Background
The incidence of thyroid cancer (THCA) has ascended steadily worldwide over the past decades, and this disease is projected to become the fourth leading type of cancer [
1]. Papillary thyroid cancer (PTC) is the most common subtype, accounting for approximately 85% of all THCA. Although patients with PTC may experience long-term and disease-specific survival after surgical treatment, poor prognosis often occurs and that is closely associated with tumor regional recurrence or metastasis [
2]. Therefore, better understanding the molecular mechanisms in PTC and identifying novel targets are still eagerly needed.
E3 ubiquitin ligases are a class of critical enzymes that can catalyse the transfer of ubiquitin to the substrate, and their genetic alteration, abnormal expression, or dysfunction account for the occurrence and progression of human cancers [
3]. Therefore, they are emerging as attractive therapeutic targets for cancer therapy [
4]. Pellino-1 (PELI1), a novel cancer-related E3 ubiquitin ligase, has been found to be upregulated and correlated with poor clinical prognosis in a variety of cancers, such as large B cell lymphomas [
5,
6], lung cancer [
7,
8] and breast cancer [
9]. In addition, PELI1 could regulate the metabolic actions of mTORC1 to suppress antitumor T cell responses in melanoma [
10]. These reports identified PELI1 was an oncogene. However, a recent study reported that PELI1 could promote radiotherapy sensitivity by inhibiting noncanonical NF-κB in esophageal squamous cancer [
11], suggesting that PELI1 was a tumor suppressor. Nevertheless, the expression patterns and functional importance of PELI1 in PTC are not known.
MicroRNAs (miRNAs), which are small non-coding RNAs, modulate the expression of cognate target genes by interacting with their mRNA 3′-untranslated region (3′-UTR), resulting in mRNA degradation or translational inhibition [
12]. Obviously, miRNAs are gene’s fine-tuner [
13,
14]. Accumulating study reveal that miRNAs can act as novel types of cancer ontogenesis or suppressors in tumor carcinogenesis [
15]. In particular, miRNAs are closely related to PTC development and progression [
16]. Therefore, whether Peli1 expression is regulated by certain miRNAs as a posttranscriptional regulation mechanism in PTC is worth exploring.
Here, we found that PELI1 was widely unregulated in PTC samples and cells. PELI1 promoted PTC cell proliferation and migration, which was associated with the activation of PI3K-AKT signaling pathway. Notably, PELI1 was inversely regulated by miR-30c-5p and was a direct functional target of miR-30c-5p in PTC. Moreover, miR-30c-5p could be incorporated by human umbilical cord mesenchymal stem cells (hUCMSC) and released in extracellular vesicles (EVs), which could inhibit PELI1 expression and PTC growth in vitro and in vivo. Our findings not only provided that miR-30c-5p/PELI1/PI3K-AKT axis might function as a key pathway regulating PTC progression, but also showed a novel translational therapeutic approach for PELI1 inhibition and PTC treatment based on miR-30c-5p-carrying-hUCMSC-EVs.
Materials and methods
Human samples
PTC tissues and human umbilical cord samples were obtained from informed and consenting PTC patients and mothers respectively at the Affiliated Hospital of Jiangsu University (Zhenjiang, China). This study was approved by the Ethics Committee of the Affiliated Hospital of Jiangsu University.
Cell culture
W3, TPC-1 and Nthy-ori 3–1 were purchased from Cell Bank of Chinese Academy of Sciences and were cultured in DMEM medium (Gibco, Carlsbad, CA) containing 10% FBS (Gibco) and 1% pen/strep (Gibco) in a humidified atmosphere at 37 °C with 5% CO
2. HUCMSCs were isolated from fresh umbilical cord samples as previously described [
17,
18] and maintained in stem cell culture medium (Cyagen, Guangzhou, China).
Lentivirus transduction and oligonucleotide transfection
Lentiviral particles for PELI1 overexpression (LV-PELI1), inhibition constructs (sh-PELI1), and their relative control (LV-NC; sh-NC, respectively) were packaged and purchased from GeneChem (Shanghai, China). PTC cells were infected with recombinant lentivirus transducing units plus 5 μg /ml polybrene (Sigma, Natick, MA) according to the manufacturer's manual. PELI1 shRNA sequences: 5′-GCCAAATGGAAGACATCAGAT-3′; scrambled shRNA: 5′- TTCTCCGAACGTGTCACGT-3′.
The synthetic miR-30c-5p mimics, mimic control, miR-30c-5p inhibitor and inhibitor control were purchased from GenePharma (Shanghai, China). The plasmids of pcDNA-Peli1 and the empty vector were kindly gifted from Professor Yichuan Xiao (Chinese Academy of Sciences, Shanghai, China). PTC cells were transfected with 50 nM miR-30c-5p mimic or 100 nM miR-30c-5p inhibitor or miR-30c-5p mimic plus 1 μg Peli1 plasmid using Lipofectamine 2000 (Invitrogen, Carlsbad, CA) according to the manufacturer’s protocol.
HUCMSC-EVs engineered by miR-30c-5p (miR-30c-5p-EVs)
HUCMSCs were transfected with 50 nM miR-30c-5p mimic or mimic NC using Lipofectamine 2000 (Invitrogen), followed by culturing with conditioned medium [
19]. MiR-30c-5p-EVs or NC-EVs were isolated from the conditioned medium by using ultra-high-speed centrifugation (Beckman Coulter Optima L-100 XP ultracentrifuge, Miami, FL) as our previously described [
17,
18].
Morphology of the miR-30c-5p-EVs was observed using transmission electron microscopy (JEM-1200EX; JEOL Ltd., Tokyo, Japan). The particle number and size distribution of the EVs were determined by using ZetaView PMX 110 (Particle Metrix, Meerbusch, Germany) according to the manufacturer’s manual.
Cell treatment
PELI1-overexpressing PTC cells (LV-PELI1) and their control cells (LV-NC) were seeded in 6-well plates. After culturing overnight, the LV-PELI1 cells were treated with LY294002 (20 μM; MedChem Express, Monmouth Junction, NJ) dissolved in DMSO or DMSO alone. After incubation of 12 h, the cells were harvested for protein extraction.
PTC cells were seeded in six-well plates (10% EVs-free FBS complete DMEM medium) and treated with PBS, hUCMSC-EVs (10
4 particles/cell), NC-EVs (10
4 particles/cell) or miR-30c-5p-EVs (10
4 particles/cell) daily for three days as previous described [
20].
Cell proliferation assay
Cell viability was determined using CCK-8 assays (KeyGEN BioTECH, Nanjing, China) following the manufacturer’s protocol. Briefly, PTC cells were seeded in 96-well plates (2 × 103/well). After the indicated hours (24, 48, 72 and 96) of incubation, CCK-8 solution (10 μL) was added to each well, followed by incubated for another 2 h. The absorbance was measured at 450 nm using a microplate reader (Synergy HT, BioTek, Biotek Winooski, VT).
For colony formation assay, W3 and TPC-1 cells transfected with lentivirus, oligonucleotide, or treated by EVs were seeded in 6-well plates (1000/well) and cultured in medium containing 10% FBS. After 10 days, the cells were fixed with methanol and stained with 0.4% crystal violet solution, finally photographed. Colonies containing more than 50 cells were counted.
Cell migration assay
PTC cells were plated into the upper Transwell chamber (W3: 5 × 104; TPC-1: 3 × 104 in 200 μl serum-free medium). The lower chamber was filled with 600 μl medium supplemented with 10% FBS. After 12 h of incubation, cells on the upper membrane surface were removed and the membranes were fixed with methanol, stained with 0.4% crystal violet solution, imaged using a Nikon microscope.
For wound healing assay, the monolayer cells were scratched by a 200-μl pipette tip. Separated cells were washed out using PBS, and images of the same fields at 48 h after the scratch were recorded under a microscope.
Mouse model study
Four-week-old female BALB/c nude mice were purchased from the Comparative Medicine Centre of Yangzhou University (Yangzhou, China).
To evaluate the effect of PELI1 on PTC growth, the W3 cells stably transfected with sh-PELI1 or control sh-NC (2 × 106 cells) were injected subcutaneously into the right or left of the mice flank respectively.
To investigate the effect of miR-30c-5p-EVs on PTC growth, nude mice were inoculated subcutaneously on right flanks with W3 cells (2 × 10
6 cells). After 7 days of tumor growth, PBS (20 μL), hUCMSC-EVs, NC-EVs, or miR-30c-5p-EVs (all kind of EVs: 2 × 10
10 in a volume of 20 μL of PBS) were administered via intra-tumor injection weekly described by Bruno et al. [
19]. On day 28, tumors were removed for examination. Tumor volume in mm
3 was calculated from the length (L) and width (w) axis of the tumors using the following formula: V = L × W
2/2.
RNA isolation and quantitative real-time PCR
Total RNA was isolated using Trizol reagent (Invitrogen) or mirVana RNA isolation kit (Ambion, Austin, TX) according to the manufacturer’s protocol. Real-time PCR was performed with All-in-one™ qPCR Mix (Genecopoeia) in a QuantStudio 5 Real-Time system (Thermo Fisher Scientific, Waltham, MA). All of the primers for real-time PCR, including PELI1 (HQP0504204), β-actin (HQP016381), Has-miR-30c-5p (HmiRQP0396) and U48 (HmiRQP9021) were purchased from Genecopoeia (Guangzhou, China). The relative expression of
PELI1 and miR-30c-5p was normalized to β-actin and U48 respectively, and evaluated by the 2
−ΔΔCt method, based on our previous description [
21,
22].
Immunohistochemical (IHC) assay
IHC analyses of tissues were conducted as described in previous study [
17,
23]. Briefly, PTC tissue sections were incubated with an antibody to PELI1 (12,053–1-AP, diluted 1: 200; Proteintech, Rosemont, IL); mice tumor sections were incubated with an antibody to Ki-67 (ab16667, diluted 1: 200; Abcam, Cambridge, MA) or MMP2 (10,373–2-ap, diluted 1: 200; Proteintech) overnight at 4 °C, followed incubating by HPR-conjugated secondary antibody. Diaminobenzidine was used as the substrate. The nuclei were counterstained with hematoxylin. All pictures were captured using a Nikon microscope. Integrated optical density of Ki-67 and MMP2 in mice tumor sections were measured by using Image-Pro Plus software (Version X; Adobe, San Jose, CA).
Western blotting
The proteins were extracted using RIPA buffer (Cell Signaling Technology Inc., Danvers, MA) and quantified using a BCA Protein Kit (Beyotime). Western blot analysis was carried out as described previously [
21]. The antibodies against PELI1 (sc-271065) was purchased from Santa cruz biotechnology (Santa Cruz, CA); Phospho-AKT (ab81283), AKT (ab179463), Ki-67 (ab16667), TSG101 (ab133586), HSP70 (ab181606) and HRP-linked anti-rabbit/mouse IgG (ab97051/ ab6728) were purchased from Abcam; MMP2 (10,373–2-ap) and GAPDH (60,004–1-lg) were purchased from Proteintech. The intensity of protein bands was quantitated using Image J (National Institutes of Health, Bethesda, MD), and data were normalized against that of the corresponding GAPDH bands.
Luciferase reporter assay
PTC cells were co-transfected with 500 ng pmiR-RB-report-h-PELI1-3′UTR (wild type and mutant type; GeneCopoeia) and 50 nM miR-30c-5p miRNA (mimics and mimic NC; GenePharma) using Lipofectamine 2000 (Invitrogen). After 48 h, cells were collected and their luciferase activity was measured using the Luc-Pair™ Duo-Luciferase HS Assay Kit (GeneCopoeia). The results are expressed as the relative firefly luciferase activity, which is obtained after normalization to Renilla luciferase activity.
Statistical analysis
The statistical analyses were performed with GraphPad Prism (Version 5.0; La Jolla, CA). Data are expressed as mean ± SD. The groups were compared using the Student’s t-test or one-way analysis of variance (Tukey Kramer post hoc tests). P < 0.05 was considered statistically significant.
Discussion
As an E3 ubiquitin ligase, PELI1 contributes to lymphoid and several solid (e.g., lung cancer, breast cancer, and melanoma) tumorigenesis [
5‐
10], which has been emphasized as valuable prognostic biomarker and attractive therapeutic targets of cancer. However, the expression and the biological function of PELI1 in PTC remain unclear. In this study, we presented the first evidence that both mRNA and protein levels of PELI1 widely upregulated in PTC tumor samples. In addition, we found that
PELI1 mRNA overexpression was associated with larger tumor size and lymph node metastasis, which consistent with the results from TCGA database that upregulation of
PELI1 in PTC patients was closely associated with
Ki-67 and lymph node metastasis. These data indicated that PELI1 potentially functions as a prognostic marker in PTC. Ectopic expression of PELI1 promoted PTC cell proliferation and migration, while PELI1 knockdown decimated these cellular behaviors of PTC cells in vitro
. More importantly, PELI1 knockdown inhibited tumor growth in subcutaneous tumor model accompanied with the decreased expression of Ki-67 and cell metastasis marker MMP2. These data strongly suggested that PELI1 contributed to PTC malignant progression and was therapeutic target for PTC. However, contradictory results regarding PELI1 expression and its roles in esophageal squamous cancer have been described recently [
11], perhaps mainly because of differences in tumor types, tumor microenvironments, animal model and so on.
PI3K/AKT pathway is closely associated with THCA development and progression and considered as new therapies for advanced THCA [
2,
26,
27]. Combined with KEGG analysis, the positive regulation of p-AKT by PELI1 in PTC cells and animal tumors was verified by using western blotting. These findings were similar to Jeon’ s report that p-AKT was elevated in PELI1-overexpressing A549 and H1299 cells, but decreased in PELI1-depleted A549 and H1299 cells [
8]. Additionally, in this study, we found that the inhibition of p-AKT significantly inhibited PELI1-mediated PTC cell proliferation and migration, which further confirmed that PELI1 promoted PTC progression, at least partly, through PI3K/AKT activation. However, the mechanism by which PELI1 activates PI3K/AKT pathway in PTC cells remains to be elucidated. It should be noted that a recent study reported that the PELI1 deficiency in T cells did not affect AKT activation [
10]. Thus, the functional roles of PELI1 in PI3K/AKT pathway might be cell type specific.
MiRNAs are thought to primarily down regulate gene expression by binding to 3′UTR of target transcripts, thereby usually be considered as fine-tuners of gene and signaling [
12‐
14]. Until now, no study has investigated the relationship between miRNAs and PELI1 in tumors. Based on bioinformatics analysis, we considered that miR-30c-5p loss might induce PELI1 accumulation in PTC, which was confirmed later by the following evidences: first, an inverse correlation between miR-30c-5p and PELI1 expression was observed in PTC tissues. Second, luciferase activity assays indicated that miR-30c-5p could bind with the 3′-UTR of
PELI1. Third, miR-30c-5p inversely regulated PELI1 mRNA and protein abundance in PTC cells. Certainly, this study did not rule out that other miRNAs may also be involved in PELI1 regulation, because an mRNA might be targeted simultaneously by many miRNAs [
12]. Furthermore, we first disclosed the biological function of miR-30c-5p in PTC. We demonstrated that miR-30c-5p overexpression inhibited PTC cell proliferation and migration in vitro, and these inhibition effects were partly abrogated by PELI1 restoration. These results not only supported the notion that miR-30c-5p is a tumor suppressor [
33‐
37] but also further confirmed the tumor-promoting function of PELI1 in PTC.
Due to poor cellular uptake and degradation after systemic delivery, delivering nucleic acid to tumors has been challenging [
38,
39]. Although liposomes and viral-based delivery systems have been assessed, all of these approaches exhibit low efficiency [
40]. Using EVs as biological vehicles to deliver tumor suppressor gene for tumor treatment is a novel and promising approach [
41,
42]. Especially, MSC is well suited for mass production of EVs that are ideal for gene delivery [
43,
44]. Our group and other investigators previously showed that MSC-EVs could effectively carry exogenous nucleic acid to influence the progression of tumor cells [
17,
20,
30,
45]. However, miRNA-carrying MSC-EVs strategy for PTC therapy has still not been explored. In this context, we selected hUCMSCs as the source of MSC-derived EVs, as hUCMSCs are better choices of MSCs for clinical application because of its higher cell vitality, higher accessibility, lower senescence, and fewer ethical constrains than other adult counterparts [
46,
47]. Our results showed that (1) miR-30c-5p-EVs could effectively delivered miR-30c-5p to PTC cell, and decrease the mRNA and protein expression of PELI1 and inhibited the PI3K/AKT pathway; (2) treatment with miR-30c-5p-EVs inhibited PTC cell proliferation and migration in vitro; and (3) miR-30c-5p-EVs were efficacious against PTC tumor growth in the BALB/c nude mice model, together with the upregulation of miR-30c-5p and significant downregulation of PELI1, p-AKT, Ki-67, and MMP2 expression. Overall, these data provided strong evidence that engineered hUCMSC-EVs delivering miR-30c-5p could effectively inhibit PELI1 expression and tumor progression in PTC, which partly promoted the clinical transformation of miR-30c-5p-PELI1 axis in tumor treatment. More importantly, in present study, we first investigated the effects of naïve hUCMSC-EVs on PTC progression, as MSC-EVs might exert various effects on cancer cell [
32]. We found hUCMSC-EVs significantly decreased PTC cell proliferation and migration in vitro and inhibited tumor growth in vivo. These findings together seemed to support the recent notion that MSC-EVs not only are versatile anti-tumor agent delivery platforms, but also can be a cell-free cancer treatment alternative [
48]. Further investigation is required to completely elucidate the role and mechanism of hUCMSC-EVs in PTC.
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