Relationship between TME scores and the grade of AGC patients
To evaluate the correlation between Immune-, Stromal-, ESTIMATE score and clinicopathological characteristics, we then obtained clinical data. As shown in Fig. 1a-c, ESTIMATE score (p<0.001), Immune score (p<0.001) and Stromal score (p<0.001) of AGC patients with G3 histological grade were notablely higher than those with G2 histological grade. These results indicated that the stromal and immune components in TME were involved in the malignant progression of AGC
Identification of DEGs related to TME
To identify the accurate discrepancy of gene profile in TME in relation to immune and stromal components along with the role it plays in AGC, the comparison analysis between normal samples and AGC samples was implemented. “Limma” package was conducted to extract TME-related DEGs. According to stromal and immune scores, heatmaps of DEGs between normal samples and AGC were shown in Fig. 1d and e. A total of 1587 up-regulated and 151 down-regulated DEGs were obtained between the high and low stromal score groups. Compared with the low immune score group, 874 DEGs in the high immune score group were up-regulated, and 355 DEGs were down-regulated. The Venn diagram showed that a total of 575 up-regulated genes and 91 down-regulated genes sharing by stromal score group and immune score group (Fig. 1f, g), the DEGs (total 666 genes) may be the determinants of TME status. Subsequently, DEGs proceeded for functional enrichment analysis. GO analysis revealed that DEGs were significantly mapped on immune-related activities, such as T cell activation, lymphocyte activation regulation, and immune receptor activity (Fig. 2a). The results of KEGG analysis indicated that DEGs were significantly enriched in pathways related to immune response (Fig. 2b). These results suggest that the participation of TME is a dominating characteristic of AGC patients.
Screening of overlapping gene via univariate Cox regression and PPI network
We performed Cox regression analysis to investigate the prognostic genes for patients with AGC, and four genes were determined (Fig. 3a). The PPI network was constructed to visualize interactions between DEGs from the STRING database (Fig. 3b). Cytoscape 3.8.1 software was used to reconstruct the PPI network and calculate the connectivity of each node in the network to determine hub genes (Fig. 3c). Interaction analysis between univariate Cox regression and PPI network revealed that MCEMP1 was the only overlapping gene (Fig. 3d).
The correlation of MCEMP1 expression with survival and clinical stage in AGC patients
AGC cases were divided into high and low expression groups in TCGA cohort, with the median of MCEMP1expression. The Kaplan-Meier survival curve exhibited that overall survival of AGC patients with low expression of MCEMP1 was better than that of the high expression group (Fig. 4a). Based on the GEPIA database, the expression of MCEMP1 was closely related to TNM stage (Fig. 4b). Survival curve indicated that high expression level of MCEMP1 was associated with poor prognosis in patients with GC (Fig. 4c).
Validation of the expression and prognostic value of MCEMP1 in AGC tissues
A total of 31 AGC patients with complete follow-up clinical data were included. The protein expression level of MCEMP1 in AGC tissues was higher than that in adjacent normal tissues detecting by IHC (Fig. 5a, b). The results of relative mRNA expression of MCEMP1 were consistent with the results of IHC (Fig. 5c). Survival analysis revealed that high expression of MCEMP1 in AGC patients led to the poor prognosis (Fig. 5d). The experimental results provide strong support for the above conclusions.
MCEMP1 participate in the modulation of immune activity in AGC
In view of MCEMP1 is highly expressed in AGC and the expression levels of MCEMP1 were positively related with the prognosis of AGC patients, GSEA was implemented in the high-expression group. The results of GSEA suggested that MCEMP1 was significantly related to immune-related signaling pathways, including the interaction of cytokines and cytokine receptors, and natural killer cell-mediated cytotoxicity (Fig. 6). The results revealed that MCEMP1 may play a role in the regulation of immune activity in AGC and is of certain significance to assess the state of TME.
Correlation of MCEMP1 with the proportion of TICs
To further verify the role of MCEMP1 and TME, CIBERSORT algorithm was performed to analyze the proportion of TICs in AGC microenvironment (Fig. 7a-c). MCEMP1 expression was significantly correlated with 8 infiltrating immune cells (Fig. 8a). Among them, the expression of MCEMP1 was negatively correlated with CD8 T cells, regulatory T cells, and resting mast cells, while it was positively correlated with resting NK cells, M0 macrophages, activated mast cells, eosinophils, and neutrophils (Fig. 8b). The results further supported the effect of MCEMP1 act on the TME.