Clinical Specimens
35 pairs of GC patient specimens were used in the study. Patients with the following criteria were excluded: with any antitumor treatment; with other cancers diagnoses. The research was approved by the Ethics Committee for Clinical Research of the University hospital affiliated with Southeast University and the informed consent was acquired from every patient.
GC datasets
The TCGA-GC of 375 GC samples and 32 normal samples were acquired from the Cancer Genome Atlas (TCGA) (https://gdc-portal.nci.nih.gov/). The m6A readers expression of 5 GC datasets were obtained from the Gene Expression Omnibus (GEO) database (http://www.ncbi.nlm.nih.gov/geo/), including GSE66229 (South Korea, 300 cases of GC, 100 normal cases), GSE54129 (China, 111 cases of GC, 21 normal cases), GSE29998 (Singapore, 50 cases of GC, 49 normal cases), GSE64951 (USA, 63 cases of GC, 31 normal cases) and GSE96668 (United Kingdom, 49 cases of GC, 11 normal cases).
Cells
Human gastric cancer cells HGC-27, SGC-7901, BGC-823, and the human gastric mucosa epithelial cell line GES-1 were purchased from the Cellcook Biotech Co., Ltd., Guangzhou, China.
Cell culture
GES-1, BGC-823 and SGC-7901 cells were cultured in RPMI-1640 medium (Gibco, USA), while HGC-27 cells were cultured in MEM medium (Gibco, USA). All media were adding 10% fetal bovine serum (FBS) (Gibco, USA), penicillin (100 U/mL) and streptomycin (100 µg/mL) (Invitrogen, USA), which all cultured in the stable environment with 5% CO2 at 37°C.
Cell transfection
The short hairpin RNA (shRNA)-mediated knockdown of IGF2BP3 was performed to interfere with the expression of IGF2BP3. IGF2BP3 shRNA (shIGF2BP3, abbreviated, shI3) and shRNA control (shNC) were purchased by HANBIO (Shanghai, China). The shI3 and shNC were transfected into HGC-27-shI3 cells. The IGF2BP3 knockdown and control HGC-27 cells are named HGC27-shI3 and HGC27-shNC, respectively. MYC overexpression plasmid and vector control were synthesized by HANYANG (Suzhou, China). They were transfected into HGC27-shI3, HGC27-shNC cells. The MYC overexpression, control HGC27-shI3, blank control HGC27-shNC cells are named HGC-shI3 + MYC, HGC-shI3 + vector, HGC-shNC + vector, respectively. All the experiment procedures were operated according to the manufacturer’s instructions from the corresponding company.
RNA isolation and the quantificational real-time polymerase chain reaction (qRT‐PCR)
Total RNAs were extracted by using TRIzol reagent (Genstar, China), and then reverse‐transcribed to complementary DNA (cDNA) by using PrimeScript RT Reagent (Genstar, China). RNA expression levels were detected by qRT-PCR through using the SYBR Premix Ex Taq (Genstar, China) and analyzed by 2−ΔΔCt method, all the results were normalized by β-actin. The primer sequences were used in this study are listed in the Table 1.
Table 1 The sequence of primers
Gene
|
Primers
|
sequence
|
IGF2BP1
|
Forward primer
|
5'-CAAAGGAGCCGGAAAATTCAAAT-3'
|
|
Reverse primer
|
5'-CGTCTCACTCTCGGTGTTCA-3'
|
IGF2BP2
|
Forward primer
|
5'-AGTGGAATTGCATGGGAAAATCA-3'
|
|
Reverse primer
|
5'-CAACGGCGGTTTCTGTGTC-3'
|
IGF2BP3
|
Forward primer
|
5'-ACGAAATATCCCGCCTCATTTAC-3'
|
|
Reverse primer
|
5'-GCAGTTTCCGAGTCAGTGTTCA-3'
|
YTHDF1
|
Forward primer
|
5'-ATGTCGGCCACCAGCGTGGACA -3'
|
|
Reverse primer
|
5'-TCATTGTTTGTTTCGACTCTGC -3'
|
YTHDF2
|
Forward primer
|
5'-CCTTAGGTGGAGCCATGATTG-3'
|
|
Reverse primer
|
5'-TCTGTGCTACCCAACTTCAGT-3'
|
YTHDF3
|
Forward primer
|
5'-TGACAACAAACCGGTTACCA-3'
|
|
Reverse primer
|
5'-TGTTTCTATTTCTCTCCCTACGC-3'
|
MYC
|
Forward primer
|
5'-CGAACACACAACGTCTTGGAGC-3'
|
|
Reverse primer
|
5'-CTGCTTGGACGGACAGGATG-3'
|
β-actin
|
Forward primer
|
5'-TCTCCCAAGTCCACACAGG-3'
|
|
Reverse primer
|
5'-GGCACGAAGGCTCATCA-3'
|
Western blot (WB)
The process of the WB experiment was operated as described in the previous research [13]. The primary antibodies against IGF2BP3, MYC, Snail, N-cadherin, vimentin, mouse-anti-β-actin, Tubulin and the goat anti-rabbit/mouse horseradish peroxidase-conjugated secondary antibody (HRP) (goat-anti-rabbit) (goat-anti-mouse) were purchased from Cell Signaling Technology (CST, USA). The band densities of specific proteins were quantified by ImageJ software. The proteins were normalized to β-actin or Tubulin.
Cell Proliferation Assay
Cells (3000 cells/well) were seeded in the 96-well plate in 6 replicates, and incubated for 12h, 24h, 48h and 72h, respectively. After that, the proliferation viability of cells was measured by the CCK8 kit (malunion, China). The Optical density (OD) was detected at 450nm by a microplate reader.
Transwell Assays
The migration and invasion assays were operated with a 3422 Transwell chamber (Corning, USA) which were coated without the Matrigel mix (BD Biosciences, USA) (migration assay) or with the Matrigel mix (invasion assay). After the cells incubated for 24h, we used 4% paraformaldehyde to fix the cells located on the lower surface of chamber for 15 minutes. And then, the cells were stained with 0.1% crystal violet dye for 15 minutes. After that, the stained cells were photographed and the number of stained cells were calculated in five randomly selected fields.
RNA binding protein immunoprecipitation (RIP)
RNA immunoprecipitation experiments were operated by using RNA Immunoprecipitation (RIP) Kit (Merck Millipore, USA), and the operating steps according to the manufacturer’s instructions. The analysis of co-precipitated RNAs were detected by qRT‐PCR.
mRNA stability assays
The stability of MYC mRNA was determined by applying actinomycin D (ActD; Final concentration: 2.5 μg/mL; Selleck, USA) mRNA stability assays in HGC27-shI3, HGC27-NC cells. At the indicated time point, mRNA degradation was analyzed by quantitative RT-PCR as described above, normalized to β-actin. The half-life (t1/2) of mRNA was calculated.
Immunohistochemistry (IHC)
Immunohistochemistry was operated on the paraffin sections. And they were dewaxed, dehydrated and rehydrated ordinally. After washing with phosphate-buffered saline (PBS), the paraffin sections were adding citrate buffer and then performed with high pressure repairing antigen. Next, the paraffin sections were blocked endogenous peroxidase activity by adding 0.3% hydrogen peroxide. Then, washing with PBS 3 times. After that, the paraffin sections were blocked by adding 10% goat serum. Then the paraffin sections were incubated with the corresponding primary antibody at 4°C for 14-16 hours. Next, the paraffin sections were washed with PBS 3 times and were added with the anti-rabbit IgG-horseradish peroxidase (HRP) for 10 minutes, at room temperature. Then, the paraffin sections were washed with PBS 3 times again. After that, the paraffin sections were visualized by using 3,3'-diaminobenzidine tetrahydrochloride (DAB). The reaction was terminated when dyeing was appropriate. Then, washing with PBS 3 times again. After the paraffin sections were washed with PBS 3 times, the paraffin sections were counterstained with hematoxylin, washed with running water, dehydrated, and mounted with neutral gum.
Statistical analysis
The SPSS 22.0 software was used to analyze the data. The mean ± standard deviation (Mean ± SD) was applied to represent the data. The 2-△△Ct method was used to analyze the qRT-PCR results. The receiver operating characteristic (ROC) curve was applied to test the diagnostic ability, and the Kaplan-Meier (K-M) curves were used to evaluate the prognostic prediction. The difference of m6A readers expression based on the TCGA database was analyzed by Wilcox analysis via using R version 3.5.1. The comparison of data was analyzed by using variance analysis, chi-square test, or non-parametric test when appropriate. The correlation between the target genes was explored by Pearson correlation analysis. The test level was α=0.05 (two-sided), P-value < 0.05 represented that the differences were statistically significant.