1. Analysis of CCNE1 expression level in pan-cancer types
First, we explore CCNE1 expression in a total of 33 cancer types through TCGA database. The results suggested that CCNE1 was significantly upregulated in 18 cancer types (BLCA, BRCA, CESC, CHOL, COAD, ESCA, HNSC, LIHC, LUAD, LUSC, PAAD, READ, STAD, UCEC, KICH, KIRC, KIRP, THCA) compared to normal samples, and no significant difference was discovered in ACC, DLBC, GBM, LAML, LGG, MESO, OV, PCPG, PRAD, SARC, SKCM, TGCT, THYM, UCS and UVM (Figure 1A). To further verify CCNE1 expression in the 18 cancer types, we took advantage of GEPIA database to finish this work. And, high expression level of CCNE1 was discovered in BLCA, BRCA, CESC, CHOL, COAD, ESCA, HNSC, LIHC, LUAD, LUSC, PAAD, READ, STAD and UCEC compared with normal samples, no significant difference was observed in KICH, KIRC, KIRP and THCA (Figure 1B-1P). In summary, CCNE1 was significantly upregulated in the 14 cancer types, including BLCA, BRCA, CESC, CHOL, COAD, ESCA, HNSC, LIHC, LUAD, LUSC, PAAD, READ, STAD and UCEC. This suggested that CCNE1 may play a very important role in improving the development of the 14 types of cancer.
2. The prognostic roles CCNE1 played in pan-cancer types
Furthermore, we analyzed the prognostic value of CCNE1 in the upon 14 types of cancer (BLCA, BRCA, CESC, CHOL, COAD, ESCA, HNSC, LIHC, LUAD, LUSC, PAAD, READ, STAD, UCEC) through GEPIA database. OS and DFS were included to evaluated its prognostic value. The results suggested that high expression level of CCNE1 in BRCA, LIHC and LUAD had more unfavorable prognosis than downregulation of CCNE1, but no significant difference was discovered in the rest types of cancer (Figure 2). For DFS, we find that upregulation of CCNE1 suggested poor prognosis in BRCA, LIHC and UCEC, also no significant difference was observed in the other types of cancer (Figure 3). Taken together, CCNE1 may be a potential biomarker for predicting the poor prognosis of BC.
3. MiR-195-5p was predicted to be the upstream miRNA of CCNE1 in BC
MiRNAs have been widely studied for its role of inhibiting its target gene expression through binding to the 3’UTR of mRNA. We speculated that CCND1 can also be regulated by miRNAs, so we predicted the potential upstream miRNAs that can bind to it through StarBase database. And, we found out 26 potential miRNAs that may can bind to CCNE1 (Figure 4A). Next, according to the specific mechanism of action between miRNAs and target gene, their expression levels should be negatively correlated. Based on this principle, we finally selected the following 5 miRNAs, including miR-26a-5p, miR-26b-5p, miR-101-3p, miR-195-5p and miR-497-5p (Figure 4B). No significant expression level correlation was found between the rest of miRNAs and CCNE1. Among the 5 selected miRNAs, we found that miR-195-5p has the most significant relevance and expression relationship with CCNE1. So, we chose miR-195-5p as the first choice for the following research. Furthermore, we determined miR-195-5p expression and its prognostic value in BC. The results suggested that miR-195-5p was significantly downregulated in BC compared to normal samples (Figure 4C), and, its expression level was significantly negatively correlated with CCNE1 expression level (Figure 4D). Also, high expression level of miR-195-5p was positively correlated with favorable prognosis in BC patients (Figure 4E). Summarize the above results, miR-195-5p might be the most potential miRNA that can regulated CCNE1 expression in BC.
4. LINC00511 was predicted to be the upstream lncRNA of miR-195-5p in BC
For further research, we screened the potential lncRNA upstream of miR-195-5p in BC through the StarBase database. A total of 97 lncRNAs that may bind to miR-195-5p were screened out (Figure 5A). It was widely known that lncRNA may play a role of the competing endogenous RNA (ceRNA) in the progression of various cancers. Based on this mechanism, the expression of lncRNA should be negatively correlated with the miRNA expression level and positively correlated with the mRNA expression level. So, we verified the expression levels of these 97 lncRNAs in BC through GEPIA database. And, the results suggested that only the 4 lncRNAs (HOXC-AS3, LINC00511, LINC00665, TRPM2-AS) were significantly upregulated in BC (Figure 5B-E). Next, we analyzed the correlation between the 4 lncRNAs and miR-195-5p or CCNE1. We find out that only LINC00511 expression was negatively correlated with miR-195-5p expression and positively correlated with CCNE1 expression at the same time (Figure 5F). So, we chose LINC00511 as the upstream lncRNA for the next research. Furthermore, we verified this result and explored the potential prognostic value of LINC00511. And, LINC00511 expression level was significantly negatively correlated with miR-195-5p expression level (Figure 5G) and positively correlated with CCNE1 expression (Figure 5H). Also, high expression level of LINC00511 predicted the poor prognosis in BC patients (Figure 5I). Taken together, LINC00511 might upregulated CCNE1 expression through competitively binding to miR-195-5p and inhibiting its expression in BC.
5. Analysis of the correlation between CCNE1 and immune cell infiltration in BC
CCNE1, as a member of cyclin, was believed to be closely related to protein synthesis and DNA replication. Therefore, we boldly assumed that it is also inseparable from tumor cell immunity. So, we analyzed the correlation between CCNE1 and immune cell infiltration in BC through TIMER database to investigate whether CCNE1 could be a potential biomarker for immunotherapy in BC. We compared the tumor immune cell infiltration level in BC with various somatic copy number alterations (SCNA) of CCNE1. The results suggested that in addition to CD8+ T cell, normal copy number or deletions or amplications of CCNE1 was observed to be correlated with increased immune cell infiltration in BC, including B cell, CD4+ T cell, macrophage, neutrophil, and dendritic cell (Figure 6A). Next, we determined the relationship between CCNE1 expression level and immune cell infiltration level in BC. We found out that high expression level of CCNE1 was significantly positively with immune cell infiltration level in BC, including B cell, macrophage, neutrophil, and dendritic cell, and, no significant difference was observed in CD4+ T cell and CD8+ T cell (Figure 6B-G). So, these findings suggested that CCNE1 may play a very significant role in immune cell infiltration in BC.
6. Analysis of the correlation between CCNE1 expression level and biomarkers of immune cell in BC
Furthermore, we analyzed the relationship between CCNE1 and biomarkers of immune cell in BC through GEPIA database, to better verify the correlation of CCNE1 with tumor immunity in BC. As shown in Table 1, CCNE1 was significantly positively correlated with the biomarkers of B cell (CD19), CD8+ T cell (CD8B), M1 macrophage (IRF5), M2 macrophage (CD163 and MS4A4A), Neutrophil (CEACAM8 and CCR7). And, CCNE1 was negatively correlated with the biomarker of Dendritic cell (CD1C), no significant difference was observed between CCNE1 and CD4+ T cell biomarker. In summary, CCNE1 was still significantly positively related to immune cell infiltration in BC.
Table 1
Correlation analysis between CCNE1 and biomarkers of immune cells in BC determined by GEPIA database
Immune cell
|
Biomarker
|
R - value
|
P - value
|
B cell
|
CD19
|
0.13
|
2.8E-05***
|
CD79A
|
0.095
|
0.0017
|
CD8+ T cell
|
CD8A
|
0.096
|
0.0016
|
CD8B
|
0.15
|
7.9E-07***
|
CD4+ T cell
|
CD4
|
0.078
|
0.011
|
M1 macrophage
|
NOS2
|
0.088
|
0.0037
|
IRF5
|
0.19
|
2.9E-10***
|
PTGS2
|
0.099
|
0.001
|
M2 macrophage
|
CD163
|
0.23
|
4.8E-15***
|
VSIG4
|
0.028
|
0.35
|
MS4A4A
|
0.13
|
1.2E-05***
|
Neutrophil
|
CEACAM8
|
0.11
|
0.00039***
|
ITGAM
|
0.011
|
0.72
|
CCR7
|
0.12
|
9.6E-05***
|
Dendritic cell
|
HLA-DPB1
|
-0.057
|
0.06
|
HLA-DQB1
|
0.034
|
0.26
|
HLA-DRA
|
0.045
|
0.14
|
HLA-DPA1
|
-0.038
|
0.22
|
CD1C
|
-0.11
|
0.00017***
|
NRP1
|
-0.1
|
0.00068
|
ITGAX
|
0.087
|
0.0041
|
***p value < 0.001.
|
7. Analysis of the correlation of CCNE1 expression level with immune checkpoints in BC
PD1 / PD-L1 and CTLA-4 are widely known for the role of immune checkpoints they played in tumor immune escape. Through upon research, we found that CCNE1 was correlated with tumor immune in BC. So, we determined the relationship between CCNE1 expression and immune checkpoints through TIMER database. The results suggested that the expression level of CCNE1 was significantly positively consistent with PD1, PDL1 and CELA-4 (Figure 7A-C). And, the positive correlation between CCNE1 and PD1 was also observed through GEPIA database (Figure 7D-F). Taken together, we considered that CCNE1 may promote the progression of BC through mediating tumor immune escape. CCNE1 might be the potential target for BC tumor immunotherapy.