It was reported that lncRNAs promotes tumorigenesis and development by competitively combining the shared miRNAs with the target gene sponge through the ceRNA mechanism[13, 16, 17]. Tumor-infiltration immune cells, which are an important part of tumors, had been revealed to play a role in tumorigenesis, progression, metastasis and drug resistance by many studies [18] [19]. GC is a heterogeneous disease. Herein, we divided GC samples into the whole group, the intestinal group and the diffuse group, which allowed us to study the common mechanisms and specific mechanisms between two Lauren classification. In our study, we constructed Lauren classification specific ceRNA network and GC ceRNA network based on differential expression, WGCNA, negatively correlated RNAs pairs. Then, correlation analyses markers of ceRNA networks with immune cells were carried out. The high AUC values of these markers of ceRNA networks identifying tumors proved their clinical application.
Based on ceRNA theory and supplementary theory [12, 20, 21], We use p < 0.01 and log2FC > 1 to identify differentially expressed RNAs because this minimizing interferential RNA pairs and avoiding missing important RNA pairs. WGCNA can make us to further screen out disrelated RNAs with tumor. Then, we performed differential expression analysis between two Lauren classifications and many cancer-related and immune-related KEGG enrichment pathways (corrected p < 0.05) indicated that there are also differences in these pathways between IGC and DGC (detailed pathways results in Table S2). The differences in cancer-related pathways prove that there are differences in many cancer characteristics between two sub-types, and also support the strong heterogeneity of GC. The DERNAs between two sub-types were took into consideration to further identify subtype-specific network and common network. we thought that even the common networks in two subtypes must have differences in the level of expression and subtype-specific networks were even more so. The violin plot illustrated some immune cells, such as T cells gamma delta, NK cells resting, Macrophages M0, Macrophages M2 and Mast cells activated, differed in IGC and DGC. The Lauren classification should be considered into immune therapy of GC.
The mRNAs in common ceRNA network were enriched in Regulation of actin cytoskeleton and MicroRNAs in cancer, which manifested that targeted mRNAs of common network were regulated by relevant miRNAs. In the ceRNA network, CFL2, FGF2 and ZEB1 were reported to be miRNA’s target associated with GC [22] [23] [24]. ZFPM2 and ZEB1 consisting in “MicroRNAs in cancer” pathway had common upstream lncRNA, namely SNHG14. It was reported to contribute to GC development through targeting miR-145/SOX9 axis [25]. However, it is possible that there are other regulation axes.
In the IGC-specific ceRNA network, hsa-miR-106b-5p, hsa-miR-17-5p and hsa-miR-93-5p have many targets, indicating their important roles. They were primarily sponged by three lncRNAs (HAND2-AS1, SNHG14 and PWAR6). So, HAND2-AS1, SNHG14 and PWAR6 deserve further investigation to verify their effect in ceRNA network of IGC. In the DGC-specific ceRNA network, hsa-miR-148b-3p and hsa-miR-16-5p respectively have seven and four targets. But lncRNAs sponging miRNAs only have SNHG14 and AC007392.3, also proving SNHG14’s vital function in GC.
It was reported that Mast cells and Macrophages made effect in GC development[26] [27]. Mast cells and Macrophages significantly differed not only between the tumor and normal tissue, but also between the two subtypes. Like the expression level of two subtypes’ cancer-related pathways, a similar pattern exists for two types of immune cells. And these two kinds of immune cells are significantly associated with multiple components in ceRNA network. Further studies on these two types of immune cells are necessary, which can help us to discover new therapeutic method or mechanism of GC.
LncRNAs and mRNAs were reported to be prognostic and diagnostic biomarkers of many cancers. Our results demonstrated lncRNAs and mRNAs of ceRNA network in all three groups showed good performance in tumor diagnosis. Perhaps they also guide clinical decision-making.
It is important to note that our results have not been validated by well-designed experiment and that is our prospective work. The public data we use are western demographic data, a conclusion should be made with caution in Asian countries. The number of DGC was relatively small, rendering the results less reliable.