A series of biological processes are involved in the occurrence and progression of EC, such as abnormal expression of genes and transcription factors, dysregulation of cellular signal transduction pathway and imbalance of cell microenvironment homeostasis. Pathological changes and molecular characteristics determine the level of risk and prognosis of patients with EC. In recent years, 1ncRNAs have been identified to exert various malignant biological behaviors in EC including differentiation, proliferation, invasion and metastasis . Therefore, it is valuable and helpful to explore the potential functions and molecular mechanisms of lncRNAs in EC, which contribute to prognostic prediction and therapeutic target of endometrial carcinoma.
In this study, 121 differentially expressed lncRNAs in UCEC were identified by circlncRNAnet, including 77 upregulated and 44 downregulated lncRNAs. We further confirmed for the first time that only high expressions of RP11-89K21.1 and RP11-357H14.1 were significantly associated with shortened OS and poor prognosis of patients with UCEC, which suggested that RP11-89K21.1 and RP11-357H14.1 played oncogene roles in the occurrence, progression of endometrial carcinoma. It was reported that the expression of lncRNAs were regulated by transcription factors . We found that EZH2 was the common transcriptional regulator of RP11-89K21.1 and RP11-357H14.1 in endometrial carcinoma with AnnoLnc, Moreover, EZH2 was positively correlated with the expression of RP11-89K21.1 and RP11-357H14.1. Some studies have showed that lncRNA DLEU2 interacted with EZH2 to promote the proliferation, migration and invasion of hepatocellular carcinoma, thus accelerating the malignant progression of hepatocellular carcinoma . In gastric cancer, lncRNA UCA1 enhanced the translation of cyclin D1 via recruiting EZH2 and further precipitated the proliferation and cell cycle progression of gastric cancer . In lung cancer, the expression of lncRNA-SVUGP2 could be suppressed by EZH2 and further promoted the occurrence and development of lung cancer via Wnt/β-catenin pathway . These studies suggest that there exists potential regulatory mechanism between EZH2 and RP11-89K21.1, RP11-357H14.1 involved in the occurrence, development and malignant biological behavior of endometrial carcinoma, and the specific mechanism remains to be further explored and verified.
Studies have shown that lncRNAs are located in different subcellular structures, including cytoplasm, nucleus, ribosome, cytosol and exosome. Functions and regulatory mechanisms of lncRNAs are closely associated with subcellular localization. We detected that RP11-89K21.1 and RP11-357H14.1 were mainly located in cytosol. Growing evidence suggested that, in the cytoplasm and cytosol, lncRNAs not only regulated the stability and translation of mRNA, but also had an impact on the post-transcriptional modification of proteins and cell signal transduction. Based on the ceRNA hypothesis, lncRNA can competitively bind to miRNAs acting as sponge of miRNAs, detaining or adsorbing miRNAs, thus relieving the inhibition of miRNAs on downstream target genes [34–35]. Some studies have shown that exosomal lncRNA ARSR could competitively bind to miR-34 and miR-449 to regulate the expression of AXL, c-MET, and then promoted the drug resistance of renal cell carcinoma . In prostate cancer, lncRNA TTTY15 acted as a ceRNA and negatively regulated miR-let-7 to promote expression of the target genes (CDK6, FN1) . In recent years, mounting studies have shown that lncRNA, acting as ceRNA, regulated the expression of downstream oncogenes and tumor suppressor genes in endometrial carcinoma through a miRNA regulatory mechanism. In endometrial carcinoma, lncRNA HOTAIR facilitated the expression of NPM1 by negatively regulating miR-646, and thereby promoting the proliferation, migration and invasion of EC cells . Maziveyi et al. reported that lncRNA TUSC7 promoted the expression of SOCS4 (SOCS5) through acing as sponge of miR-616, thus inhibiting the proliferation, migration and invasion of endometrial carcinoma . We further explored the potential role of ceRNA network mechanism regulated by RP11-89K21.1 and RP11-357H14.1 in the progression of EC. The binding miRNAs of RP11-89K21.1 and RP11-357H14.1 were retrieved from miRTarBase and 4 overlapped miRNAs (miR-27b, miR-4770, miR-143, miR-204) were downregulated in UCEC, and other RP11-89K21.1 binding miRNA (miR-125a-5p, miR-125b-5p, miR-139-5p, miR-670-3p) and RP11-357H14.1 binding miRNA (miR-24-1-5p, miR-503) were also decreased in UCEC. miRNAs were involved in a variety of malignant biological behaviors and mechanisms such as proliferation, invasion and migration of tumors. The expression of miR-27b-3, miR-204-5p was decreased in EC, and high expression of miR-27b-3 and miR-204-5p could significantly inhibit the proliferation, migration and invasion of EC cells [40–41]. The expression of miR-143 and miR-503 were also downregulated in EC, and high expression of miR-503 inhibited the proliferation and cell cycle of EC cells through negatively regulating CCND1 [42–43]. These findings indicated that RP11-89K21.1 and RP11-357H14.1 may play oncogene roles in endometrial carcinoma by regulating candidate miRNAs and their targeted genes. Therefore, we have successfully constructed a new LncRNA-miRNA-mRNA ceRNA regulatory network associated with the prognosis of patients with EC, and further experiments are required to verify molecular mechanisms in the regulatory network.
Many studies have shown that lncRNAs affects the initiation and development of tumors by regulating a variety of molecular mechanisms and signaling pathways. Researchers observed LncRNA LSINCT5 promoted proliferation, invasion and metastasis of EC cells by regulating HMGA2/Wnt/β-catenin signaling pathway . LncRNA OGFRP1 promoted the malignant progression of endometrial carcinoma by regulating the miR124-3p/SIRT1 axis and activating the PI3K/AKT/GSK-3β pathway . In order to better clarify the biological function, molecular mechanism and regulatory network of RP11-89K21.1 and RP11-357H14.1-related targeting genes in EC, we carried out GO and KEGG enrichment analysis with Metascape. It was found that RP11-89K21.1 and RP11-357H14.1-related targeting genes were mainly involved in vasculature development, tissue morphogenesis, cell growth and differentiation, regulation of protein kinase activity and cellular response to stress. KEGG enrichment analysis showed that RP11-89K21.1 and RP11-357H14.1-related targeting genes were significantly enriched in microRNAs in cancer, cytokine-mediated signaling pathway, transmembrane receptor protein tyrosine kinase signaling pathway, apoptotic signaling pathway. The above signaling pathways were closely associated the progression and biological behaviors of EC . Therefore, we speculated that RP11-89K21.1 and RP11-357H14.1 can affect the occurrence, development and biological behavior of EC by regulating the above tumor-related pathways, which provided more evidences for further exploring the molecular mechanisms of RP11-89K21.1 and RP11-357H14.1in endometrial carcinoma.
Accumulating studies have demonstrated that a large number of immune cells and cytokines can be observed in EC, which can enhance the endogenous anti-tumor immune response and affect prognostic value and immunotherapy of EC. Immunotherapy plays a well-established role in the treatment of EC. Our results showed that the expression of RP11-89K21.1 was negatively correlated with CD8_T cell, Macrophage and positively correlated with CD4_T cell, Neutrophil. The expression of RP11-357H14.17 was negatively correlated with CD8_Tcell and positively correlated with CD4_Tcell. Studies have shown that CD8_T cell and Macrophage could participate in the malignant progression of EC and serve as a potential therapeutic target for EC . CD4_T cell could promote the capacity of initiating CD4_T cell rapidly by mediating immune response, and kill tumor cells directly or indirectly by stimulating and recruiting CD8_T cell cells or other immune cells . The number of CD4_T cells in peripheral blood of patients with EC was significantly increased . Neutrophil was the main type of immune cells in tumors, which can eliminate pathogens and prevent host from being infected by microorganisms, playing a key role in chemotherapy resistance and anti-angiogenesis therapy of tumors . Some studies have displayed that neutrophils were closely correlated with survival and prognosis of patients with EC . The results showed that the above immune cells were of great value in the occurrence, development and prognosis of EC, suggesting that RP11-89K21.1 and RP11-357H14.1 affected the survival and prognosis of EC by regulating the infiltration of immune cells in tumor microenvironment, which can provide new directions and novel therapeutic targets for immunotherapy of EC.