Discussion
Although the cure and survival rates of testicular cancer are high, the main treatment methods are chemotherapy and resection (15), which presents a great burden on the patient quality of life. In addition, the incidence of seminoma is rising. The lifestyles of males in different regions vary, while the incidence rate also differs (16). It is estimated that by 2030, there will be 65,827 new cases worldwide, an increase of 10,561 cases from 2012 (17). Although multiple approaches have reduced mortality, treatment resistance, disease relapse and treatment-derived side effects in particular, are important issues at present (18). Therefore, it is important to develop novel specific targeted therapies for the treatment of seminoma.
In our study, a total of 287 DEGs were screened, including 110 upregulated genes and 177 downregulated genes. The upregulated genes were enriched in ‘viral carcinogenesis’, ‘leukocyte transendothelial migration’ and ‘CAMs’, while the downregulated genes were mainly enriched in ‘amphetamine addiction’, ‘long-term potentiation’ and ‘oocyte meiosis in diabetic complications’. Moreover, by constructing the PPI network, we identified five high-degree hub genes, including TOP2A, UBE2C, PTPRC, MKI67 and CENPA. Among them, all hub genes were upregulated in seminoma. Finally, we used UALCAN to analyse the expression of these hub genes; all the hub genes were reported to be significant. Then, we predicted the association between the expression of the hub genes and the prognosis of TGCT patients. Based on GEPIA, the overexpression of all hub genes was related to an unfavourable prognosis in patients with testicular cancer. Among them, we found that the overexpression of PTPRC was an unfavourable prognostic factor for patients with seminoma.
TOP2A is the molecular target of several clinically useful chemotherapeutic drugs and has been used to treat a variety of tumours, including breast cancer, prostate cancer and endometrial cancer (19). Certain studies have suggested that the overexpression of TOP2A may be associated with the poor prognosis of these malignant diseases. For seminoma, TOP2A overexpression was associated with aggressive clinical behaviours (20). Coleman et al (21) and Sano and Shuhin (22) suggested that TOP2A may be a marker of seminoma cell proliferation, and TOP2A was easily detected in seminoma. Additionally, studies have also revealed that TOP2A is related to primary tumours (23–25). In prostate cancer, Labbé et al (26) found that TOP2A and EZH2 mRNA and protein upregulation was linked to a subgroup of primary and metastatic patients with more aggressive disease, and exhibited a notable overlap of genes involved in mitotic regulation, these results further support the hypothesis of TOP2A as a biomarker for the early identification of patients with increased metastatic potential that may benefit from adjuvant or neoadjuvant targeted therapy approaches (26). UBE2C serves as the key component in the ubiquitin proteasome system by partnering with the anaphase-promoting complex (APC/C). Upregulated UBE2C protein expression has been reported in various types of human tumours (27). Mo et al (28) conducted an immunoassay to examine 209 breast cancer (BRCA) tissue samples and 53 normal tissue samples, and found that UBE2C is highly expressed in BRCA. Furthermore, the expression of UBE2C was positively correlated with tumour size (24). Wang et al (29) revealed that the level of phosphorylated aurora kinase A (p-AURKA) decreased markedly via the Wnt/β-catenin and PI3K/AKT signalling pathways following the knockdown of UBE2C with a small interfering RNA. The signalling pathway suppressed the occurrence and development of gastric cancer, and their data suggested that the activity of AURKA may be regulated by UBE2C via modulation of the activity of APC/C (29), UBE2C may be a novel marker in the diagnosis of gastric cancer (25); however, little is known about UBE2C in seminoma. PTPRC is a member of the protein tyrosine phosphatase (PTP) family. PTPs are signalling molecules that regulate a variety of cellular processes, including cell growth, differentiation, mitosis, and oncogenic transformation (30). Porcu et al (31) demonstrated that the downregulation of CD45 (encoded by PTPRC) expression sensitizes T cells to cytokine stimulation, as observed by increased JAK/STAT signalling, whereas the overexpression of CD45 decreases cytokine-induced signalling. In our study, PTPRC, which may serve an important role in cytokine induction, was upregulated in seminoma. The expression of MKI67 is strongly associated with tumour cell proliferation and growth, and is widely employed in routine pathological investigations as a proliferation marker (32). It was revealed that the expression of P53 and Wnt signalling correlated with that the expression of MKI-67 in several types of cancer (33–36). Downregulated MKI67 may be involved in cancer; in our study, it was downregulated in seminoma. Five pivotal genes detected in this study have been reported to be overexpressed in various human cancers, are associated with their prognosis and are significantly expressed in testicular seminoma tissues; but no significant difference in prognosis was reported. The role of these genes in TGCT is unclear; thus, further investigation is required.
Compared with normal testis samples, 11 DEMs were acquired in GSE59520 in seminoma samples. In the present study, hsa-miR-1182 was downregulated in seminoma samples. Zhou et al (37) reported that hsa-miR-1182 is dysregulated in bladder cancer tissues and cell lines, in which functional assays were then performed, the overexpression of miR-1182 significantly inhibits bladder cancer cell proliferation, colony formation and invasion (37,38); however, the effects of hsa-miR-1182 in seminoma are yet to be determined. Hsa-miR-650 has been reported in many cancers. For example, Zhou et al (39) observed that the expression of miR-650 in tumour tissues had a positive association with OS. Hsa-miR-650 inhibited cell growth and invasion in vitro and in vivo (40,41). Furthermore, miR-650 targeted AKT2 and suppressed the activation of the AKT2/glycogen synthase kinase-3β/E-cadherin (39). Interestingly, Yang et al (42) suggested that phosphatase and tensin homolog/AKT signalling affects the expression of TOP2A, reducing cell growth and inducing the apoptosis of human breast cancer MCF-7 cells through ATP and caspase-3 signalling pathways (42). In our study, TOP2A was identified as the target gene of hsa-miR-650, and hsa-miR-650 was downregulated in seminoma, while TOP2A was upregulated. Thus, we proposed that in seminoma, the downregulation of hsa-miR-650 could lead to the activation of the AKT pathway, upregulating TOP2A to affect seminoma cell migration and proliferation. At present, few studies have been conducted in the investigation of hsa-miR-934. For hsa-miR-1204, Xu et al (43) revealed that hsa-miR-1204 expression was significantly correlated with tumour size. The expression levels of hsa-miR-1204 and glucose transporter-1 (GLUT-1) were significantly high in ovarian cancer (OC) patients (43). The expression levels of hsa-miR-1204 were positively correlated with the expression levels of GLUT-1 in OC patients. Hsa-miR-1204 overexpression significantly promoted GLUT-1 expression, glucose uptake and cell proliferation. In our study, the target gene of hsa-miR-1204, CENPA, was revealed to mostly function in kinetochores and regulate cell division. The overexpression of CENPA is significantly related to colon cancer and neoplastic germ cells (44,45). Hsa-miR-1204 and its target gene CENPA were both upregulated in seminoma; kinetochores are unique centromere macromolecular protein structures that attach chromosomes to the spindle for proper movement and segregation, during this process, an increasing amount of ATP is required (46), and the overexpression of hsa-miR-1204 can significantly promote GLUT-1 expression, glucose uptake and ATP production (43). Thus, this pathway may affect the expression of CENPA; however, the association between CENPA and hsa-miR-1204 requires further investigation. In addition, hsa-miR-661 has been reported in non-small-cell lung cancer and OC (47,48). Hoffman et al (49) found that low miR-661 expression correlates with poor outcomes in BRCA that typically express wild-type p53. In the present study, miR-661 was downregulated in seminoma. Of note, hsa-miR-1203 has been reported to be dysregulated in prostate cancer, small cell carcinoma of the oesophagus and oesophageal squamous cell carcinoma (50–52). In addition, Prashad et al (53) reported that miR-665 suppresses neuroblastoma tumorigenesis by inhibiting c-MYC and suggested the potential of hsa-miR-665 as an antineuroblastoma therapeutic factor. Dong et al (54) found that miR-665 was downregulated in osteosarcoma tissues compared with nontumourous tissues, and the expression of miR-665 was inversely associated with the expression of Rab23 in the osteosarcoma tissues. These results suggest that miR-665 could act as a tumour suppressor gene in the development of osteosarcoma (54); it has also been reported to be related to the Wnt/β-catenin signalling pathway (55). In our study, miR-665 was downregulated in seminoma, and the target gene MKI67 was also associated with the Wnt/β-catenin signalling pathway (34). For hsa-miR-640, Li et al (56) demonstrated that miR-640 was downregulated in paclitaxel-resistant formalin-fixed paraffin-embedded tumour samples; however, Zhou et al (57) found that miR-640 is related to the vascular endothelial growth factor receptor 2-mTOR pathway. In the present study, hsa-miR-640 was downregulated in seminoma, and its target gene, MKI67, was also associated with mTOR (58).
In summary, TOP2A, MKI67, PTPRC and UBE2C were revealed to be potentially associated with the PI3K/AKT and Wnt/β-catenin signalling pathways, while hsa-miR-650 and hsa-miR-665 were proposed to be linked the PI3K/AKT and Wnt/β-catenin signalling pathways. Moreover, TOP2A and MKI67 were strongly associated with the target genes of hsa-miR-650 and hsa-miR-665, respectively.
At present, few bioinformatics analyses have been conducted to investigate DEGs and DEMs in seminoma. Of the DEGs screened in this study, only TOP2A and PTPRC have been reported in seminoma (59,60), to the best of our knowledge. Additionally, we screened the differential expression of genes from array data and predicted target genes of DEMs which were proposed to act together on the PI3K/AKT and Wnt/β-catenin signalling pathways with a strong correlation (29,39). The PI3K/AKT and Wnt/β-catenin signalling pathways participate in the growth, invasion, and migration of cancer cells in a variety of ways (61–63). TOP2A, MKI67, PTPRC and UBE2C could be used as potential diagnostic biomarkers and therapeutic molecular targets for seminoma. In addition, the main treatment methods for seminoma in clinical practice are chemotherapy and testicular resection, which undoubtedly cause great physical burden to patients, particularly in individuals aged 15–24 years (7,64). Therefore, our findings of the present study, including the genes identified, may serve as a basis for exploring gene therapy for seminoma in the future.
In this study, 287 differential genes for testicular seminoma were detected from the GEO database, and 5 pivotal genes and 8 miRNAs were screened, all of which were significantly differentially expressed in testicular cancer tissues. Among them, we predicted the target genes of the miRNAs. TOP2A, MKI67, PTPRC and UBE2C were determined to be associated with the PI3K/AKT and Wnt/β-catenin signalling pathways, and hsa-miR-650 and hsa-miR-665 were associated with the PI3K/AKT and Wnt/β-catenin signalling pathways. Furthermore, TOP2A and MKI67 were strongly associated with the target genes of hsa-miR-650 and hsa-miR-665, respectively. To the best of our knowledge, hsa-miR-934 has not been investigated. There may be certain associations that are yet to be identified; the hub genes we reported could have notable impact on cell proliferation and migration in testicular seminoma. In addition, in patients with testicular seminoma, PTPRC overexpression is an unfavourable prognostic factor, and further studies are needed to verify our findings. The results of the present study suggested that TOP2A, MKI67, CENPA, PTPRC, UBE2C, hsa-miR-650, hsa-miR-665, hsa-miR-640, hsa-miR-1182, hsa-miR-1203, hsa-miR-661 and hsa-miR-1204 may be potential targets for seminoma therapy.