Patients and samples
Breast cancer tissues and adjacent non-cancerous Tissue samples and clinicopathologic data were obtained from the Breast Cancer Research Center Biobank (BCRC-BB), Iran . All the patients were diagnosed with BC and no chemotherapy or radiotherapy was done before the operation. Specimens were immediately frozen into liquid nitrogen and stored at -80 ̊ C. Informed consent forms were provided for each subject and the study protocol was approved by the research committee at Tarbiat Modares University.
Cell culture and transient transfection
Human breast cell lines, namely, MCF7, SKBR3, MDA-MB-231 (obtained from the Pasteur Institute, Iran) were cultured in HDMEM medium (Gibco), containing 10% FBS (Gibco), and 100 U/ml penicillin, 100 µg/ml streptomycin(Sigma) followed by incubation in 37 ̊ C in with 5% CO2.
Full-length Linc-Pint cDNA was amplified and cloned into pCDNA3.1(+) expression vector (Promega, Madison, WI, USA) at the provided restriction sites. The accuracy of the recombinant vector was confirmed by sequencing.
Cell line were cultivated in complete medium without antibiotics overnight, and transfected with TurboFect reagent (Thermo Fisher Scientific), following the manufacturer's instruction after reaching proper confluency.
RNA extraction and cDNA synthesis
Total RNA was extracted from BC tissues and cell lines using RiboEx reagent (GeneAll) and quantified with agarose gel electrophoresis and Nanodrop instrument. In order to remove genomic DNA contamination, DNaseI treatment was performed at 37 ̊ C for 30 minutes followed by heat and EDTA inactivation. Reverse transcription was done using 1µg total RNA, Random hexamer, oligo-dT mix primers, and Prime Script II Reverse transcriptase(Takara, Japan) at 42 ̊ C for 70 min, subsequently RT inactivation at 72 ̊ C for 10 min. Besides, for miR detection, polyA tail was added to the 3’ end of RNAs before cDNA synthesis (polyA polymerase, NEB, UK).
RT-qPCR
RT-qPCR was performed using BioFACT™ 2X Real-Time PCR Master Mix in StepOne system (Applied Biosystems, USA). Transcriptional levels of target genes were measured in duplicate and normalized to Beta-2-Microglobulin (B2M) and U48, as reference genes, following the ΔΔCt formula. Primer sequences are listed in Table1.
Cell cycle assay
The cells were transfected with Linc-Pint-variant D or mock control vectors using TurboFect reagent. The cells were trypsinized and harvested 36 hrs after transfection, and centrifuged at 12000 rpm for 5 minutes, then washed in cold PBS twice. Subsequently, fixing with 70% ice-cold ethanol (Bidestan, Iran) and stained with PI (Sigma, USA)/RNase A (Thermo scientific, USA) staining solution following incubation at 37 ̊ C for 30min away from light. The samples were subjected to BD Flow Cytometer (BioScience, San Diego, CA, USA). The test was performed in duplicate and results were analyzed by flowing software version 2.5.0.
Scratch Assay
The MCF7 cells were grown in 24-well plates as 80% confluent. Thereafter, the cells were wounded with a 100-μl pipette tip and then transiently transfected with Linc-Pint containing or empty vectors. The cell migration was photographed at 0, 24, and 48 h after transfection.
Dual-Luciferase Reporter Assay
PsiCHECK-2 dual luciferase vector (Promega) was used to clone the Linc-Pint joined to luciferase ORF sequence. To study direct interaction, HEK293T cells were co-transfected with wild-type (control) reporter plasmid (psi-check2 construct) and miR-7 (mock vector) using TurboFect Reagent (Thermo Scientific). A fragment with no predicted microRNA recognition element (MRE) for miR-7 was used as a control. Forty-eight hours after transfection using dual-glo luciferase reporter system, the activities of the Firefly and Renilla luciferases were measured sequentially from cell lysates, according to the manufacturer's instructions (Promega). Firefly luciferase units were normalized against Renilla luciferase units to control the transfection efficiency.
TOP/FLASH assay
MCF7 cells were transfected with Linc-Pint expressing and 0.2Mg TOPflash vector. After 48 hours MCF7 cells were lysed using Lysis buffer and was used for the measurement of luciferase activities using a luciferase reporter assay kit (Promega) and luminometer.
Statistical analysis
Data are reported as means ± SEM. Graph pad prism version 6 were used for statistical analysis. Unpaired student’s t-test and one way ANOVA were used for comparisons amongst two or multiple groups. P-value < 0.05 was considered as statistically significant.