Background
Gallbladder cancer (GBC) is the most common biliary tract malignant cancer, which is highly lethal and has an extremely poor prognosis [
1,
2]. Due to its non-specific symptoms and highly invasive property, most GBC patients are diagnosed at advanced stages [
3]. Hence, most GBC patients at advanced stages are not candidates for surgical resection [
4]. Unfortunately, until now the only curative treatment for GBC is still surgery [
5]. Therefore, the mean survival time for GBC ranges from 13.2 months to 19 months [
6]. The poor outcome of GBC and the lack of efficient therapies request better understanding of molecular mechanisms underlying GBC tumorigenesis and metastasis, and developing more efficient targeted therapies for GBC.
Although many aberrantly expressed and mutated molecular events have been identified in GBC, most of these focused on protein-coding genes [
7]. Recently, with the great progressions of genome and transcriptome sequencing, many non-protein-coding genes have been identified, which accounts for about 70% of the genome, with only 2% of the genome encoding proteins [
8]. Most of these non-protein-coding genes transcribe long non-coding RNAs (lncRNAs) [
9]. lncRNA is a class of RNA with limited protein coding potential and more than 200 nucleotides in length [
10]. Accumulating evidences revealed that lncRNAs are frequently involved in many pathophysiological processes, including cancers [
11‐
15]. Many lncRNAs are dysregulated in cancers [
16‐
19]. Furthermore, many lncRNAs are revealed to control cell proliferation, cell cycle, cell apoptosis, senescence, cell migration, cell invasion, drug resistance of cancer cells and so on [
20‐
23]. For example, lncRNA-PAGBC is reported to be up-regulated in GBC and promote GBC tumorigenesis via competitively binding miR-133b and miR-511 [
24]. LncRNA-CCAT1 is reported to be up-regulated in GBC and promote GBC development via negative regulating miR-218-5p [
25]. LncRNA HOXA-AS2 is also up-regulated in GBC and promotes GBC proliferation and epithelial-mesenchymal transition [
26]. LncRNA GCASPC is reported to be down-regulated in GBC and inhibit pyruvate carboxylase-dependent cell proliferation of GBC cells [
27]. LncRNA H19 is reported to be up-regulated and have oncogenic roles in GBC via modulating miR-342-3p and FOXM1 [
28]. In our previous study, we investigated the expression and roles of lncRNA SPRY4-IT1 in GBC and found that lncRNA SPRY4-IT1 is upregulated in GBC and promotes GBC cell proliferation, migration, and invasion [
29]. Although several lncRNAs have been reported to be involved in GBC, the expression and roles of most of lncRNAs in GBC are still unclear.
In this study, we searched differentially expressed lncRNAs in GBC via analyzing public available microarray data and identified a novelly differently expressed lncRNA in GBC. We further analyzed the expression, clinical significances, roles, and mechanisms of action of this lncRNA in GBC.
Methods
Clinical specimens
A total of 102 pairs of GBC tissues and adjacent non-tumor tissues were obtained from GBC patients with written informed consent who underwent surgery at Eastern Hepatobiliary Surgery Hospital (Shanghai, China). All these GBC patients did not receive any pre-operative treatments. The tissue specimens were confirmed by histopathological diagnosis. All resected specimens were immediately snap-frozen in liquid nitrogen and stored at − 80 °C until RNA extraction. The Review Board of Eastern Hepatobiliary Surgery Hospital reviewed and approved this study.
Cell lines and treatments
The human non-tumorigenic biliary epithelial cell line H69 and GBC cell lines SGC-996, NOZ, GBC-SD, and EH-GB2 were obtained from the Institute of Biochemistry and Cell Biology of the Chinese Academy of Sciences (Shanghai, China) or maintained in our hospital [
30]. The cells were maintained in Dulbecco’s Modified Eagle’s Medium (Gibco BRL, Grand Island, NY, USA) supplemented with 10% fetal bovine serum (Gibco) in a humidified incubator containing 5% CO
2 at 37 °C. Where indicated, the GBC cells were treated with 5 ng/mL doxorubicin (Selleck, Houston, TX, USA) for 24 h, 5 μM p-STAT3 inhibitor SC144 (Selleck) for 72 h, or 20 ng/mL IL-11 (Gibco) for 72 h.
Quantitative real-time polymerase chain reaction (qRT-PCR)
Total RNA was extracted from tissues and cells using TRIzol Regent (Invitrogen, Carlsbad, CA, USA) in accordance with the manufacturer’s instruction, followed by being treated with DNase I (Takara, Dalian, China) to remove genomic DNA. Reverse transcription was carried out using the extracted RNA and the M-MLV Reverse Transcriptase (Invitrogen) in accordance with the manufacturer’s instruction. Quantitative real-time polymerase chain reaction (qRT-PCR) analyses were performed using SYBR® Premix Ex Taq™ II (Takara) on ABI StepOnePlus Real-Time PCR System (Applied Biosystems, Foster City, CA, USA) in accordance with the manufacturers’ instructions. The quantification of the expression of RNA was normalized to the expression of β-actin. The expression of RNA was calculated using the comparative Ct method. The sequences of the primers were as follows: for HEGBC, 5’-CACAGGAATCTGAAAAAC-3' (forward) and 5’-TAGTGAGAATCAAAGGCA-3' (reverse); for IL-11, 5’-GCTGCAAGGTCAAGATGGTT-3' (forward) and 5’-GCTGGGTGGCGTTCTATC-3' (reverse); for BCL2, 5’-CTTCGCCGAGATGTCCAG-3' (forward) and 5’-CCCAGCCTCCGTTATCCT-3' (reverse); for Cyclin D1, 5’-TCCTCTCCAAAATGCCAGAG-3' (forward) and 5′- GGCGGATTGGAAATGAACTT -3′ (reverse); for Survivin, 5’-GCAGCCCTTTCTCAAGGACC-3′ (forward) and 5’-AGTGGATGAAGCCAGCCTCG-3′ (reverse); for TSLNC8, 5’-CACCTCCATTCAACCAATAAGC-3′ (forward) and 5’-ACCCTGTCCCCAATAACCC-3′ (reverse); and for β-actin, 5’-GGGAAATCGTGCGTGACATTAAG-3′ (forward) and 5’-TGTGTTGGCGTACAGGTCTTTG-3′ (reverse).
5' and 3' rapid amplification of cDNA ends (RACE)
The transcriptional initiation and termination sites of HEGBC were determined using the 5' and 3' rapid amplification of cDNA ends (RACE) assays with the 5′/3’ RACE Kit (Roche, Mannheim, Germany) in accordance with the manufacturer’s instruction. The sequences of the primers for RACE assays were as follows: SP1, 5’-CATCAGCACATAACTCGTCC-3'; SP2, 5’-AGATTCCTGTGCTTGCTTACTC-3′; SP3, 5’-GGCTTCTACACTGCCACCTGC-3'; and SP5, 5’-GCAAGCACAGGAATCTGAAAAAC-3'.
Plasmids and stable cell lines construction
For construction of HEGBC overexpression plasmid, HEGBC full-length sequences were PCR amplified using Thermo Scientific Phusion Flash High-Fidelity PCR Master Mix (Thermo-Fisher Scientific, Waltham, MA, USA) and subcloned into the BamH I and EcoR I sites of the pcDNA3.1 plasmid (Invitrogen), termed as pcDNA3.1-HEGBC. The sequences of the primers were as follows: 5’-CGGGATCCGGGAAATGAGGACCACC-3' (forward) and 5’-GGAATTCAATATGCAAAACTTTACATTTTAGTG-3' (reverse). The empty plasmid pcDNA3.1 was used as negative control. Two pairs of cDNA oligonucleotides repressing HEGBC expression were designed, synthesized, and inserted into the SuperSilencing shRNA expression plasmid pGPU6/Neo (GenePharma, Shanghai, China), termed as shHEGBC-1 and shHEGBC-2. The target sites are 5’-GGAGCTTCCAGAAGTGGTTTC-3' and 5’-GCTGATGAGAGACATGTTTGT-3'. A scrambled shRNA was used as negative control and termed as shControl.
For construction of HEGBC stably overexpressed GBC cells, pcDNA3.1-HEGBC or pcDNA3.1 was transfected into SGC-996 and NOZ cells, and then the cells were selected with 800 μg/mL neomycin for 4 weeks. For construction of HEGBC stably depleted GBC cells, shHEGBC-1, shHEGBC-2, or shControl was transfected into GBC-SD and EH-GB2 cells, and then the cells were selected with 1 μg/mL puromycin for 4 weeks.
Cell proliferation, apoptosis, and migration assays
Cell proliferation was detected with Glo cell viability assay and Ethynyl deoxyuridine (EdU) incorporation assay. For Glo cell viability assay, 2000 indicated GBC cells were plated into 96-well plates and cultured for indicated time. At each indicated time, the luminescence values were detected using the CellTiter-Glo® Luminescent Cell Viability Assay (Promega, Madison, WI, USA) in accordance with the manufacturer’s instruction. EdU incorporation assay was performed with the EdU kit (Roche) in accordance with the manufacturer’s instruction. Results were acquired using the Zeiss fluorescence photomicroscope (Carl Zeiss, Oberkochen, Germany) and quantified via counting at least five random fields. Cell apoptosis was detected with terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labelling (TUNEL) assay. After being treated with 5 ng/mL doxorubicin for 24 h, indicated GBC cells were used to perform TUNEL assay with the In-Situ Cell Death Detection Kit (Roche) in accordance with the manufacturer’s instruction. Results were acquired using the Zeiss fluorescence photomicroscope (Carl Zeiss) and quantified via counting at least five random fields. Cell migration was detected with transwell assay. For transwell assay, 40,000 indicated GBC cells re-suspended in serum-free media with 1 μg/ml Mitomycin C to inhibit cell proliferation were placed into the upper chamber of transwell insert (8-μm pore size; Millipore, Bedford, MA, USA). Medium containing 10% FBS was added to the lower chamber. After incubation for 48 h, the GBC cells remaining on the upper membrane were removed with cotton wool, and whereas the cells migrating through the membrane were fixed with methanol, stained with 0.1% crystal violet, imaged using the Zeiss fluorescence photomicroscope (Carl Zeiss), and quantified via counting at least five random fields.
To establish in vivo tumorigenesis model, 2 × 106 indicted GBC cells in 50 μL phosphate buffered saline mixed with 50% matrigel (Invitrogen) were subcutaneously injected into the flanks of 6 weeks old male athymic nude mice (SLRC Laboratory Animal Center, Shanghai, China). Subcutaneous tumor volumes were detected every 7 days with caliper for 28 days and calculated as a × b2 × 0.5 (a, longest diameter; b, shortest diameter). At the 28th day after injection, the mice were sacrificed and subcutaneous tumors were resected and weighted. The resected subcutaneous tumors were fixed in formalin, paraffin embedded, deparaffinized, rehydrated, and antigen retrieved. For immunohistochemical staining of Ki67, the sections were incubated with primary antibody for Ki67 (Cell Signaling Technology, Boston, MA, USA), followed by being incubated with a horseradish peroxidase-conjugated secondary antibody (Cell Signaling Technology). Finally, the slides were visualized with 3, 3-diaminobenzidine. For detection of cell apoptosis of subcutaneous tumors, the sections were used to perform TUNEL assay with the In-Situ Cell Death Detection Kit (Roche) in accordance with the manufacturer’s instruction. Liver metastasis model was established with intra-splenic injection of 2× 106 indicated GBC cells. Mice were allowed to grow for 6 weeks, and then the mice were sacrificed, and the livers were resected. The liver metastatic foci number was counted via HE staining. The Review Board of Eastern Hepatobiliary Surgery Hospital reviewed and approved the use of animals.
Isolation of cytoplasmic and nuclear RNA
Cytoplasmic and nuclear RNA were isolated and purified using the Cytoplasmic & Nuclear RNA Purification Kit (Norgen, Belmont, CA, USA) in accordance with the manufacturer’s instruction. The isolated RNA was detected by qRT-PCR as described above.
Chromatin isolation by RNA purification (ChIRP) assay
ChIRP assay was performed with the Magna ChIRP RNA Interactome Kit (Millipore) in accordance with the manufacturer’s instruction. Antisense DNA probes against HEGBC were designed and synthesized by Biosearch Probe Designer. The sequences of the probes were as follows: 1, 5'-gaaaccacttctggaagctc-3'; 2, 5'-gcttgcttactcatgtacat-3'; 3, 5'-tgtggtttttcagattcctg-3'; 4, 5'-aagcaggcaaattagtgggc-3'; 5, 5'-aactcgtccttattttagtc-3'; 6, 5'-aacatgtctctcatcagcac-3'; 7, 5'-ttcttttgaactgtgtcaca-3'. ChIRP-derived DNA was quantified using qRT-PCR to detect enrichment of chromatin. The sequences of the primers were as follows: for the promoter of IL11, 5’-CTTTGCTTCTCTGGTGTGTC-3' (forward) and 5’-CTGGTGAGGTCATTGGCGT-3' (reverse); for the promoter of ACTB, 5’-GGCTGGCTTTGAGTTCCTA-3' (forward) and 5’-CCCACCGTCCGTTGTATGT-3' (reverse).
Chromatin immunoprecipitation (ChIP) assay
ChIP assay was performed with the EZ-Magna ChIP A/G (17–10,086, Millipore) and a p-STAT3 antibody (5 μg per reaction; 9131, Cell Signaling Technology, Boston, MA, USA) in accordance with the manufacturer’s instruction. ChIP-derived DNA was quantified using qRT-PCR to detect enrichment of chromatin. The sequences of the primers were as follows: for the − 668 site of HEGBC promoter, 5’-CACACTGGATTTGTTTCTG-3' (forward) and 5′-GGGTGGTTGGGTTTTTTTT-3' (reverse); for the − 930 site of HEGBC promoter, 5’-CTGCCAACCTGGAAGAAA-3' (forward) and 5’-TTAGGGATTAGGAACCCC-3' (reverse); for the − 1211 site of HEGBC promoter, 5’-ATGTAGTATCATGAGCCTGGG-3′ (forward) and 5’-GCAAAGTTATGGAAGCCGTG-3′ (reverse); for the − 1556 site of HEGBC promoter, 5’-GCAAAGAGAGGCAGGAGT-3′ (forward) and 5’-TGCTGGGTAAATGAGGACA-3′ (reverse); for the distal non-binding site (negative control, NC) of HEGBC promoter, 5’-GTTGTCTCATTGTGTCCC-3′ (forward) and 5’-TGTGTGTTTTTCCCTCTTG-3′ (reverse).
RNA immunoprecipitation (RIP) assay
RIP assay was performed with the Magna RIP RNA-Binding Protein Immunoprecipitation Kit (Millipore) and p-STAT3 antibody (5 μg per reaction; Cell Signaling Technology), STAT3 antibody (5 μg per reaction; Cell Signaling Technology), RPLP0 antibody (5 μg per reaction; Abcam, Hong Kong, China), or negative control IgG in accordance with the manufacturer’s instruction. RIP-derived RNA was quantified using qRT-PCR to detect enrichment of lncRNAs.
Enzyme linked immunosorbent assay (ELISA)
IL-11 concentration in the culture medium collected for 48 h from indicated GBC cells were measured with the Human IL-11 ELISA Kit (Dakewei Biotech Company, Shanghai, China) in accordance with the manufacturer’s instruction.
Western blot analysis
Total proteins were extracted from indicated GBC cells using RIPA buffer (Beyotime, Shanghai, China) and separated by 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by being transferred to NC membrane. After being blocked with 5% bovine serum albumin, the membranes were incubated with primary antibodies against p-STAT3 (Cell Signaling Technology), STAT3 (Cell Signaling Technology), or β-actin (Sigma-Aldrich, Saint Louis, MO, USA). After being washed, the membranes were incubated with IRDye 800CW goat anti-rabbit IgG or IRDye 700CW goat anti-mouse IgG (Li-Cor, Lincoln, NE, USA), and detected using Odyssey infrared scanner (Li-Cor).
Luciferase reporter assays
The promoter of HEGBC containing the predicted p-STAT3 binding sites was PCR amplified using Thermo Scientific Phusion Flash High-Fidelity PCR Master Mix (Thermo-Fisher Scientific) and subcloned into the Kpn I and Xho I sites of the pGL3-basic vector (Promega), termed as pGL3-HEGBC-pro. The sequences of the primers were as follows: 5’-GGGGTACCCTATTGCTGCACTCACACACCC-3′ (forward) and 5’-CCGCTCGAGCGCCAGAGCCCAAGCTATC-3′ (reverse). The empty vector pGL3-basic was used as negative control. The p-STAT3 binding sites mutated HEGBC promoter was synthesized by GenScript (Nanjing, China) and subcloned into the Kpn I and Xho I sites of the pGL3-basic vector, termed as pGL3-HEGBC-pro-mut. The constructed luciferase reporter plasmids were cotransfected with the pRL-TK plasmid expressing renilla luciferase into NOZ cells. 12 h later after transfection, the NOZ cells were treated with 5 μM SC144 or 20 ng/mL IL-11 for 72 h. Then the luciferase activity was measured using Dual-Luciferase® Reporter Assay System (Promega) in accordance with the manufacturer’s instruction.
Statistical analysis
Statistical analyses were carried out using the GraphPad Prism Software. For comparisons, Wilcoxon signed-rank test, Mann-Whitney test, Pearson chi-square test, Log-rank test, Student’s t test, or Pearson’s correlation analysis was performed as indicated. P < 0.05 was regarded as statistically significant.
Discussion
Human transcriptome sequencing identified 58,648 lncRNAs, of which 79% were unannotated [
36]. Among these lncRNAs, only a few were investigated in cancers. As to GBC, only several lncRNAs were investigated, including SPRY4-IT1 [
29], CCAT1 [
25], MALAT1 [
37], H19 [
28], GCASPC [
27], UCA1 [
38], HOXA-AS2 [
26], PAGBC [
24], AFAP1-AS1 [
39], LET [
40], LOC344887 [
41], HOTAIR [
42], and ROR [
43]. Due to the huge number of lncRNAs in human cells, we could not rule out other lncRNAs which may also play critical roles in GBC. Therefore, we re-analyzed the public available microarray data about the differentially expressed lncRNAs in GBC. Intriguingly, we identified a novel lncRNA HEGBC, which is significantly up-regulated in GBC tissues and cell lines, compared with adjacent non-tumor tissues and non-tumorigenic biliary epithelial cell line, respectively. Increased expression of HEGBC is positively correlated with GBC extension, lymph node metastasis, and TNM stages. Furthermore, increased expression of HEGBC predicts poor outcome of GBC patients. Thus, this study identified a novel GBC-associated lncRNA HEGBC which indicates poor prognosis of GBC patients. The expression pattern and clinical significances of HEGBC in other cancers need further investigation.
Subsequently, in vitro functional assays showed that enhanced expression of HEGBC increased cell viabilities, promoted cell proliferation and migration, and inhibited cell apoptosis of GBC cells. Conversely, depletion of HEGBC decreased cell viabilities, inhibited cell proliferation and migration, and induced cell apoptosis of GBC cells. In vivo xenograft assays showed that enhanced expression of HEGBC promoted GBC tumor growth and liver metastasis, and while depletion of HEGBC inhibited GBC tumor growth and liver metastasis. Therefore, our data suggested that HEGBC functions as an oncogene in GBC, and implied that HEGBC may be a potential therapeutic target for GBC. Whether the oncogenic role of HEGBC is GBC specific or tumor general needs further study.
The excessive activation of STAT3 signaling pathway has been found in many cancers, including GBC [
44,
45]. In response to stimulation of cytokines or growth factors, STAT3 is phosphorylated by receptor associated kinases, translocates to cell nucleus, and activates the transcription of many target genes that regulating cell viability, apoptosis, and so on. The activated STAT3 has oncogenic roles in many cancers, including GBC [
46,
47]. In this study, we found that HEGBC activated STAT3 signaling pathway. Further mechanistic investigations revealed that the nucleus-localized HEGBC directly bound the promoter of
IL11, which stimulates the activation of STAT3. Via binding the promoter of
IL11, HEGBC activated the transcription of
IL11, and further upregulated the expression and secretion of IL-11. The auto-secreted IL-11 further stimulated the activation of STAT3. Intriguingly, except the activation of IL-11/STAT3 signaling by HEGBC, we also found that STAT3 directly bound the promoter of
HEGBC and activated the transcription of
HEGBC. Thus, HEGBC/IL-11/STAT3 form a positive regulatory loop in GBC. The double positive regulatory roles amplified the aberrant expressions and roles of the participators. Loss-of-function assays showed that depletion of IL-11 attenuated the oncogenic roles of HEGBC in GBC. In addition, the expression of HEGBC is positively associated with that of IL-11 in GBC tissues. These data supported the positive interaction between HEGBC and IL-11 and suggested that HEGBC exerts its oncogenic roles at least partially via activating IL-11/STAT3 signaling. Although the oncogenic roles of STAT3 are well known, the roles of IL-11 in cancer are relatively unknown. Previous studies have revealed the critical roles of IL-11 in tumorigenesis of liver, colon, and gastric cancers [
48,
49]. In this study, we further verified that IL-11 also has critical roles in GBC. Therefore, our data suggest that HEGBC/IL-11/STAT3 regulatory loop may be potential therapeutic targets for GBC.