Microarray data preprocessing. Following quality assessment and removing inaccurate expression data, 691 DEGs (152 down-regulated and 539 up-regulated) (Figure.2A); and 122 DElncRNAs (78 down and 44 up-regulated) (Figure.2B), were identified in breast cancer samples compared to controls in gene chip GSE45827. Then, 60 DEmiRs (31 down-regulated and 29 up-regulated) were determined in gene chip GSE59247 (Figure.2C). A total of 38 DECs with 17 up-regulated and 41 down-regulated circRNAs were determined in gene chip GSE101123 (Figure.2D). Subsequently, 20 circRNAs were selected based on adjusted P-value, consisting of 10 down-regulated and 10 up-regulated circular RNAs. All data are presented in the Supplementary file (Table 1_4).
Identication of circRNA–miRNA interactions. Evidence suggests that some circular RNAs containing specific miRNA binding sites can reduce miRNA suppression to target mRNA, thus playing an important role in tumorigenesis. We predicted miRNAs that could trap by circRNAs to construct the circRNA-miRNA regulatory network using three online databases, CSCD, CircBank, and CircInteractome. Latter, we selected circRNAs that could intersect with more than two DEmiRNAs. Therefore, 24 circRNA-miRNA pairs consisting of 7 DEcircRNAs (3upregulated and 4 downregulated) and 14 DEmiRNAs were maintained. The fundamental structure of the 7 circRNAs including MRE (microRNA response element), RBP (RNA binding protein), and ORF (open reading frame) elements are exhibited in Figure.3. The basic characteristics of the 7 circRNAs are listed in Table 1.
Table 1
Basic characteristics of these 7 circRNAs.
Alias | CircRNA ID | Strand | CircRNA type | Position | Gene symbol | Regulation |
hsa_circRNA_102348 | hsa_circ_0007535 | + | exonic | chr18:33722243–33739978 | ELP2 | Down |
hsa_circRNA_100640 | hsa_circ_0002727 | - | exonic | chr10:88230748–88233730 | WAPAL | Down |
hsa_circRNA_100070 | hsa_circ_0005240 | - | exonic | chr1:16464347–16464925 | EPHA2 | Down |
hsa_circRNA_100332 | hsa_circ_0014130 | + | exonic | chr1:151206672–151212515 | PIP5K1A | Down |
hsa_circRNA_102140 | hsa_circ_0044927 | - | exonic | chr17:58275620–58292135 | USP32 | Up |
hsa_circRNA_100805 | hsa_circ_0007001 | - | exonic | chr11:46515157–46529920 | AMBRA1 | Up |
hsa_circRNA_104940 | hsa_circ_0089153 | + | exonic | chr9:134011326–134022971 | NUP214 | Up |
Indication of lncRNA–miRNA interactions. A total of 203 lncRNA probes were identified in GSE59247 datasets with adjusted P-value < 0.01. Next, 122 lncRNAs probe ID with |logFC| > 0.5 and adjusted P-value < 0.01 were detected among 11 normal and 130 breast tissue samples. Based on the potential interaction between miRNAs and lncRNAs, the interactions between lncRNA and 14 DEmiRNAs that linked with DEcircRNAs, were detected by DIANA TOOLs databases (https://diana.e-ce.uth.gr/lncbasev3). To improve the reliability of data, two filters (breast tissue selection and high confidence level) were applied. If the predicted miRNAs in the database were not matched with 14 DEmiRNAs, they would be eliminated. Then, lncRNAs that could intersect with more than two DEmiRNAs were selected. Using this technique, 37 lncRNA-miRNA interaction pairs including 9 DElncRNAs and 8 DEmiRNAs were identified. The basic information of the 9 lncRNAs is listed in Table 2.
Table 2
Basic characteristics of the 9 lncRNAs which are dominated as important molecules in breast cancer regulatory network.
lncRNA ID | Alias | Strand | lncRNA type | Position | Regulation |
FTX | XIST Regulator | - | intergenic | chrX:73946555–74293574 | Up |
MALAT1 | Metastasis Associated Lung Adenocarcinoma Transcript 1 | + | intergenic | chr11:65496267–65509085 | Up |
NORAD | Non-Coding RNA Activated By DNA Damage | - | intergenic | chr20:36045299–36051016 | Up |
TUG1 | Taurine Up-Regulated 1 | + | intergenic | chr22:30969158–30985225 | Up |
ZFAS1 | ZNFX1 Antisense RNA 1 | + | antisense | chr20:49276739–49361131 | Up |
OIP5-AS1 | OIP5 Antisense RNA 1 | + | sense-overlapping | chr15:41283963–41508868 | UP |
LINC01000 | Long Intergenic Non-Protein Coding RNA 1000 | + | intergenic | chr7:128633015–128664182 | Up |
LINC02210 | Long Intergenic Non-Protein Coding RNA 2210 | + | intronic | chr17:45,620,328 − 45,816,543 | Down |
MAPKAPK5-AS1 | MAPKAPK5 Antisense RNA 1 | - | antisense | chr12:111,839,703 − 111,843,005 | Up |
Ppi Network Construction And Module Analysis
To predict the interaction relevance, the STRING database was applied. As a result, 629 nodes and 4252 protein pairs with a combined weight score of > 0.4 were found in the network (Supplementary Table 5). All nodes with a combined score of > 0.9 were imported into Cytoscape software for visualization. After clustering analysis with MCODE, six modules with a score of > 5 were detected(Supplementary Table 6). After centrality analysis, the top 50 nodes with the degree, closeness, and betweenness indices values, higher than the mean value of the whole network, were considered as key nodes. Figure 4 shows the PPI network of the selected DEGs.
Functional Annotation
Enrichment analysis renders an approach for facilitating the biological interpretation of outcomes from high-throughput datasets (34). To obtain the biological functions of the 50 top DEGs, DO functional, GO analyses, and KEGG pathway enrichment was conducted using the cluster Profiler package of R software. The functional characterization of miRNAs was exploited using DIANA-miRPath v3 (Supplementary Table 7). Using disease ontology analysis of 50 top DEGs, revealed that 23 of them were associated with breast carcinoma, hereditary breast, and ovarian cancer, and breast disease (P < 0.05). Gene ontology enrichment in BP terms revealed that these DEGs were mainly involved in response to steroid hormone, regulation of protein serine/threonine kinase activity, response to ketonea antibiotic, response to oxygen levels, Fc receptor signaling pathway, positive regulation of T cell activation, positive regulation of leukocyte cell-cell adhesion, regulation of DNA metabolic process, leukocyte cell-cell adhesion, cell junction assembly, and positive regulation of cell-cell adhesion. For CC, DEGs were mainly enriched in focal adhesion, cell-substrate adherens junction, and cell-substrate junction. For MF, DEGs were mainly enriched in RNA polymerase II core promoter sequence-specific DNA binding, protease binding, and integrin binding (P < 0.05). In the KEGG pathway analysis, the top enriched pathways included bacterial invasion of epithelial cells, focal adhesion, proteoglycans in cancer, Rap1 signaling pathway, regulation of actin cytoskeleton, PI3K-Akt signaling pathway, tight junction, and ECM-receptor interaction (P < 0.05). The results are demonstrated in Fig. 5A-C. In addition, the cluster Profiler package of R software and DIANA MirPath web server was used to conduct GO analysis and KEGG pathway analysis for 14 miRNAs, respectively. For BP, 14 DEmiRs were mainly enriched in the regulation of angiogenesis, regulation of endothelial cell migration, and regulation of epithelial cell migration (P < 0.05). Moreover, the top five KEGG analysis pathways included Proteoglycans in cancer, Adherens junction, Cell cycle, FoxO signaling pathway, and Hippo signaling pathway (P < 0.05) ( Fig. 5D).
Identification of hub genes. In biological networks, hub nodes are crucial proteins, because they are more likely associated with disease pathogenesis. Hence, we selected 12 hub genes based on centrality indices, MCODE results, DO, and functional enrichment analysis including RHOA, EZH2, KIT, FOXO3, HSP90B1, NCOA3, RAC1, IGF1, CAV1, CXCR4, CCNB1, and ITGB1.
Prediction of miRNA target genes. MiRwalk database was searched to determaine the interaction between 14 DEmiRs and 691DEGs. If the predicted genes from the database were not considered as hub nodes, they would be removed from our list. Using this approach, 821 miRNA-mRNA interaction pairs were obtained between 14 miRNA and 691 differentially expressed genes. Also, 43 interaction pairs were identified between 14 miRNAs and 12 hub mRNAs.
The Prognostic Value Of Hub Mrnas
The clinical outcomes of key genes were evaluated through survival analysis. GEPIA webserver was applied to determine whether the expression of hub genes were related to the breast cancer patients’ overall survival (OS) and disease-free survival (DFS). This analysis indicated that for FOXO3, lower expression is closely related to improved OS (Logrank p = 0.0091; Fig. 6A). Besides, overexpression of RHOA is slightly associated with better DFS in BC patients (Logrank p = 0.015; Fig. 6B). Moreover, higher expression of KIT is associated with slightly higher survival rate in BC patients and this effect was altered over time (Logrank p = 0.016; Fig. 6C). All the other hub genes did not significantly influence the prognosis of patients with breast cancer.
Construction Of A Circrna/lncrna–mirna–mrna Network
The circRNA/lncRNA–miRNA–mRNA competitive network was established through merging the circRNA–miRNA, lncRNA–miRNA, and miRNA–mRNA interactions using Cytoscape software (Fig. 7). This network contained 7 circRNAs, 14 miRNAs, 9 lncRNA,12 hub genes, and 378 DEGs, which presented a global outlook into the convolutedlinks between circRNAs, lncRNAs, miRNAs, and mRNAs in breast tumors.
Intermodulation Of Ncrnas And Their Targeted Gene
Non-coding RNA as main actors in gene regulatory networks, directly or indirectly regulate the function of mRNAs and the disruption of these regulatory networks which are reported in various types of cancer(35–37). Here, we showed the intermodulation of the distinct regulatory mechanism among various ncRNA and their targeted genes in breast tumors.
Based on the present study, circ_0007535, circ_0014130, and circ_0007001 circRNAs, which could intersect with four miRNAs were selected. circ-0007535 and circ_0014130 were down-regulated, while circ_0007001 was up-regulated in cancer tissues versus normal tissues. In our predicted circRNA-miRNA network, miR-183, miR-188, miR-7, and miR-630 were recognized as target miRNAs for circ_0007535. There is uncertainty about the action mechanism of miR-183 in cancers. miR-183 has been reported to work as an oncogene or tumor suppressor in a wide range of human cancers(38). Several studies suggested that miR-183 acts as an oncogenic factor in human breast cancer thereby promotes cell proliferation and inhibits apoptosis in BC. For example, Yan Cheng et al found that miR-183 was upregulated in breast tumors, enhances cell proliferation migration, invasion, and inhibits cell apoptosis by targeting PDCD4(39). Besides, the miR-183/-96/-182 cluster is highly expressed in most breast cancers and promotes cell proliferation and migration(40). What’s more, overexpression of mir-183 and mir-494 serves a critical role in BC metastasis and increases the growth and spread of cancer cells in human BC cell lines (41). In our results, miR-183 was up-regulated in breast cancer tissues and based on mirwalk prediction, it can regulate the expression of FOXO3, RHOA, RAC1, CAV1, IGF1, NCOA3, CCNB1, and ITGB1. Along with circ_0007535, we found three possible DEcircRNAs, circ_0002727, circ_0044927, and circ_0089153 can intercommunicate with miR-183 and thereby regulate the expression of above 12 DEGs. Multiple studies show that miR-188 as a potent tumor suppressor, induces apoptosis, and inhibits proliferation in breast cancer cells (42). In our results, there was down-regulation of miR-188 in breast cancer tissues. We identified four probable crosstalk between these miRNAs and circRNAs, including circ_0007535-miR188-FOXO3/RHOA/IGF1, and circ_0002727-miR188-FOXO3/RHOA/IGF1. In the current study, it was found that circ_0014130 may adsorb corresponding miRNA through engaging with miRNA binding sites. It’s MREs were detected via online tools including miR-1207, miR-200b, and miR-200c. As a target miRNAs, miR-1207-5p act as an oncogene and stimulates BC cell growth and proliferation by targeting STAT6 (43). In triple-negative breast cancer (TNBC), antagomir-1207-5p/chemotherapy combination increases sensitivity to treatment (44, 45). Instead, miR-1207-5p acts as an antioncogene by impairing cell spreading, migration, and invasion in gastric cancer (46) and lung cancer (47). However, in our results, miR-1207 was down-regulated in luminal cancer tissues versus normal tissues, and further study required to explain the action mechanism of miR-1207 in luminal tumors. In this paper,we predicted miR-1207-5p as a target for circ_0014130 and hsa_circ_0007001 which may present a promising strategy for BC regulation. In addition, miR-200b-3p and miR-200c were associated with the ER status of BC cells and were down-regulated in the basal TNBC compared to ER+/epithelial cancer cell lines (48). They can repress a program of mesenchymal genes to keep an epithelial state and inhibit metastasis in breast cancer (48–50). Consequently, triple-negative breast cancer cells could benefit from the restoration of these microRNAs. Based on our assessment, there are links between circ_0007001 and miR-200b-3p in breast tumors, thus, inhibition of circ_0007001 by RNA interference (RNAi) may be an interesting target for TNBC treatment.
In this study, also a second regulatory network, interactions between differentially expressed lncRNAs, miRNAs, and mRNAs were determined. In our in silico assessments, among 9 selected DElncRNAs, five including NORAD, MALAT1, TUG1, ZFAS1, OIP5-AS1 could intersect with more than three DEmiRNAs like miR-183, miR-182, miR-7, miR149, miR-200b, miR,200c, miR-101, and miR-342. All of the above five LncRNAs were upregulated and could function as oncogenic ncRNAs contributing to the progression and invasivasion of breast tumors through modulating downstream pathways. Therefore, it is imperative to explore the molecular pathways implicated in BC drug resistance or tumor metastasis to refine therapeutic outcomes. Increased expression of lncRNA-NORAD in breast cancer tissues facilitates proliferation and invasion of breast cancer cells and is associated with poor prognosis.The study by Ke Zhou et al. showed that lncRNA NORAD was overexpressed in breast cancerous tissues and stimulated BC cell progression by regulating the TGF-β pathway (51). We showed that NORAD could promote the occurrence and development of breast tumors by adsorbing miR-183, miR-182, miR-7, miR149, miR,200c, miR-101, and miR-342 as a sponge to regulate the expression of 12 hubs DEmRNAs including FOXO3, RHOA, EZH2, KIT, HSP90B1, NCOA3, RAC1, IGF1, CAV1, CXCR4, CCNB1, and ITGB1. Another lncRNA, taurine upregulated 1 gene (TUG1) is a lncRNA associated with diverse types of cancer such as breast tumors. The expression and action mechanism of TUG1 in breast carcinoma is a quite arguable subject. The study by Teng Li. demonstrated that the TUG1 expression was enhanced in breast cancer tissues and highly invasive BC cell lines and was related to clinical and pathologic tumor characteristics including tumor size, distant metastasis, and TNM staging(52). Whereas other studies reported downregulation of TUG1 in triple-negative BC and that its expression increases cisplatin sensitivity in TNBC cells (53). Based on our results, TUG1 could regulate the expression of 12 hubs DEmRNAs including FOXO3, RHOA, EZH2, KIT, HSP90B1, NCOA3, RAC1, IGF1, CAV1, CXCR4, CCNB1, and ITGB1by trapping miR-183, miR-182, miR-7, and miR-101. In most studies, Metastasis Associated Lung Adenocarcinoma Transcript 1 (MALAT1) is commomly overexpressed and acts as a poor prognosticator lncRNAs in some types of cancers, including breast tumors (54, 55). The action mechanism of MALAT1 on breast cancer cell proliferation is disputable, as reported that MALAT1 can act as metastasis promoter (56) and cell proliferation suppressor (57). The controversial evidence in the role of MALAT1 in tumorigenesis from distinct studies may be based on the specific tumor subtypes or different cell types (58, 59). Likewise, MALAT1 might regulate the above mentioned hub DEGs by trapping miR-183, miR-342, miR-7,miR-200b, miR-200c, and miR-101. The study by Haibing Xiao et al., revealed that MALAT1 can modulate ZEB2 expression via trapping miR-200s as a competing endogenous RNA and serve as a possible therapeutic target in clear cell kidney carcinoma (60). Similarly, MALAT1 promotes melanoma expansion by inhibiting the expression and function of miR-183 and ITGB1 signal activation(61). Furthermore, the repressive function of miR-101 on the autophagy and growth of colorectal cancer cells was abrogated by MALAT1(62). Consequently, NORAD, TUG1, and MALAT1 may be desirable biomarkers for breast cancer diagnosis and therapeutic targets in breast cancer management. It is noteworthy that these ncRNAs could interact with other 378 DEGs in the network and construct a complex regulatory RNA network. This study listed many ncRNAs, which might bind to miRNAs to regulate breast cancer progression. All potential circRNA–miRNA–mRNA and lncRNA–miRNA–mRNA crosstalks in breast cancer are summarized in Table 3.
Table 3
All potential circRNA–miRNA–mRNA and lncRNA–miRNA–mRNA axes in breast cancer.
DEcircRNA | DElncRNA | DEmiRNA | DEG |
circ-0007535 circ-0044927 circ-0089153 circ-0002727 | NORAD MALAT1 OIP5-AS1 TUG1 FTX LINC01000 LINC02210 | miR-183 | RHOA IGF1 CCNB1 ITGB1 RAC1 FOXO3 CAV1 |
circ-0014130 circ-0044927 | NORAD MALAT1 OIP5-AS1 TUG1 ZFAS1 FTX LINC02210 MAPKAPK5-AS1 | miR-101 | RHOA EZH2 RAC1 HSP90B1 FOXO3 |
circ-0007001 | NORAD | miR-149 | FOXO3 CXCR4 KIT |
circ-0044927 | NORAD TUG1 ZFAS1 | miR-182 | IGF1 FOXO3 CAV1 NCOA3 |
circ-0014130 circ-0007001 | MALAT1 OIP5-AS1 ZFAS1 LINC01000 LINC02210 MAPKAPK5-AS1 | miR-200b | RHOA EZH2 |
circ-0014130 | NORAD MALAT1 LINC01000 MAPKAPK5-AS1 | miR-200c | RHOA FOXO3 CAV1 NCOA3 |
Consequently, triple-negative breast cancer cells could benefit from the restoration of these microRNAs. Based on our assessment, there are links between circ_0007001 and miR-200b-3p in breast tumors, thus, inhibition of circ_0007001 by RNA interference (RNAi) may be an interesting target for TNBC treatment.
In this study, also a second regulatory network, interactions between differentially expressed lncRNAs, miRNAs, and mRNAs were determined. In our in silico assessments, among 9 selected DElncRNAs, five including NORAD, MALAT1, TUG1, ZFAS1, OIP5-AS1 could intersect with more than three DEmiRNAs like miR-183, miR-182, miR-7, miR149, miR-200b, miR,200c, miR-101, and miR-342. All of the above five LncRNAs were upregulated and could function as oncogenic ncRNAs contributing to the progression and invasivasion of breast tumors through modulating downstream pathways. Therefore, it is imperative to explore the molecular pathways implicated in BC drug resistance or tumor metastasis to refine therapeutic outcomes. Increased expression of lncRNA-NORAD in breast cancer tissues facilitates proliferation and invasion of breast cancer cells and is associated with poor prognosis.The study by Ke Zhou et al. showed that lncRNA NORAD was overexpressed in breast cancerous tissues and stimulated BC cell progression by regulating the TGF-β pathway (51). We showed that NORAD could promote the occurrence and development of breast tumors by adsorbing miR-183, miR-182, miR-7, miR149, miR,200c, miR-101, and miR-342 as a sponge to regulate the expression of 12 hubs DEmRNAs including FOXO3, RHOA, EZH2, KIT, HSP90B1, NCOA3, RAC1, IGF1, CAV1, CXCR4, CCNB1, and ITGB1. Another lncRNA, taurine upregulated 1 gene (TUG1) is a lncRNA associated with diverse types of cancer such as breast tumors. The expression and action mechanism of TUG1 in breast carcinoma is a quite arguable subject. The study by Teng Li. demonstrated that the TUG1 expression was enhanced in breast cancer tissues and highly invasive BC cell lines and was related to clinical and pathologic tumor characteristics including tumor size, distant metastasis, and TNM staging(52). Whereas other studies reported downregulation of TUG1 in triple-negative BC and that its expression increases cisplatin sensitivity in TNBC cells (53). Based on our results, TUG1 could regulate the expression of 12 hubs DEmRNAs including FOXO3, RHOA, EZH2, KIT, HSP90B1, NCOA3, RAC1, IGF1, CAV1, CXCR4, CCNB1, and ITGB1by trapping miR-183, miR-182, miR-7, and miR-101. In most studies, Metastasis Associated Lung Adenocarcinoma Transcript 1 (MALAT1) is generally overexpressed and acts as a poor prognosticator lncRNAs in some types of cancers, including breast tumors (54, 55). The action mechanism of MALAT1 on breast cancer cell proliferation is disputable, as reported that MALAT1 can act as metastasis promoter (56) and cell proliferation suppressor (57). The controversial evidence in the role of MALAT1 in tumorigenesis from distinct studies may be based on the specific tumor subtypes or different cell types (58, 59). Likewise, MALAT1 might regulate the above mentioned hub DEGs by trapping miR-183, miR-342, miR-7,miR-200b, miR-200c, and miR-101. The study by Haibing Xiao et al., revealed that MALAT1 can modulate ZEB2 expression via trapping miR-200s as a competing endogenous RNA and serve as a possible therapeutic target in clear cell kidney carcinoma (60). Similarly, MALAT1 promotes melanoma expansion by inhibiting the expression and function of miR-183 and ITGB1 signal activation(61). Furthermore, the repressive function of miR-101 on the autophagy and growth of colorectal cancer cells was abrogated by MALAT1(62). Consequently, NORAD, TUG1, and MALAT1 may be desirable biomarkers for breast cancer diagnosis and therapeutic targets in breast cancer management. It is noteworthy that these ncRNAs could interact with other 378 DEGs in the network and construct a complex regulatory RNA network. This study listed many ncRNAs, which might bind to miRNAs to regulate breast cancer progression. All potential circRNA–miRNA–mRNA and lncRNA–miRNA–mRNA crosstalks in breast cancer are summarized in Table 3.