Patients and serum samples
CRC and para-carcinoma tissue samples were collected from seven patients diagnosed with primary CRC at the People's Hospital of Zhengzhou (Zhengzhou, China). The clinicopathological characteristics of the patients are presented in Table 1. The levels of CRNDE, miR-320a-5p, and APPL1 mRNA were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR). APPL1 protein expression levels were determined by western blotting. All samples were collected after receiving written informed consent and all procedures were performed with the approval of the internal review and ethics boards of the People's Hospital of Zhengzhou.
Construction of CRNDE-interference vector
CRNDE-interference vectors (5′-GATGTGTTTCAATCTAGATGC-3′) were constructed using pSicoR, following standard procedures for target gene identification, design, preparation and transfection of pcDNA3.1, and transfection using Lipofectamine® RNAiMAX (11668-027; Invitrogen, Carlsbad, CA, USA). Cells were divided into three groups: control, empty vector (EV [sh-CRNDE]), and short hairpin (sh)-CRNDE (interference vector [IV]). Transfection efficiency was determined by qRT-PCR.
miR-320a mimics were purchased from Hanbio Biotechnology Co., Ltd. (Shanghai, China). Cells were divided into three groups: control, empty vector (EV [miR-320a]), and miR-320a overexpression (OV). miR-320a expression levels were evaluated by qRT-PCR.
Cell culture
The human CRC cell lines, Lovo, HCT-116, COLO 205, HT-29, and SW480, and the normal colon epithelial cell line, NCM460, were purchased from the cell bank of the Chinese Academy of Sciences (Shanghai, China). The cells were cultured in RPMI 1640 medium (Gibco, Carlsbad, CA, USA) supplemented with 10% (v/v) fetal bovine serum (FBS), 10 U/mL penicillin, and 100 mg/mL streptomycin (Gibco) at 37°C with 5% CO2. CRNDE expression levels were determined by qRT-PCR and the protein expression levels of APPL1 were determined by western blotting.
Cell Counting Kit-8
Cells were seeded in a 96-well plate at 5 × 103 cells/mL in RPMI 1640 medium containing 10% FBS and were treated for 24, 48, or 72 h. To evaluate cell proliferation, 10 μL of Cell Counting Kit-8 solution was added to each well and the cells were cultured at 37°C for 4 h. Optical density was measured at 450 nm using a plate reader (Multiskan FC; Thermo Fisher Scientific, Waltham, MA, USA).
Transwell assays
Cells were cultured in serum-free smooth muscle cell medium (SMCM, 1101; ScienCell, Carlsbad, CA, USA) for 24 h before the experiment and were then resuspended in SMCM containing 1% FBS at 1 × 105 cells/mL. The cells were then seeded into transwell chambers and 0.75 mL of SMCM containing 10% FBS was added to the lower chambers of the 24-well plate. After culturing the cells in 5% CO2 at 37°C for 48 h, 1 mL of 4% formaldehyde was added to each well, and the plate was incubated at room temperature for 10 min for immobilization. After 30 min of incubation with 0.5% crystal violet (PAB180004; Bioswamp, Wuhan, China), the cells were observed under a microscope.
Flow cytometry
HCT-116 cells (5 × 104 cells/mL) were washed twice with phosphate-buffered saline (PBS). For apoptosis experiments, cells were resuspended in 200 μL of binding buffer and incubated with 10 μL of annexin V-FITC and 10 μL of propidium iodide (PI) for 30 min at 4℃ in the dark. This was followed by incubation with 300 μL of binging buffer. For cell cycle experiments, cells were fixed with 700 μL of anhydrous ethanol for 24 h and incubated with 400 μL of PI for 10 min. Data were analyzed using CytExpert software (Beckman Coulter, Brea, CA, USA).
qRT-PCR
Cells were extracted using TRIzol reagent according to the manufacturer’s instructions and cDNA was synthesized using a reverse transcriptase kit (639505; TAKARA, Osaka, Japan). qRT-PCR was performed with a real-time PCR system (CFX-Connect 96; BIO-RAD, Hercules, CA, USA) using a SYBR Green PCR Kit (KM4101; KAPA Biosystems, Wilmington, MA, USA). Each PCR reaction was performed in duplicate using the following conditions: denaturation at 95°C for 3 min; 39 cycles of 95°C for 5 s, 56°C for 10 s, and 72°C for 25 s; 65°C for 5 s; and 95°C for 50 s. The results were analyzed using the 2-△△Ct method. The PCR primers were designed by Nanjing Kingsy Biotechnology Co., Ltd. (Nanjing, China) and the sequences are listed in Table 2.
Western blotting
Protein extracts (20 μg) were prepared from lung tissue, separated by 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and transferred to polyvinylidene fluoride membranes (IPVH00010; Millipore, Burlington, MA, USA). Membranes were blocked with 5% milk in Tris-buffered saline (pH 7.6) containing 0.1% Tween 20 and incubated overnight at 4°C with specific primary antibodies against the following proteins: APPL1 (1:1,000, PAB33847, Bioswamp), Bax (1:1,000, PAB30040, Bioswamp), Bcl-2 (1:1,000, PAB30041, Bioswamp), cleaved caspase-3 (1:500, ab32042; Abcam, Cambridge, UK), and GAPDH (1:2,000, PAB36264, Bioswamp). After three washes with PBS/Tween 20, the membranes were incubated with horseradish peroxidase-conjugated secondary goat anti-rabbit IgG (1:20,000, PAB160011, Bioswamp) for 2 h at room temperature. Protein bands were visualized by enhanced chemiluminescence color detection (Tanon-5200; TANON, Shanghai, China) and analyzed using AlphaEase FC gel image analysis software (Alpha Innotech, San Leandro, CA, USA).
Luciferase reporter assay
HCT-116 cells were co-transfected with 50 nM miR-320a mimics and 200 ng of wild-type (WT) or mutant FOXO4-3′-UTR or 200 ng of WT or mutant APPL1-3′-UTR using Lipofectamine 2000 (Invitrogen) following the manufacturer’s instructions. After 48 h, the cells were processed using a Dual-Luciferase Reporter Assay System (Promega, Madison, WI, USA), and luciferase activity was measured using a GloMax20/20 Luminometer (Promega). Luciferase activity in HCT-116 cells was normalized to the Renilla/firefly luciferase signal.
Statistical analysis
Data are expressed as the mean ± standard deviation. Data between groups were compared using a Student’s t-test or one-way analysis of variance using SPSS 22 statistical software 9IBM, Armonk, NY, USA). P < 0.05 was considered statistically significant.