In developing countries, hepatocellular carcinoma (HCC) is the most common pathological type of liver cancer. Most HCC patients could not prolong their life due to tumor metastasis or recurrence, and the specific mechanism remains unclear. Although it has been proven that radical liver cancer resection is an effective treatment for early HCC, patients could not diagnose in time, most patients still cannot be cured. The mechanism of HCC is mainly discussed from the genetic level, and the molecular mechanism is of great significance for the treatment of HCC. Non-coding RNA (ncRNA), including lnc RNA, microRN and circRNA, is transcribed from the genome without being translated into protein. NcRNA can control gene expression at various levels, including epigenetic modification [14, 15], transcription[15], RNA splicing[16, 17], scaffold assembly[17], etc. CircRNAs has tissue-specific expression pattern and has potential to be biomarker, so it could be used as clinical diagnosis and prognostic indicators. Due to the role of circRNA in HCC has not been fully elucidated, the bioinformation analysis of circRNAs mediate ceRNA regulatory network.
Based on public databases (GEO and TCGA), we compared the differentially expressed genes in HCC. Based on multiple databases, a ceRNA axis (circRNA / miRNA / mRNA) in HCC was established. Additionally, functional analysis was performed to infer the biological functions of key genes in HCC. Finally, the key tumor suppression axis (hsa_circ_0077210/hsa-miR-92b-3p/CPEB3 and ACADL) was constructed. Our data provided a new way of mining circRNA related to the ceRNA axis in HCC, and identified potential prognostic and therapeutic targets.
In recent years, non-coding RNA has received extensive attention. With the ceRNA hypothesis has been put forward, the role of circRNA in the occurrence of HCC has more motivation to be detached. Previous studies have shown that circRNA has transcriptional disorder in many cancers, including HCC, which might be related to tumor proliferation and metastasis. Zheng et al. found that by inhibiting the expression of circSEPT9, the proliferation, migration and invasion of triple-negative breast cancer (TNBC) could be inhibited, and the apoptosis and autophagy of TNBC cells could be induced [18]. The result showed that circRNA played significant role in occurrence and development of refractory breast cancer. Yang et al. verified the RNA expression level of circPTK2 in colon cancer and normal colon tissues, and verified that the expression content of circPTK2 is related to the clinical stage of colon cancer patients, and in vitro and PDTX models, verified that the increase in circPTK2 expression can be Promote the metastasis of colon cancer [19]. The results of Chen et al. confirmed that circSnx5 could act as a miR-544 sponge to reduce Suppressors of cytokine signaling 1 (SOCS1) target inhibition and inhibit the nuclear transport of PU.1, and regulate dendritic cell (DC) activation and function [20].
MiRNA, belong to non-coding RNA, could affect the pathological process of various cancers by affecting the expression level of oncogenes or tumor suppressor genes. Fan et al. investigated the association between serum microRNA and checkpoint inhibitor response in non-small cell lung cancer (NSCLC), and the results showed that the statistically significant improvement in patient progression-free survival (PFS) was correlated with the 10 highly expressed miRNA patterns And in NSCLC patients treated with anti-PD1 drugs, changes in circulating miRNAs are related to the effects of anti-PD1 drugs and patient prognosis [21]. The results showed that the transcription level of microRNAs was related to the tolerance and effectiveness of immunotherapy. Research of Cheray et al. showed that many members of miRNA contain 5mc, and some fragments of cytosine residues could methylate miRNA, and inhibit the formation of miRNA/mRNA duplexes, resulting in the loss of the duplex's function of suppressing gene expression, and further led to the occurrence of glioblastoma multiforme (GBM) [22]. Explaining the interaction mechanism of miRNA and exosomes is also a hot topic. Shi et al. confirmed that the upregulation of miR-520b in exosomes might hinder the proliferation, migration and invasion of pancreatic cancer (PC) cells and induce apoptosis of PC cells by targeting ZNF367 [23]. In fact, the role of hsa-miR-92b-3p had been partly detacted in many cancers. For example, wang et al. confirmed that upregulated hsa-miR-92b-3p could weaken the G0/G1 phase and induce migration and invasion of esophageal squamous cell carcinoma (ESCC) cells in vitro by directly targeting Kruppel-like factor-4 (KLF4) and Data Science and Cybersecurity Center 2 (DSC2) [24]. However, the relationship between has-miR-92b-3p and HCC and its regulatory mechanism have not been elucidated.
We predicted CPEB3 and ACADL through the downstream gene prediction of hsa-miR-92b-3p with a series of screening conditions. In fact, CPEB3 and ACADL might participate in the several progress of HCC. Tang et al. found that CPEB3 was involved in the regulation of mir-452-3p in HCC, and down-regulating the expression of CPEB3 could induce autophagy of HCC cells and increase the migration, invasion and proliferation abilities of HCC cells [25]. Zhao et al. found that in liver cancer, the expression levels of ACADL and YAP are negatively correlated [26]. Huang et al. confirmed that the lack of ACADL can promote the occurrence of HCC by reducing the expression level of Phosphatase and tensin homology deleted on chromosome ten (PTEN) [27]. It had been demonstrated that YAP suppresses PTEN via regulating miR-29 [28]. Therefore, ACADL may inhibit the occurrence of liver cancer through YAP/PTEN signaling pathway.
Based on the GSEA analysis of CPEB3 and ACADL, a visual overview of the mechanisms by which CPEB3 and ACADL regulate HCC development. The results show that CPEB3 and ACADL can actively regulate the cell cycle, G2M checkpoint, mammalian target of rapamycin 1 (mTORC1) signaling, myc targets v1, myc targets v2 and wnt beta catenin signaling. In the background of HCC, the downstream of mTORC1 includes (S6K1, also known as p70S6 kinase) S6K1, rpS6, 4E-BP1 and epithelial-mesenchymal transition (EMT) processes [29]. The depletion of S6K1 could be followed by many immune responses, such as the activation of major histocompatibility complex major histocompatibility complex (MHC) I cell surface receptor members, and the fluctuation of antigen processing and interferon signaling. Discoveries indicated that S6K1 inhibitors with bevacizumab (anti-VEGF antibody) had potential to modulate the immune response against HCC and immunotherapy methods for HCC [30, 31]. O-GlcNAc transferase (OGT) regulated macrophage inflammation by suppressing S6K1 phosphorylation [32]. In addition, IL-2, IL-4, IFN-γ or TNF-α, in tumor B lymphoid cells, could up-regulate S6K1 signaling to enhance cell viability stimulated by B-cell activating factor of the TNF family (BAFF) [33]. CPEB3 might inhibit the occurrence of HCC by regulating the cell cycle and enhancing the phosphorylation of S6K1 to activate the mTORC1 signaling pathway. Because, the expression level of ACADL was also related to the various immune cells, the hsa_circ_0077210—hsa-miR-92b-3p—CPEB3/ACADL regulation axis might be related to the immune regulation process of HCC.
There are some limitations in our research. First, our ceRNA regulatory axis was based on bioinformatics analysis; the circRNA / miRNA/mRNA regulatory network needs to be confirmed in vivo and in vivo. Second, the expression level of hsa_circ_0077210 needs to be verified in a large sample of RNA samples from HCC patients, and that hsa_circ_0077210 transcription level is related to prognosis. Third, our sample size limited us to univariate and multivariate analysis based on the pathological data of patients.