Background
Gastric cancer is one of the most common malignancies worldwide. Although incidence and mortality of gastric cancer has been dramatically decreased over the last decades worldwide, the declines are becoming less remarkable in some countries [
1]. The main reason may be that there are limited treatment options and patients in advanced stages could not be cured by surgical removal [
2]. Moreover, 5-year survival rates of gastric cancer are decreased with gastric cancer progression [
3] and metastatic stage could lead to poor outcomes [
4]. In Chinese Qinghai, the Tibetan ethnic group has a higher incidence of gastric cancer than the Han ethnic group [
5]. Thus, there is an urgent need to develop effective treatments to improve diagnosis and reduce burden of gastric cancer in gastric cancer-infected Tibetan.
A number of key genes with abnormal expression in the progression of gastric cancer have been screened out. For example, the over-expression of
SPAG9 (sperm associated antigen 9) correlates with poor prognosis and leads to gastric cancer invasion and chemo-resistance [
6]. In terms of Tibetan with gastric cancer, the expression pattern of tumor-associated antigen MG(7)-Ag is abnormal and it can be used as a reliable marker to predict gastric cancer at early stage [
7]. The polymorphisms of prostate stem cell antigen gene are also associated with gastric cancer in Tibetans [
8]. Therefore, the identification of key genes can improve diagnosis and management of gastric cancer in Tibetan.
MicroRNAs (miRNAs) are a group of small non-coding RNAs that have important roles in the development of numerous cancer types, through down-regulation of the target genes [
9,
10]. Multiple miRNAs are expressed aberrantly and are involved in the progression and prognosis of gastric cancer [
11]. Therefore, investigating role of miRNAs in gastric cancer could provide new insight into the biological mechanism of this disease. Reportedly, miR-21 is up-regulated in gastric cancer and its dysregulation can enhance cell proliferation, invasion and migration through down-regulating a set of tumor suppressor genes, such as
RECK (reversion-inducing-cysteine-rich protein with kazal motifs) [
12]. In addition, miR-544a could activate the Wnt signaling pathway by stabilizing the β-catenin in nucleus and its inhibition may be a therapeutic method for metastatic gastric cancer [
13]. However, the research on miRNAs in gastric cancer in Tibetan is really rare and therefore, the exploration of miRNAs in the progression of gastric cancer in Tibetan is of great significance.
In the present study, the paired cancerous and adjacent non-cancerous tissue samples were collected from 10 patients with gastric cancer, and further conducted for miRNA expression profiling analysis. Differentially expressed miRNAs (DE-miRs) were screened out between two sample groups, followed by identification of target genes based on bioinformatics methods. Furthermore, functional enrichment analysis was performed for the DE-miRs so as to reveal their potential roles in progression of gastric cancer.
Discussion
MiRNAs exert regulatory effects on gene expression in humans, resulting in cell growth, differentiation and apoptosis via down-regulating target genes in cancer [
21]. In the present study, a total of 27 DE-miRs were screened out, including hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p, which targeted the most genes. Furthermore, the three miRNAs were significantly enriched in cancer-related pathways, including Wnt signaling pathway, MAPK (mitogen-activated protein kinase) signaling pathway and Jak-STAT (Janus kinase-signal transducer and activator of transcription) signaling pathway.
Wnt signaling pathway is implicated in cancer development and its hyperactivation can lead to enhanced tumorigenicity and increased metastatic potential [
22]. In gastric cancer, overexpressed miR-544a is demonstrated to activate WNT signaling pathway which further contributes to the disease progression [
13]. In the present study, we identified that hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p were remarkably enriched in Wnt signaling pathway. Reportedly, miR-148a inhibits the metastasis of hepatocellular carcinoma via acting on Wnt signaling pathway [
23]. MiR-363 down-regulates the expression of myeloid cell leukemia-1 [
24] whose expression correlates with phosphorylated glycogen synthase kinase-3beta, the key component of Wnt signaling pathway in breast cancer [
25]. Notably, the above miRNA targets, such as
Wnt1, were significantly enriched in Wnt signaling pathway. We can speculate that the miR-148a, miR-148b and miR-363 may play significant roles in gastric cancer progression via regulating the Wnt signaling pathway.
Besides, MAPK signaling pathway is dysregulated in gastric cancer, leading to abnormal cell proliferation and metastasis [
26]. Moreover, the signaling pathway is implicated in drug resistance in gastric cancer by regulating the expression of apoptotic proteins
Bax (BCL2-associated X protein)/
Bcl-
2 (B-cell CLL/lymphoma 2) [
27]. Our enrichment analysis showed that hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p were also significantly enriched in MAPK signaling pathway. In breast cancer, miR-148a acts as a tumor suppressor via targeting
IGF-
IR (insulin-like growth factor-I receptor) and
IRS1 (insulin receptor substrate 1) and further suppressing the downstream MAPK signaling pathway [
28]. Besides, miR-363 is found to be down-regulated in gastric cancer and its down-regulation is associated with tumor differentiation, TNM stage and lymph-node metastasis [
29]. Notably, the suppression of their common target
KLF4 could inhibit the expression of various
Erk5 (mitogen-activated protein kinase 7) targets and further affect the MAPK cascade in the regulation of endothelial integrity in cancer [
30]. The enrichment of miR-148a, miR-148b and miR-363 in MAPK signaling pathway may suggest a joint contribution to gastric cancer development via involving MAPK signaling pathway.
Additionally, hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p were found to be dramatically enriched in Jak-STAT signaling pathway. Jak-STAT serves as a straightforward mechanism whereby cells sense environmental cures and further regulate cell growth and differentiation in cancer [
31]. The inhibition of Jak-STAT signaling pathway can lead to decreased cell proliferation and enhanced cell apoptosis in gastric cancer cells [
32]. Exogenous miR-363 promotes cell growth, progression and tumorsphere formation of SC-M1 gastric cancer cells, and the knockdown of miR-363 suppresses tumorigenesis of SC-M1 cells [
33]. MiR-148a/b is dysregulated and their haplotype is significantly correlated with gastric cancer [
34].
S1PR1, one of the common targets of miR-148a-3p, -148b-3p and -363-3p, is implicated in
NFκB/IL-
6/STAT3/S1PR1 amplification loop that is important for chronic colitis-related cancer and can be suggested as therapeutic option [
35]. The enrichment of the three miRNAs in Jak-STAT signaling pathway implies their involvement in gastric cancer progression via Jak-STAT signaling pathway.
We should note that there were some limitations in the present study. Herein, although we demonstrated a significant enrichment of dysregulated hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p in cancer-related pathways in patients with gastric cancer, we did not further validate their expressions, nor demonstrate their roles in cancer-related pathways using systematically functional experiments. Moreover, as there are only 10 samples enrolled in this study, we did not further consider the DE-miRs among different stages. Besides, the present results were just obtained based on microarray analysis and bioinformatics prediction, and needed to be further validated in future. However, this study can be regarded as a preliminary study and to an extent provide some valuable directions for future studies, especially for researches on gastric cancer in Tibetan.
In summary, the present study identified a downregulation of hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p in gastric cancer in Tibetan using microarray analysis. What is more, we demonstrated their significant enrichment in cancer-related pathways, including Wnt signaling pathway, MAPK signaling pathway and Jak-STAT signaling pathway. These findings suggested the potential usage of hsa-miR-148a-3p, hsa-miR-148b-3p and hsa-miR-363-3p as diagnostic and therapeutic biomarkers for gastric cancer-infected Tibetan. However, further experimental validations are in urgent need to confirm these results.
Authors’ contributions
YL and CZ carried out the molecular studies, FT participated in the sequence alignment, JZ, CS and CW drafted the manuscript. PY carried out the study. YL participated in the sequence alignment. MW and JD participated in the design of the study and performed the statistical analysis. RC, GR, YL and CZ conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.