Currently, an increasing number of studies are focused on using bioinformatics analyses of previously published data to identify factors that play a vital role in various cancers. In our previous study, we found that the expression of EMILIN2 increased with increasing LGG grade. A previous study identified that EMILIN2 could play an important role in angiogenesis, platelet activation, thrombus formation, clot retraction and breast cancer [10–11, 18]. However, few studies have examined the function of EMILIN2 in glioma, especially in LGG.
In the present study, we first discovered that EMILIN2 is more highly expressed in WHO grade III compared to grade II LGG in the data from TCGA and the CGGA, which revealed that the altered expression of EMILIN2 might significantly regulate the progression of LGG. Similar results were found for EMILIN2 expression in gastric tumours and ovarian serous tumours [19–21].
Moreover, we analysed the correlation between EMILIN2 expression and methylation and found that the expression of EMILIN2 was negatively associated with EMILIN2 methylation in LGG. EMILIN2 hypermethylation and low expression also predicted good OS in LGG. Then, the prognostic and clinical value of EMILIN2 was identified based LGG from the CGGA database, which was similar to the findings from the TGGA database in terms of IDH, WHO grades and OS. We further identified the prognostic value of EMILIN2 DNA methylation. Almost all sites were significantly related to OS, which verified the prognostic relevance of EMILIN2. Many studies have indicated that the relationship between specific DNA methylation sites and the expression of neighbouring genes ranges from weak to moderate, and there are few genes that are regulated by DNA methylation [1, 5–7]. In our study, we found that EMILIN2 was obviously and negatively regulated by its DNA methylation. EMILIN2 methylation status and its expression might be a potent biomarker of OS. A similar result was found in breast cancer [22]. Similarly, the prognostic value of EMILIN2 has been reported in lung adenocarcinoma [23].
Furthermore, the LGG database from CGGA was used to reconfirm the prognostic and clinical value of EMILIN2 and showed a similar result: the expression of EMILIN2 was remarkably associated with clinical parameters such as histology, WHO grade, IDH1 mutation and even survival status. Moreover, univariate and multivariate Cox regression analyses were performed, and the results showed that EMILIN2 could be an independent prognostic biomarker (p = 0.018, hazard ratio = 1.180 (1.029 − 1.354)); PRS type, WHO grade, and 1p19q_codeletion could also be independent prognostic factors in LGG. Furthermore, we performed GO and KEGG analyses to reveal the function of EMILIN2 in CGGA. The results implied that EMILIN2 might be involved in immune-related biological functions.
A lot of studies have found that tumour-infiltrating immune cells play an important role in the progression and development of cancer [24–27]. Few studies have pointed out the relationship between EMILIN2 and immune infiltration. Therefore, the TIMER database was used to detect the relationship between immune infiltration and EMILIN2 expression. In our study, our results first revealed that the levels of immune infiltration were significantly correlated with EMILIN2 expression in LGG. Furthermore, we observed that EMILIN2 expression was positively correlated with B cells in LGG. Additionally, EMILIN2 was significantly associated with OS at different levels of immune infiltration, which again suggested the prognostic significance of EMILIN2 in LGG.
Additionally, the correlation between EMILIN2 expression and the markers of immune cells indicated that EMILIN2 might regulate tumour immunology in LGG. Studies have reported a positive correlation between elevated CD8 + T cells in the tumour microenvironment (TME) and good prognosis in cancer [28]. The gene markers of CD8 + T cells, T cells (general), and B cells such as CD8A, CD8B, CD3D, CD3E, CD2, CD19, CD79A, CD86, and CD115 showed significantly positive correlations with EMILIN2 expression, which verified the prognostic and immune value of EMILIN2. Macrophages play an important role in maintaining tissue homeostasis and modulating the immune response against pathogens as scavengers [29]. Thus, we detected correlations between biomarkers of M1 and M2 macrophages and tumour-associated macrophages (TAMs), revealing the potential regulatory function of EMILIN2 in macrophages. In addition, our results shown in the Table 3 indicated that EMILIN2 could activate Tregs and induce T cell exhaustion. Moreover, helper T cells were reported to have the strongest relationship with clinical outcome in early-stage vulvar cancer [30]. Our study showed that there were many significant correlations between EMILIN2 expression and various markers of T helper cells (Th1, Th2, Tfh, and Th17) in LGG, which indicated that EMILIN2 might regulate T cell functions and influence the clinical outcome in LGG. EMILIN2 expression negatively correlated with that of STAT5B, an important role in the maintenance of normal immune function and homeostasis [31], but positively correlated with the expression of Treg and T cell exhaustion markers (CCR8, FOXP3, TGF-β (TGFB1), PD-1, CTLA4, LAG3, GZMB, and TIM-3) in LGG. These results suggest that EMILIN2 plays a vital role in the regulation of immune infiltrating cells in LGG. However, additional experiments to identify the potential mechanisms of EMILIN2 are urgently needed in the future.
In summary, EMILIN2 expression negatively correlated with EMILIN2 methylation, potentially contributes to the regulation of immune infiltration and is a potential biomarker of OS in LGG.