Breast cancer was a common malignant tumor in female population, with an increasing prevalence in the past decade[33]. It becomes a major heath threaten to females and the public health worldwide, though clinical therapies including surgery, radiotherapy, chemotherapy and targeted therapy for breast cancer have been rapidly developing. Several epidemiological studies had highlighted an increased incidence[3] and bad prognosis[34] of breast cancer in female patients with chronic HBV infection. Therefore, this study investigated the mechanism that lies behind such association by analysing the involvement of HBV-related exosomal miRNA in the changes of gene expression with breast cancer. Via the identification of the key genetic targets that mediated the effects of HBV infection on the progression breast carcinoma, our results provided novel targets for the development of therapeutic strategy and prognostic biomarkers for breast cancer.
Firstly, our results found that miRNAs from the serum exosomes of female CHB patients, expression of hsa-miR-363 and hsa-miR-1237 showed significant down-regulation hsa-miR-1260, hsa-miR-100, hsa-miR-1287, hsa-miR-148a, hsa-miR-99a, hsa-miR-125b, hsa-miR-885-5p was significant up-regulation, in compared to uninfected individuals. Exosomes played critical roles in signal transmission within the human body through endocytosis and absorbance of organs, and has been implicated in occurrence and development of carcinoma[19]. Our hypothesis was that the changes of exosomal miRNAs that were indued by the chronic HBV infection affects breast cells via the endocytososis of exosomes in the circulatory system. This could lead to changes of related gene expression in the breast cancer cells, triggering the process of cainogenesis.
To prove this hypothesis, we identified the potential target genes of those miRNAs that showed a differential expression in CHB patients, which were then cross-analysed with genes showing differentially expression in breast cancer.
Through GO analysis, we found that CC was mainly located in the cytoplasmic membrane components, cytoskeleton and actin skeleton. These components were associated with tumor cell invasion and metastasis, cell adhesion[35, 36] and tumor cell immune tolerance[37]. BP were mainly concentrated in cellular response to hormone stimulus, regulation of signal transduction[38] and regulation of epithelial cell proliferation[39]. These biological process were closely related to the occurrence and development of breast cancer. MF cluster analysis showed that the DEGs functions mainly include a variety of actins[40], integrins[41], and kinase anchoring and activity[42]. These functions were also closely related to the occurrence of tumors. The results of KEGG analysis showed that many pathways in these gene-enriched pathways were closely related to cancer progression, such as pathways in cancer, Ras signaling pathway[43], PI3K-Akt signaling pathway[44]. It shows that these DEGs can regulate the occurrence, development, invasion and metastasis of breast cancer through a variety of signaling pathways. We constructed a PPI network in the STRING database, and used the MCC algorithm in Cytoscape to get the top ten hub genes. Then we used UALCAN and ONCOMINE database to verify the relative expression levels of these hub genes in breast cancer tissues and found that all the hub genes were dysregulated in breast cancer tissue and the result was consistent. HPA database was used to verify the protein expression level of hub genes. We found statistically different results in the protein expression level of GNG2, ADCY5, CX3CL1, CXCL11, S1PR1. Therefore, female CHB patients may affect the occurrence and development of breast cancer by regulating the expression of miRNAs in exosomes to manipulate the expression of hub genes in breast tissue.
Chemokines were secreted proteins with a molecular weight of 8-14kDa in the cytokine family[45]. Both immune and tumor cells can express multiple chemokines. According to the number of conserved cysteines in the N-terminal domain of these proteins, they were divided into four families: CC, CXC, CX3C and XC families[46]. Chemokines played an important role in tumorigenesis and development. CX3CL1 was a chemokine with a cysteine signature motif -Cys-X-X-X-Cysat the N-terminal end[47]named neurotactin[48]or fractalkine[49]which was highly expressed in brain[50], blood vessels[51], bone[52]and other tissues. Increased expression of CX3CL1 in tumor tissues will cause anti-cancer CD4 + T cells, CD8 + T cells, dendritic cells and NK cells to accumulate around the tumor to kill tumor cells[53, 54]. High expression of CX3CL1 in breast cancer[55], gastrointestinal cancer[56], lung adenocarcinoma[57]was closely related to good prognosis. On the contrary, advanced tumors will secrete TGF-β to reduce the expression of intracellular CX3CL1[58]. It will inhibit the aggregation of anti-tumor cells to tumor tissues and promote tumor development. By bioinformatics analysis, we found that miR-885-5p was highly expressed in serum exosomes of female CHB patients which would inhibit CX3CL1 expression in breast cells. And the lower expression of CX3CL1 was correlated with higher lymph node metastasis rate in breast cancer patients. Patients with higher lymph node metastasis rate had significantly worse prognosis[59], which may be associated with a worse prognosis for patients with lower expression of CX3CL1. CXCL12 was originally considered to be a growth factor of pre-B cells and was closely related to lymphocyte survival and embryonic development [60]. At present, a large number of basic studies had found that CXCL12 promoted the occurrence and development of multiple tumors, invasion and metastasis[61, 62] and resistance to chemotherapeutics[63, 64] through multiple signaling pathways by combining with CXCR4[65, 66]. And some clinical studies had found that breast cancer patients with high expression of CXCL12 had a poor prognosis[67, 68]. But there were many basics[69], clinical researches and meta-analysis[70, 71] found that high expression of CXCL12 will prolong the survival of patients. By bioinformatics analysis, we found that high expression of miR-125b-5p and miR-1260a in serum exosomes suppressed CXCL12 expression in breast tissue. The bc-GenExMiner database showed that low CXCL12 expression was positively correlated with HER-2 positive status. HER-2 positive status was associated with poor prognosis[72]. This may be related to the poor prognosis of patients with low CXCL12 expression in the K-M plotter database. In addition, the main metastatic feature of CXCL12 comes from the biological functions of CXCR4. By inhibiting the expression of CXCR4, the effect of breast cancer immunotherapy was enhanced[73]. We searched CXCR4 expression of breast cancer in UALCAN and K-M plotter found that CXCR4 expression was highly expressed in breast cancer tissues(Fig. 5), and the RFS was poor when the expression of CXCR4 was low(Fig. 8). This result indicated that it may not be the increase in endogenous CXCL12 expression, but the high expression of CXCR4 caused by other reasons, that leads to the poor prognosis of breast cancer patients. This had also been confirmed by some researches that decreasing expression of endogenous CXCL12 will enhance the expression of CXCR4 to accept external CXCL12 and enhance mitotic ability[69]. Interestingly, we also observed that miR-1237-3p which can inhibit CXCL12 expression was lowly expressed in the serum exosomes of female CHB patients. Whether this change will affect the overall expression of CXCL12 in breast tissue needs to be further investigated. CXCL1, a small chemokine belonging to the CXC chemokine family, was closely related to inflammation[74], angiogenesis[75], tumor formation[76] and so on. CXCL1 can promote the invasion and metastasis of breast cancer cells by activating ERK to promote the expression of MMP2/9[77].Breast cancer cells promote CXCL1/S100A8/9 survival axis through high expression of TNF-α to promote breast cancer cells to resist chemotherapy[78]. In addition, a large number of clinical studies have found that high expression of CXCL1 was associated with the poor prognosis of a large number of tumors[79].However, we have obtained the opposite result in breast cancer through bioinformatics technology. In this research, we found that high expression of miR-885-5p in serum exosomes of female CHB patients suppressed CXCL1 expression in breast tissue. The low expression of CXCL1 in breast cancer tissue was positively correlated with poor prognosis of breast cancer. Some researchers had found that the expression of CXCL1 in breast cancer tissue specimens was significantly lower than that in normal tissues[80]. Unfortunately, they had not made a reasonable explanation for this. This conflict may require further research. CXCL11 was induced by IFN-γ, IFN-β and IFN-α[81], mainly through the combination of CXCR3[82] or CXCR7 to play biological function[83]. CXCL11 promoted the self-renewal ability, tumorigenicity and anti-chemotherapeutic ability of liver cancer cells through the CXCR3/ERK1/2 signaling pathway[84]. Inhibition of CXCL11 expression can inhibit tumor cell proliferation[85] and epithelial-mesenchymal transition[86]. Our results found that compared with the expression level of miR–363-3p in serum exsomes of normal women, the expression of miR–363-3p was lower in serum exosomes of female CHB patients. This difference will lead to high expression of CXCL11 in breast tissue. High expression of CXCL11 was positively associated with nodal status rate, which may predict a poor prognosis. In addition we obtained similar results in the K-M plotter database, that high expression of CXCL11 was associated with poor prognosis of breast cancer patinets.
Current studies have found that heterotrimers G proteins were involved in various biological activities such as cell proliferation, differentiation[87]and angiogenesis[88]. G protein g2 subunit ( GNG2) was one of the subunits of G protein β dimer. It was expressed in fetal tissue, adrenal gland and brain. It regulated a series of intracellular effects, including ion channels and adenylate cyclase[89]by activating Phospholipase cη2 (PlcH2) neurotransmitter deliver[90]. Reducing the expression of GNG2 can activate c-SRC and promote AKT signaling pathway, which were closely related to breast cancer cell proliferation[91], invasion and metastasis[92]. Our study found that elevated miR-125b-5p expression in serum exosomes of female CHB patients may lead to the low expression of GNG2 in breast cancer tissue, and breast cancer patients with low expression of GNG2 will lead to a poor prognosis.
LPAR1 was the earliest discovered lysophosphatidic acid receptor[93]which was expressed in brain, heart, colon, small intestine and placenta[94]. In combination with Gαi/o,Gαq/11 and Gα12/13, LPAR1 can activate AKT, rho, MAPK and PLC to affect cell survival, differentiation, adhesion and migration[95]. The role of LPAR1 in breast cancer was still unclear. Some studies had found that LPAR1 inhibitor can inhibit breast cancer cell metastasis to the lung and liver[96]. Nevertheless, other studies had found that inhibiting LPAR1 expression can promote the proliferation, invasion and metastasis of breast cancer cells[97].Our study found that elevated miR-125b-5p expression in serum exosomes of female CHB patients may lead to LPAR1 down-regulated in breast cancer tissues. Low expression of LPAR1 was positively associated with HER-2 positive status in breast cacaer. HER-2 positive status was associated with poor prognosis[72], which may explain patients with low expression of LPAR1 had poor prognosis. However, we also observed that miR-1237-3p, which can inhibit LPAR1 expression, was decreased in serum exosomes of such patients. Whether this change will affect the expression of LPAR1 in breast cancer needs to be confirmed by more studies.
Protein Coupled Receptors (GPCR) were the unique family of transmembrane receptors and interaction with a diversity set of ligands such as lips, pets, chemokines, odorants, homones and pheromones to achieve its function[98]. At present, it was found that GPR17 was mainly confined to oligodendrocyte cell lines and was very important for myelin formation in oligodendrocytes[99]. It was considered to be closely related to multiple sclerosis[100]. GPR17 agonists can inhibit glioma cell proliferation[101]. At present, there was still no relevant research about GPR17 in breast cancer. According to our results, the expression of GPR17 in breast cancer was reduced by the high expression of miR-1260a, miR-1287-5p and miR-885-5p in serum exosomes of female CHB patients. And the low expression of the gene was correlated with the poor prognosis. This was similar to the results of GPR17 in glioma but it needs to be further confirmed in breast cancer. We also observed that miR-1237-3p and miR-363-3p, which inhibited the expression of GPR17, were lowly expressed in serum exosomes of female CHB patients. More basic and clinical studies should be undertaked to confirme whether this change affected GPR17 expression in breast cancer.
Adenylate cyclase can convert ATP into the second messenger cAMP, and influence sugar, lipid and protein metabolism through signal transmission. ADCY5 belongs to the adenylate cyclase family and consists of twelve transmembrane domains, which catalyze the conversion of ATP. It was a cyclic AMP, which was the second messenger of G protein-coupled receptors[102].The low expression of ACDY5 after DNA methylation was related to the low prognosis of lung cancer[103]. The decrease of ACDY5 promoted the occurence of prostate cancer[104]. Using bioinformatics technology, we found that highly expressed miR-1260a in serum exosomes of female CHB patients will suppress ADCY5 expression in breast tissue and low expression of ACDY5 was associated with a poor prognosis. At present, the relationship between ADCY5 and malignant tumors was not clear. Studies have found that ADCY5 decline can promote mouse cell autophagy to promote mouse cell survival and resist apoptosis [105], whether this can explain the relationship between ADCY5 decline and the malignancy remained to be further research. ADCY3 was widely expressed in tissues throughout the body, and its role in tumors had not yet been determined. Studies had found that its high expression can promote the occurrence and development of gastric cancer through over-expression of CREB[106], and inhibiting ADCY3 expression by miR-335 can inhibit gastric cancer cells invasion and metastasis[107]. However, other studies had found that promoting the expression of ADCY3 can inhibit the invasion and metastasis of pancreatic cancer [108]. Through bioinformatics technology, researchers found that the expression of ADCY3 in malignant glioma was lower than that in normal tissues, and the low expression of ADCY3 was related to the poor prognosis[109]. Our research speculated that female CHB patients may inhibit the expression of ADCY3 in breast tissue through high expression of miR-125b-5p in serum exosomes. This alteration would promote breast cancer and was positively correlated with HER-2 positive status. This change can explain the association of low expression of ADCY3 with poor prognosis in the K-M plotter.
S1P receptor (S1PR1) was a biologically active sphingolipid metabolite that mediated S1P activity and promoted cell proliferation and survival[110, 111]. S1PR1 was widely expressed in vascular endothelium and it was very important for embryonic blood vessel formation and maturation[112]. The role of S1PR1 in tumors was unclear currently. Some studies had found that S1PR1 and STAT3 stimulated and activated each other to enhance tumor growth[113]. In addition, S1PR1 can also promote tumor development by activating multiple signaling pathways[114–116]. S1PR1 can promote breast cancer cell survival by down-regulating the pro-apoptotic protein Bim and up-regulating the anti-apoptotic protein Mcl-1[117]. S1PR1 inhibitors can enhance the toxicity and anti-proliferative effects of carboplatin on breast cancer cells[118]. However, some researchers had found that inhibiting the expression of S1PR1 can promote breast cancer and improve survival [119]. S1PR1 regulates the activation of RhoA and inhibits the mimic angiogenesis of breast cancer cells to inhibit tumor growth and distant metastasis[120]. Some researchers had found that the expression of S1PR1 in breast cancer tissues was significantly lower than that in normal tissues by integrating TCGA data, and lower expression of S1PR1 indicated a worse prognosis[121]. By analyzing relevant data, we also found that miR-1287-5p in serum exosomes of female CHB patients may inhibit the expression of S1PR1 in breast tissue. Low expression of S1PR1 was positively associated with poor prognosis. This is consistent with some other scholars.
By comparing the expression of miRNAs in serum exosomes of chronic HBV-infected female with uninfected female, we clarified the reasons why female with chronic HBV infection were more likely to develop breast cancer and had a worse prognosis. Since the data used for the analysis were obtained from multiple online bioinformatics resources, there may be some bias caused by confounding factors. And these theories need to be confirmed in more basic and clinical research.