GRHL2 mRNA expression in pan-cancer
To check the expression of GRHL2 in all cancer types, we analyzed the expression level of GRHL2 mRNA in Oncomine database. The results showed that the expression of GRHL2 was higher in bladder cancer, breast cancer, colorectal cancer, lung cancer and ovarain cancer tissues when compared with their corresponding GRHL2 mRNA expression in pan-cancer
To check the expression of GRHL2 in all cancer types, we analyzed the expression level of GRHL2 mRNA in Oncomine database. The results showed that the expression of GRHL2 was higher in bladder cancer, breast cancer, colorectal cancer, lung cancer and ovarain cancer tissues when compared with their corresponding normal tissues (Figure 1A). We also performed a comprehensive analysis on 33 types of tumors from TCnormal tissues (Figure 1A). We also performed a comprehensive analysis on 33 types of tumors from TCGA. Among them, 18 kinds of tumors overexpressed GRHL2 (Figure 1B). In addition, data from the Cancer Cell Line Encyclopedia (CCLE) database revealed that the high expression of GRHL2 mRNA was also detected in 28 kinds of cancer cell lines, especially in breast cancer cell lines (Figure 1C). Therefore, our results indicate that GRHL2 might play an important role in breast cancer.
Expression of GRHL2 in breast cancer
Further investigation by using HPA database, we found that GRHL2 was low expressed in normal breast tissues (Figure 2A) and over expressed in cancer tissues (Figure 2B). It was also confirmed from GEPIA database that GRHL2 was more expressed in cancer tissues (n = 1085) than in normal tissues (n = 291) (Figure 2C). Immunohistochemical staining obtained from HPA also confirmed GRHL2 protein expression was higher in tumor tissues than in normal tissues (Figure 2D).
Next, we further verified the correlation between GRHL2 mRNA levels and clinical data of breast cancer patients, including age, gender, and cancer stages. It can be seen that the expression of GRHL2 is not correlated with age, cancer stage and nodal metastasis status (P >0.05), but significantly correlated with gender (Figure 3A-D) (P <0.05).
The prognostic value of GRHL2
We used Kaplan-Meier plotter to assess the prognostic value of GRHL2. GRHL2 can predict the poorer overall survival (OS) of kidney renal clear cell carcinoma (KIRC) (P <0.05), however, it could not predict relapsing free survival (RFS) (P =0.05) (Figure 4A, B). For pancreatic ductal adenocarcinoma (PDA), GRHL2 has predictive effect on OS and RFS (Figure 4C, D) (P <0.05). In a total of 1643 and 1089 BC patients, the higher GRHL2 was associated with poorer OS and RFS (P <0.05) (Figure 4E, F).
In order to further verify the prognostic role of GRHL2, PrognoScan and GEPIA database were used. The data in PrognoScan mainly comes from the GEO database. Overexpression of GRHL2 in three breast cancer data sets and one bladder cancer data set is associated with poorer survival (DMFS, distant metastasis-free survival, and OS) (Figure 5A-D). GEPIA database also showed GRHL2 high expression was related to poorer OS in breast cancer (Figure 5E).
GRHL2 expression is a diagnostic biomarker for breast cancer
In order to evaluate the diagnostic value of GRHL2, the ROC curve was generated from the data of the TCGA database. The area under the ROC curve is 0.818, indicating a higher diagnostic value of GRHL2 for breast cancer (Figure 6).
Correlation between GRHL2 expression and immune cells infiltration in breast cancer
In order to evaluate the correlation between GRHL2 expression and immune cells infiltration in breast cancer, we used the TIMER database for analysis. GRHL2 expression level is significantly correlated with tumor purity, positively correlated with CD8+ cells, macrophages, and neutrophils infiltration, negatively correlated with DC infiltration, and has no significant correlation with B cells and CD4+ cells (Figure 7A). We further evaluated the relationship of several immune cell infiltration levels with GRHL2 gene copy number, and found that CD4+ cells and macrophages was related to GRHL2 gene copy number in breast cancer (Figure 7B).
Relationships between GRHL2 expression and immune markers
In order to further explore the potential relationship between GRHL2 and immune markers, we used TIMER and GEPIA to observe B cells, CD8+ T cells, M1/M2 macrophages, tumor-associated macrophages, monocytes, NK cells, neutrophils and DC markers in breast cancer. And we also analyzed different functional T cells, including Tfh, Th1, Th2, Th9, Th17, Th22, Treg and T cell exhaustion (Table 1 and Figure 8). In TIMER, after adjusting tumor purity, GRHL2 expression level was significantly correlated with 22 of the 45 immune cell markers in breast cancer (Table 1).
As shown in Figure 7A, CD8+ T cells and macrophages in breast cancer have the closer relationship with GRHL2 expression. Therefore, we further analyzed the immune cell markers in GEPIA (Table 2). Interestingly, B cell marker CD19, CD38 and MS4A1 were negatively related with GRHL2 in breast cancer, not in normal tissue (Table 2). These results indicate that the different immune cells related to GRHL2 might involve in breast cancer aggressiveness under different microenvironment.
Function enrichment analysis
To clarify the genes and signal transduction pathways related with GRHL2, we performed KEGG and GO analysis. We first used the LinkedOmic database to analyze the upstream and downstream genes co-expressed with GRHL2 in the volcano map (Figure 9A-C). KEGG and GO analysis identified 3 main group related to tumor aggressiveness (Figure 9D-E). The first group included lymphocyte activation and Th1, Th2 and Th17 cell differentiation. This further verified the analysis results of TIMER and GEPIA, which demonstrated that GRHL2 could regulate immune cells infiltration in tumor tissue. The second group included establishment or maintenance of cell polarity, regulation of actin filament length and polymerization, actin filament polymerization or depolymerization. This was consistent with previous research[15], which demonstrated GRHL2 could regulate EMT. Our result suggested that GRHL2 might regulate actin filament status to determine EMT phenotype of tumor cells. The third group included cell cycle, DNA replication, nuclear division, mismatch repair, nucleotide excision repair, double-strand break repair, cell adhesion molecules, NF-kappa β signaling pathway, PI3K-Akt signaling pathway and positive regulation of angiogenesis. This suggested GRHL2 could involve in cell cycle control and have an effect on tumor cell proliferation. In addition, GRHL2 might promote tumor invasiveness by cooperation with NF-kappa β signaling pathway and PI3K-Akt signaling, affecting cell adhesion molecules expression and regulating angiogenesis.
Methylation could regulate GRHL2 expression
In order to further elucidate the mechanism of regulating GRHL2 expression in breast cancer, we explored the correlation between GRHL2 expression level and methylation. First, the analysis results of GRHL2 from the UALCAN database showed that promoter methylation level in normal tissues is higher than that in cancer tissues (Figure 10A). The analysis results in DiseaseMeth version 2.0 are the same as those in UALCAN (Figure 10B). In addition, we analyzed the relationship between GRHL2 mRNA expression and methylation level through the Cbioportal database, which was negatively correlated (Figure 10C). Then, the results of MEXPRESS analysis showed that in the DNA methylation sequences of GRHL2, there are 25 methylation sites that are negatively correlated with its expression level (Figure 10D). One of the probes, cg15679829, is related to promoter methylation of GRHL2 in MethSurv. And we analyzed this methylation site with survival in this database, which showed no significance (Figure 10E). However, the density and the methylation level of GRHL2 were different in different age groups of BC (Figure 10F-G). It can be seen from the density graph that the β-value is 0.844, which is significant (β-value>0.6). These results demonstrate that the promoter methylation of GRHL2 could regulate GRHL2 expression.