Cell culture and treated
BMECs were cultured with Dulbecco's Modified Eagle Medium: Nutrient Mixture F-12 (DMEM/F12) (11330032, Gibco, California, USA) containing 10% fetal bovine serum (FBS; 26140079, Gibco), Penicillin-Streptomycin Solution (100 U/ml each of penicillin and streptomycin) (C0222, Beyotime, Shanghai, China) as previous reports[16].
For the experiment of sodium acetate treatment, BMECs were planted into 6-well plates and cultured with DMEM/F12 containing 10% FBS. After 12 h, the cells were starved of FBS for 12 h, and then treated with sodium acetate supply (AS+, final concentration is 12.00 mmol/L) or sodium acetate depletion (AS-) for 24 h, the medium of each group was collected for the testing of TG secretion and the cells were collected for Western blotting (WB) or Co-Immunoprecipitation (Co-IP). For the experiment of gene function evaluation, BMECs were first treated with gene overexpression or silencing and then treated with AS + or AS-.
Western blotting (WB)
The WB was completed with normally procedure. The total protein concentrations of each group sample was tested by BCA Protein Assay Kit (P0012S, Beyotime). About 30 µg of protein in each group sample was separated with 10% SDS-PAGE gel and then transferred onto the polyvinylidene fluoride (PVDF) membrane (FFP24, Beyotime). The PVDF membrane was blocked with TBSTw (ST671, Beyotime) solution containing 5% bovine serum albumin (BSA, ST025, Beyotime), and then incubated with primary antibody (diluted with blocking solution). The membrane was washed three times with TBSTw, and then incubated with HRP-conjugated secondary antibody (diluted with blocking solution). Then the membrane was washed three times with TBSTw, and visualized with Super ECL Plus (P0018M, Beyotime). The primary antibodies used in this experiment were as following: anti-β-Actin (1: 1000, #4970, Cell Signaling Technology, Massachusetts, USA), anti-SREBP1 (1: 1000, ab191857, Abcam, Cambridgeshire, UK), anti-ARA160 (TMF1) (1:500; sc-398411, Santa Cruz Biotechnology, California, USA), anti-ACC (1: 1000, #3662S, Cell Signaling Technology, USA), anti-FAS (1: 1000, ab22759, Abcam, UK), anti-SCD (1: 1000, ab23331, Abcam, UK), anti-FABP3 (1: 1000, ab45966, Abcam, UK), anti-Lamin B1 (1: 1000, ab16048, Abcam, UK), anti-β-Tubulin (1:500; sc-5274, Santa Cruz Biotechnology, USA), anti-Myc (1:1000, AM933, Beyotime), anti-Flag (1:1000, AF519, Beyotime).
Triglyceride (TG) secretion
The secretion of TG was evaluated by measuring the concentration of TG in the collected medium. The content of triglyceride (TG) in the medium was tested using the Triglyceride test kit (BC0625, Solarbio Science & Technology Co., Ltd, Beijing, China) according to the manufacturer’s instructions.
Immunofluorescence (IF)
The experiment of IF was completed as previously reported[17]. The cells were planted on cover slips in 6-well plates and normal cultured. After 12 h, the cells treated with AS + orAS- or/and gene overexpression or silencing. The cell crawling were made as previously reported[18]. The primary antibodies used in this study were anti-TMF1 and anti-SREBP1 and the secondary antibodies were goat-anti-mouse Alexa fluor 488-conjugated IgG (1:500, bs-0296G-AF488, bioss, Beijing, China) and goat-anti-rabbit Alexa fluor 647-conjugated IgG (1:500, bs-0295G-AF647, bioss, China). The nucleus is stained using 4', 6-diamidino-2-phenylindole (DAPI; C1002, Beyotime) or Propidium Iodide (PI; P3566, Invitrogen, California, USA). The fluorescence was observed with laser scanning confocal microscopy (LEICA, Germany).
Plasmid construction and cell transfection
The overexpression plasmid of TMF1-Myc or SREBP1-Flag was constructed as previously reported[19]. The specific primers using in this research were showed in Table 1. The eukaryotic expression plasmids used in this study were pCMV-C-Flag (D2632, Beyotime) and pCMV-C-Myc (D2672, Beyotime).
Table 1
Primer sequences used for plasmid construction
Gene
name
|
Primer sequence (5'-3')
|
Forward primer
|
Reverse primer
|
TMF1
|
TCCCCCGGGATGAGCTGGTTCAACGCCTCCCAG (the Smal I site is underlined)
|
GCTCTAGAACTGAGCCTTTGTCTTAGAAGTTC (the Xbal I site is underlined)
|
SREBP1
|
TCCCCCGGGATGGACGAGCCACCCTTCAACG (the Smal I site is underlined)
|
GCTCTAGAGCTGGAGGTCACAGTGGTCCCAC (the Xbal I site is underlined)
|
For the experiment of gene overexpression, BMECs were planted into 6-well plates and normal cultured. After 12 h, the medium was changed with OPTI-MEM medium (11058021, Gibco, USA), and the overexpression plasmid (SREBP1-Flag or TMF1-Myc) was transfected with Lipo6000™ Transfection Reagent (C0526, Beyotime) according to the manufacturer’s instructions. The empty plasmids of pCMV-C-Flag or pCMV-C-Myc were also transfected as control.
Small interfering RNA (siRNA) transfection
The specific siRNA of TMF1gene, SREBP1 gene and negative control (NC) used in this study were synthesized by GenePharma Co.,Ltd (GenePharma, Shanghai, China). The sequences of siRNA used in this research were shown in Table 2. The si-TMF1, si-SREBP1 and NC were transfected using Lipo6000™ Transfection Reagent. The experimental process was the same as that of overexpression plasmid transfection and it was according to the manufacturer’s instructions of Lipo6000™ Transfection Reagent.
Table 2
Gene name
|
siRNA sequence (5’-3’)
|
TMF1
|
Sense
|
GCCCAGAAGUCUAUUGACATT
|
Antisense
|
UGUCAAUAGACUUCUGGGCTT
|
SREBP1
|
Sense
|
CCUAUUUGACCCACCCUAUTT
|
Antisense
|
AUAGGGUGGGUCAAAUAGGTT
|
Negative control
|
Sense
|
UUCUCCGAACGUGUCACGUTT
|
Antisense
|
ACGUGACACGUUCGGAGAATT
|
Nuclear and cytoplasmic protein extraction
The treated cells were harvested and the nuclear and cytoplasmic protein were extracted using Nuclear and Cytoplasmic Protein Extraction Kit (P0027, Beyotime) according to the manufacturer’s instructions. The Lamin B1 and β-Tubulin were used as the marker of nuclear protein and cytoplasmic protein, respectively.
Co-Immunoprecipitation (Co-IP)
BMECs were treated with no transfected, transfected with TMF1-Myc or/and SREBP1-Flag. Then the cell lysis of each group was collected with cell lysis buffer for western and IP (P0013, Beyotime) containing 1 mM Phenylmethanesulfonyl fluoride (PMSF) (ST506, Beyotime). The experiment of Co-IP was completed using the Protein A + G Agarose (P2012, Beyotime) according to the manufacturer’s instructions. The primary antibody used for Co-IP in this research was anti-TMF1 or anti-Myc and the antibodies used to test the immunoprecipitate were as follows: anti-TMF1, anti-Myc, anti-Flag and anti-SREBP1.
Statistical analysis
The data was analyzed using GraphPad Prism 7 software and reported as mean ± standard deviation (n = 3). p < 0.05 was considered statistically significant. Grey-scale scanning of WB band and the co-localization of IF were analyzed with ImageJ2X software. All data of this study were averaged from three independent experiments.