Cell culture and Clinical specimens
The human breast cancer cell lines (BT-549, T-47D, MDA-MB-468, MDA-MB-231, MCF-7), the noncancerous breast epithelial cell line HBL-100, and the human embryonic kidney (HEK) 293T cells were purchased from the American Type Culture Collection (ATCC). All cell lines were cultured following the instructions of ATCC.
Blood samples were obtained from the Central Hospital of Wuhan. Eighty breast cancer patients and 80 healthy controls were included in the study. Twenty paired blood samples were collected, including preoperative and postoperative blood from breast cancer patients. The newly diagnosed breast cancer patients had received no chemotherapy or radiotherapy before sample collection. All healthy subjects did not have any diseases or injuries. Peripheral blood samples from participants were collected in tubes containing EDTA and were processed within 4 h by centrifugation at 1000 g for 15 min at 4°C. The supernatant was then gently transferred to a fresh RNase-free 1.5-ml tube and cryopreserved at − 80°C immediately. The study was approved by the Ethical and Scientific Committees of the Central Hospital of Wuhan, and all participants provided informed consent during enrollment.
Rna Isolation And Qrt-pcr
RNA was extracted by TRIzol reagent (Invitrogen, Carlsbad, CA, USA). BCAR4 was measured by SYBR Green (Applied Biosystems, Carlsbad, CA, USA) in StepOne™ Real-Time PCR System (Applied Biosystems). MiR-644a was measured with a bulge-loop miRNA real-time PCR kit (RiboBio, Guangzhou, China). GAPDH was used as the endogenous control for BCAR4 and U6 for miR-644a. The relative expression of BCAR4 and miR-644a was calculated by 2–△△Ct in breast cancer cells and by 2–△Ct for that in plasma. The primers for BCAR4 were as follows: sense, ATA CAA TGG CGT AAT CAT AGC, and antisense, AGA CAT TCA GAG CAA GAC A. GAPDH: sense, GGG AGC CAA AAG GGT CAT, and antisense, GAG TCC TTC CAC GAT ACC AA.
Cell Transfection
MiR-644a mimic, or miR-644a inhibitor, small interfering RNAs (siRNAs) targeting BCAR4, and their respective negative controls were all obtained from RiboBio (Guangzhou, China). Transfection was performed using ExFect® Transfection reagent (Vazyme, Nanjing, China) according to the manufacturer’s guidelines.
Colony Formation Assay
MCF-7 or MDA-MB-231 cells were seeded into 12-well plates with 500 cells/well and incubated for ten days. Plates were then gently washed with PBS and stained with 0.1% crystal violet (Beyotime, Nantong, China). A colony containing more than 50 cells was counted as one colony.
Wound Healing Assay
For cell mobility assay, MCF-7 or MDA-MB-231 cells were seeded into 6-well plates ( 4×105 cells/well). An artificial wound was made by scratching the confluent cell monolayer with a sterile 200 µl pipette tip 24 h after transfection. Then, cells were incubated in a medium containing 1% FBS. After scratching for 0 h and 48 h, wound healing images were photographed at magnification 100x using an IX81 microscope (Olympus, Tokyo, Japan). The migration rate was determined by ImageJ software.
Transwell Assay
To further investigate breast cancer cell migration and invasion, transwell chambers (Corning, NY, USA) were used. MCF-7 or MDA-MB-231 cells were detached and suspended in 200 µL serum-free medium 24 h after transfection. A total of 2×104 cells were added into the upper chamber for migration assay or a total of 3×104 cells were added into the upper chamber coated with Matrigel (BD Biosciences, CA, USA) for invasion assay. The bottom chambers were filled with the 600 µL complete culture medium. After being cultured for 48h, cells that migrated or invaded the lower filter surfaces were fixed and then stained with 0.1% crystal violet (Beyotime). Images (magnification, x100) were taken from each membrane, and the numbers of migrated or invaded cells were counted using an IX81 microscope (Olympus).
Drug Sensitivity Assay And Cck8 Assay
The DOX (Selleck Chemicals) sensitivity of cells was detected using the CCK8 kit (Beyotime) by measuring the IC50 value (the concentration of DOX resulted in 50% decline of the absorbance compared with control). MCF-7 or MDA-MB-231 cells were seeded into 96-well plates with 5000 cells/well and incubated with different concentrations of DOX(5 nM, 10 nM, 30 nM, 100 nM, 200 nM, 500 nM, 1000 nM and 2000 nM). After treatment for 48 h, CCK-8 solution was then added to wells and incubated for another 4 h. The absorbance was recorded at 450 nm by the EnSpire multimode reader (PerkinElmer, Waltham, MA).
Western Blot Assay
Western blot analysis was performed according to the description previously [20]. The following primary antibodies were used: rabbit polyclonal anti-ABCB1(1: 500, Proteintech, Rosemont, USA), rabbit monoclonal anti-CCR7 (1:10000, Abcam, Cambridge, MA), mouse monoclonal anti-ERK1/2 (1:2000, Proteintech), mouse monoclonal anti-P38 MAPK (1: 2000, Proteintech). rabbit monoclonal anti-phospho-p44/42 MAPK(Erk1/2)(Thr202/Tyr204, 1: 1000, Cell Signaling Technology, Danvers, MA, USA), rabbit monoclonal anti-phospho-p38 MAPK (Thr180/Tyr182, 1 : 1000, Cell Signaling Technology), mouse monoclonal anti-E-cadherin (1:2000, Proteintech), mouse monoclonal anti-Vimentin(1:5000, Proteintech), rabbit polyclonal anti-VEGF(1 : 1000, Proteintech). Rabbit polyclonal anti-GAPDH(1:5000, Proteintech) was used as an internal control.
Luciferase Reporter Assay
For the BCAR4 luciferase reporter assay, pRL-TK-BCAR4 or pRL-TK-BCAR4 mutant vectors and pGL3 control (Promega, Madison, WI) were transfected into HEK293T cells along with miR-644a mimic or miR-644a inhibitor using ExFect® Transfection reagent (Vazyme) according to the instructions of the manufacturer. For miR-644a target gene CCR7 luciferase reporter assay, pRL-TK-CCR7-3΄UTR or pRL-TK- CCR7-3΄UTR mutant vectors and pGL3 control (Promega) were transfected into HEK293T cells along with miR-644a mimic or miR-644a inhibitor using ExFect® Transfection reagent (Vazyme). The luciferase activity was measured 48 h after transfection using the Dual-Glo luciferase reporter assay system (Promega) according to the guidelines of the manufacturer. Luminescence values were recorded by a Victor X2 multilabel reader (PerkinElmer).
In Vivo Assay
Female athymic four-week-old BALB/c nude mice were purchased from HFK Bio-Technology Co. Ltd. (Beijing, China). A total of 5×106 MDA-MB-231 cells, resuspended in Opti-MEM, were injected into the mammary fat pad. Tumor volume was analyzed as V = D × d2 × 0.5 (D, the longer diameter; d, the shorter diameter). When the tumor reached about 60 mm3, the mice were divided into a si-control group (n = 5) and a si-BCAR4 group ( n = 5) randomly. In vivo si-BCAR4 or the control (1nmol / 20g body weight) was directly administered into the implanted tumor two times per week for three weeks. One month after the first injection of si-BCAR4 or the control, all mice were anesthetized with 1% pentobarbital sodium. The tumors, lungs, and livers were obtained and then fixed in formalin for hematoxylin and eosin (HE) staining or immunohistochemistry. The rabbit polyclonal anti-CCR7 (1:200, Proteintech) was used to determine CCR7 expression. The mouse monoclonal anti-E-cadherin (1:1000, Proteintech), mouse monoclonal anti-Vimentin (1: 1000, Proteintech), rabbit polyclonal anti-VEGF (1:200, Proteintech) was used to detect E-cadherin, Vimentin and VEGF expression respectively.
Statistical analysis
All statistical analyses were performed using SPSS 22.0 software. The one-way analysis of variance (ANOVA), χ2 test or the student’s t-test was carried out for comparison between groups. All experiments were independently repeated at least three times. P value < 0.05 represents statistically significance. *P < 0.05, ** P < 0.01, ***P < 0.001.