Background
On a global scale, bladder cancer (BC) is considered as one of the most common cancers [
1]. BC is also considered as the fourth main reason of cancer-associated deaths in males worldwide [
2]. Though various therapeutic methods have been utilized in medical treatment, BC patients in advanced stage still confront with poor prognosis outcome [
3]. Multifocality, high rates of relapse and lack of sensitive target in early period diagnosis are the major reasons of the poor prognosis of BC [
4]. Therefore, it is paramount to find sensitive therapeutic target of BC.
Long non-coding RNAs (lncRNAs) refer to those genes with exceeding 200 nucleotides (nt) in length but without the capacity to encode proteins [
5]. LncRNAs have been reported to be abnormally expressed in various cancers, and exerts an irreplaceable function in the carcinogenesis and progression of malignancies [
6‐
11]. LncRNAs are associated with different pathological cellular processes, such as cell proliferation, apoptosis, invasion as well as migration. For example, lncRNA UCA1 facilitates cell growth and migration, yet refrains cell apoptosis in gastric cancer by up-regulating PDL1 through sponging miR-26a/b, miR-193a and miR-214 [
12]. LncRNA SNHG1 regulates colorectal cancer epithelial-mesenchymal transition (EMT) process and impacts cell activity via binding with miR-497/miR-195-5p [
13]. Hence, targeting lncRNA could hopefully be a theoretical treatment method in cancers.
The prevalent ceRNA hypothesis reveals that lncRNA could influence the function of target gene via competitively binding to miRNA [
14,
15]. KCNQ1OT1 is a novel identified lncRNA. Its role in some diseases including cancers has been explored [
16,
17]. For example, in colorectal cancer, KCNQ1OT1 serves as ceRNA to facilitate cell migration and EMT process via regulating the expression of miR-217/ZEB1 [
18]. While its function in BC still unclear. This study aims to explore whether KCNQ1OT1 functions as ceRNA mechanically in BC tumorigenesis and evolvement, so as to provide a possible target for BC prognosis and treatment.
Materials and methods
Human tissue samples
From June 2012 to January 2018, 70 bladder cancer specimens and corresponding normal tissues were gathered from Affiliated Hospital of Beihua University. Patients who provided these tissues did not receive any treatment before being operated. Every patient signed informed consent, based on the review of Ethics of committee of Affiliated Hospital of Beihua University.
Cell culture
Human bladder epithelial immortalized cell (SV-HUC-1) as well as bladder cancer cells (UM-UC-3, T24, HT-1376 and HT-1197) were provided by Chinese Academy of Sciences (Beijing, China). The above cells were cultured at 37 °C in a moist incubator containing 5% CO2 in RPMI-1640 (Invitrogen, Waltham, MA, USA) supplied with 10% FBS (Invitrogen), 1% penicillin (Sigma-Aldrich, Milan, Italy) or streptomycin (Sigma-Aldrich).
Cell transfection
Transfected cells were put into a 6-well plate until cells was 80% confluence. T24 and HT-1197 cells were co-transfected with shRNAs targeting KCNQ10T1 (sh-KCNQ10T1#1/2), PCBP2 (sh-PCBP2#1/2) and shNC. The pcDNA3.1 vector for PCBP2 was used for overexpression studies. The miR-145-5p mimics, NC mimics and miR-145-5p inhibitor were gained from Genechem (Shanghai China). All plasmids were transfected into cells using Lipofectamine 2000 (Invitrogen).
Quantitative real-time polymerase chain reaction (qRT-PCR)
Total RNA was isolated from BC cells (T24 and HT-1197) or BC patient tissues according to the reference method TRIzol Reagent (Invitrogen). PrimeScript RT reagent Kit (TaKaRa, Tokyo, Japan) was applied to synthesize cDNA, which was used for qPCR analysis. SYBR Green Master Mix (Applied Biosystems, Foster City, CA, USA) was utilized on 7500 Real-time PCR System (Applied Biosystems), with cDNA as template. The gene expression was calculated by the 2
−ΔΔCt method. GAPDH or U6 was the internal control [
1].
Wound healing assay
Cells were placed into 6-well plates at first and cultivated in normal cell growth fluid. Sterile pipette was applied for scratching the cell layer to made scratches. After that, the cells were cleaned and cultured in another medium. Eventually, wound closure was collected at different times.
Western blot
Total proteins were extracted through a Total Protein Extraction Kit (KeyGen Biotech, Nanjing, China). Concentrations of protein were examined under BCA commercial kit (KeyGen). Proteins were separated using SDS-PAGE and then moved onto PVDF membranes (Millipore, Carlsbad, USA). Membranes were sealed in non-fat milk and then incubated with given primary antibodies: anti-MMP2 (1:1000, ab37150, Abcam, Cambridge, USA), anti-MMP7 (1:1000, ab5706, Abcam), anti-Bcl-2 (1:1000, ab32124, Abcam), anti-bax (1:1000, ab32503, Abcam), anti-caspase 3 (1:1000, ab13847, Abcam), anti-cleaved caspase-3 (1:1000, ab2302, Abcam), anti-caspase 8 (1:1000, ab25901, Abcam), anti-cleaved caspase-8 (1:1000, ab25901, Abcam), anti-caspase 9 (1:1000, ab32539, Abcam), anti-cleaved caspase-9 (1:1000, ab2324, Abcam), anti-E-cadherin (1:1000, ab15148, Abcam), anti-N-cadherin (1:1000, ab76057, Abcam) and anti-GAPDH (1:1000, ab8245, Abcam). GAPDH was used as a measurement control for other proteins. Moreover, the membranes were co-cultured with goat anti-mouse IgG H&L (Cy3®) preadsorbed (1:2000, ab97035, Abcam) secondary antibodies for 1 h darkness. Chemiluminescence system (Invitrogen) was employed to observe the protein bands.
Cell-counting kit 8(CCK-8) and colony formation assays
About CCK-8 assay, cultured T24 and HT-1197 cells were collected to 6-well plates with the density of 1 × 10
4 cells/well, and then which were mixed with CCK8 reagent (Dojindo, Kumamoto, Japan) for 2 h. The absorption at 450 nm was evaluated at the indicated time points by utilizing microplate reader (EL340; Bio-Tek Instruments, Hopkinton, MA, USA). As for colony formation assay, (800–1000) cells were plated in the six-well plates. Change the medium every 3 days. After 14 days of incubation, PBS (Solibao technology, Shanghai, China) was used to wash and methanol (Grass biotechnology, Nanjing, China) was applied to wash and fix it for 10 min, and then stained with crystal violet (Beyotime Biotechnology, Nantong, China) for 5 min. The visible colony numbers then were counted [
19].
Transwell-invasion assay
T24 and HT-1197 cells in apical compartment were cultured with serum-free medium, and the basolateral chamber was filled with 10% FBS medium. Cells were plated on the top compartment of membrane pre-coated with Matrigel for invasion assay. 24 h later, invaded cells were fixed in methanol (Solarbio, Beijing, China) and dyed in crystal violet (Solarbio). The cell numbers were recorded and photographed randomly from 5 chosen fields by an inverted microscope (Olympus, Tokyo, Japan).
Flow cytometry assay
Cell apoptosis was evaluated by an annexin/PI Kit (KeyGen). T24 and HT-1197 cells were washed by using PBS (Solarbio) and rehanged, then fixed in 70% cooled ethanol (Solarbio). Ultimately, the rate of apoptosis was analyzed by Flow Cytometer (BD Bioscience, Massachusetts, USA).
Terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) assay
TUNEL assays were carried out conforming to supplier’s protocols. After rising twice by PBS, cells of T24 or HT-1197 were fixed and permeabilized by paraformaldehyde (Solarbio) and 0.25% Triton-X 100, respectively. In short, the above cells were stained in DAPI (Invitrogen) or Merge (Invitrogen). Then, cells were surveyed and photographed by fluorescence microscopy (Olympus).
Subcellular fractionation assay
Subcellular isolation of RNAs in T24 and HT-1197 cells was carried out via Cytoplasmic and Nuclear RNA Purification Kit (Norgenbiotek Corporation, Thorold, Canada). Then the relative expression of KCNQ1OT1 was determined by qRT-PCR. Besides, GAPDH/U6 was regarded as cytoplasmic and nuclear control, separately.
Fluorescence in situ hybridization (FISH) assay
GenePharma was used to design the FISH probes of KCNQ1OT1. T24 and HT-1197 cells were immobilized for 10 min in 4% PFA and washed with PBS (Sigma-Aldrich) for three times. Subsequently, PBS containing with 0.5% Triton X-100 was applied for cell permeabilization. Following washing, pre-hybridization buffer (Sigma-Aldrich) was added into each well to incubate, which lasted for half an hour. The slide was hybridized with KCNQ1OT1 FISH probe, and then was washed three times with 2× Saline Sodium Citrate (SSC; Sigma-Aldrich) at 42 °C. Hoechst 33342 solution (Invitrogen) was used to stain cells. Finally, fluorescent signal was observed by using the microscope [
20].
Luciferase reporter assay
The wild-type and mutant binding sites of miR-145-5p in KCNQ1OT1 sequence or PCBP2 3′UTR were sub-cloned into pmirGLO dual-luciferase vector to construct plasmids, named KCNQ1OT1-Wt/Mut or PCBP2-Wt/Mut. Later, the plasmids were co-transfected with miR-145-5p mimics into T24 or HT-1197 cells, respectively. At last, the activity of luciferase was examined by Dual-luciferase Reporter System (Promega, Massachusetts, USA). Relative firefly luciferase activity was normalized to Renilla luciferase activity.
RNA pull down assay
The miR-145-5p-Wt, miR-145-5p-Mut and NC were biotin labeled into Bio-miR-145-5p-Wt, Bio-miR-145-5p-Mut or Bio-NC. Then, cell lysates were cultivated after 48 h and co-incubated with the biotinylated probe and M-280 streptavidin magnetic beads (Sigma). And the level of KCNQ10T1 was analyzed using qRT-PCR subsequently.
RNA immunoprecipitation (RIP) assay
RIP assays were employed for investigating the potential interaction under a Magna RNA-Binding Protein Immunoprecipitation Kit (Millipore). RNA was extracted via the Total RNA Isolation Kit (Invitrogen), and qRT-PCR was carried out. The lysates were co-cultured in magnetic beads covering anti-Ago2 and IgG in RIP buffer. Eventually, the relative expression quantity was measured by qRT-PCR.
Tumor growth in nude mice
Approximately 1 × 107 cells were injected into the nude mice subcutaneously. Tumor growth was recorded to measure the width or length, and the volume and weight of the tumor was calculated at indicated times. The experiment was permitted by the ethics of committee.
Immunofluorescence (IF) staining
T24 or HT-1197 cells were place in 6-well plates and incubated on sterilized coverslips. After cells were treated under different conditions separately, then 4% paraformaldehyde was used to fix cells. Afterwards, 0.5% Triton X-100 was used to make cell permeabilization, which lasted for 10 min at room temperature. Subsequently, 5% BSA (Amersco) was employed to block cells in PBST for one hour, which were incubated with primary antibodies against E-cadherin and N-cadherin at 4 °C for one whole night, then cultured with fluorochrome-labeled anti-rabbit secondary antibody (MultiSciences), which lasted for one hour at room temperature. Additionally, DAPI (1:5000, Beyotime) was applied to stain the coverslips, which were observed by a fluorescence microscopy (Nikon). Adobe Photoshop 6.0 software was utilized to merge the images.
Statistical analysis
Data were showed as mean ± SD. SPSS (Chicago, IL, USA) and GraphPad Prism 5 software (San Diego, CA) were applied to make statistical analysis. Significance of the variance between two or several groups was assessed by Student’s t test or ANOVA. Gene expression correlation was conducted by Pearson’s correlation analysis. P value less than 0.05 had statistically significance. The above experiments were made at least thrice.
Discussion
Long non-coding (lncRNAs) have been widely reported to be related to various human malignancies. Besides, lncRNAs can exert its effects on pathological process through regulating gene transcription and downstream gene expression level [
22]. Recently, KCNQ1OT1, as a novel lncRNA, was found to be significantly up-regulated in non-small-cell lung cancer (NSCLC) tissues and cell lines and positively correlated with poor prognosis [
23]. Moreover, KCNQ1OT1 was aberrantly highly expressed in breast cancer (BRCA) tissues and cell lines, and it could deteriorate tumor progression via regulating miR-145/CCNE2 expression [
24]. Based on these researches, we supposed that KCNQ1OT1 might serve as an oncogene in tumors. In present study, we confirmed that KCNQ1OT1 exhibited abnormally high expression in BC tissues and cell lines, besides, BC patients with advanced stage (III/IV) enjoyed higher level of KCNQ1OT1 than those with early stage (I/II), which was closely associated with tumor cell biological function and pathological processes. Further, knockdown of KCNQ1OT1 dampened cell proliferation, migration, invasion and EMT, while expedited cell apoptosis. Silencing KCNQ1OT1 also repressed xenografts growth in vivo. All these findings indicated that KCNQ1OT1 is an oncogene in BC progression.
To date, accumulating studies have found that lncRNA could act as a competing endogenous RNA (ceRNA) of microRNA (miRNA) and restore the miRNA downstream target gene function to a large extent. For instance, lncRNA WDFY3-AS2 can regulate the expression of RORA via sponging miR-18a in ovarian cancer [
25]. Also, in diabetic cardiomyopathy (DCM), lncRNA DCRF can up-regulate PCDH17 expression through sponging miR-551b-5p, leading to increased cardiomyocyte autophagy in DCM [
26]. Likewise, some lncRNAs involved in the tumorigenesis of BC have been reported as well. For example, lncRNA OXCT1-AS1 could bind with miR-455-5p and decrease the combination of miR-455-5p with JAK1, thus increasing expression of JAK1 in BC [
27]. MiR-145-5p, a target of KCNQ1OT1, was found to be significantly down-regulated and was a tumor suppressor in some tumors [
28,
29]. In this study, we also noticed a remarkable down-regulation of miR-145-5p in BC tissues and cell lines. We further proved that KCNQ1OT1 mainly located in cytoplasm was an effective sponge of miR-145-5p. Moreover, the interactions between KCNQ1OT1 and miR-145-5p via luciferase activity report and RNA pull down assays. Additionally, miR-145-5p suppression counteracted the inhibiting influence of KCNQ1OT1 knockdown in BC cell proliferation, migration and invasion.
Further, we selected PCBP2 as candidate target gene of miR-145-5p as it exhibited dramatically the lowest expression among the twelve predicted combinable genes after up-regulation of miR-145-5p. PCBP2 was reported to play a tumor facilitator role in several cancers. For example, PCBP2 expression was up-regulated in pancreatic ductal adenocarcinoma (PDAC) and was correlated with advanced PDAC stages as well as poor diagnosis [
30]. In present study, we observed that the expression of PCBP2 was also up-regulated in BC tissues and cell lines. PCBP2 depletion inhibited cell proliferation, migration and invasion, but stimulated cell apoptosis in BC. In addition, overexpression of PCBP2 reversed the tumor-suppressing function caused by sh-KCNQ1OT in BC. More specifically, KCNQ1OT1 overexpression can aggravate cell proliferation, migration and invasion yet inhibit cell apoptosis via up-regulating PCBP2 expression as miR-145-5p sponge in BC.
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