to determine the mRNA expression levels of genes incells. GAPDH was used as endogenous controls and further analyzed by the 2∆DDCT method. All the primers used for qPCR are listed in the supplement data. Statistical analysis was performed on the fold change
Total proteins were isolated from A549 and H1299 cells and dissolved in Ripa buffer which containing protease inhibitor (sigma, USA). The total protein concentration was determined by BCA analysis kit (Rockford Pierce, Illinois, USA). Total protein samples (30 mg) were analyzed by 10% SDS-PAGE gel and transferred to PVDF membrane. After the blocking procedure, the cell membrane was incubated overnight with primary antibody and secondary antibodies. Then, visualized in Imager (Bio-Rad) using ECL system (Thermo Fisher Scientific, 34095). The following antibodies were used: ANGPTL4 (1:5000, abcam, MA, USA), GLS (1:1000, abcam, MA, USA),CPT1 (1:1000, abcam, MA, USA), GAPDH (1:5000, abcam, MA, USA)
Statistical Analyses
All experimental results were analyzed by SPSS 17.0 software and expressed as mean ± SEM. Standard ANOVA procedures followed by multiple pairwise comparison adjusted with Bonferroni corrections were performed for cell viability assays. Unpaired Student’s t-tests were used to analyse all the other results. Significance was considered at p < 0.05.