Invasiveness is one of the aggressive features of EOC, particularly the advanced high-grade disease. In contrast, LMP tumors often behave as a located lesion within the tissue covering the ovary. Although most of LMP tumors will keep a mild status for a long period, a certain proportion of them display non-invasive extra-ovarian implants and also possess the potential to progress into invasive ovarian cancer[23, 24]. Moreover, the borderline category of ovarian tumors (LMP) is an ongoing challenging and controversial area in gynecologic pathology due to difficulty in accurate classification of implants. Thus, the lack of accurate markers for distinguishing EOC from LMP will lead to incorrect diagnosis, inappropriate treatment and adverse consequences. In this study, we integrated three gene chips from GEO databases and selected 234 DEGs (including 81 upregulated DEGs and 152 downregulated DEGs) between LMP and EOC samples, and further functional analysis was performed.
The KEGG analysis displayed that the common upregulated DEGs were mainly enriched in Cell cycle and Oocyte meiosis, while the common downregulated genes were enriched in Huntington's disease. In addition, the GO analysis showed that the common upregulated DEGs were mainly associated with Protein binding, Nucleoplasm and Nucleus, while the common downregulated genes were mainly associated with Cilium, Microtubule, and Motile cilium. Indeed, many studies have indicated that the Cell cycle[26, 27], Oocyte meiosis[28, 29], Protein binding[30, 31], Nucleoplasm[32, 33], Nucleus, Microtubule[35, 36], Cilium and Motile cilium[37, 38] are highly associated with the tumorigenesis and progression of EOC. However, the association between Huntington's disease and EOC still remains unclear. In brief, these functional enrichment results have certain guiding significance. Furthermore, a PPI network was constructed based on the DEGs, and then the MCODE plug-in filtered out three related clusters. We further performed functional analysis of cluster 1 and found that the results are consistent with the previous analysis. Next, 20 hub genes with the highest degrees of connectivity in the PPI network were identified through the CytoHubba plug-in. Subsequently, the GSE12172 dataset was used to further verify the expression levels of these hub genes in LMP and EOC samples, and the results showed that all hub genes were higher expressed in EOC tissues compared with LMP tumors, meaning that these genes may be crucial to tumorigenesis and progression in EOC. Meanwhile, ROC curve analysis demonstrated that all these genes had better diagnostic efficiency for differentiating EOC from LMP tumors. In addition, survival analysis of these hub genes demonstrated that 5 upregulated genes (CCNB1, KIF20A, ASPM, AURKA, and KIF23) were significantly associated with a poorer OS in EOC patients, which may be partly attributed to the tumor immunosuppressive microenvironment when performing the Pearson correlation analysis between 5 core genes’ expression and the level of different immune checkpoint proteins. In order to further understand the biological functions of these 5 genes in EOC, we performed the KEGG pathway enrichment analysis for them. As a result, we observed that all 5 core genes were enriched in “DNA replication”, “Mismatch repair”, “Fanconi anemia pathway”, “Cell cycle”, “Homologous recombination” and “Nucleotide excision repair”, and “DNA replication” was the key player in them all. Meanwhile, the top 3 enriched KEGG terms in them were “DNA replication”, “Cell cycle”, “Mismatch repair”, “Homologous recombination” and “Proteasome”. Next, the 5 core genes and their current researches in ovarian cancer were introduced as follows.
CCNB1, also called Cyclin B1, is an important mitotic cyclin and produce complexes with p34(cdc2), which function in the G2 and M phases of the cell cycle. Meanwhile, the overexpression of CCNB1 has been reported in many tumors, including EOC[40–43], and a plenty of studies revealed that cyclin B1 is implicated in the differentiation, proliferation, apoptosis, metastasis and chemoresistance of ovarian cancer cell[44–46].
Kinesin family member 20A (KIF20A), a member of the kinesin superfamily-6, is a microtubule-associated motor protein localized to the Golgi apparatus that is required for cell cycle mitosis[47, 48]. Recently, KIF20A has been reported to be involved in the proliferation of EOC, and also could be served as a useful prognostic biomarker for EOC patients[49–51].
Abnormal spindle-like microcephaly-associated (ASPM) gene, also called as abnormal spindle microtubule assembly, is located on chromosome 1q31 and encodes the ASPM protein. Many studies have reported that ASPM is highly expressed in a variety of cancers and is related to poor clinical prognosis, including EOC[53–56].
AURKA, as a family of serine/threonine kinases, localizes to centrosomes and mitotic spindles where it mediates mitotic progression and chromosomal stability. Mounting evidence suggests that AURKA is involved in the tumorigenesis and progression of EOC[58–61].
KIF23, a human homolog of mouse Kif23, is a member of kinesin motor protein involved in the regulation of cytokinesis[62, 63]. Recently, Tong Lia et al has showed that KIF23 was mainly related to cell cycle and positively associated with poor prognosis in EOC patients. Meanwhile, they also found that both miR-424-5p and miR-503-5p can directly targeted to 3’UTR of KIF23 to suppress the expression of KIF23 and inhibit ovarian cancer cell proliferation and migration.
Finally, NetworkAnalyst was applied to screen the chemicals that were associated with the 5 core genes and we found that CCNB1, AURKA, and KIF20A were clearly the three interactive core genes that link most chemicals. Moreover, the top 15 chemicals screened by Cytoscape were found to be related with all 5 genes. Among them, valproic acid[65, 66], Calcitriol[67, 68], cobaltous chloride, Copper Sulfate[70, 71], Genistein, 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide, Methotrexate, Mustard Gas and Cyclosporine all have been showed to have antitumor activity against EOC in vitro or vivo, whereas bisphenol A[77, 78], cadmium[79, 80], Aflatoxin B1 and Estradiol[82, 83] all have cancer-promoting activity in EOC. However, Lucanthone and Latex have not been studied in EOC till now despite they showed anti-cancer effects in other cancers[84, 85]. Thus, additional studies and clinical trials are needed to identify and explore their effect on EOC in future.