OC is one of the most common malignant tumors in female reproductive organs, and its incidence ranks third only after cervical cancer and uterine body cancer. Currently, OC is divided into four grades according to FIGO (International Federation of Obstetrics and Gynecology), and each grade is classified according to the location and status of the tumors []. Although this classification can guide the treatment and prognosis of OC,]the etiology and pathogenesis of OC are still unclear []. Meanwhile, given that its clinical symptoms are atypical, it is difficult to get early diagnosis and treatment, and it seriously affects the quality of life of female patients. Some studies have pointed out the overall treatment of OC is unsatisfactory, such as 80% of patients with OC are advanced patients, 70% of patients will relapse []. It’s remarkable that one third of patients with advanced OC cannot live for 5 years [,]. Therefore, the early diagnosis of OC is still a difficult problem. Screening key genes related to OC by integrated bioinformatics and exploring their possible biological processes will promote the development of early diagnosis of OC, and may improve the prognosis of OC and the quality of patients’ life.
Previous studies have shown that multiple signaling pathways and tumor immune infiltration regulate the progression of OC []. For example, Huang et al. have pointed out high CD8+lymphocytes density in tumor tissues is significantly associated with the improved progression free survival in high-grade serous OC []. Besides, many gene mutations, epigenetic regulation, transcriptional regulation and translation modification have also been reported to be associated with the progression of OC []. However, most cases of OC without an early finding are not candidates for curative therapies, which may be one of the reasons for poor patient prognosis. Thus, it is urgent for seeking the potential markers for diagnosis and treatment with high efficiency. Microarray technology enables us to explore the genetic alterations in OC, and has been proved to be a useful approach to identify new biomarkers in other diseases.
In this study, we combined with GEO database, TCGA data and a variety of comprehensive bioinformatics methods to screen out the key genes related to OC and further explore the possibly related molecular biological mechanisms. Through analyzing GEO2R, GO and KEGG pathways, we found that VEGFA, ZWINT, CDKN2A, SLC2A1, TOP2A, CCND1, KPNA2, and SMC4 were significantly up-regulated in OC, while MKI67 and FGF2 were significantly down-regulated. Meanwhile, these genes mainly functioned in protein binding, cytoplasm, nucleus, extracellular exosome, membrane, cell division and cell adhesion. Moreover,, we further proved that CCND1, TOP2A, SMC4 and FGF2 might regulate the occurrence of OC through miRNAs, gene mutations, acetylation (H3K4Me and H3K27AC), methylation through searching for TCGA, UCSC, TIMER and TargetScan software. In our research, although these key genes have nothing to do with lncRNA, lncRNA may be involved in ovarian cancer through other genes[,].As we known, CCND1, a proto-oncogene associated with cell division cycle, has been reported to be related with breast cancer, bladder cancer, parathyroid cancer, lymphoma, and lung cancer[], and it also promotes the cell proliferation via mediating the transition from G1 phase to S phase of cell cycle. At present, some studies have also shown that CCND1 participates in regulation of OC []. CCND1 silencing could break DNA double strands [], thus inhibiting the growth of OC. However, the mechanism is still unknown. Therefore, the mutation, methylation and acetylation of genes that we have analyzed through bioinformatics would provide a certain degree of reference value for further in-depth study.
Topoisomerase (DNA) II alpha (TOP2A) could convert DNA superhelix into a relaxed state. Previous studies have confirmed that TOP2A is generally overexpressed in OC tissues, and they speculate that TOP2A may be functioned as a potential biomarker []. A new study also shows that TOP2A can be used as a marker of PEG-Lyposomal doxorubicin (PLD) response in epithelial OC [], and can also participate in the p53 signaling pathway to coordinate the occurrence of various malignant tumors []. However, the mechanism of TOP2A regulating OC is still unknown, and phenotypic studies are still in progress. Here, we proved that it would be useful for researchers studying TOP2 through the methylation and acetylation.. It is well known that SMC4, a structural maintenance of chromosomes, is an important component of the core catalytic group of condensin. The main role of condensin is to regulate the dynamic changes of chromosomes during cell cycle. However, the in vivo conformation and molecular mechanism of the heterodimers formed by SMC4 in condensers are still unclear. Recent studies have demonstrated that mutation of SMC4 gene further affects chromosomal stability after the change of condensin, further leading to the occurrence of various cancers, such as breast cancer and colorectal cancer. Meanwhile, SMC4 can bind with SMC2 to form SMC2/SMC4 heterodimer structure (the core catalytic group of condensers). However, there is no similar research report involved in oophoroma. FGF2 has been reported to have an effective angiogenesis effect in vivo and in vitro [] through stimulating the growth of smooth muscle cells and promoting wound healing and tissue regeneration. Besides, it may also play an important role in the differentiation and function of the nervous system and in the regeneration of eyes and bones []. Recent studies have revealed that miRNA–936 targets FGF2 to suppress the epithelial OC aggressiveness by deactivating the PI3K/Akt pathway. Consistent with this report, we also found that FGF2 could target miRNAs to regulate the occurrence of OC, but the reported miRNA–936 and PI3K/Akt pathway are not the key factors for the role of FGF2.
On the other hand, GO and KEGG pathway enrichment analysis results showed that the common differential genes were mostly significant enriched in protein binding, cytoplasm, nucleus, extracellular exosome, membrane, cell division, cell adhesion, pathways in cancer, bladder cancer, pancreatic cancer, and p53 signaling pathway. Combining with the recent theories that OC exosomes can act as coordinators of pre-metastatic niche formation, biomarkers suitable for liquid biopsy and targets for chemotherapy [,,], it is very important to identify whether these key genes exist in the OC exosomes. As we know, P53 mutations are associated with poor prognosis, because that P53 can suppress cancer progression by inducing cell cycle arrest or apoptotic process, and can respond to a variety of cell stress signals. Based on these data, we propose that CCND1, TOP2A, SMC4 and FGF2 may regulate the occurrence of OC through miRNA, gene mutation and epigenetic (methylation and acetylation). Unfortunately, there’s still no research carried out to explore the regulatory role of these key candidate genes in OC.
It is particularly noteworthy the 4 key candidate genes acetylation. UCSC results showed that CCND1, TOP2A, SMC4 and FGF2 had H3K4Me and H3K27AC acetylation sites in our study. Previous studies have shown that H3K4Me acetylation of these genes can up-regulate the expression of BIRC3, thereby further inhibiting the growth of OC by promoting cell apoptosis and inhibiting proliferation []. Based on these data, CCND1/TOP2A/SMC4/FGF2-H3K4Me-BIRC3 pathway may be involved in OC.