With the advent of the era of abundant biological data, bioinformatics technology provides a more convenient platform for researchers. Using high-throughput sequencing data to classify a large number of samples can better reflect the characteristics and heterogeneity of tumors. The classification of cancer subtypes can not only describe the characteristics of tumors from multiple dimensions but also help predict patient prognosis and guide immunotherapy [15, 23, 24]. However, previous studies have not fully considered the interaction between tumor and immunity. The progress of a cancer depends not only on the cancer cells but also on the TIME. The TIME is the internal environment of tumor malignant progression, which affects tumor progression and immunotherapy [25, 26]. In this study, a hierarchical clustering algorithm was used to divide the GC samples into three clusters based on the enrichment of 29 immune cell types. Significant differences in the immune score, stromal score, tumor purity, and immune-related gene expression were found in the three cell infiltration clusters. Moreover, the CIBERSORT algorithm was used to analyze the proportion of 22 immune cells in the three clusters, and the results showed significant differences among the three groups. Survival analysis also showed a significant difference in the survival rates among the three groups. These results suggest that the immune cell infiltration pattern in TIME played a crucial role in the progression of GC. The DEGs among the different immune-infiltrating clusters were identified, and enrichment analysis was conducted. The PPI network was constructed, and the hub genes were identified. Integration of the angiogenesis-related genes and Cox regression analysis showed that VCAM1 may play an important role in the regulation of the TIME and angiogenesis. VCAM1 expression was also found to be significantly higher in the GC tissues than in the normal tissues and was associated with clinical stage and survival in the patients with GC. This result suggested that VCAM1 may play an important role in the occurrence and development of GC and may be a therapeutic target and prognostic indicator of GC.
VCAM1 is an important member of the immunoglobulin superfamily and is considered to be a cell adhesion molecule that contributes to the regulation of inflammation-related vascular adhesion and trans-endothelial migration of white blood cells . Studies have shown that VCAM1 plays a vital role in various diseases, such as rheumatoid arthritis, asthma, and cancer [28, 29]. VCAM1 expression can be induced by the activation of proinflammatory cytokines, such as tumor necrosis factor, interleukin, and adipocytokine visfatin . In high levels of inflammation and cancer, VCAM1 can also be activated by autosecretory or paracrine expression. For example, VCAM1 is highly expressed in the tissues of colorectal cancer (CRC) and has been strongly associated with aggressiveness, clinical features, and poor prognosis in patients with CRC . In addition, recent studies have shown that cancer-associated fibroblasts (CAFs) secrete VCAM1 to enhance the growth and invasion of cancer cells by activating the AKT and MAPK signaling pathways of lung cancer cells . Moreover, CAF-derived VCAM1 molecules have been found to interact with integrin αvβ1/5 to promote the invasion of GC cells in vitro and in vivo . The serum concentrations of ICAM-1 and VCAM1 in patients with GC have been found to be significantly higher than those in the healthy controls, and their expression levels were significantly correlated with tumor stage, gastric wall invasion, distant metastasis, and prognosis. In this study, VCAM1 was significantly associated with the occurrence, development, and survival of GC. These findings further suggest that VCAM1 may be a potential biomarker for the diagnosis and prognosis of GC.
The potential role of VCAM1 in regulation of the TIME was also explored. TISIDB database analysis showed that VCAM1 expression was significantly correlated with immunostimulatory genes, chemokines, and chemokine receptors in various cancers, especially in GC. The correlation between VCAM1 and infiltrated immune cells in TIME was analyzed according to the CIBERSORT algorithm and TIMER database. The results showed that VCAM1 expression was associated with various infiltrating immune cells, such as B cells, CD8+T cells, and CD4+T cells. Furthermore, GSEA showed that VCAM1 was involved in the regulation of immunity and angiogenesis, including the chemokine signaling pathway and JAK-STAT signaling pathway. Chemokine signaling and the JAK-STAT signaling pathway are involved in immune function and the growth and differentiation of cells. The abnormal activation of both processes can easily lead to the occurrence of tumors [35–37]. Most cytokine-induced immune responses also depend on these processes [38, 39]. PIK3CA mutations were reported in 5% of GCs, and mutations in this gene led to the constructional activation of this pathway . Gong et al. examined 86 patients who were undergoing gastrectomy and found that activated STAT3 was associated with multiple angiogenesis factors, which in turn was found to contribute to the progression of GC . Studies have also shown that the expression of PD-L1 in GC is mainly regulated by the JAK-STAT pathway-related interferon gamma . In this study, the results also showed that the expression of VCAM1 was significantly correlated with various immunostimulatory genes, such as CD274(PD-L1) and CTLA4(Figure 6A).
Embelin, an IAP inhibitor, has been reported to accelerate tumor-infiltrating T cell numbers and enhance antitumor immune response by restoring VCAM1 expression in tissue endothelial cells in an animal model of ductal adenocarcinoma of pancreatic cancer. Liu et al. found that the VCAM1 expression was positively correlated with glioblastoma multiforme of monocyte adhesion, and knockout of VCAM1 could eliminate the enhancement of monocyte adhesion . In addition, macrophages are attracted to the tumor microenvironment by soluble VCAM1, promoting the drug resistance of pancreatic cancer cells to gemcitabine. The change in the soluble VCAM1 in the plasma is an independent prognostic factor of gemcitabine treatment in patients with advanced pancreatic cancer . All data suggest that VCAM1 may be a promising key regulator of the GC immune microenvironment and involved in the regulation of immune activity status in the TIME. However, the regulatory mechanism between different VCAM1 expression levels and the immune microenvironment of patients with GC and the detailed immune cell regulation map need further studies.