LGG account for 6.4% of all primary CNS tumors in adults[15]. The median overall survival (OS) for LGG (WHO grade II), undifferentiated glioblastoma (WHO grade III), and glioblastoma multiforme (WHO grade IV) was 78.1-, 37.6- and 14.4 months, separately.[16] LGG have higher survival rates and better prognosis than high-grade glioma( HGG ). Many LGG inevitably progress to high-grade gliomas. Gliomas can hardly be completely cured by surgical resection[17]. Therefore, it is necessary to explore the mechanism of low-grade glioma metastasis, which can early identify the high-risk group, and provide targeted therapy. M6A is the most common mRNA post-transcriptional modification in mammals. This dynamic and reversible epigenetic modification affects the fate of RNA molecules and further regulates mammalian cell differentiation, immunity and apoptosis. Studies have shown that the imbalance of m6A is involved in the development of glioma[6, 18, 19]. M6A can regulate cell self-renewal, differentiation, invasion and apoptosis by regulating gene expression. In LGG, m6A modification is significantly associated with angiogenesis. Each of the 17 m6A regulators and 36 ARGs exhibited a significant self-positive correlation[19]. The researcher found that three m6a-lncRNAs including ELOA-AS1, HOXB-AS1 and FLG-AS1 were closely related to the prognosis of LGG patients. We also found that seven ANRG genes (ANGPTL2, BAG1, CDH2, IFI27, PTK2B, SOD2, UBE2C) have a significant relationship with the prognosis of LGG patients. Cancer cells can resist anoikis in several ways such as secreting growth factors, activating pro-survival signaling pathways, and altering integrin expression patterns[20]. Given the widespread post-translational modification of m6A on RNA molecules, m6A affects the metastasis and deterioration of low-grade gliomas by regulating the expression of anoikis-related genes. However, the relationship between m6A regulator and anoikis and their effect on LGG are still not clear.
We screened out four m6A related anoikis genes (ANXA5, KIF18A, BRCA1 and HOXA10), and found that they were all positively correlated with the risk score. ANXA5 gene encodes a protein called Annexin A5, which is a calcium binding protein and belongs to the annexin protein family. ANXA5 is one of the most common protein, which is overexpressed in a series of cancers and participates in the multi-step process of tumor development. It has been reported that annexin A5 plays a role in promoting tumorigenesis and metastasis in various cancers such as pancreatic adenocarcinoma, sarcoma, breast cancer and prostate cancer[21]. At present, there are few reports about ANXA5 in LGG. A study reported that ANXA5 polymorphism increased the risk of glioma in patients and suggested poor prognosis[22]. The research reveal that annexin A5 is the transcriptional target of Snail, and which can activate the PI3K/Akt/NF-κB signaling pathway[23]. KIF18A encodes the protein of Kinesin family member 18A. This protein is involved in the process of cell mitosis, and is an important microtubule dynamin. This study found that the expression of KIF18A was related to the occurrence and development of LGG. The expression level of KIF18A in LGG tissues was higher, and which was positively correlated with the size of the tumor and the proliferation ability of the tumor cells[24]. Studies have also found that high expression of KIF18A may indicate an increased risk of malignant transformation from low-grade gliomas to high-grade gliomas[24, 25]. BRCA1 is a genetic gene associated with the breast cancer, which is involved in biological processes such as DNA repair and gene expression regulation. There is no definite study of BRCA1 in glioma, but it has been reported that the mutation of BRCA1 gene may be related to some types of brain tumor, such as metastatic brain tumor of breast cancer and ependymoma[25]. BRCA1 gene methylation may also play a crucial role in tumor development[26]. The relationship between LGG and BRCA1 still deserves further study. HOXA10 is a member of the human HOX gene family, which is involved in regulating biological processes such as embryonic development and cell differentiation. At present, the research of HOXA10 in glioma is still limited. Some studies have shown that the high expression level of HOXA10 is related to the malignancy of glioma, poor prognosis, and tumor immunity[27–29]. In all, past reports on these genes provide strong evidence for our research.
In this paper, we completed the pathway enrichment analysis of the above four genes. There are not many studies on the specific mechanism of the four genes in LGG, and the gene functional pathways involved. Among them, ANXA5 was involved in apoptosis, IL2 STAT5 signaling and so on. The activation of IL2 receptor binding leads to the activation of JAK protein tyrosine kinase, which promotes the phosphorylation and activation of STAT5, and further regulates the transcription and expression of target genes. A literature reported that glioma is involved in tumor growth and metastasis through the PI3K/Akt/NF-κB signaling pathway[23]. IL2 STAT5 signaling and IL2 activation can lead to the activation and phosphorylation of PI3K, thereby further activating the AKT signaling pathway and promoting cell proliferation and survival. In the pan-cancer analysis from the perspective of pyroptosis, the IL2-STAT5 signaling pathway was significantly associated with the prognosis of LGG[30]. Inhibition of IL2-STAT5 signaling pathway can inhibit the proliferation and invasion of LGG cells, and promote the apoptosis of tumor cells and the block the immune escape. IL2-STAT5 signaling pathway may become an important therapeutic target in low-grade gliomas.
Another gene we are interested in is BRCA1. BRCA1 has received great attention in breast cancer, but little research in glioma. When BRCA1 gene mutates or loses its function, it will lead to abnormal biological processes such as DNA damage repair and cell cycle, thereby increasing the risk of the occurrence and development in breast cancer[31]. It has been reported that BRCA1-related proteins inhibit the proliferation and migration of glioma cells, and the self-renewal of glioma stem cells through the TGF-β/PI3K/AKT/mTOR signaling pathway. BRCA1-related proteins are significantly related to the prognosis of glioma patients[32], which is consistent with our research. In low-grade gliomas, the mechanism of BRCA1 in epithelial mesenchymal transition, mitotic spindle, glycolysis also deserves further study.
In this article, we performed immune infiltrating cell analysis. Studies have shown that low-grade gliomas and high-grade gliomas are significantly different[33]. The increase of immune cells and stromal cells is significantly related to the good prognosis of tumors[33, 34]. This is consistent with our results that the immune score of the low-risk group was significantly higher than that of the high-risk group. We also noticed that activated CD4 T cell, Gamma delta T cell and natural killer T cell were positively correlated with biomarkers, while activated B cell was negatively correlated with KIF18 A and BRCA1. The study also reported that freshly isolated NKT cells from glioma patients are functionally equivalent to cells from healthy controls[35]. This suggests that activating natural killer T cells to dissolve tumor cells in low-grade gliomas is a possible targeted therapy strategy. Activated B cell is significantly negatively correlated with KIF18 A and BRCA1.At present, there are very few studies on this type of cells. Our results show that tumor invasion may be achieved by inhibiting activated B cell in low-grade gliomas, and its related research mechanism remains to be further studied.